The California Baseline Ozone Transport Study (CABOTS) was
conducted in the late spring and summer of 2016 to investigate the influence
of long-range transport and stratospheric intrusions on surface ozone
(O3) concentrations in California with emphasis on the San Joaquin
Valley (SJV), one of two extreme ozone non-attainment areas in the US.
One of the major objectives of CABOTS was to characterize the vertical
distribution of O3 and aerosols above the SJV to aid in the
identification of elevated transport layers and assess their surface
impacts. To this end, the NOAA Earth System Research Laboratory (ESRL)
deployed the Tunable Optical Profiler for Aerosol and oZone (TOPAZ) mobile
lidar to the Visalia Municipal Airport (36.315∘ N,
119.392∘ E) in the central SJV between 27 May and 7 August 2016.
Here we compare the TOPAZ ozone retrievals with co-located in situ surface
measurements and nearby regulatory monitors and also with airborne in situ measurements
from the University of California at Davis–Scientific Aviation (SciAv)
Mooney and NASA Alpha Jet Atmospheric eXperiment (AJAX) research aircraft.
Our analysis shows that the lidar and aircraft measurements agree, on
average to within 5 ppbv, the sum of their stated uncertainties of 3 and 2 ppbv, respectively.
Introduction
The San Joaquin Valley (SJV) of California is one of only two “extreme”
ozone (O3) non-attainment areas remaining in the United States
with a 2016 ozone design value, i.e., the metric used by the U.S. EPA to
determine air quality compliance that is calculated as the 3-year average of
the fourth highest measured maximum daily 8 h average mixing ratio (MDA8),
which is more than 20 parts per billion by volume (ppbv) greater than the
primary National Ambient Air Quality Standard (NAAQS) of 70 ppbv (https://www3.epa.gov/airquality/greenbook/hdtc.html,
last access: 18 March 2019). Such high O3
concentrations are harmful to human health (U.S. Environmental
Protection Agency, 2014) and impair plant growth and productivity (Avnery
et al., 2011a, b), adversely affecting both the USD 15 billion annual crop yield (https://quickstats.nass.usda.gov/results/9438C760-67AB-3AFB-B182-8484DB20A903, last access: 18 March 2019) in the SJV and the iconic forests of the nearby Sequoia National Park and Kings
Canyon National Park (Panek et al., 2013).
The need to better understand the causes for the high surface O3 in the
San Joaquin Valley has motivated several major air quality studies over the
years including the San Joaquin Valley Air Quality Study (SJVAQS) in 1990
(Lagarias and Sylte, 1991), the Central California Ozone
Study (CCOS) in 2000, (Reynolds et al., 2010) and the California
Research at the Nexus of Air Quality and Climate Change (CalNex) field
campaign in 2010 (Ryerson et al., 2013; Brune et al., 2016). More
recently, this issue was addressed by the 2016 California Baseline Ozone
Transport Study (CABOTS) organized and supported by the California Air
Resources Board (CARB) (https://www.arb.ca.gov/research/cabots/cabots.htm, last access: 18 March 2019).
CABOTS was designed to
investigate the contributions of background O3
(Jaffe et al., 2018) and the influence of
stratospheric intrusions (Lin et al., 2012a) and long-range transport
from Asia (Lin et al., 2012b) on surface O3 concentrations in the
SJV during late spring and summer. Characterization of the vertical
distribution of O3 in the lower and middle free troposphere above the
SJV and upwind regions with an accuracy of at least 10 %, the nominal
accuracy of ECC ozonesondes in the troposphere (Smit et al., 2014), was a
key objective of the campaign, and O3 profiles were measured using
three different techniques (lidar, aircraft, and ozonesondes) in various
parts of California. Integration of these datasets requires that these
measurements be intercompared (Ancellet and Ravetta, 2005;
Beekmann et al., 1995; Kempfer et al., 1994; Schäfer et al., 2002) and
any differences among the various techniques understood and characterized.
For pollution studies it is important that this validation includes the
lowest 100 m, which is inaccessible to most ozone lidars (Wang et al., 2017).
In this paper, we compare O3 measurements from the NOAA Earth System Research Laboratory ESRL
multi-angle Tunable Optical Profiler for Aerosol and oZone (TOPAZ) lidar
with in situ measurements from nearby regulatory and research surface monitors, and
also with instruments flown aboard the UC Davis–Scientific Aviation Mooney
(Trousdell et al., 2016) and Alpha Jet research aircraft
based at NASA's Ames Research Center (Hamill et al., 2016; Yates et al.,
2015). These comparisons, together with those from the multi-lidar
(including TOPAZ) and ozonesonde Southern California Ozone Observation
Project (SCOOP) intercomparison conducted by the NASA-sponsored Tropospheric
Ozone Lidar Network (TOLNet) immediately after CABOTS
(Leblanc et al.,
2018), provide this validation.
(a) Topographic map showing the air basins of California (dashed black lines); the San Joaquin Valley Air Basin (SJVAB) is outlined in heavy
solid black. Interstate highways and urban areas are shown in gray. The
filled red triangles show the CABOTS measurement sites at Bodega Bay (BBY),
Half Moon Bay (HMB), Visalia Municipal Airport (VMA), and Chews Ridge
Observatory (CRO). (b) The same as (a) but showing an enlarged view of the area
surrounding the VMA. The solid and dotted–dashed gray lines represent the major
highways and railroads, respectively, with the heavier solid line showing
CA-99 (see text). The filled black squares show the six closest regulatory
O3 monitors active during the CABOTS campaign: Visalia (VIS), Hanford
(HFD), Santa Rosa Rancheria (SRR), Fresno–Drummond St. (FRD), Parlier (PRL),
and Porterville (PRV). The elevation scale is the same as in (a).
California Baseline Ozone Transport Study (CABOTS)
The CABOTS field campaign was conducted between mid-May and mid-August of
2016. The primary measurements (see Fig. 1a) included electrochemical cell
(ECC) ozonesondes (Johnson et al., 2002) launched
daily from Bodega Bay (38.319∘ N, 123.075∘ E, 12 m above mean sea level, a.s.l.)
(6 May–17 August) and Half Moon Bay (37.505∘ N,
122.483∘ E, 9 m a.s.l.) (15 July–17 August) by the San Jose State
University (SJSU), in situ aircraft sampling of O3 and other compounds above
central California by the University of California, Davis (UC
Davis)–Scientific Aviation (Trousdell et al., 2016) and
the NASA Alpha Jet Atmospheric eXperiment (AJAX)
(Yates et al., 2015), and ozone and backscatter
lidar measurements by the truck-based NOAA ESRL TOPAZ lidar system
(Alvarez et al., 2011) at the Visalia Municipal Airport (VMA,
36.315∘ N, 119.392∘ E, 88 m a.s.l.)
(27 May–18 June and 18 July–7 August) (Fig. 2). Surface O3
measurements were also made at the ozonesonde and lidar sites and at the UC
Davis monitoring station at the Chews Ridge Observatory (36.306∘ N, 121.567∘ E, 1520 m a.s.l.) (Asher et al., 2018) in the Santa
Lucia Mountains west of Visalia, as well as using the extensive networks of
regulatory surface monitors maintained by the California Air Resources Board
and the San Joaquin Valley Air Pollution Control District (SJVAPCD).
Aerial view of the Visalia Municipal Airport (VMA) showing the 1 km lidar slant path line of sight as a yellow arrow with the TOPAZ truck
located at the base. The Scientific Aviation Mooney and AJAX Alpha Jet are
shown flanking the NOAA ESRL TOPAZ truck below the Google Earth image.
Mooney and TOPAZ photos by Andrew O. Langford. Alpha Jet photo by Wilfred von Dauster.
The Bodega Bay and Half Moon Bay sites were located on the coast to sample
the Pacific inflow, and the VMA was chosen for the TOPAZ operations because
of its central location in the SJV, the availability of the runway and
airspace for low approaches and aircraft profiles, and the presence of the
co-located SJVAPCD wind profiler and radio acoustic sounding system (RASS)
(Bao et al., 2008). The TOPAZ truck was parked on
the west side of the VMA between the airport runway and the
heavily trafficked multilane CA-99 and adjacent San Joaquin Valley Railroad
(SJVR) (Fig. 2). The VMA is located about 10 km west of downtown Visalia
(pop. 130 000) and lies about one-third (60 km) of the way from Fresno to
Bakersfield (Fig. 1a, b). Visalia is located about 400 km from Bodega Bay
and 300 km from Half Moon Bay, which limited the usefulness of comparisons
between the lidar and ozonesondes.
