Chemical Processes related to ozone production in remote areas
Ozone in the atmosphere is an important oxidant and a greenhouse gas. In-situ measurements of O3, NO, OH, HO2 and actinic radiation are used to derive ozone tendencies from the difference between ozone production and loss. The experimental results are compared to simulations with global chemistry transport models to test our understanding of ozone formation. The results show a clear tendency for ozone production in the continental boundary layer and in the in the upper troposphere, while the marine boundary layer and the middle troposphere are characterized by a tendency for ozone destruction. Measurements of these species can also be used to evaluate the photochemical steady state (PSS) between NO and NO2. The deviations observed under low NOx conditions indicate that a yet unidentified oxidant is needed to explain the photochemical conditions observed in the remote marine boundary layer.
Bozem, H., Butler, T. M., Lawrence, M. G., Harder, H., Martinez, M., Kubistin, D., Lelieveld, J., and Fischer, H.: Chemical processes related to net ozone tendencies in the free troposphere, Atmos. Chem. Phys., 17, 10565–10582, https://doi.org/10.5194/acp-17-10565-2017, 2017a.
Hosaynali Beygi, Z., Fischer, H., Harder, H. D., Martinez, M., Sander, R., Williams, J., Brookes, D. M., Monks, P. S., and Lelieveld, J.: Oxidation photochemistry in the Southern Atlantic boundary layer: unexpected deviations of photochemical steady state, Atmos. Chem. Phys., 11, 8497-8513, https://doi.org/10.5194/acp-11-8497-2011, 2011.
The role of formaldehyde and hydrogen peroxide for the oxidizing power of the troposphere
Both HCHO and H2O2 strongly affect the oxidizing power of the troposphere due to their double role as radical reservoir species (HOx production by H2O2 and HCHO photolysis) and radical sinks (due to wet and dry deposition). They are ideal to study the interplay between chemistry, transport and physical removal. Thus, they are suitable candidates to evaluate atmospheric models. In the free troposphere above the boundary layer, chemistry, transport and cloud processing determine the distribution of HCHO and H2O2. Surprisingly, studies in the outflow of deep convective clouds indicate that both species are transported from the boundary layer to the upper also despite their rather large solubility in raindrops. Ship-based measurements of H2O2 and HCHO in the marine boundary layer allow the study of their dry deposition loss to the ocean surface. The situation gets even more complex in the continental boundary layer. Beside additional sources for both species, the deposition is more complex due to exchange with the vegetation. Another complication is the diurnal change in the boundary layer height that results in entrainment during sunrise. This complex environment, where horizontal and vertical transport, complex chemistry and deposition all play significant roles poses challenges for 3D-models.
Bozem, H., Pozzer, A., Harder, H., Martinez, M., Williams, J., Lelieveld, J., and Fischer, H.: The influence of deep convection on HCHO and H2O2 in the upper troposphere over Europe, Atmos. Chem. Phys., 17, 11835–11848, https://doi.org/10.5194/acp-17-11835-2017, 2017b.
Fischer, H., Pozzer, A., Schmitt, T., Jöckel, P., Klippel, T., Taraborrelli, D., and Lelieveld, J.: Hydrogen peroxide in the marine boundary layer over the South Atlantic during the OOMPH cruise in March 2007, Atmos. Chem. Phys., 15, 6971–6980, https://doi.org/10.5194/acp-15-6971-2015, 2015.
Fischer, H., Axinte, R., Bozem, H., Crowley, J. N., Ernest, C., Gilge, S., Hafermann, S., Harder, H., Hens, K., Königstedt, R., Kubistin, D., Mallik, C., Martinez, M., Novelli, A., Parchatka, U., Plass-Dülmer, C., Pozzer, A., Regelin, E., Reiffs, A., Schmidt, T., Schuladen, J., and Lelieveld, J.: Diurnal variability, photochemical production and loss processes of hydrogen peroxide in the boundary layer over Europe, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-1179, 2018.
Klippel, T., Fischer, H., Bozem, H., Lawrence, M. G., Butler, T., Jöckel, P., Tost, H., Martinez, M., Harder, H., Regelin, E., Sander, R., Schiller, C. L., Stickler, A., and Lelieveld, J.: Distribution of hydrogen peroxide and formaldehyde over Central Europe during the HOOVER project, Atmos. Chem. Phys., 11, 4391-4410, https://doi.org/10.5194/acp-11-4391-2011, 2011.
The identification of air masses using chemical tracers
Long-lived trace gases like CO and CH4 can be used to identify air mass origins. Methane emissions are strong over Southeast Asia due to abundant rice fields. Thus, CH4 is an ideal tracer to study the influence of the Indian summer monsoon on upper tropospheric air masses over the eastern Mediterranean and the Arabian Peninsula. To establish a dynamic connection between enhanced CH4 mixing ratios and potential methane sources in south-east Asia, backward trajectories can be used that intersect deep convective clouds over India and Bangladesh. The relation between CO and O3 is a versatile tool to identify stratosphere-troposphere exchange processes, since both species exhibit strong gradients across the tropopause. In the troposphere, high CO and Low O3 mixing ratios prevail, while low CO and high O3 mixing ratios characterize the stratosphere. Exchange between the two reservoirs leads to mixing lines in O3-CO correlation plots, which can be used to study the underlying dynamical processes.
Hoor, P., Gurk, C., Brunner, D., Hegglin, M. I., Wernli, H., and Fischer, H.: Seasonality and extent of extratropical TST derived from in-situ CO measurements during SPURT, Atmos. Chem. Phys., 4, 1427-1442, https://doi.org/10.5194/acp-4-1427-2004, 2004.
Tomsche, L., Pozzer, A., Ojha, N., Parchatka, U., Lelieveld, J., and Fischer, H.: Upper tropospheric CH4 and CO affected by the South Asian summer monsoon during the Oxidation Mechanism Observations mission, Atmos. Chem. Phys., 19, 1915–1939, https://doi.org/10.5194/acp-19-1915-2019, 2019.