the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Aug 2024
Measurement Report: Diurnal Variability of NO2 and HCHO Lower Tropospheric Vertical Profiles in Southeastern Los Angeles
Abstract. Ground level ozone in excess of United States ambient air quality standards remains a prevalent issue across Southern California, particularly in the summer months. To improve our understanding of the vertical distribution of ozone precursors in southern California, we used ground-based MAX-DOAS measurements in Whittier CA to simultaneously retrieve both near-surface mole fractions and vertical column densities of both NO2 and HCHO. While vertical column densities of NO2 are well correlated with TROPOMI observations over the study period (R=0.77), HCHO VCDs and FNRs derived from MAX-DOAS observations are less well correlated (R=0.44 and 0.35, respectively). These observations also show differing diurnal cycles between near surface mixing ratios and vertical column densities due to variability in the vertical profile that will be increasingly critical to understand given the ongoing shift from sun synchronous to geostationary satellite observations. Ratios of HCHO to NO2, commonly referred to as FNR, derived from satellite-based measurements are used to diagnose ozone production chemistry over regions without consistent surface based measurements. Using ground-based measurements, we determine FNRs using both surface mole fractions and vertical column densities, finding FNRs derived from surface mole fractions are generally lower than those derived from column based measurements. Evaluating ozone exceedance probability as a function of FNR for both quantities suggests the transition between a VOC limited and NOx limited regimes may begin at lower FNR values than those derived from satellite based measurements in East LA. We find these differences in FNR derived form ground based and satellite based measurements are driven by variability in the vertical distribution of HCHO. These impacts are most pronounced in late afternoon, when ozone exceedances are most prevalent.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(3536 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-1460', Anonymous Referee #2, 05 Nov 2024
The authors present a valuable dataset, with two years of MAX-DOAS measurements in Southern California. They compare these measurements with TROPOMI data and examine the diurnal variation of lower troposphere vertical column densities (VCD) and surface mole fraction for NO2 and HCHO. They further combined the dataset with ozone measurements from Pico Rivera to understand the ozone sensitivity in this region. They find that NO2 and HCHO have different vertical distributions throughout the day, which significantly impact the derived HCHO to NO2 (FNR) ratio, whether derived from surface values or total columns. This ratio has been used for identifying the threshold values that indicate a shift between NOx-limited and VOC-limited ozone production regimes. The finding has important implications on how to interpret satellite-derived FNR in the context of ozone sensitivity. The dataset is interesting, but I find that the analysis can be further improved. Here a few comments:
1. There is very little discussion about the details of comparison between MAX-DOAS and TROPOMI. Was there any quality control on TROPOMI level 2 data? Did you filter out any data that is considered low quality?
Would it be possible that the difference between MAX-DOAS and TROPOMI NO2/HCHO VCD (Figures 2 and 3) can be due to the difference in vertical sensitivity and a priori profiles ? This has been discussed in several studies (Dimitropoulou et al., 2020; Verhoelst et al., 2021)? Could the authors examine these discrepancies on both NO₂ and HCHO, possibly by recalculating TROPOMI values using mean MAX-DOAS vertical profiles? While I do not suggest extensive additional work, this step would improve our understanding of the observed differences between MAX-DOAS and TROPOMI results.
2. Are there any other ground-based in situ or remote-sensing measurements of HCHO and NO2 available in this region? If so, do they support the MAX-DOAS data presented here? It would strengthen the study if the MAX-DOAS results were compared with other data sources in the area.
3. This work has been comparing with Jin et al. (2020), which is a study based on satellite data and noontime ozone. Note that ozone production often peaks around noontime, which coincides with satellite overpass time. It is unclear if the authors are focusing on noontime observations for their ozone sensitivity analysis. I recommend focusing on the surface and column FNR comparison specifically at noontime, as done in Jin et al. (2020).
4. In Figure 5, the authors show that surface or LT-VCD derived threshold FNR are lower than the satellite derived values, due to a large fraction of HCHO aloft. This is likely due to secondary production of HCHO that takes place aloft while NO2 is from primary emissions, leading to different vertical distribution. It would be useful to have some discussion on the possible reasons for different vertical distributions between HCHO and NO, and potential impact on ozone production.
5. Figure 4. Can you add ozone diurnal profile here to Figure 4?
Technical comments:
6. Line 136 Kim 2016 wrong citation.
7. Please define FNR in its first appearance.
References
Dimitropoulou, E., Hendrick, F., Pinardi, G., Friedrich, M. M., Merlaud, A., Tack, F., De Longueville, H., Fayt, C., Hermans, C., Laffineur, Q., Fierens, F., and Van Roozendael, M.: Validation of TROPOMI tropospheric NO2 columns using dual-scan multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Uccle, Brussels, Atmospheric Meas. Tech., 13, 5165–5191, https://doi.org/10.5194/amt-13-5165-2020, 2020.
