The variability of methane, nitrous oxide and sulfur hexafluoride in Northeast India
High-frequency atmospheric measurements of methane (CH<sub>4</sub>), nitrous oxide (N<sub>2</sub>O) and sulfur hexafluoride (SF<sub>6</sub>) from Darjeeling, India are presented from December 2011 (CH<sub>4</sub>)/March 2012 (N<sub>2</su...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/13/10633/2013/acp-13-10633-2013.pdf |
| Summary: | High-frequency atmospheric measurements of methane (CH<sub>4</sub>),
nitrous oxide (N<sub>2</sub>O) and sulfur hexafluoride (SF<sub>6</sub>)
from Darjeeling, India are presented from December 2011
(CH<sub>4</sub>)/March 2012 (N<sub>2</sub>O and SF<sub>6</sub>) through
February 2013. These measurements were made on a gas chromatograph
equipped with a flame ionization detector and electron capture
detector, and were calibrated on the Tohoku University, the Scripps
Institution of Oceanography (SIO)-98 and SIO-2005 scales for
CH<sub>4</sub>, N<sub>2</sub>O and SF<sub>6</sub>, respectively. The
observations show large variability and frequent pollution events in
CH<sub>4</sub> and N<sub>2</sub>O mole fractions, suggesting significant
sources in the regions sampled by Darjeeling throughout the year.
By contrast, SF<sub>6</sub> mole fractions show little variability and
only occasional pollution episodes, likely due to weak sources in
the region. Simulations using the Numerical Atmospheric dispersion
Modelling Environment (NAME) particle dispersion model suggest that
many of the enhancements in the three gases result from the
transport of pollutants from the densely populated Indo-Gangetic
Plains of India to Darjeeling. The meteorology of the region varies
considerably throughout the year from Himalayan flows in the winter
to the strong south Asian summer monsoon. The model is consistent
in simulating a diurnal cycle in CH<sub>4</sub> and N<sub>2</sub>O mole
fractions that is present during the winter but absent in the summer
and suggests that the signals measured at Darjeeling are dominated
by large-scale (~100 km) flows rather than local
(<10 km) flows. |
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| ISSN: | 1680-7316 1680-7324 |