Using estimates of particulate matter (PM), PM10 and PM2.5 made from the mass size distributions measured regularly using a Quartz Crystal Microbalance (QCM) impactor for the period October 1998-December 2000 at the coastal station Trivandrum, the long-term average values (for 27 months) of PM10 and PM2.5 are estimated. The season wise shares of PM10 and PM2.5 to PM are computed. Results indicate highest contribution of PM10 to PM during local summer/pre-monsoon while the contribution of PM2.5 to PM peaks during local winter. These shares are lowest during monsoon months. Average values of PM10 and PM2.5 were found to be around 50 and 43 μg m -3 under ambient conditions. For making an environmental assessment these values are corrected for humidity changes and reduced to a constant RH level of 50%. An order of magnitude estimate is made of the sea salt contribution to the total based on recent measurements during the INDOEX. After these apportionments, it is found that even though the PM10 concentration is well below the standards set by several national environmental agencies, the PM2.5 concentration appears to be quite critical. The findings are discussed.