Ozone measurement platformsNOAA-ESRL TOPAZ lidar
The TOPAZ differential absorption lidar (DIAL) system was originally
developed for the profiling of O3 and particulate backscatter in the
planetary boundary layer and lower free troposphere from NOAA Twin Otter
aircraft (Alvarez et al., 2011; Langford et al., 2010, 2011, 2012; Senff et al.,
2010). The lidar was
reconfigured for mobile ground-based measurements in 2012 and deployed in
this configuration to several field campaigns including the 2013 Las Vegas
Ozone Study (LVOS) (Langford et al., 2015) prior to CABOTS. The lidar is
installed in the back of a medium box truck (see Fig. 2) equipped with a
commercial UV absorption monitor for in situ O3 measurements (2B Technologies
model 205) that samples air 5 m above the surface and an Airmar 150WX
weather station to measure temperature, pressure, relative humidity, and
wind speed and direction. The 2B model 205 has been approved by the EPA as a
federal equivalent method (FEM) for surface O3 monitoring and has a
nominal (1σ) precision and accuracy that is the greater of 1 ppbv or
2 % for 10 s averages. Modified versions of the same instrument were flown
on both the Scientific Aviation Mooney and NASA Alpha Jet. Comparisons
between the NOAA 2B at the VMA and a mobile calibration source operated by
CARB revealed a 3 % low bias in the recorded 2B measurements that has been
corrected in the data used here.
The eye-safe TOPAZ lidar is built around a low pulse energy (∼100µJ), high repetition rate (1 kHz) quadrupled Nd:YLF pumped
Ce:LiCAF laser that is retuned between each pulse to generate light at
three different wavelengths from 286 to 294 nm with an effective repetition
rate of 333 Hz for each wavelength (Alvarez et al., 2011). The laser
pulses are transmitted and the lidar return signals collected by a coaxial
transmitter and receiver equipped with a commercial (Licel)
photomultiplier-based dual analog or photon counting system. This hybrid data
acquisition system was installed in 2016 and replaced the original fast
analog data acquisition system that was optimized for aircraft operations
(Alvarez et al., 2011; Wang et al., 2017). This modification increased the
maximum useful range to ∼6 km during the day and to more than
8 km at night, depending on the laser power, atmospheric extinction, and
solar background light.
The truck-mounted version of TOPAZ incorporates a large scannable turning
mirror above the vertically pointing transmitter and receiver to allow profile
measurements at different slant angles. These slant profiles can be combined
to create vertical profiles that start much closer to the ground (25–30 m)
than conventional vertically staring lidar systems (Proffitt and
Langford, 1997). During CABOTS, the scanning mirror was moved sequentially
between elevation angles of 90, 20, 6, and 2∘ with a 225 s
averaging time at 90∘ and 75 s averaging times at the other three angles. The cycle was repeated approximately every 8 min and the
vertical projections combined to create a single vertical profile starting
at 27.5±5 m above ground level (a.g.l.). This approach assumes a fair
degree of horizontal homogeneity and the lidar slant paths were oriented
parallel to the VMA runway (135∘) over open farmland to avoid
populated neighborhoods and minimize the effects of NO emissions from the
often heavy traffic on CA-99 (see Fig. 2), which could locally titrate
ozone and create strong horizontal concentration gradients near the surface.
The O3 profiles shown here were retrieved using two wavelengths
(∼287 and 294 nm) with 30 m range gates and a smoothing
filter that increased from 270 m wide at the minimum range (815±15 m)
to 1400 m wide at the maximum range (8 km). The effective vertical
resolution increased from ∼10 m near the surface to
∼150 m above 500 m a.g.l. and 900 m at 6 km. Profiles of the
backscatter from aerosols, smoke, and dust were retrieved with a constant
7.5 m resolution at 294 nm. The ozone profiles were computed using the
O3 absorption cross sections from Malicet et al. (1995)
and an iterative technique to correct for differential aerosol backscatter
and extinction that assumes a backscatter-to-extinction ratio of 40 and
fixed Ångström coefficients of 0 for backscatter and -0.5 for extinction
(Alvarez et al., 2011). These values offer a good compromise for a wide
variety of particulate types (Völger et al., 1996). The actual aerosol
composition in the SJV was not measured during CABOTS, but measurements
during the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES)
typically found a mix of organics, sulfate, nitrate, ammonium, and soil dust
in the northern part of the valley (Zaveri et al., 2012). Smoke from the
Soberanes Fire near Big Sur dominated the aerosol mix in the SJV during the
second intensive operating period (IOP). We varied the aerosol backscatter Ångström coefficient between
-1 and 1 and the aerosol extinction Ångström coefficient between 0 and -1
for a “worst case scenario” of a thin smoke layer with very high aerosol
backscatter embedded in an otherwise clean atmosphere to estimate the error
in the ozone retrieval introduced by using these fixed parameters. The sharp
aerosol gradients at the smoke layer edges tend to magnify errors in the
ozone retrieval if the aerosol correction is not properly implemented.
Temperature and pressure profiles interpolated from the 3 h National Centers
for Environmental Prediction (NCEP) North American Regional Reanalysis
(NARR) using the grid point closest to the TOPAZ lidar location were used to
account for the temperature dependence of the O3 cross sections and to
convert O3 number densities to mixing ratios. The total uncertainties
in the 8 min ozone retrievals in the absence of strong aerosol gradients are
estimated to increase from ±3 ppbv below 4 km to ±10 ppbv at
the top of the profile. When strong backscatter gradients are present, the
O3 uncertainty can potentially increase by another ±3 ppbv.
UC Davis–Scientific Aviation Mooney
The University of California at Davis and Scientific Aviation, Inc.
(http://www.scientificaviation.com, last access: 18 March 2019) conducted a series of research flights
above the SJV during the summer of 2016 using a Scientific Aviation
single-engine Mooney TLS or Ovation aircraft as part of the CARB-supported
Residual Layer Ozone Study (RLO) (https://www.arb.ca.gov/research/apr/past/14-308.pdf, last access: 18 March 2019).
Several of these
flights overlapped with the TOPAZ operations during CABOTS, as did some of
the 12 additional flights (EPA) funded by the U.S. EPA and the Bay Area Air
Quality Management District (BAAQMD). The Mooney carried a 2B Technologies
model 205 O3 monitor, an EcoPhysics model CLD88 (NO) with a
photolytic converter to measure NO and NO2, and a Picarro 2301f cavity
ring-down spectrometer (CRDS) to measure CO2, CH4, and H2O
(Trousdell et al., 2016). The 2B model 205 was used with
the minimum integration time of 2 s, which corresponds to a mean distance of
150 m at the typical level flight speed (the data stream was sampled at 1 s
intervals). As noted above, the 2B has a nominal accuracy of 2 % for
concentrations above 50 ppbv and a precision of 2 % for concentrations
above 50 ppbv if 10 s averages are used. If the limiting noise is randomly
distributed, this implies a precision of 5 % for concentrations greater than 50 ppbv and 2 s averages.
Calibrations of the Scientific Aviation 2B using an external ozone source
(2B, model 306) found the instrument to have offsets and slopes less than
1.5 ppb and within 4 % of unity, respectively.
NASA Alpha Jet Atmospheric eXperiment (AJAX)
The NASA Ames Alpha Jet Atmospheric eXperiment (AJAX)
(Hamill et al., 2016) sampled O3 and other
tropospheric constituents above California during CABOTS using a two-person
jet based at Moffett Field, CA (MF, 37.415∘ N,
122.050∘ E). The Alpha Jet carried an external wing pod
with a modified commercial UV absorption monitor (2B Technologies Inc.,
model 205) to measure O3 (Ryoo et al., 2017; Yates et al., 2013, 2015) and a (Picarro model 2301 m) cavity ringdown analyzer to
measure CO2, CH4, and H2O (Tanaka et al., 2016). A second
wing pod carried a nonresonant laser-induced fluorescence instrument to
measure formaldehyde (CH2O) (St. Clair et al., 2017). The pod
mounting kept the residence times of the sample inlets to less than 2 s. The
aircraft is also equipped with GPS and inertial navigation systems to
provide altitude and position information, and the NASA Ames-developed
meteorological measurement systems to provide highly accurate
pressure, temperature, and 3-D wind data. The 2B O3 data, recorded
every 2 s, are averaged over 10 s to increase the signal-to-noise ratio.
