A new assessment of global and regional budgets, fluxes, and lifetimes of atmospheric reactive N and S gases and aerosols.

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Date: June 28, 2022
From: Atmospheric Chemistry and Physics(Vol. 22, Issue 12)
Publisher: Copernicus GmbH
Document Type: Article
Length: 706 words

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Abstract :

We used the EMEP MSC-W (European Monitoring and Evaluation Programme Meteorological Synthesizing Centre - West) model version 4.34 coupled with WRF (Weather Research and Forecasting) model version 4.2.2 meteorology to undertake a present-day (2015) global and regional quantification of the concentrations, deposition, budgets, and lifetimes of atmospheric reactive N (N.sub.r) and S (S.sub.r) species. These are quantities that cannot be derived from measurements alone. In areas with high levels of reduced N.sub.r (RDN = NH.sub.3 + NH4+), oxidized N.sub.r (OXN = NO.sub.x + HNO.sub.3 + HONO + N.sub.2 O.sub.5 + NO3-+ "Other OXN" species), and oxidized S.sub.r (OXS = SO.sub.2 + SO42-), RDN is predominantly in the form of NH.sub.3 (NH4+ typically 20 %), OXN has majority gaseous species composition, and OXS predominantly comprises SO42- except near major SO.sub.2 sources. Most continental regions are now "ammonia rich", more so than previously, which indicates that, although reducing NH.sub.3 emissions will decrease the RDN concentration, decreasing these emissions will have little effect on mitigating secondary inorganic aerosol (SIA). South Asia is the most ammonia-rich region. Coastal areas around East Asia, northern Europe, and the north-eastern United States are "nitrate rich" where NH.sub.4 NO.sub.3 formation is limited by NH.sub.3 . These locations experience transport of OXN from the adjacent continent and/or direct shipping emissions of NO.sub.x, but NH.sub.3 concentrations are lower. The least populated continental areas and most marine areas are "sulfate rich". Deposition of OXN (57.9 TgN yr.sup.-1, 51 %) and RDN (55.5 TgN yr.sup.-1, 49 %) contribute almost equally to total nitrogen deposition. OXS deposition is 50.5 TgS yr.sup.-1 . Globally, wet and dry deposition contribute similarly to RDN deposition; for OXN and OXS, wet deposition contributes slightly more. Dry deposition of NH.sub.3 is the largest contributor to RDN deposition in most regions except for the Rest of Asia area and marine sectors where NH.sub.3 emissions are small and RDN deposition is mainly determined by the transport and rainout of NH4+ (rather than rainout of gaseous NH.sub.3). Thus, reductions in NH.sub.3 would efficiently reduce the deposition of RDN in most continental regions. The two largest contributors to OXN deposition in all regions are HNO.sub.3 and coarse NO3- (via both wet and dry deposition). The deposition of fine NO3- is only important over East Asia. The tropospheric burden of RDN is 0.75 TgN, of which NH.sub.3 and NH4+ comprise 32 % (0.24 TgN; lifetime of 1.6 d) and 68 % (0.51 TgN; lifetime of 8.9 d) respectively. The lifetime of RDN (4.9-5.2 d) is shorter than that of OXN (7.6-7.7 d), which is consistent with a total OXN burden (1.20 TgN) almost double that of RDN. The tropospheric burden of OXS is 0.78 TgS with a lifetime of 5.6-5.9 d. Total nitrate burden is 0.58 TgN with fine NO3- only constituting 10 % of this total, although fine NO3- dominates in eastern China, Europe, and eastern North America. It is important to account for contributions of coarse nitrate to global nitrate budgets. Lifetimes of RDN, OXN, and OXS species vary by a factor of 4 across different continental regions. In East Asia, lifetimes for RDN (2.9-3.0 d), OXN (3.9-4.5 d), and OXS (3.4-3.7 d) are short, whereas lifetimes in the Rest of Asia and Africa regions are about twice as long. South Asia is the largest net exporter of RDN (2.21 TgN yr.sup.-1, 29 % of its annual emission), followed by the Euro_Medi region. Despite having the largest RDN emissions and deposition, East Asia has only small net export and is therefore largely responsible for its own RDN pollution. Africa is the largest net exporter of OXN (1.92 TgN yr.sup.-1, 22 %), followed by Euro_Medi (1.61 TgN yr.sup.-1, 26 %). Considerable marine anthropogenic N.sub.r and S.sub.r pollution is revealed by the large net import of RDN, OXN, and OXS to these areas. Our work demonstrates the substantial regional variation in N.sub.r and S.sub.r budgets and the need for modelling to simulate the chemical and meteorological linkages underpinning atmospheric responses to precursor emissions.

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Gale Document Number: GALE|A708507348