Abstract
Abstract. IASI observations of tropospheric ozone over the Beijing, Shanghai and Hong Kong areas during one year (2008) have been analysed, demonstrating the capability of space-borne infrared nadir measurements to probe seasonal and even day-to-day variations of lower tropospheric ozone (0–6 km partial columns) on the regional scale of highly populated areas. The monthly variations of lower tropospheric ozone retrieved from IASI clearly show the influence of the Asian summer monsoon that brings clean air masses from the Pacific during summer. They exhibit indeed a sharp ozone maximum in late spring and early summer (May–June) followed by a summer minimum. The time periods and the intensities of the maxima and of the decreases are latitude-dependent: they are more pronounced in Hong Kong and Shanghai than in Beijing. Moreover, IASI provides the opportunity to follow the spatial variations of ozone over the surroundings of each megacity as well as its daily variability. We show here that the large lower tropospheric ozone amounts (0–6 km partial columns) observed with IASI are mainly downwind the highest populated areas in each region, thus possibly suggesting the anthropogenic origin of the large ozone amounts observed. Finally, an analysis of the mean ozone profiles over each region – for selected days with high ozone events – in association with the analysis of the meteorological situation shows that the high ozone amounts observed during winter are likely related to descents of ozone-rich air from the stratosphere, whereas in spring and summer the tropospheric ozone is likely enhanced by photochemical production in polluted areas and/or in air masses from fire plumes.
Highlights
Ozone (O3) is a key trace gas in the troposphere that plays a significant role in atmospheric chemistry, air quality and atmospheric radiative forcing
In this paper we have studied one year of IASI observations of tropospheric ozone over three Chinese highly populated areas (5◦×5◦ in latitude and longitude around each city)
The monthly mean variations of lower tropospheric ozone measured with IASI show the influence of the summer Asian monsoon on the ozone concentrations in the lower troposphere with a sharp maximum in late spring and early summer (May–June) followed by a decrease during summer
Summary
Ozone (O3) is a key trace gas in the troposphere that plays a significant role in atmospheric chemistry, air quality and atmospheric radiative forcing. G. Dufour et al.: IASI observations of seasonal and day-to-day variations of tropospheric ozone tropospheric ozone amounts produced over China are increasing, having a significant regional influence on the temporal and spatial variabilities of air quality in East Asia, and up to the hemispheric scale due to the long-range transport across the Pacific In particular we evaluate the possibilities of retrieving the seasonal variations of tropospheric ozone and of probing its day-to-day variations These regions have been selected because they enclose the largest Chinese megacities and large industrial regions (the Pearl River Delta is the world’s major consumer goods manufacturing base) and because they lie in different latitudes from the tropics to the midlatitudes. In the three regions and on its day-to-day variations, respectively
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