Ozone calibrations were performed before or after each flight using an external
ozone source (2B Technologies Inc., model 306 referenced to the NIST scale,
certified annually). Raw flight O3 data were corrected using the
linearity correction factor and zero-offset from the calibration closest in
time to the flight. Overall accuracy of the O3 instrument is determined
to be 3 ppbv or better at 10 s resolution, with uncertainty improving at
lower altitudes, as determined from pressure chamber tests; see Yates et
al. (2013) for a more detailed error analysis.
Results and comparisons
The TOPAZ measurements were conducted over two 3-week intensive operating
periods (IOPs) in the late spring (27 May to 18 June) and summer (18 July to
7 August) of 2016. A total of 440 h of lidar data was recorded during
the first (1654 profiles over 22 days) and second (1686 profiles over 21 days) IOPs with an average of more than 10 h of nearly continuous
measurements per day. The skies above Visalia were mostly cloud free during
the study, with only a few profiles truncated by high clouds during IOP1.
However, during IOP2 the SJV was fumigated by smoke from the Soberanes Fire
that started on 22 July about 200 km west of Visalia near Big Sur.
Comparisons between lidar and surface measurements
The NOAA 2B ozone monitor operated continuously at the VMA throughout the
TOPAZ deployment, with the system response checked during each IOP by an
external mobile calibration source operated by CARB. These calibration
checks revealed a 3 % low bias in the NOAA 2B instrument that has been
corrected in the data shown here. Figure 3 plots time series (Pacific
daylight time, PDT) of the 1 min averaged in situ surface mixing ratios
(gray dots) measured 5 m above the ground from each IOP together with the
TOPAZ mixing ratios retrieved from a height of 27.5±5 m (black line)
and a range of 815±15 m along the slant path above the agricultural
fields to the southeast (see Fig. 2). Figure 4a is an enlarged view of the
VMA surface measurements (gray line) from 9 to 13 June together with the mixing
ratios from the 27.5 m TOPAZ measurements (filled black circles). Also
plotted are the 1 h average ozone mixing ratios measured 6.7 m a.g.l. by the
CARB regulatory Teledyne API 400 monitor located on N. Church Street in
Visalia (102 m a.s.l.) about 10 km to the east of VMA (solid black line) and
measured 5 m a.g.l. by the SJVAPCD Teledyne API 400 monitor in Hanford (82 m a.s.l.) about 22 km to the west of VMA (dotted black line). The four sets of
measurements agreed fairly well during the day but diverged markedly at
night and in the early morning when O3 was removed by surface
deposition and titration by NOx within the surface layer. The losses
were greatest at the VMA monitor which was located in the TOPAZ truck next
to the heavily trafficked CA-99 and SJVR railroad line. Titration by NO was
undoubtedly much greater here, but there were no NOx measurements available
to confirm this hypothesis. Much smaller losses were measured by the rural
Hanford monitor and intermediate losses were measured by the Visalia monitor,
which is located on a downtown rooftop. A scatterplot of all of the
coincident TOPAZ and in situ measurements from CABOTS (Fig. 4b, filled
gray circles) shows that the in situ concentrations measured at VMA were
often much smaller than the concentrations measured 815±15 m away by
the lidar, and even titrated to zero under some conditions. The data
converge (filled black circles) when the comparison is restricted to
conditions when the two measurements are expected to sample a common
airmass; i.e., during the day after the nocturnal inversion has dissipated
(09:00 to 18:30 PDT) and the winds were southeasterly (125 to 145∘)
and greater than 2.5 m s-1. The results of orthogonal distance
regression (ODR) fits of these data are shown both in the figure and in
Table 1. We use ODR fits that assume that both variables can have
uncertainties, for our analyses instead of simple linear regressions, which
assume that all of the uncertainties lie in the dependent variable. Fits of
the filtered data give a slope of 1.00±0.03 and an intercept of
-2.6±1.5 ppbv where the errors represent the 95 % confidence limits
of the ODR fits.
Time series plots (local Pacific daylight time, PDT) of the
O3 concentrations retrieved 815±15 m downrange and 27.5 m above
the surface by TOPAZ (black line) with the measurements from the in situ 2B monitor
sampling 5 m a.g.l. at the TOPAZ location (gray dots) during the first (a) and
second (b) IOPs. The dashed and dotted lines show the 2008 (75 ppbv) and 2015 (70 ppbv) O3 NAAQS, respectively.
(a) A 4-day time series (9–13 June) showing the O3
concentrations in air sampled 5 m a.g.l. above the TOPAZ truck at the VMA (gray
line) and the O3 mixing ratios at a height of 27.5±5 m and
distance of 815±15 m retrieved from the TOPAZ measurements (filled
black circles). The solid black and dotted staircase lines show the 1 h
measurements from the Visalia and Hanford regulatory monitors. (b) Scatterplot comparing the 27.5 m TOPAZ measurements to the interpolated 5 m
in situ measurements. The filled gray circles (with dotted ODR fit) show the entire
CABOTS dataset from Fig. 3, and the filled black circles (with dashed ODR
fit) show only those measurements made during the day (09:00 to 18:30 PDT)
when the winds were southeasterly (125 to 145∘) and greater than
2.5 m s-1. The solid line shows the 1:1 correspondence.
Figure 5 compares the 27.5 m TOPAZ O3 measurements to the regulatory
O3 surface measurements from the monitors at Visalia (8.5 km) and
Hanford (24 km) described above, and from the more distant SJVAPCD monitors
at Parlier (34 km) and Porterville (43 km). The TOPAZ mixing ratios were
slightly higher than those at Visalia and Hanford but lower than those at
Parlier and Porterville, which are closer to the Sierra foothills and
measure some of the highest O3 concentrations found in the SJVAB. The
degree of correlation decreased with distance as expected, yet remained
quite good more than 40 km from the VMA at Porterville. This suggests that
the O3 measurements acquired at the VMA during CABOTS can be considered
representative of the central San Joaquin Valley.
Scatterplots with ODR fits comparing the 27.5 m TOPAZ
measurements with the 1 h measurements from the regulatory monitors at
(a) Visalia–N. Church Street, (b) Hanford, (c) Parlier, and (d) Porterville. The
measurements in the upper box and x axis label refer to the distance from
the VMA and sampling height above ground, respectively. The Visalia monitor
is operated by the California Air Resources Board. The remaining three are
operated by CARB and the SJVAPCD. The TOPAZ measurements are interpolated to
the 1 h time base of the regulatory measurements for the comparison.
Comparisons between lidar and aircraft measurements
Comparisons between the ground-based lidar and aircraft measurements are
subject to much larger uncertainties arising from spatial and temporal
sampling differences compared with the comparison with nearby surface
monitors. During CABOTS, the fixed wing aircraft conducted both low
approaches above the VMA runway (see Fig. 2) and spiral profiles around
the airport but never directly sampled the vertical column probed by the
lidar. The comparisons were also conducted as brief elements of multi-hour
sampling flights with other objectives, and time constraints and air traffic
considerations sometimes contributed to the spatial and temporal mismatches.
The piston-engine Mooney took about 25 min to execute an ascending
profile from the surface to 3 km, while the Alpha Jet took about 9 min
(similar to the 8 min TOPAZ integration time) to conduct a descending
profile from 3 km to the surface. Spatial mismatches were also created by
the vertically smoothing of the DIAL retrieval, which can both smooth and
displace sharp vertical concentration gradients seen by the aircraft.
Similar considerations apply to comparisons between lidars and ozonesondes
since balloons have a finite rise time and can be carried many kilometers
downwind from the launch site (Leblanc et al., 2018). Despite these caveats,
we show that the lidar and aircraft measurements usually agreed to within
±10 %, the nominal accuracy of ECC ozonesondes in the troposphere
(Smit et al., 2014), which is the generally accepted reference standard for
ozone profile measurements.
