Field studies of reactive nitrogen chemistry
Nighttime Chemistry: NO3 and N2O5
The photochemically driven, OH-initiated oxidation processes during the day are supplemented or, for some classes of volatile organic compounds (VOCs) such as terpenes or CH3SCH3, even surpassed by night-time reactions with the NO3 radical. NO3 can initiate and propagate nocturnal radical chemistry, linking HO2 and NOx chemistry and significantly impact on the oxidation rates of several classes of atmospheric traces gases. In air masses with sufficient NO2, N2O5 mixing ratios often exceed those of NO3 and the heterogeneous hydrolysis of N2O5 on tropospheric aerosol can substantially modify the amount of reactive nitrogen available for daytime photochemical O3 production. We measure pptv levels NO3 and N2O5 in the field using cavity-ring-down spectroscopy (see Methods, Field 1). We also measure the lifetime of NO3 with respect to its reactions with organic trace gases directly (see Methods, Field 4) and examine its role in day- and night-time oxidation of biogenic trace gases.
Sobanski, N., Tang, M. J., Thieser, J., Schuster, G., Pöhler, D., Fischer, H., Song, W., Sauvage, C., Williams, J., Fachinger, J., Berkes, F., Hoor, P., Platt, U., Lelieveld, J., and Crowley, J. N.: Chemical and meteorological influences on the lifetime of NO3 at a semi-rural mountain site during PARADE, Atmos. Chem. Phys., 16, 4867-4883, 10.5194/acp-16-4867-2016, 2016.
Phillips, G. J., Thieser, J., Tang, M. J., Sobanski, N., Schuster, G., Fachinger, J., Drewnick, F., Borrmann, S., Bingemer, H., Lelieveld, J., and Crowley, J. N.: Estimating N2O5 uptake coefficients using ambient measurements of NO3, N2O5, ClNO2 and particle-phase nitrate, Atmos. Chem. Phys., 16, 13231-13249, 10.5194/acp-16-13231-2016, 2016.
Liebmann, J., Karu, E., Sobanski, N., Schuladen, J., Ehn, M., Schallhart, S., Quéléver, L., Hellen, H., Hakola, H., Hoffmann, T., Williams, J., Fischer, H., Lelieveld, J., and Crowley, J. N.: Direct measurement of NO3 radical reactivity in a boreal forest, Atmos. Chem. Phys., 2018, 3799-3815, 10.5194/acp-18-3799-2018, 2018.
Organic Nitrates and the Reactive Nitrogen Budget
Organic nitrates are formed in the atmosphere by degradations of VOCS in the presence of NOX and are initiated by the OH-radical and O3 during the day and by the NO3 radical at night-time. Organic nitrates can exist both as peroxy-nitrates (PNs) and alkyl-nitrates (ANs), which have different characteristics with regard to their atmospheric lifetime and loss processes, depending on the identity of the parent organic molecule. We measure peroxy-acetylnitrate (the dominant PN) using chemical ionisation mass spectrometry (Methods, Field 2) whereas ANs are measured by cavity-ring-down spectroscopy (see Methods, Field 3). As air masses age, freshly emitted NOX (NO + NO2) is converted to NOY (NOX + inorganic and organic nitrates in both gas- and particle phase). We analyse the lifetime of NOX and the partitioning of reactive nitrogen to understand the competition between recycling and loss of NOX which impact e.g. on photochemical O3 formation. We measure NOX and NOY using cavity-ring-down spectroscopy (Methods, Field 4).
Sobanski, N., Thieser, J., Schuladen, J., Sauvage, C., Song, W., Williams, J., Lelieveld, J., and Crowley, J. N.: Day- and Night-time Formation of Organic Nitrates at a Forested Mountain-site in South West Germany, Atmos. Chem. Phys., 17, 4115-4130, 2017.
Crowley, J. N., Pouvesle, N., Phillips, G. J., Axinte, R., Fischer, H., Petäjä, T., Nölscher, A., Williams, J., Hens, K., Harder, H., Martinez-Harder, M., Novelli, A., Kubistin, D., Bohn, B., and Lelieveld, J.: Insights into HOx and ROx chemistry in the boreal forest via measurement of peroxyacetic acid, peroxyacetic nitric anhydride (PAN) and hydrogen peroxide, Atmos. Chem. Phys., 18, 13457-13479, 10.5194/acp-18-13457-2018, 2018.
Chlorine chemistry is best known for its pivotal role in the formation of the stratospheric polar ozone hole but is also present in the lower atmosphere in both reactive and un-reactive forms. Originating from e.g. acid-displacement from sea-salt or incineration we find reactive chlorine in the form of ClNO2 and HCl. The release of Cl atoms from either of these reservoirs can impact on rates of oxidation of VOCs and thus photochemical ozone formation. We assess the impact of chlorine chemistry in different environments via measurements of ClNO2 and HCl using chemical ionisation mass spectrometry (see Methods, Field 2).
Phillips, G. J., Tang, M. J., Thieser, J., Brickwedde, B., Schuster, G., Bohn, B., Lelieveld, J., and Crowley, J. N.: Significant concentrations of nitryl chloride observed in rural continental Europe associated with the influence of sea salt chloride and anthropogenic emissions, Geophys. Res. Lett., 39, L10811, doi:10.1029/2012GL051912, 2012.
Philipp G. Eger, Nils Friedrich, Jan Schuladen, Justin Shenolikar, Ivan Tadic, James Brooks, Eoghan Darbyshire, Efstratios Bourtsoukidis, Achim Edtbauer, Lisa Ernle, Michael Pikridas, Sebastian Tauer , Stephan Borrmann , Frank Drewnick , Horst Fischer , Hartwig Harder , Jonathan Williams , Jos Lelieveld , and John N. Crowley: Shipborne measurements of ClNO2 in the Mediteranean Sea and around the Arabian Peninsula during summer, to be submitted to Atmos. Chem. Phys., 2019.