Articles | Volume 10, issue 11
Research article
17 Nov 2017
Research article |  | 17 Nov 2017

Quantification of the effect of modeled lightning NO2 on UV–visible air mass factors

Joshua L. Laughner and Ronald C. Cohen

Abstract. Space-borne measurements of tropospheric nitrogen dioxide (NO2) columns are up to 10x more sensitive to upper tropospheric (UT) NO2 than near-surface NO2 over low-reflectivity surfaces. Here, we quantify the effect of adding simulated lightning NO2 to the a priori profiles for NO2 observations from the Ozone Monitoring Instrument (OMI) using modeled NO2 profiles from the Weather Research and Forecasting–Chemistry (WRF-Chem) model. With observed NO2 profiles from the Deep Convective Clouds and Chemistry (DC3) aircraft campaign as observational truth, we quantify the bias in the NO2 column that occurs when lightning NO2 is not accounted for in the a priori profiles. Focusing on late spring and early summer in the central and eastern United States, we find that a simulation without lightning NO2 underestimates the air mass factor (AMF) by 25 % on average for common summer OMI viewing geometry and 35 % for viewing geometries that will be encountered by geostationary satellites. Using a simulation with 500 to 665 mol NO flash−1 produces good agreement with observed NO2 profiles and reduces the bias in the AMF to  <  ±4 % for OMI viewing geometries. The bias is regionally dependent, with the strongest effects in the southeast United States (up to 80 %) and negligible effects in the central US. We also find that constraining WRF meteorology to a reanalysis dataset reduces lightning flash counts by a factor of 2 compared to an unconstrained run, most likely due to changes in the simulated water vapor profile.

Short summary
NO2 (a gas that plays an important role in air quality) can be measured by satellite-based instruments. These measurements require a best guess of the vertical distribution of NO2 and are very sensitive to the changes in that distribution near the top of the troposphere (~ 12 km). NO2 concentrations at this altitude are strongly influenced by lightning; therefore, we study how different representations of lightning in models that provide that best guess affect the NO2 measured by satellites.