UC Davis–Scientific Aviation Mooney
The RLO flights were executed as a series of 2–3-day deployments with as
many as four flights per day lasting 2 to 3 h each between Fresno and
Bakersfield. Two of these deployments, RLO2 (2–4 June) and RLO4 (24–26 July), overlapped with the first and second TOPAZ IOPs, respectively, and
included low approaches at VMA on most of the flights with spiral profiles
near VMA on several. Both deployments occurred as warm temperatures
(> 40 ∘C) and weak anticyclonic winds associated with
synoptic high-pressure systems resulted in the buildup of surface ozone
across the South Coast Air Basin and San Joaquin Valley Air Basin. The highest
measured MDA8 O3 in the SJVAB during the first IOP was recorded on 4 June at Clovis (91 ppbv),
which lies about 65 km northwest of VMA (see Fig. 1b). The highest reported MDA8 O3 during the second IOP (and the
year) was recorded on 27 July at Parlier (101 ppbv), which lies midway
between Clovis and the VMA. The monitors at Visalia and Hanford reported
MDA8 concentrations of 72 and 88 ppbv, respectively, on 4 June, and 83 and
85 ppbv on 27 July. Figure 3 shows that the highest O3 mixing ratios
measured by the VMA surface monitor and TOPAZ (27.5 m a.g.l.) were also
recorded on these 2 days.
(a) Map of the San Joaquin Valley showing the RLO flight tracks
coincident with the TOPAZ measurements (RLO2 and RLO4). The filled black
squares show the regulatory surface monitors. The CABOTS sampling sites at
CRO and VMA are marked by red triangles. The other abbreviations are the
Fresno (FAT), Visalia (VIS), and Bakersfield (BFL) airport codes. Note that
VMA and VIS refer to the same airport.
(b) The same as (a) but with the EPA flight tracks (EPA1 and EPA2).
The flight tracks from all of the Mooney sorties during the RLO2 and RLO4
deployments are plotted in Fig. 6a. FLT29 (RLO4) was a transit flight from
the Scientific Aviation home base near Sacramento to Fresno. The remaining
RLO flights were between Fresno and Bakersfield as noted above. The two EPA
deployments (27–29 July and 4–6 August) were of longer duration than the RLO
flights with morning and afternoon sorties that placed more emphasis on
cross-valley measurements and transects to the coast (Fig. 6b) including
profiles above the South Bay (EPA1) and Chews Ridge (EPA2). The afternoon
flights during both series included legs to Visalia.
Figure 7 shows the sections of the RLO and EPA flight tracks that passed
within 5 km of TOPAZ (dashed black circles). Most of these flights included
low (<10 m) passes along the VMA runway that approached within
∼350 m horizontally of the TOPAZ truck and within 1000 m of
the center of the 27.5 m a.g.l. TOPAZ slant path measurements (see Fig. 2).
Figure 8a–d show time series of the 27.5 m TOPAZ and 5 m in situ measurements
during all of the RLO and EPA low approaches together with the ozone
measured by the aircraft between the surface and 25 m a.g.l. All of the
aircraft measurements lie within 10 % of the O3 retrieved by TOPAZ
with the exception of the much higher values (> 100 ppbv)
measured by the Mooney around 14:00 PDT on 3 June (Fig. 8a; see below). The
scatterplots in Fig. 8e and f show that the aircraft also measured much
higher concentrations than the in situ surface monitor during the night and early
morning, in agreement with the lidar measurements in Fig. 4. The
differences were smaller on 27 July than on 3 June, and also less pronounced
than those in Fig. 4. Closer agreement between the aircraft and surface
measurements might be expected since some of the aircraft measurements were
made within 200 m of the lidar truck (see Fig. 2). The dark blue points
show that the low bias in the surface measurements decreased during the day
after the surface inversion had dissipated (there were too few measurements
to effectively filter them by wind speed or direction). The mean ODR fit
parameters based on the measurements from both RLO2 and RLO4 listed in Table 1 are very similar to those found for the lidar, which suggests that the
filtered surface measurements still have low bias that could be either
instrumental or sampling related.
RLO and EPA flight tracks in the vicinity of TOPAZ. (a) RLO2
(2–4 June), (b) RLO4 (24–26 July), (c) EPA1 (27–29 July), and (d) EPA2 (4–6 August).
Each color represents a different flight. The red triangle with a black square marks
the location of TOPAZ at the VMA and the dashed black circles show the 5 km
radius used for the profile comparisons. The lone black square represents the
Visalia–N. Church St. O3 monitor.
Figure 9 compares the aircraft and lidar O3 measurements made during
five of the ascending profiles conducted by the Mooney near the VMA. FLT19 was
conducted in the early afternoon of 3 June and FLT33, FLT35, FLT36, and
FLT37 were conducted over the 24 h period beginning just after local
midnight on 25 July. The four consecutive TOPAZ profiles acquired during the
time required for the Mooney to reach the top of each profile
(∼15–30 min at a climb rate of ∼2.2 m s-1) are plotted in each panel. The gray envelopes show the lidar mean
profile ±10 %. The differences between consecutive profiles reflect
the combined effects of atmospheric variability and the precision of the
lidar measurements.
Overall, the agreement between the TOPAZ and Mooney profiles in Fig. 9 is
within ±10 %, but there are some notable discrepancies. Most of
these arise from the coarser vertical resolution of the lidar retrievals,
which smooth out abrupt concentration changes such as those seen at the top
of the boundary layer (∼0.8 km a.g.l.) in Fig. 9a and between
2 and 3 km in Fig. 9e where several narrower layers are smoothed into one
broad layer in the lidar profile. Figure 9e also shows that the agreement
between the lidar and aircraft measurements is better at low altitudes where
the addition of the slant path measurements significantly improves the
effective vertical resolution of the lidar. Fine-scale variability in
O3 also contributes to some of the observed differences, particularly
on 3 June when the aircraft-measured O3 concentrations varied by as
much 25 ppbv during the low approach over the VMA runway. This unusually
large variability is also seen in the large and rapid changes in the lidar
measurements near the top of the boundary layer (Fig. 9a) and challenges
the assumptions about horizontal homogeneity used in the calculation of the
TOPAZ vertical profiles near the surface.
(a–d) Time series of the surface in situ O3 (gray dots) and
27.5 m TOPAZ O3 (red line) measured during the RLO and EPA low
approaches on (a) 2–5 June, (b) 24–27 July, (c) 27–30 July, and (d) 4–7 August 2016.
The red envelope shows the TOPAZ data ±3 ppbv, the
nominal accuracy of the lidar retrievals. The blue squares represent the 1 s
sampled (2 s recorded) Scientific Aviation measurements made between the
surface and 25 m a.g.l. The filled yellow circles in (a) and (c) show 2 s
measurements from AJAX low approaches (see text). Panels (e) and (f) show
scatterplots of the in situ surface measurements and the Scientific
Aviation data from the RLO flights in panels (a) and (b), respectively. The
ODR fit parameters refer to the dark blue points which represent the
measurements from daytime (08:30–18:30 PDT) flights.
The lidar profiles from 26 July (Fig. 9e) also show large
profile-to-profile changes in the narrow high O3 layer lying just above
the top of the nocturnal boundary layer (∼0.3 km a.s.l.). The 25
and 26 July measurements (Fig. 9b–e) were made several days after the
Soberanes Fire started and the low-altitude “layer” near 400 m in Fig. 9e is actually a short-lived puff of smoke and elevated O3 from the
fire. This is more obvious in the expanded view of the profiles shown in
Fig. 10a. Only two of the four lidar profiles from Fig. 9e are plotted:
the first profile coinciding with the aircraft measurements (solid trace,
±10 %) and the profile acquired 16–24 min later when the puff
had mostly disappeared (dashed trace). The corresponding lidar backscatter
measurements are plotted in Fig. 10b, and Fig. 10c shows the NO2
and H2O profiles measured by the aircraft. The backscatter measurements
show that the TOPAZ retrievals are unaffected by strong backscatter
gradients, which can create second derivative-like inflection points in the
DIAL O3 profiles (Kovalev and McElroy, 1994). The absence of
a corresponding structure in the aircraft NO2 and H2O profiles
confirms that the high O3 layer seen in the lidar and aircraft
measurements was not an artifact caused by interferences from these species,
which weakly absorb between 280 and 300 nm (Proffitt and Langford,
1997).
