https://escholarship.org/content/qt8mf445sh/qt8mf445sh.pdf?t=nu02or

Atmospheric composition change – global and regional air quality

Atmospheric aerosols can be categorized into primary particles, which are directly emitted by their sources, and secondary particles, generated in the atmosphere from gaseous inorganic and organic precursors. For example, atmospheric oxidation of sulfur containing compounds leads to sulfuric acid and its salts, which represent a major secondary inorganic component of atmospheric aerosols. Likewise, oxidation of nitrogen oxides leads to nitric acid or its salts, which are also abundant in aerosols. The ocean surface, which covers three-quarters of the planet, offers a remarkably dynamic and chemically complex surface for interfacial reactions in the marine boundary layer. The porous nature of permanent or perennial snowpacks adds a tremendous amount of surface area, with which the atmosphere interacts. In short, solar radiation can provide the energy to initiate reactions while atmospherically available surfaces or condensed phases may act to reduce the required energy for a given photochemical pathway, for instance, by allowing a longer wavelength for reaction of species associated with a surface or bulk phase environment.

Heterogeneous photochemistry in the atmosphere.

. The oxygen isotopic composition (Δ17O) of atmospheric nitrate is a function of the relative abundance of atmospheric oxidants (O3, ROx=OH+HO2+RO2) and the formation pathway of nitrate from its precursor NOx (=NO+NO2). Coupled observations and modeling of nitrate Δ17O can be used to quantify the relative importance of chemical formation pathways leading to nitrate formation and reduce uncertainties in the budget of reactive nitrogen chemistry in the atmosphere. We present the first global model of atmospheric nitrate Δ17O and compare with available observations. The largest uncertainty for calculations of nitrate Δ17O is the unconstrained variability in the Δ17O value of tropospheric ozone. The model shows the best agreement with a global compilation of observations when assuming a Δ17O value of tropospheric ozone equal to 35‰ and preferential oxidation of NOx by the terminal oxygen atoms of ozone. Calculated values of annual-mean nitrate Δ17O in the lowest model layer (0–200 m above the surface) vary from 7‰ in the tropics to 41‰ in the polar-regions. The global, annual-mean tropospheric inorganic nitrate burden is dominated by nitrate formation via NO2+OH (76%), followed by N2O5 hydrolysis (18%) and NO3+DMS/HC (4%). Calculated nitrate Δ17O is sensitive to the relative importance of each nitrate formation pathway, suggesting that observations of nitrate Δ17O can be used to quantify the importance of individual reactions (e.g. N2O5 hydrolysis) leading to nitrate formation if the Δ17O value of ozone is known.

/pdf/quantifying-atmospheric-nitrate-formation-pathways-based-on-3gog1xzw60.pdf

Quantifying atmospheric nitrate formation pathways based on a global model of the oxygen isotopic composition (Δ 17 O) of atmospheric nitrate

A strong, unambiguous negative trend is found in the nitrogen isotopic composition (delta15N) of nitrate over the industrial period, on the basis of a 100-meter ice core from Summit, Greenland. This record indicates that ice-core nitrate reflects changes in nitrogen oxide (NOx) source emissions and that anthropogenic emissions of NOx have resulted in a 12 per mil decline in delta15N of atmospheric nitrate from preindustrial values to present. Variations in the isotopic composition of nitrate may affect the interpretation of other records of environmental change that are affected by atmospheric nitrate.

https://science.sciencemag.org/content/sci/324/5932/1288.full.pdf

Anthropogenic Impacts on Nitrogen Isotopes of Ice-Core Nitrate

. As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate Chemistry, Aerosols and Transport), this paper studies the sources of equivalent black carbon (EBC), sulphate, light-scattering aerosols and ozone measured at the Arctic stations Zeppelin, Alert, Barrow and Summit during the years 2000–2007. These species are important pollutants and climate forcing agents, and sulphate and EBC are main components of Arctic haze. To determine where these substances originate, the measurement data were combined with calculations using FLEXPART, a Lagrangian particle dispersion model. The climatology of atmospheric transport from surrounding regions on a twenty-day time scale modelled by FLEXPART shows that the stations Zeppelin, Alert and Barrow are highly sensitive to surface emissions in the Arctic and to emissions in high-latitude Eurasia in winter. Emission sensitivities over southern Asia and southern North America are small throughout the year. The high-altitude station Summit is an order of magnitude less sensitive to surface emissions in the Arctic whereas emissions in the southern parts of the Northern Hemisphere continents are more influential relative to the other stations. Our results show that for EBC and sulphate measured at Zeppelin, Alert and Barrow, northern Eurasia is the dominant source region. For sulphate, Eastern Europe and the metal smelting industry in Norilsk are particularly important. For EBC, boreal forest fires also contribute in summer. No evidence for any substantial contribution to EBC from sources in southern Asia is found. European air masses are associated with low ozone concentrations in winter due to titration by nitric oxides, but are associated with high ozone concentrations in summer due to photochemical ozone formation. There is also a strong influence of ozone depletion events in the Arctic boundary layer on measured ozone concentrations in spring and summer. These results will be useful for developing emission reduction strategies for the Arctic.

/pdf/source-identification-of-short-lived-air-pollutants-in-the-2p9032lt5k.pdf

Source identification of short-lived air pollutants in the Arctic using statistical analysis of measurement data and particle dispersion model output

Atmospheric nitrogen oxides (NOx =NO+ NO2) play a pivotal role in the cycling of reactive nitrogen (ultimately deposited as nitrate) and the oxidative capacity of the atmosphere. Combined measurements of nitrogen and oxygen stable isotope ratios of nitrate collected in the Arctic atmosphere were used to infer the origin and fate of NOx and nitrate on a seasonal basis. In spring, photochemically driven emissions of reactive nitrogen from the snowpack into the atmosphere make local oxidation of NOx by bromine oxide the major contributor to the nitrate budget. The comprehensive isotopic composition of nitrate provides strong constraints on the relative importance of the key atmospheric oxidants in the present atmosphere, with the potential for extension into the past using ice cores.

http://science.sciencemag.org/content/sci/322/5902/730.full.pdf

Nicolas Yan

Papers

Tracing the origin and fate of NOx in the Arctic atmosphere using stable isotopes in nitrate.

Supporting Online Material for Tracing the Origin and Fate of NOx in the Arctic Atmosphere Using Stable Isotopes in Nitrate