Verhoelst, T., Compernolle, S., Pinardi, G., Lambert, J.-C., Eskes, H. J., Eichmann, K.-U., Fjæraa, A. M., Granville, J., Niemeijer, S., Cede, A., Tiefengraber, M., Hendrick, F., Pazmiño, A., Bais, A., Bazureau, A., Boersma, K. F., Bognar, K., Dehn, A., Donner, S., Elokhov, A., Gebetsberger, M., Goutail, F., Grutter de la Mora, M., Gruzdev, A., Gratsea, M., Hansen, G. H., Irie, H., Jepsen, N., Kanaya, Y., Karagkiozidis, D., Kivi, R., Kreher, K., Levelt, P. F., Liu, C., Müller, M., Navarro Comas, M., Piters, A. J. M., Pommereau, J.-P., Portafaix, T., Prados-Roman, C., Puentedura, O., Querel, R., Remmers, J., Richter, A., Rimmer, J., Rivera Cárdenas, C., Saavedra de Miguel, L., Sinyakov, V. P., Stremme, W., Strong, K., Van Roozendael, M., Veefkind, J. P., Wagner, T., Wittrock, F., Yela González, M., and Zehner, C.: Ground-based validation of the Copernicus Sentinel-5P TROPOMI NO2 measurements with the NDACC ZSL-DOAS, MAX-DOAS and Pandonia global networks, Atmospheric Meas. Tech., 14, 481–510, https://doi.org/10.5194/amt-14-481-2021, 2021.
Citation: https://doi.org/10.5194/egusphere-2024-1460-RC1 - AC1: 'Comment on egusphere-2024-1460', Peter Peterson, 07 Apr 2025
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RC2: 'Comment on egusphere-2024-1460', Anonymous Referee #3, 07 Feb 2025
This measurement report provides an overview of MAX-DOAS measurements performed from Whittier College over the course of ~2 years. Measurements of NO2 and HCHO from MAX-DOAS were analyzed and compared to TROPOMI retrievals. Diurnal variations of vertical column densities were also analyzed and demonstrated similar patterns of variability observed in previous studies. Uniquely, using a combination of surface and MAX-DOAS column measurements, the ratios of HCHO to NO2 (FNR) were analyzed to better understand the ozone production regimes in the eastern LA area. FNR values were found to be lower over the Whittier College site compared to downtown Los Angeles. The findings highlight the need to carefully distinguish near surface chemistry from above surface chemistry when using FNRs to better disentangle ozone chemistry.
Line 85: The authors reference “high spatial resolution grid” when talking about retrieving vertical profiles. I think the authors meant to say “high vertical resolution grid”. Please clarify.
Line 104: Check for switches between present and past tense throughout the manuscript.
Line 120-125: It would be useful to briefly mention the possible reasons why TROPOMI would be higher during the study period and besides the possible long range transport of wildfire plumes. Have previous studies, whether in agreement or contrast, highlighted any biases in the TROPOMI HCHO apriori profile in urban areas?
Citation: https://doi.org/10.5194/egusphere-2024-1460-RC2 - AC1: 'Comment on egusphere-2024-1460', Peter Peterson, 07 Apr 2025
- AC1: 'Comment on egusphere-2024-1460', Peter Peterson, 07 Apr 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-1460', Anonymous Referee #2, 05 Nov 2024
The authors present a valuable dataset, with two years of MAX-DOAS measurements in Southern California. They compare these measurements with TROPOMI data and examine the diurnal variation of lower troposphere vertical column densities (VCD) and surface mole fraction for NO2 and HCHO. They further combined the dataset with ozone measurements from Pico Rivera to understand the ozone sensitivity in this region. They find that NO2 and HCHO have different vertical distributions throughout the day, which significantly impact the derived HCHO to NO2 (FNR) ratio, whether derived from surface values or total columns. This ratio has been used for identifying the threshold values that indicate a shift between NOx-limited and VOC-limited ozone production regimes. The finding has important implications on how to interpret satellite-derived FNR in the context of ozone sensitivity. The dataset is interesting, but I find that the analysis can be further improved. Here a few comments:
1. There is very little discussion about the details of comparison between MAX-DOAS and TROPOMI. Was there any quality control on TROPOMI level 2 data? Did you filter out any data that is considered low quality?
Would it be possible that the difference between MAX-DOAS and TROPOMI NO2/HCHO VCD (Figures 2 and 3) can be due to the difference in vertical sensitivity and a priori profiles ? This has been discussed in several studies (Dimitropoulou et al., 2020; Verhoelst et al., 2021)? Could the authors examine these discrepancies on both NO₂ and HCHO, possibly by recalculating TROPOMI values using mean MAX-DOAS vertical profiles? While I do not suggest extensive additional work, this step would improve our understanding of the observed differences between MAX-DOAS and TROPOMI results.
2. Are there any other ground-based in situ or remote-sensing measurements of HCHO and NO2 available in this region? If so, do they support the MAX-DOAS data presented here? It would strengthen the study if the MAX-DOAS results were compared with other data sources in the area.
