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| Titel |
Chemical composition of pre-monsoon air in the Indo-Gangetic Plain measured using a new air quality facility and PTR-MS: high surface ozone and strong influence of biomass burning |
| VerfasserIn |
V. Sinha, V. Kumar, C. Sarkar |
| 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 ; 14, no. 12 ; Nr. 14, no. 12 (2014-06-16), S.5921-5941 |
| Datensatznummer |
250118811
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| Publikation (Nr.) |
 copernicus.org/acp-14-5921-2014.pdf |
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| Zusammenfassung |
| One seventh of the world's population lives in the Indo-Gangetic Plain (IGP)
and the fertile region sustains agricultural food crop production for much of
South Asia, yet it remains one of the most under-studied regions of the world
in terms of atmospheric composition and chemistry. In particular, the
emissions and chemistry of volatile organic compounds (VOCs) that form
surface ozone and secondary organic aerosol through photochemical reactions
involving nitrogen oxides are not well understood. In this study, ambient
levels of VOCs such as methanol, acetone, acetaldehyde, acetonitrile and
isoprene were measured for the first time in the IGP. A new atmospheric
chemistry facility that combines India's first high-sensitivity proton
transfer reaction mass spectrometer, an ambient air quality station and a
meteorological station, was used to quantify in situ levels of several VOCs
and air pollutants in May 2012 at a suburban site in Mohali (northwest IGP).
Westerly winds arriving at high wind speeds (5–20 m s−1) in the
pre-monsoon season at the site were conducive for chemical characterization
of regional emission signatures. Average levels of VOCs and air pollutants in
May~2012 ranged from 1.2 to 2.7 nmol mol−1 for aromatic VOCs, 5.9 to
37.5 nmol mol−1 for the oxygenated VOCs, 1.4 nmol mol−1 for
acetonitrile, 1.9 nmol mol−1 for isoprene, 567 nmol mol−1 for
carbon monoxide, 57.8 nmol mol−1 for ozone, 11.5 nmol mol−1 for
nitrogen oxides, 7.3 nmol mol−1 for sulfur dioxide,
104 μg m−3 for PM2.5 and 276 μg m−3 for
PM10. By analyzing the one-minute in situ data with meteorological
parameters and applying chemical tracers (e.g., acetonitrile for biomass
burning) and inter-VOC correlations, we were able to constrain major emission
source activities on both temporal and diel scales. Wheat residue burning
caused massive increases (> 3 times the baseline values) for all the
measured VOCs and primary pollutants. Other forms of biomass burning at night
were also a significant source of oxygenated VOCs and isoprene (r2 with
acetonitrile ≥0.5 for nighttime data), which is remarkable in terms of
atmospheric chemistry implications. Surface ozone exceeded the 8 h national
ambient air quality limit of 100 μg O3 m−3
(~50 ppbv) on a daily basis, except for 17 May 2012, when a severe dust
storm event (PM2.5 > 800 μg m−3;
PM10 > 2700 μg m−3) characterized by long-range
transport from the west impacted the site. The novel data set and results
point to the occurrence of high primary emissions of reactive VOCs. They also
highlight the urgent need for establishing more comprehensive observational
facilities in the IGP to constrain the spatial and seasonal variability of
atmospheric chemical constituents. Such efforts will enable a
mechanistic-level understanding of the in situ chemical processes controlling
the formation of surface ozone, a necessary step for effective ozone
mitigation and improvement of the regional air quality. |
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