Influence of a dust storm on carbon monoxide and water vapor over the Indo-Gangetic Plains

Dust storms are meteorological phenomena that produce air quality hazards over specific regions lasting from a few hours to many days. They are common in the western part of India during the months of April-June, particularly over Delhi and the surrounding Indo-Gangetic (IG) plains. In this paper, a dust storm event over Delhi, Kanpur and Varanasi during 1-11 April 2005 was used to study the vertical changes in the atmosphere. We studied data from the Measurement of Pollution in the Atmosphere (MOPITT) instrument onboard the Terra satellite, daytime vertical carbon monoxide ( CO) mixing ratio and the Atmospheric Infra-red Sounder ( AIRS) onboard the Aqua satellite water vapor mass mixing ratio associated with dust storm over three locations in the IG plains. Evidence of vertical transport of CO to upper troposphere ( UT) is observed from stability indices derived from radiosonde data, NCEP reanalysis wind and HYSPLIT model over Delhi. The strong upward convection during dust storms reduces CO in the lower troposphere and increases CO at around 350 hPa pressure level. Water vapor mass mixing ratio shows an increase at 700-850 hPa pressure level during the dust storm event over all locations. The changes of water vapor mass mixing ratio and CO during the dust storm are found to be more pronounced over Delhi and Kanpur while they are comparatively less over Varanasi, due to low intensity during transport of dust from west to east in the IG plains. The increased concentration of CO and water vapor mass mixing ratio at different pressure levels 350 hPa and 700-850 hPa respectively with corresponding decrease in surface concentration ( at pressure level 700-1000 hPa and 925-1000 hPa respectively) have been investigated during a major dust storm period. The changes in CO and water vapor mass mixing ratio are found to be consistent with the observed changes in vertical stability of the atmosphere.