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| Titel |
Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season |
| VerfasserIn |
S. Fadnavis, K. Semeniuk, M. G. Schultz, M. Kiefer, A. Mahajan, L. Pozzoli, S. Sonbawane |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 20 ; Nr. 15, no. 20 (2015-10-19), S.11477-11499 |
| Datensatznummer |
250120100
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| Publikation (Nr.) |
 copernicus.org/acp-15-11477-2015.pdf |
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| Zusammenfassung |
The Asian summer monsoon involves complex transport patterns with large-scale
redistribution of trace gases in the upper troposphere and lower
stratosphere (UTLS). We employ the global chemistry–climate model
ECHAM5–HAMMOZ in order to evaluate the transport pathways and the
contributions of nitrogen oxide species peroxyacetyl nitrate (PAN), NOx and HNO3 from
various monsoon regions, to the UTLS over southern Asia and vice versa.
Simulated long-term seasonal mean mixing ratios are compared with trace gas
retrievals from the Michelson Interferometer for Passive Atmospheric
Sounding aboard ENVISAT(MIPAS-E) and aircraft campaigns during the monsoon
season (June–September) in order to evaluate the model's ability to
reproduce these transport patterns.
The model simulations show that there are three regions which contribute
substantial pollution to the South Asian UTLS: the Asian summer monsoon
(ASM), the North American monsoon (NAM) and the West African monsoon (WAM).
However, penetration due to ASM convection reaches deeper into the UTLS
compared to NAM and WAM outflow. The circulation in all three monsoon
regions distributes PAN into the tropical latitude belt in the upper
troposphere (UT). Remote transport also occurs in the extratropical UT where
westerly winds drive North American and European pollutants eastward where
they can become part of the ASM convection and lifted into the lower
stratosphere. In the lower stratosphere the injected pollutants are
transported westward by easterly winds. Sensitivity experiments with
ECHAM5–HAMMOZ for simultaneous NOx and non-methane volatile organic
compounds (NMVOCs) emission change (−10 %) over ASM, NAM and WAM confirm similar transport. Our analysis shows
that a 10 % change in Asian emissions transports ~ 5–30 ppt of PAN
in the UTLS over Asia, ~ 1–10 ppt of PAN in the UTLS of
northern subtropics and mid-latitudes, ~ 7–10 ppt of HNO3
and ~ 1–2 ppb of ozone in UT over Asia. Comparison of emission
change over Asia, North America and Africa shows that the highest transport of
HNO3 and ozone occurs in the UT over Asia and least over Africa.
The intense convective activity in the monsoon regions is associated with
lightning and thereby the formation of additional NOx. This also
affects the distribution of PAN in the UTLS. Simulations with and without
lightning show an increase in the concentrations of PAN (~ 40 %), HNO3 (75 %), NOx (70 %) and ozone (30 %) over the
regions of convective transport. Lightning-induced production of these
species is higher over equatorial Africa and America compared to the ASM
region. This indicates that the contribution of anthropogenic emissions to
PAN in the UTLS over the ASM is higher than that of lightning. |
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