TY - JOUR

T1 - Variations in surface ozone at Nainital

T2 - a high-altitude site in the central Himalayas

AU - Kumar, Rajesh

AU - Naja, Manish

AU - Venkataramani, S.

AU - Wild, O.

PY - 2010/8/17

Y1 - 2010/8/17

N2 - Surface ozone measurements have been made for the first time at Nainital (29.37 degrees N, 79.45 degrees 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 high-altitude 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.

AB - Surface ozone measurements have been made for the first time at Nainital (29.37 degrees N, 79.45 degrees 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 high-altitude 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.

KW - TROPOSPHERIC OZONE

KW - AIR-POLLUTION

KW - UNITED-STATES

KW - RURAL SITE

KW - URBAN SITE

KW - NEW-DELHI

KW - INDIA

KW - EMISSIONS

KW - CHINA

KW - ASIA

U2 - 10.1029/2009JD013715

DO - 10.1029/2009JD013715

M3 - Journal article

VL - 115

SP - -

JO - Journal of Geophysical Research: Atmospheres

JF - Journal of Geophysical Research: Atmospheres

SN - 0747-7309

M1 - D16302

ER -