Profile plots comparing the TOPAZ (black lines) and Scientific
Aviation (red squares) O3 measurements on (a) FLT19, 3 June; (b) FLT33,
25 July; (c) FLT35 25 July; (d) FLT36, 25 July; and (e) FLT37, 26 July. The
dotted, short-dashed, solid, and long-dashed lines show the four consecutive
8 min lidar profiles acquired during the aircraft profiles. The gray
envelopes show the mean lidar profile ±10 % as reference. Note the
large variability near the surface and the sharp transition at 800 m in the 3 June aircraft measurements (see Fig. 3a).
NASA Alpha Jet Atmospheric eXperiment (AJAX)
AJAX conducted four research flights over the SJV while TOPAZ was operational,
with two additional flights (21 June and 7 July) between the two IOPs. The
Alpha Jet executed descending spiral profiles from 4 to 5 km down to the
surface that ended in low approaches on three of these flights: AJX190 on 3 June, AJX191 on 15 June, and AJX195 on 21 July. The aircraft also conducted
a very low approach (∼5 m) at VMA on 28 July (AJX196) but did
not execute a full profile. These low approach measurements are represented
by the filled yellow circles in Fig. 8a and c. The first and last
flights (AJX190 and AJX196) coincided with the high-ozone episodes mentioned
earlier, and the third flight (AJX195) also occurred during a period of high
pressure. The second flight (AJX191) was conducted as a deep closed low
moved into the Pacific Northwest, however, bringing unseasonably cool
temperatures (26 ∘C) and strong surface winds to the SJV. This
cyclonic system advected a large Asian pollution plume across the valley in
the middle troposphere, but surface ozone remained low with the peak MDA8
O3 concentration in the SJVAB only reaching 59 ppbv at the
Sequoia–Kings Canyon monitor.
(a) Expanded view of the lidar and aircraft O3 profiles from
Fig. 9e plotted with coincident (b) lidar backscatter and (c) aircraft
NO2 and H2O profiles. The solid black profile (±10 % in
gray) in (a) shows the lidar profile coinciding with the aircraft
measurements below 1 km; the dashed black line shows the profile measured
16–24 min later. This is also true for the backscatter profiles in (b). The
horizontal gray band highlights the smoke puff from the Soberanes Fire.
Figures 11 and 12 are similar to Figs. 6 and 7 but instead show the AJAX
flight tracks. The first AJAX flight (AJX190) on 3 June during IOP1
overlapped with the UC Davis–Scientific Aviation RLO2 deployment. AJX191
took place about 2 weeks later in IOP1, and AJX195 occurred several days
prior to the RLO4 deployment in IOP2. AJAX also executed profiles (not shown
here) above and upwind of Chews Ridge on AJX190 and AJX191, near Bodega
Bay on AJX191 and 195, and the Soberanes Fire plume on AJX196.
Figure 13 displays coincident AJAX and TOPAZ profiles in plots similar to
those shown for the Mooney in Fig. 9 but with an extended vertical axis
to reflect the higher range of these profiles. The points in Fig. 13 are
sparser than those in Fig. 9 in part because of the 10 s averaging time,
and in part because the Alpha Jet executed its descending profiles with an
airspeed of about 110 m s-1 compared to about 60 m s-1 for the
ascending Mooney profiles.
Map of the San Joaquin Valley showing the AJAX flight tracks on 3 June (AJX190), 15 June (AJX191), 21 July (AJX195), and 28 July (AJX196). The
abbreviations and symbols are the same as in Fig. 6.
AJAX flight tracks in the vicinity of the VMA (red triangle with a black square). The
lone black square represents the Visalia–N. Church St. O3 monitor and the
dashed black circle marks the 5 km radius window used for the profile
comparisons. The heavy gray lines show the major highways and the black
dotted–dashed lines the railroads.
The agreement between the Alpha Jet and TOPAZ measurements is within ±10 % on all 3 days except for 3 June (Fig. 13a), when the measured
aircraft and retrieved lidar concentrations differ by as much as 12 ppbv
(20 %) at 2.5 km a.s.l. and 20 ppbv (∼50 %) at 5.2 km a.s.l.
The disparities between the inbound and outbound measurements in Fig. 13a
show that the Alpha Jet encountered strong horizontal gradients below 800 m
in the boundary layer when it arrived at the VMA about 3 h after the
Mooney found similar horizontal variability (see Figs. 8a and 9a). The
Google Earth map and latitude–altitude and longitude–altitude plots in
Fig. 14 better illustrate the extent of the horizontal variability in the
boundary layer. These figures also show weaker horizontal gradients above 3 km where the disagreement between the lidar and aircraft is most pronounced.
Summary of the lidar, surface, and aircraft comparisons.
ABRatio ±1σ (A/B)Diff. ±1σ (A-B)Slope* (A vs. B)Int.* (A vs. B)TOPAZVMA1.06±0.082.9±3.7 ppbv1.00±0.03-2.6±1.5 ppbvSciAvVMA1.07±0.105.0±5.0 ppbv1.01±0.01-4.5±1.1 ppbvTOPAZSciAv1.01±0.040.8±2.8 ppbv1.00±0.131.0±9.0 ppbvTOPAZAJAX1.08±0.064.2±0.8 ppbv1.07±0.131.8±3.4 ppbv
* From orthogonal distance regression (ODR) fits. Uncertainties are 95 %
confidence limits.
Discussion
The results of the different O3 comparisons are summarized in Table 1.
As was noted above, comparisons between the lidar and aircraft profiles are
subject to uncertainties arising from sampling differences introduced by the
intrinsic vertical smoothing of the lidar retrievals and horizontal
displacements between the aircraft and lidar. The potential impact of
horizontal displacements on the comparisons when the O3 spatial
variability is large is illustrated by Fig. 14, and a good example of the
differences created by the lidar smoothing is seen near the top of the
boundary layer around 0.8 km in Fig. 9a. These uncertainties can be
reduced by averaging the measurements to be compared over larger volumes.
Figure 15 compares the lidar and aircraft measurements from the profiles
plotted in Figs. 9 and 13, and from several other RLO and EPA flights not
shown, with each individual profile averaged over 1 km segments (0 to 1 km,
1 to 2 km, etc.). This averaging decreases the influence of O3 spatial
variability and also reduces the statistical uncertainties in both the
lidar retrievals and aircraft measurements, with the effective temporal
averaging of the AJAX and SciAv measurements increasing to about 2 and 4 min, respectively. Each point in the scatterplots of Fig. 15a and b
represents the mean mixing ratio from one of these 1 km segments, with the
error bars showing the standard deviation of the mean. The intercepts and
slopes derived from orthogonal distance regressions of both datasets overlap
with zero and unity, respectively, within the 95 % confidence limits of
the ODR fits. The lower panels (Fig. 15c and d) plot the same data as
differences which show that the TOPAZ and SciAv measurements (Fig. 15c)
agree to within 1 ppbv on average, and the TOPAZ and AJAX measurements
(Fig. 15d) to within 4.2 ppbv. Neither plot shows evidence of a systematic
altitude dependence in the differences.
Profile plots comparing the TOPAZ (black lines) and 10 s AJAX
(red squares) measurements on (a) AJX190, 3 June; (b) AJX191, 15 June; and
(c) AJX195, 21 July. The closed squares correspond to the Alpha Jet descent
and the open squares the subsequent climb out. Note the differences between
these measurements. The dotted, dashed, and solid lines show the order of
the three 8 min lidar profiles that bracket the AJAX profile. The gray
envelopes show the mean lidar profile ±10 % as reference. The
significance of the dashed oval in (b) is discussed in the text.
(a) Google Earth image of the TOPAZ and AJAX profiles from 3 June 2016 showing the spatial variations across the ∼8 km
diameter spiral profile by the Alpha Jet during its descent and climb out
over the VMA. (b, c) AJAX and TOPAZ profiles from Fig. 13a plotted as a
function of latitude (b) and longitude (c). Both plots are 10 km
wide. Note the strong horizontal gradients below 1.2 km.
