Surface ozone and its precursors at two sites in the northeast coast of India

Abstract

<smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="City" downloadurl="http://www.5iamas-microsoft-com:office:smarttags"><smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place" downloadurl="http://www.5iantlavalamp.com/"><smarttagtype namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="State" downloadurl="http://www.5iamas-microsoft-com:office:smarttags"> Diurnal and seasonal behavior of surface ozone (O₃)at Kolkata (22.36°N, 88.24°E) and Haldia (22.05°N, 88.03°E), two tropical urban sites situated on the northeast coast of India, has been studied. The main sources of pollution at these two sites are a large number of small industries, oil refineries and thermal power plant in addition to heavy vehicular traffic. Along with O₃, the behavior of its precursors, viz. CO, NO_x(oxides of nitrogen) and non-methane hydrocarbons (NMHCs) have also been studied. Diurnal and seasonal behavior of these species has been found to be different at different times of the year. During monsoon months, O₃ and its precursors do not show any diurnal variation. Distinct diurnal variation of O₃ is found only during October - March with maximum value around 1500 hrs LT. The minimum value of ozone is found around midnight. For CO and NO_x, distinct diurnal variations are found during October – February for Kolkata only, with minimum value around 1500 hrs LT and maximum value around midnight. The diurnal variation of these two species appears to be nearly identical. At Haldia, CO has a weak diurnal variation during November - February with maximum value at midnight and minimum value around 1500 hrs LT. At Haldia, for NO_x no diurnal variation is observed. NMHC does not show any distinct diurnal variation at any site but its value is highest during winter. Using a simplified 1D steady state photochemical scheme, an attempt has been made to reproduce the daytime winter ozone values for both the sites. While O₃ values at Kolkata could be reproduced to some extent, those at Haldia are very much underestimated. The effect of wind appears to be insignificant. </smarttagtype></smarttagtype></smarttagtype>