Effects of convection and long-range transport on the distribution of carbon monoxide in the troposphere over India

Özet

Variability in the tropospheric distributions of carbon monoxide (CO) over five selected regions of Indiahas been studied using the MOPITT data for the period of 2001e2014. The average seasonal profiles showhighest mixing ratios at 900 hPa in the boreal winter and lowest in the Indian summer monsoon over allthe study regions. We observe a slight increase in CO levels from 500 hPa to 200 hPa over all the locations.The CO mixing ratios are found to be higher by about 10e40% around 300e200 hPa as comparedto 900 hPa over Ahmedabad, Hyderabad and Trivandrum during monsoon period. This could be due tolifting of polluted air by convection and getting trapped in the anticyclonic winds over the Indian regionduring the monsoon. Most of the 7 day back trajectories over these regions show transport of thepolluted air mass from the major biomass burning regions of central Africa and SE Asia. The results showdominance of the seasonal amplitude at 900 hPa over all the regions, while inter-annual variabilitydominates mostly over Ahmedabad, Hyderabad and Trivandrum at 300 hPa. In order to check the abilityof different models in capturing the observed variability, the results have been compared with simulationsfrom two chemistry transport models (MOZART and EMAC). This comparison shows that both themodels perform reasonably well in simulating the basic features such as annual variation as well asincrease in CO around 300e200 hPa due to convection during the monsoon season.