Both lidar–aircraft comparisons are limited by the small number of common
measurements with only three profiles available for the AJAX comparisons. The
SciAv comparisons include data from seven flights, but only the five profiles shown
in Fig. 9 extend above 2 km and only three of those reach 3 km. These limited
datasets make the comparisons more sensitive to the influence of individual
points. For example, the point surrounded by the dashed circle in Fig. 15d
includes the measurements from within the dashed oval in Fig. 13b where
the lidar retrieval is clearly smoothing out the vertical gradient compared to
the aircraft measurements. If this measurement point is excluded, the mean
TOPAZ–AJAX difference decreases to 3.9±2.6. In either case, the
differences between the TOPAZ lidar retrievals and the in situ surface and
aircraft measurements lie within the combined uncertainties of the different
measurements and well within the 10 % accuracy standard set by the ECC
ozonesonde.
(a, b) Scatterplots comparing the TOPAZ lidar retrievals
to in situ O3 measurements from seven SciAv Mooney and three NASA Alpha Jet flights,
respectively, averaged over 1 km vertical bins. The error bars show the
standard deviations of the 1 km column means. (c, d) Differences
between the 1 km mean TOPAZ and aircraft measurements from (a) and
(b) plotted as a function of altitude. The vertical dashed lines show the mean
differences. The dashed circle in (d) corresponds to the dashed oval in
Fig. 13b (see text).
Time–height curtain plots of the TOPAZ ozone measurements from
(a) 25 to 26 July with the Scientific Aviation profiles from FLT35, FLT36, and FLT37
superimposed and (b) 15 June with the coincident AJAX profile superimposed.
The aircraft measurements made within 5 km of VMA (arrows) are highlighted
by squares and colorized using the same scale as the TOPAZ data. The high
O3 layers around 3 km a.s.l. in (a) are related to the Soberanes Fire; the
measurements plotted in the lower right corner of (a) correspond to the data
shown in Fig. 10.
Summary and conclusions
The lidar, aircraft, and ozonesonde profiles acquired during the 2016 CABOTS
field campaign provide an unprecedented look at the vertical distribution of
lower tropospheric O3 above California during late spring and summer.
The good agreement between the low-elevation TOPAZ measurements and the
collocated and regional (< 45 km) surface monitors suggests that the
measurements made at the VMA during CABOTS can be considered representative
of the central San Joaquin Valley. Comparisons between the NOAA TOPAZ lidar
profiles and the surface and aircraft measurements agree within the stated
uncertainties, and we conclude that all of these O3 measurements may be
used with confidence.
The coordinated lidar and aircraft sampling of O3 above the central San
Joaquin Valley during CABOTS also illustrates the synergy between the two
types of measurements. Lidar can provide long time series of the O3
(and backscatter) vertical distributions above a fixed location while the
aircraft can place the lidar measurements within a larger spatial context
and measure other important parameters. This synergy is illustrated by the
two time–height curtain plots displayed in Fig. 16. Figure 16a shows the
continuous TOPAZ measurements from a 14 h time span on 25–26 July with
the data from SciAv FLT35, FLT36, and FLT37 superimposed. The aircraft
measurements made within 5 km of VMA are highlighted by colored squares
outlined in white. Figure 16b is similar but shows 10 h of continuous
TOPAZ measurements from 15 June with the AJAX measurements (AJX191)
superimposed.
The CABOTS ozonesondes were launched too far away (> 300 km) from
the VMA to allow quantitative comparisons with the lidar. However, TOPAZ was
relocated to the NASA Jet Propulsion Laboratory (JPL) Table Mountain
Facility (TMF) in the San Gabriel Mountains immediately after CABOTS for the
Southern California Ozone Observation Project (SCOOP), a multiple lidar and
ozonesonde intercomparison organized by the NASA-sponsored Tropospheric
Ozone Lidar Network or TOLNet
(https://www-air.larc.nasa.gov/missions/TOLNet/, last access: 18 March 2019) at the NASA JPL TMF
(Leblanc et al.,
2018). The results from the SCOOP intercomparison and those presented here
complete the inter-validation of the CABOTS lidar, aircraft, and ozonesonde
profile measurements.
Data availability
CARB provided surface monitoring data (available at:
https://www.arb.ca.gov/aqmis2/aqdselect.php, CARB, 2019). NOAA provided TOPAZ ozone lidar data
(available at: https://www.esrl.noaa.gov/csd/groups/csd3/measurements/cabots/topaz.php, NOAA, 2019).
NASA provided the AJAX aircraft data (available at: https://www.esrl.noaa.gov/csd/groups/csd3/measurements/cabots/ajax.php, NASA, 2019).
UC Davis provided the Scientific Aviation aircraft data (available at: https://www.esrl.noaa.gov/csd/groups/csd3/measurements/cabots/ucdavis/Aircraft/, UC Davis, 2019).
Competing interests
The authors declare that they have no conflict of
interest.
Acknowledgements
The California Baseline Ozone Transport Study (CABOTS) field measurements
described here were funded by the California Air Resources Board (CARB) under
contract nos. 15RD012 (NOAA ESRL), 14-308 (UC Davis), and 17RD004
(NASA Ames). We would like to thank Jin Xu and Eileen McCauley of CARB for
their support and assistance in the planning and execution of the project
and are grateful to the CARB and the San Joaquin Valley Unified Air Pollution
Control District (SJVAPCD) personnel who provided logistical support during
the execution of the field campaign. We would also like to thank
Cathy Burgdorf-Rasco of NOAA ESRL and CIRES for maintaining the CABOTS data
site. The NOAA team would also like to thank Ann Weickmann, Scott Sandberg,
and Richard Marchbanks for their assistance during the field campaign. The
NOAA-ESRL lidar operations were also supported by the NOAA Climate Program
Office, Atmospheric Chemistry, Carbon Cycle, and Climate (AC4) Program and
the NASA-sponsored Tropospheric Ozone Lidar Network (TOLNet,
http://www-air.larc.nasa.gov/missions/TOLNet/, last access:
18 March 2019). The UC
Davis–Scientific Aviation measurements were also supported by the U.S.
Environmental Protection Agency and Bay Area Air Quality Management District
through contract no. 2016-129. Ian C. Faloona was also supported by the
California Agricultural Experiment Station, hatch project CA-D-LAW-2229-H.
The NASA AJAX project was also supported with Ames Research Center director's
funds, and the support and partnership of H211, LLC is gratefully
acknowledged. Josette E. Marrero and Ju-Mee Ryoo were supported through the
NASA Postdoctoral Program, and Mimi E. McNamara was funded through the Center
for Applied Atmospheric Research and Education (NASA MUREP).
The views, opinions, and findings contained in
this report are those of the author(s) and should not be construed as an
official National Oceanic and Atmospheric Administration or U.S. Government
position, policy, or decision.
Review statement
This paper was edited by Folkert Boersma and reviewed by two anonymous referees.
ReferencesAlvarez, R. J., II, Senff, C. J., Langford, A. O., Weickmann, A. M., Law,
D. C., Machol, J. L., Merritt, D. A., Marchbanks, R. D., Sandberg, S. P.,
Brewer, W. A., Hardesty, R. M., and Banta, R. M.: Development and
Application of a Compact, Tunable, Solid-State Airborne Ozone Lidar System
for Boundary Layer Profiling, J. Atmos. Ocean Tech., 28, 1258–1272,
10.1175/Jtech-D-10-05044.1, 2011.Ancellet, G. and Ravetta, F.: Analysis and validation of ozone variability
observed by lidar during the ESCOMPTE-2001 campaign, Atmos. Res.,
74, 435–459, 10.1016/j.atmosres.2004.10.003, 2005.Asher, E. C., Christensen, J. N., Post, A., Perry, K., Cliff, S. S., Zhao,
Y. J., Trousdell, J., and Faloona, I.: The Transport of Asian Dust and
Combustion Aerosols and Associated Ozone to North America as Observed From a
Mountaintop Monitoring Site in the California Coast Range, J. Geophys.
