Influences of regional pollution and long range transport over Hyderabad using ozone data from MOZAIC

Abstract

Long-term (2005–2011) MOZAIC (Measurements of OZone and water vapor by Airbus In-Service air Craft) ozone data have been investigated over Hyderabad (17.37° N, 78.47°E, 489 m amsl), India using back-air trajectories and contribution from regional pollution and long-range transport are assessed. Ozone data are grouped and analysed according to the air-mass residence time over the central India, marine region and Africa/Middle East regions. Ozone shows a linear dependence on air-mass residence time over the central India region for about six days. Rate of ozone increase is maximum during summer (boundary layer 6.8 ± 0.9 ppbv/day, lower free troposphere 2.4 ± 0.4 ppbv/day) and minimum during winter (boundary layer 1.5 ± 0.2 ppbv/day, lower free troposphere 0.8 ± 0.7 ppbv/day). The background ozone is estimated by extrapolating the linear regression line to zeroth residence day and is found to be significantly lower during summer/monsoon (15.8 ± 2.4 ppbv) within the boundary layer due to influence of marine air-mass. Monthly variation of the boundary layer ozone shows a distinct peak during March–April months. Simultaneous investigation of fire counts and potential source contribution function analysis confirms that Indo-Gangetic Plain (IGP) outflow has a significant contribution in ozone enhancement over even at this southern region throughout the year except in summer-monsoon season. The ozone in regionally polluted air masses influenced by the central Indian region is found to be higher than average ozone by 6–15% within the boundary layer and by 5–9% in the lower troposphere during different seasons. The marine air shows a lower ozone level by 4–28 ppbv throughout the year within the boundary layer. Role of long-range transport from Africa/Middle East is found to be significant in the lower troposphere and shows 4.4 ppbv and 9 ppbv higher ozone mixing ratio during summer and autumn, respectively.