Modelling of near-surface ozone over South Asia |
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Authors: | Magnuz Engardt |
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Institution: | 1.Swedish Meteorological and Hydrological Institute,Norrk?ping,Sweden |
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Abstract: | Hourly, three-dimensional, fields of tropospheric ozone have been produced for 12 consecutive months on a domain covering
South Asia, using the regional Eulerian off-line chemistry transport model MATCH. The results were compared with background
observations to investigate diurnal and seasonal variations of near-surface ozone in the region. MATCH reproduced the seasonality
of near-surface ozone at most locations in the area. However, the current, and previous, studies indicate that the model consequently
overestimate night-time concentrations, while it occasionally underestimates the day-time, near-surface, ozone concentrations.
The lowest monthly-mean concentrations of near-surface ozone are typically experienced in June–September, coincident with
the rainy season in most areas. The seasonality is not identical across the domain; some locations have a completely different
trend. Large areas in Northern India and Nepal show a secondary minimum during the cold winter season (December–January).
High concentrations of near-surface ozone are found over the oceans, close to the Indian subcontinent, due to the less efficient
dry deposition to water surfaces; over parts of Tibet due to influence of free tropospheric air and little deposition to snow
covered surfaces; and along the Gangetic valley due to the large emissions of precursors in this region. Monthly-mean ozone
concentrations in the densely populated northern India range from 30–45 ppb(v). The model results were also used to produce maps of AOT40. The results point towards similar levels of AOT40 in India as
in Europe: large areas of India show 3-month AOT40 values above 3 ppm(v) hours.
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Keywords: | AOT40 Crop yield India MATCH Modelling Ozone |
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