Res.-Atmos., 123, 5667–5680, 10.1029/2017jd028075, 2018.Avnery, S., Mauzerall, D. L., Liu, J. F., and Horowitz, L. W.: Global crop
yield reductions due to surface ozone exposure: 2. Year 2030 potential crop
production losses and economic damage under two scenarios of O-3 pollution,
Atmos. Environ., 45, 2297–2309, 10.1016/j.atmosenv.2011.01.002, 2011a.Avnery, S., Mauzerall, D. L., Liu, J. F., and Horowitz, L. W.: Global crop
yield reductions due to surface ozone exposure: 1. Year 2000 crop production
losses and economic damage, Atmos. Environ., 45, 2284–2296,
10.1016/j.atmosenv.2010.11.045, 2011b.Bao, J. W., Michelson, S. A., Persson, P. O. G., Djalalova, I. V., and
Wilczak, J. M.: Observed and WRF-simulated low-level winds in a high-ozone
episode during the Central California Ozone Study, J. Appl. Meteorol. Clim.,
47, 2372–2394, 10.1175/2008jamc1822.1, 2008.
Beekmann, M., Ancellet, G., Martin, D., Abonnel, C., Duveerneuil, G.,
Eideliman, F., Bessemoulin, P., Fritz, N., and Gizard, E.: Intercomparison
of tropospheric ozone profiles obtained by electrochemical sondes, a ground
based lidar and an airborne UV-photometer, Atmos. Environ., 29, 1027–1042,
1995.Brune, W. H., Baier, B. C., Thomas, J., Ren, X., Cohen, R. C., Pusede, S.
E., Browne, E. C., Goldstein, A. H., Gentner, D. R., Keutsch, F. N.,
Thornton, J. A., Harrold, S., Lopez-Hilfiker, F. D., and Wennberg, P. O.:
Ozone production chemistry in the presence of urban plumes, Faraday
Discuss., 189, 169–189, 10.1039/c5fd00204d, 2016.CARB: Surface monitoring data, available at: https://www.arb.ca.gov/aqmis2/aqdselect.php, last access: 18 March 2019.Hamill, P., Iraci, L. T., Yates, E. L., Gore, W., Bui, T. P., Tanaka, T.,
and Loewenstein, M.: A New Instrumented Airborne Platform for Atmospheric
Research, B. Am. Meteorol. Soc., 97, 397–404, 10.1175/Bams-D-14-00241.1,
2016.Jaffe, D. A., Cooper, O. R., Fiore, A. M., Henderson, B. H., Tonneson, G.
S., Russell, A. G., Henze, D. K., Langford, A. O., Lin, M., and Moore, T.:
Scientific assessment of background ozone over the U.S.: Implications for
air quality management, Elem. Sci. Anth., 6,
56,
10.1525/elementa.309, 2018.Johnson, B. J., Oltmans, S. J., Vomel, H., Smit, H. G. J., Deshler, T., and
Kroger, C.: Electrochemical concentration cell (ECC) ozonesonde pump
efficiency measurements and tests on the sensitivity to ozone of buffered
and unbuffered ECC sensor cathode solutions, J. Geophys. Res., 107,
4393, 10.1029/2001jd000557, 2002.Kempfer, U., Carnuth, W., Lotz, R., and Trickl, T.: A Wide-Range Ultraviolet
Lidar System for Tropospheric Ozone Measurements – Development and
Application, Rev. Sci. Instrum., 65, 3145–3164, 10.1063/1.1144769, 1994.Kovalev, V. A. and McElroy, J. L.: Differential Absorption Lidar
Measurement of Vertical Ozone Profiles in the Troposphere That Contains
Aerosol Layers with Strong Backscattering Gradients – a Simplified Version,
Appl. Optics, 33, 8393–8401, 10.1364/Ao.33.008393, 1994.Lagarias, J. S. and Sylte, W. W.: Designing and Managing the San Joaquin
Valley Air-Quality Study, J. Air Waste Manage. Assoc., 41, 1176–1179,
10.1080/10473289.1991.10466912, 1991.Langford, A. O., Senff, C. J., Alvarez, R. J., Banta, R. M., and Hardesty,
R. M.: Long-range transport of ozone from the Los Angeles Basin: A case
study, Geophys. Res. Lett., 37, L06807, 10.1029/2010gl042507, 2010.Langford, A. O., Senff, C. J., Alvarez, R. J., Banta, R. M., Hardesty, R.
M., Parrish, D. D., and Ryerson, T. B.: Comparison between the TOPAZ
Airborne Ozone Lidar and In Situ Measurements during TexAQS 2006, J. Atmos.
Ocean. Tech., 28, 1243–1257, 10.1175/Jtech-D-10-05043.1, 2011.Langford, A. O., Brioude, J., Cooper, O. R., Senff, C. J., Alvarez, R. J.,
Hardesty, R. M., Johnson, B. J., and Oltmans, S. J.: Stratospheric influence
on surface ozone in the Los Angeles area during late spring and early summer
of 2010, J. Geophys. Res., 117, D00V06, 10.1029/2011JD016766, 2012.Langford, A. O., Senff, C. J., Alvarez, R. J., Brioude, J., Cooper, O. R.,
Holloway, J. S., Lin, M. Y., Marchbanks, R. D., Pierce, R. B., Sandberg, S.
P., Weickmann, A. M., and Williams, E. J.: An overview of the 2013 Las Vegas
Ozone Study (LVOS): Impact of stratospheric intrusions and long-range
transport on surface air quality, Atmos. Environ., 109, 305–322,
10.1016/J.Atmosenv.2014.08.040, 2015.Leblanc, T., Brewer, M. A., Wang, P. S., Granados-Muñoz, M. J., Strawbridge, K. B., Travis, M., Firanski, B., Sullivan, J. T.,
McGee, T. J., Sumnicht, G. K., Twigg, L. W., Berkoff, T. A., Carrion, W., Gronoff, G., Aknan, A., Chen, G., Alvarez, R. J.,
Langford, A. O., Senff, C. J., Kirgis, G., Johnson, M. S., Kuang, S., and Newchurch, M. J.: Validation of the TOLNet lidars:
the Southern California Ozone Observation Project (SCOOP), Atmos. Meas. Tech., 11, 6137–6162, 10.5194/amt-11-6137-2018, 2018.Lin, M. Y., Fiore, A. M., Cooper, O. R., Horowitz, L. W., Langford, A. O.,
Levy, H., Johnson, B. J., Naik, V., Oltmans, S. J., and Senff, C. J.:
Springtime high surface ozone events over the western United States:
Quantifying the role of stratospheric intrusions, J. Geophys. Res., 117,
D00v22, 10.1029/2012jd018151, 2012a.Lin, M. Y., Fiore, A. M., Horowitz, L. W., Cooper, O. R., Naik, V.,
Holloway, J., Johnson, B. J., Middlebrook, A. M., Oltmans, S. J., Pollack,
I. B., Ryerson, T. B., Warner, J. X., Wiedinmyer, C., Wilson, J., and Wyman,
B.: Transport of Asian ozone pollution into surface air over the western
United States in spring, J. Geophys. Res., 117, D00v07,
10.1029/2011JD016961, 2012b.Malicet, J., Daumont, D., Charbonnier, J., Parisse, C., Chakir, A., and
Brion, J.: Ozone UV Spectroscopy, 2. Absorption Cross-Sections and
Temperature-Dependence, J. Atmos. Chem., 21, 263–273, 10.1007/Bf00696758,
1995.NASA: AJAX aircraft data: available at: https://www.esrl.noaa.gov/csd/groups/csd3/measurements/cabots/ajax.php, last access: 18 March 2019.NOAA: TOPAZ ozone lidar data, available at: https://www.esrl.noaa.gov/csd/groups/csd3/measurements/cabots/topaz.php, last access: 18 March 2019.Panek, J., Saah, D., Esperanza, A., Bytnerowicz, A., Fraczek, W., and
Cisneros, R.: Ozone distribution in remote ecologically vulnerable terrain
of the southern Sierra Nevada, CA, Environ. Pollut., 182, 343–356,
10.1016/j.envpol.2013.07.028, 2013.
Proffitt, M. H. and Langford, A. O.: Ground-based differential absorption
lidar system for day or night measurements of ozone throughout the free
troposphere, Appl. Optics, 36, 2568–2585, 1997.
