the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Nov 2023
A comprehensive evaluation of enhanced temperature influence on gas and aerosol chemistry in the lamp-enclosed oxidation flow reactor (OFR) system
Abstract. Oxidation flow reactors (OFRs) have been widely used to investigate the formation of secondary organic aerosol (SOA). However, the UV lamps that are commonly used to initiate photochemistry in OFRs can lead to increases in the reactor temperature with consequences that have not been assessed in detail. In this study, we systematically investigated the temperature distribution inside an Aerodyne Potential Aerosol Mass OFR and the associated impacts on flow and chemistry arising from lamp heating. A lamp-induced temperature enhancement was observed, which was a function of lamp driving voltage, number of lamps, lamp types, OFR residence time, and positions inside OFR. Under common OFR operational conditions (e.g., < 5 days of equivalent atmospheric OH exposure under low-NOx conditions), the temperature enhancement was usually within 1–5 °C. Under extreme (but less commonly used) settings, the heating could reach 15 °C. The influence of the increased temperature over ambient conditions on the flow distribution, gas, and condensed phase chemistry inside OFR was evaluated. We found that the increase in temperature changes the flow field, leading to a reduced tail on the residence time distribution and corresponding oxidant exposure due to faster recirculation. According to simulation results from a box model using radical chemistry, the variation of absolute oxidant concentration inside of OFR due to temperature increase was small (<5 %). The temperature influences on existing and newly formed OA were also investigated, suggesting that the increase in temperature can impact the yield, size, and oxidation levels of representative biogenic and anthropogenic SOA types. Recommendations for temperature-dependent SOA yield corrections and OFR operating protocols that mitigate lamp-induced temperature enhancement and fluctuations are presented. We recommend blowing air around the outside of the reactor with fans during OFR experiments to minimize the temperature increase inside OFR. Temperature increases are substantially lower for OFRs using less powerful lamps than the Aerodyne version.
- Preprint
(2452 KB) - Metadata XML
-
Supplement
(2910 KB) - BibTeX
- EndNote
Status: final response (author comments only)
-
RC1: 'Comment on amt-2023-230', Anonymous Referee #1, 15 Dec 2023
The manuscript by Pan et al. investigates the impact of lamp-induced heating in an Aerodyne PAM-OFR, assessing the temperature distribution, flow dynamics, and chemical consequences resulting from UV lamp heating. The authors have used CFD simulation, KinSim kinetic model, and SOM model to investigate how the temperature affects the flow and average OH exposure and how the enhanced temperature impacts the chemistry of gas-phase reactions and SOA formation. They find that the temperature enhancement can be up to 15 ℃ and it has impacts on the gas-phase chemistry and the yield, size, and oxidation levels of SOA. Overall, this manuscript gives a relatively comprehensive evaluation of the increased temperature on the chemical processes in the PAM-OFR. However, some concerns need to be addressed before the manuscript can be considered for publication in AMT.
1. The authors find that the heating inside PAM-OFR is mainly from the heat transfer of the hot quartz sleeve (heated by the lamps) but not from the optical radiation. This is true since UV radiation generates little heat. Based on this finding, I would expect that the authors recommend moving the lamps out of the reactor, which can overcome the heating issue caused by the lamps. This can be found in the design of other OFRs in previous studies (e.g., Huang et al., Atmos. Meas. Tech., 10, 839–867, 2017; Simonen et al., Atmos. Meas. Tech., 10, 1519–1537, 2017; Li et al., Atmos. Chem. Phys., 19, 9715–9731, 2019) and should be discussed in “Section 3.5 Approaches to reduce the heating effect”.
2. The authors use the SOM model to investigate the influence of temperature on SOA formation, which highly relies on the performance of the model under different temperatures. It would be helpful to conduct SOA formation experiments with different temperatures to get accurate decreases in SOA yield under high temperatures. This comparison can be done with or without efficient heat removal methods including a high volume of N2 purge air and external fans as the authors have shown in the manuscript.
3. Similarly, SOA formation experiments with different voltage setting strategies need to be added in Section 3.5 to show the effectiveness.
4. The high temperature also leads to lower RH. How would this influence the SOA formation?
5. It is confusing when comparing Figure 3 and Figure 6b. (1) The horizontal distance is >400 mm in Fig. 3 but <200 mm in Fig. 6b. (2) The temperature shows a monotonic increasing trend from the inlet to the outlet in Fig. 3 but a minimum in the middle in Fig. 6b. Can the authors further explain the differences?
6. Although PAM-OFR is the most commonly used OFR, there are many other types of OFRs. For other OFRs that put lamps outside of the reactor (like the ones listed above), the heating issue is not as serious as PAM-OFR. Using the terminology “OFR” in the Conclusion may lead to misunderstanding. Therefore, I would suggest the authors use the terminology “PAM-OFR” rather than “OFR” throughout the manuscript.Citation: https://doi.org/10.5194/amt-2023-230-RC1 -
RC2: 'Comment on amt-2023-230', Anonymous Referee #2, 18 Feb 2024
Pan et al. observed a lamp-induced enhanced temperature inside the PAM-OFR based on measurements and investigated the impacts on flow and chemistry using model simulations. They find that the temperature enhancements have negligible impacts on gas-phase reactions, while large impacts on the SOA yields, chemical composition, and aerosol-phase chemistry. This study provides relatively systematically and detailed heating effects on chemistry inside the PAM-OFR, and should be suitable for publication in AMT. However, I have a few concerns that I would like the authors to address and some suggestions for improving the clarity of presentation.
1. The authors use “PAM-OFR” in the introduction and methods sections, while “OFR” is used in the rest of the manuscript. Can the authors use one terminology to keep constant throughout the manuscript?
2. The authors find shorter residence time under the enhanced temperature than non-heated PAM-OFR. Generally, shorter reaction time leads to lower SOA yields. How would this contribute to lower SOA yields in SOM modeling results? Compared to gas-phase products evaporation, which is more important?
3. For low and high NOx conditions, what are the concentration levels? If the authors intend to distinguish the fate of peroxy radicals in two conditions, NO concentrations should also be provided.
4. It would be helpful if the authors can provide experiment results to show the heating effects on SOA formation inside the PAM-OFR, e.g. using vs not using the external fans.
5. Line 573: “decreased” not “deceased” I would say.
6. Line 585: one bracket is redundant.
Citation: https://doi.org/10.5194/amt-2023-230-RC2 - RC3: 'Comment on amt-2023-230', Anonymous Referee #3, 20 Feb 2024
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 262 | 101 | 19 | 382 | 21 | 12 | 20 |
- HTML: 262
- PDF: 101
- XML: 19
- Total: 382
- Supplement: 21
- BibTeX: 12
- EndNote: 20
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1