[1] Surface ozone measurements have been made for the first time at Nainital (29. 37°N, 79.45°E, 1958 m amsl), a high-altitude site in the central Himalayas, between October 2006 and December 2008. Diurnal variations in ozone do not show the daytime photochemical build-up typical of urban or rural sites. The seasonal variation shows a distinct ozone maximum in late spring (May; 67.2 ± 14.2 ppbv) with values sometimes exceeding 100 ppbv and a minimum in the summer/monsoon season (August; 24.9 ± 8.4 ppbv). Springtime ozone values in the central Himalayas are significantly higher than those at another highaltitude site (Mt. Abu) in the western part of India. Seasonal variations in ozone and the processes responsible for the springtime peak are studied using meteorological parameters, insolation, spatial and temporal classifications of air mass trajectories, fire counts, and simulations with a chemical transport model. Net ozone production over the Northern Indian Subcontinent in regionally polluted air masses is estimated to be 3.2 ppbv/day in spring but no clear build-up is seen at other times of year. Annual average ozone values in regionally polluted air masses (47.1 ± 16.7 ppbv) and on high insolation days (46.8 ± 17.3 ppbv) are similar. Background ozone levels are estimated to be 30-35 ppbv. Regional pollution is shown to have maximum contribution (16.5 ppbv) to ozone levels during May-June and is about 7 ppbv on an annual basis, while the contribution of long-range transport is greatest during January-March (8-11 ppbv). The modeled stratospheric ozone contribution is 2-16 ppbv. Both the trajectory analysis and the model suggest that the stratospheric contribution is 4-6 ppbv greater than the contribution from regional pollution. Differences in the seasonal variation of ozone over high-altitude sites in the central Himalayas (Nainital) and western India (Mt. Abu) suggest diverse regional emission sources in India and highlight the large spatial and temporal variability in ozone over the Indian region.

[1] The influences of the springtime northern Indian biomass burning are shown for the first time over the central Himalayas by using three years (2007)(2008)(2009) . These biomass burning induced changes over the central Himalayan atmosphere during spring may also lead to enhanced short-wave absorption above clouds and might have an impact on the monsoonal rainfall.

Simultaneous in situ measurements of ozone, CO, and NO y have been made for the first time at a high altitude site Nainital (29. 37°N, 79.45°E, 1958 m above mean sea level) in the central Himalayas during [2009][2010][2011]. CO and NO y levels discern slight enhancements during the daytime, unlike in ozone. The diurnal patterns are attributed mainly to the dynamical processes including vertical winds and the boundary layer evolution. Springtime higher levels of ozone (57.5 ± 12.6 ppbv), CO (215.2 ± 147 ppbv), and NO y (1918 ± 1769.3 parts per trillion by volume (pptv)) have been attributed mainly to regional pollution supplemented with northern Indian biomass burning. However, lower levels of ozone (34.4 ± 18.9 ppbv), CO (146.6 ± 71 ppbv), and NO y (1128.6 ± 1035 pptv) during summer monsoon are shown to be associated with the arrival of air mass originated from marine regions. Downward transport from higher altitudes is estimated to enhance surface ozone levels over Nainital by 6.1-18.8 ppbv. The classification based on air mass residence time, altitude variations along trajectory, and boundary layer shows higher levels of ozone (57 ± 14 ppbv), CO (206 ± 125 ppbv), and NO y (1856 ± 1596 pptv) in the continental air masses when compared with their respective values (28 ± 13 ppbv, 142 ± 47 ppbv, and 226 ± 165 pptv) in the regional background air masses. In general, positive interspecies correlations are observed which suggest the transport of air mass from common source regions (except during winter). Ozone-CO and ozone-NO y slope values are found to be lower in comparison to those at other global sites, which clearly indicates incomplete in situ photochemistry and greater role of transport processes in this region. The higher CO/NO y value also confirms minimal influence of fresh emissions at the site. Enhancements in ozone, CO, and NO y during high fire activity period are estimated to be 4-18%, 15-76%, and 35-51%, respectively. Despite higher CO and NO y concentrations at Nainital, ozone levels are nearly similar to those at other global highaltitude sites.

[1] During a comprehensive aerosol field campaign as part of Indian Space Research Organization Geosphere Biosphere Programme (ISRO-GBP), aircraft measurements of vertical profiles of aerosol black carbon (BC) were made during winter, for the first time, at Kanpur (80°20 0 E and 26°26 0 N), an urban industrial location in Northern India. Two vertical profiling from the same day (morning and afternoon) of BC showed that BC decreases with height up to $600 m and then increases up to 900 m before becoming more or less constant with height. Potential temperature profile, derived from concurrent measurements of temperature, shows a stable layer at the same altitude where BC shows increased concentration. This vertical structure of boundary layer was further confirmed by separate temperature and relative humidity profiles obtained from balloonsondes during December. The increased BC at $900 m suggests the presence of enhanced BC layer, which will have significant implications to BC radiative forcing and modifying cloud properties.

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[1] Simultaneous surface level measurements of O 3 , CO, methane, and light nonmethane hydrocarbons (NMHCs) were made over the Bay of Bengal during a cruise campaign between 19 February and 28 February 2003. The mixing ratios of O 3 , CO, methane, ethane and acetylene were observed in the ranges of 20-52 ppbv, 126-293 ppbv, 1.65-1.85 ppmv, 622-2088 pptv and 134-1388 pptv, respectively, during the campaign period. Ratios of some measured trace gases have been used to estimate the level of photochemical processes and transport times of air parcels. Three types of air masses have been identified on the basis of source regions and transport pathways. The study region is frequently affected by transport of pollutants from the nearby continental emission sources, but the strongest pollution event during this period was due to long-range transport from extratropical Northern Hemisphere. These higher mixing ratios of trace gases are due to faster transport of air parcels from the source regions via free troposphere. On the basis of C 2 H 2 /CO ratio, it is also observed that this pollution plume was photochemically fresh. Latitudinal distributions of all the measured trace gases show significant north-south decreasing trends. In particular, gradients in the mixing ratios of NMHCs over the Bay of Bengal compare 2-3 times higher than those observed over the Arabian Sea, the Indian Ocean and the Pacific Ocean. Comparisons with previous measurements over the Arabian Sea and the Indian Ocean show significantly higher levels of these trace gases over the Bay of Bengal.Citation: Lal, S., L. K. Sahu, and S. Venkataramani (2007), Impact of transport from the surrounding continental regions on the distributions of ozone and related trace gases over the Bay of