Reynolds, S., Bohnenkamp, C., Kaduwela, A., Katayama, B., Shipp, E., Sweet, J., Tanrikulu, S., and Ziman, S.: Central California Ozone
Study: Synthesis of Results, in: Nato Sci Peace Sec B, edited by: Steyn, D. and Rao, S., Dordrecht, 571–574, 2010.Ryerson, T. B., Andrews, A. E., Angevine, W. M., Bates, T. S., Brock, C. A.,
Cairns, B., Cohen, R. C., Cooper, O. R., de Gouw, J. A., Fehsenfeld, F. C.,
Ferrare, R. A., Fischer, M. L., Flagan, R. C., Goldstein, A. H., Hair, J.
W., Hardesty, R. M., Hostetler, C. A., Jimenez, J. L., Langford, A. O.,
McCauley, E., McKeen, S. A., Molina, L. T., Nenes, A., Oltmans, S. J.,
Parrish, D. D., Pederson, J. R., Pierce, R. B., Prather, K., Quinn, P. K.,
Seinfeld, J. H., Senff, C. J., Sorooshian, A., Stutz, J., Surratt, J. D.,
Trainer, M., Volkamer, R., Williams, E. J., and Wofsy, S. C.: The 2010
California Research at the Nexus of Air Quality and Climate Change (CalNex)
field study, J. Geophys. Res., 118, 5830–5866, 10.1002/Jgrd.50331, 2013.Ryoo, J. M., Johnson, M. S., Iraci, L. T., Yates, E. L., and Gore, W.:
Investigating sources of ozone over California using AJAX airborne
measurements and models.: Assessing the contribution from longrange
transport, Atmos. Environ., 155, 53–67, 10.1016/j.atmosenv.2017.02.008,
2017.Senff, C. J., Alvarez, R. J., Hardesty, R. M., Banta, R. M., and Langford,
A. O.: Airborne lidar measurements of ozone flux downwind of Houston and
Dallas, J. Geophys. Res., 115, D20307, 10.1029/2009jd013689, 2010.
Schäfer, K., Fommel, G., Hoffmann, H., Briz, S., Junkermann, W., Emeis,
S., Jahn, C., Leipold, S., Sedlmaier, A., Dinev, S., Reishofer, G.,
Windholz, L., Soulakellis, N., Sifakis, N., and Sarigiannis, D.:
Three-dimensional ground-based measurements of urban air quality to evaluate
satellite derived interpretations for urban air pollution, Water Air
Soil Pollut., 2, 91–102, 2002.Smit, H. G. J., DeBacker, H., Braathen, G., Claude, H., Davies, J., Deshler, T., Johnson, B., Kyro, E., Kivi, R., Oltmans, S., Sasaki, T., Schmidlin, F., Smit, H., Staehelin, J., Stubi, R., Tarasick, D., Thompson, A., Viatte, P., and Witte, J.: Quality Assurance and Quality Control for Ozonesonde Measurements in GAW,
World Meteorological Organization, Report No. 201, available at: https://library.wmo.int/pmb_ged/gaw_201_en.pdf (last access:
19 March 2019), 2014.St. Clair, J. M., Swanson, A. K., Bailey, S. A., Wolfe, G. M., Marrero, J. E., Iraci, L. T., Hagopian, J. G., and
Hanisco, T. F.: A new non-resonant laser-induced fluorescence instrument for the airborne in situ measurement of
formaldehyde, Atmos. Meas. Tech., 10, 4833–4844, 10.5194/amt-10-4833-2017, 2017.Tanaka, T., Yates, E., Iraci, L. T., Johnson, M. S., Gore, W., Tadic, J.,
Loewenstein, M., Kuze, A., Frankenberg, C., Butz, A., and Yoshida, Y.:
Two-Year Comparison of Airborne Measurements of CO2 and CH4 With GOSAT at
Railroad Valley, Nevada, Geoscience and Remote Sensing, IEEE T. Geosci. Remote, 54, 4367–4375, 10.1109/Tgrs.2016.2539973, 2016.Trousdell, J. F., Conley, S. A., Post, A., and Faloona, I. C.: Observing entrainment mixing, photochemical ozone
production, and regional methane emissions by aircraft using a simple mixed-layer framework, Atmos. Chem. Phys., 16, 15433–15450, 10.5194/acp-16-15433-2016, 2016.UC Davis: Scientific Aviation aircraft data, available at:
https://www.esrl.noaa.gov/csd/groups/csd3/measurements/cabots/ucdavis/Aircraft/, last access: 18 March 2019.
U.S. Environmental Protection Agency: Policy Assessment for the Review of
the Ozone National Ambient Air Quality Standards, Research Triangle Park,
North CarolinaEPA-452/R-14-006, 2014.
Völger, P., Bösenberg, J., and Shult, I.: Scattering properties of
selected model aerosols calculated at UV-wavelengths: Implications for DIAL
measurements of tropospheric ozone, Contributions to Atmospheric Physics,
69, 177–187, 1996.Wang, L., Newchurch, M. J., Alvarez II, R. J., Berkoff, T. A., Brown, S. S., Carrion, W., De Young, R. J., Johnson, B. J.,
Ganoe, R., Gronoff, G., Kirgis, G., Kuang, S., Langford, A. O., Leblanc, T., McDuffie, E. E., McGee, T. J., Pliutau, D.,
Senff, C. J., Sullivan, J. T., Sumnicht, G., Twigg, L. W., and Weinheimer, A. J.: Quantifying TOLNet ozone lidar accuracy
during the 2014 DISCOVER-AQ and FRAPPÉ campaigns, Atmos. Meas. Tech., 10, 3865–3876, 10.5194/amt-10-3865-2017, 2017.Yates, E. L., Iraci, L. T., Roby, M. C., Pierce, R. B., Johnson, M. S., Reddy, P. J., Tadic, J. M., Loewenstein, M., and
Gore, W.: Airborne observations and modeling of springtime stratosphere-to-troposphere transport over California,
Atmos. Chem. Phys., 13, 12481–12494, 10.5194/acp-13-12481-2013, 2013.
Yates, E. L., Iraci, L. T., Austerberry, D., Pierce, R. B., Roby, M. C.,
Tadic, J. M., Loewenstein, M., and Gore, W.: Characterizing the impacts of
vertical transport and photochemical ozone production on an exceedance area,
Atmos. Environ., 109, 342–350, 10.1016/j.atmosenv.2014.09.002, 2015.Zaveri, R. A., Shaw, W. J., Cziczo, D. J., Schmid, B., Ferrare, R. A., Alexander, M. L., Alexandrov, M., Alvarez, R. J., Arnott, W. P., Atkinson, D. B.,
Baidar, S., Banta, R. M., Barnard, J. C., Beranek, J., Berg, L. K., Brechtel, F., Brewer, W. A., Cahill, J. F., Cairns, B., Cappa, C. D., Chand, D.,
China, S., Comstock, J. M., Dubey, M. K., Easter, R. C., Erickson, M. H., Fast, J. D., Floerchinger, C., Flowers, B. A., Fortner, E.,
Gaffney, J. S., Gilles, M. K., Gorkowski, K., Gustafson, W. I., Gyawali, M., Hair, J., Hardesty, R. M., Harworth, J. W., Herndon, S.,
Hiranuma, N., Hostetler, C., Hubbe, J. M., Jayne, J. T., Jeong, H., Jobson, B. T., Kassianov, E. I., Kleinman, L. I., Kluzek, C., Knighton, B.,
Kolesar, K. R., Kuang, C., Kubátová, A., Langford, A. O., Laskin, A., Laulainen, N., Marchbanks, R. D., Mazzoleni, C., Mei, F., Moffet, R. C.,
Nelson, D., Obland, M. D., Oetjen, H., Onasch, T. B., Ortega, I., Ottaviani, M., Pekour, M., Prather, K. A., Radney, J. G., Rogers, R. R.,
Sandberg, S. P., Sedlacek, A., Senff, C. J., Senum, G., Setyan, A., Shilling, J. E., Shrivastava, M., Song, C., Springston, S. R.,
Subramanian, R., Suski, K., Tomlinson, J., Volkamer, R., Wallace, H. W., Wang, J., Weickmann, A. M., Worsnop, D. R., Yu, X.-Y.,
Zelenyuk, A., and Zhang, Q.: Overview of the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES), Atmos. Chem. Phys., 12, 7647–7687,
10.5194/acp-12-7647-2012, 2012.