3. This work has been comparing with Jin et al. (2020), which is a study based on satellite data and noontime ozone. Note that ozone production often peaks around noontime, which coincides with satellite overpass time. It is unclear if the authors are focusing on noontime observations for their ozone sensitivity analysis. I recommend focusing on the surface and column FNR comparison specifically at noontime, as done in Jin et al. (2020).
4. In Figure 5, the authors show that surface or LT-VCD derived threshold FNR are lower than the satellite derived values, due to a large fraction of HCHO aloft. This is likely due to secondary production of HCHO that takes place aloft while NO2 is from primary emissions, leading to different vertical distribution. It would be useful to have some discussion on the possible reasons for different vertical distributions between HCHO and NO, and potential impact on ozone production.
5. Figure 4. Can you add ozone diurnal profile here to Figure 4?
Technical comments:
6. Line 136 Kim 2016 wrong citation.
7. Please define FNR in its first appearance.
References
Dimitropoulou, E., Hendrick, F., Pinardi, G., Friedrich, M. M., Merlaud, A., Tack, F., De Longueville, H., Fayt, C., Hermans, C., Laffineur, Q., Fierens, F., and Van Roozendael, M.: Validation of TROPOMI tropospheric NO2 columns using dual-scan multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Uccle, Brussels, Atmospheric Meas. Tech., 13, 5165–5191, https://doi.org/10.5194/amt-13-5165-2020, 2020.
Verhoelst, T., Compernolle, S., Pinardi, G., Lambert, J.-C., Eskes, H. J., Eichmann, K.-U., Fjæraa, A. M., Granville, J., Niemeijer, S., Cede, A., Tiefengraber, M., Hendrick, F., Pazmiño, A., Bais, A., Bazureau, A., Boersma, K. F., Bognar, K., Dehn, A., Donner, S., Elokhov, A., Gebetsberger, M., Goutail, F., Grutter de la Mora, M., Gruzdev, A., Gratsea, M., Hansen, G. H., Irie, H., Jepsen, N., Kanaya, Y., Karagkiozidis, D., Kivi, R., Kreher, K., Levelt, P. F., Liu, C., Müller, M., Navarro Comas, M., Piters, A. J. M., Pommereau, J.-P., Portafaix, T., Prados-Roman, C., Puentedura, O., Querel, R., Remmers, J., Richter, A., Rimmer, J., Rivera Cárdenas, C., Saavedra de Miguel, L., Sinyakov, V. P., Stremme, W., Strong, K., Van Roozendael, M., Veefkind, J. P., Wagner, T., Wittrock, F., Yela González, M., and Zehner, C.: Ground-based validation of the Copernicus Sentinel-5P TROPOMI NO2 measurements with the NDACC ZSL-DOAS, MAX-DOAS and Pandonia global networks, Atmospheric Meas. Tech., 14, 481–510, https://doi.org/10.5194/amt-14-481-2021, 2021.
Citation: https://doi.org/10.5194/egusphere-2024-1460-RC1 - AC1: 'Comment on egusphere-2024-1460', Peter Peterson, 07 Apr 2025
-
RC2: 'Comment on egusphere-2024-1460', Anonymous Referee #3, 07 Feb 2025
This measurement report provides an overview of MAX-DOAS measurements performed from Whittier College over the course of ~2 years. Measurements of NO2 and HCHO from MAX-DOAS were analyzed and compared to TROPOMI retrievals. Diurnal variations of vertical column densities were also analyzed and demonstrated similar patterns of variability observed in previous studies. Uniquely, using a combination of surface and MAX-DOAS column measurements, the ratios of HCHO to NO2 (FNR) were analyzed to better understand the ozone production regimes in the eastern LA area. FNR values were found to be lower over the Whittier College site compared to downtown Los Angeles. The findings highlight the need to carefully distinguish near surface chemistry from above surface chemistry when using FNRs to better disentangle ozone chemistry.
Line 85: The authors reference “high spatial resolution grid” when talking about retrieving vertical profiles. I think the authors meant to say “high vertical resolution grid”. Please clarify.
Line 104: Check for switches between present and past tense throughout the manuscript.
Line 120-125: It would be useful to briefly mention the possible reasons why TROPOMI would be higher during the study period and besides the possible long range transport of wildfire plumes. Have previous studies, whether in agreement or contrast, highlighted any biases in the TROPOMI HCHO apriori profile in urban areas?
Citation: https://doi.org/10.5194/egusphere-2024-1460-RC2 - AC1: 'Comment on egusphere-2024-1460', Peter Peterson, 07 Apr 2025
- AC1: 'Comment on egusphere-2024-1460', Peter Peterson, 07 Apr 2025
Peer review completion
Journal article(s) based on this preprint
Data sets
Whittier_CH2O_NO2_MAXDOAS_20200326 Peter Peterson https://doi.org/10.5281/zenodo.11117573
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Lisa Hernandez
Leslie Tanaka
Alejandro Dunnick
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3536 KB) - Metadata XML