High ozone at coastal sites in India

We present the field measurements of surface ozone (O3) made across the coast in five locations at three stations Poombuhar (11.14° N, 79.9° E), Tranquebar (11° N, 79.9° E) and TR Pattinam (10.46° N, 79.9° E) along the west coast of the Bay of Bengal, India in December 2000 and 2002 and in April 2001 and 2003. Measurements show a higher concentration of surface O3 up to 4.0-6.9 parts per billion by volume (ppbv) at the coastline as compared to the concentration of surface O3 at a distance 20 km inland. The higher coastline O3 concentration is attributed to the short-lived chlorine species with a lifetime of less than 10 minutes generated from the chemical reaction of sea salt particles. Mean O3 concentration decreases inland with distance from the coastline. Furthermore, the greatest difference between the coastline surface O3 concentration and O3 concentration 20 km inland was 4.8-6.4 ppbv, observed at 10 h in the morning, which is related to the morning peak of chlorine molecule (Cl2) concentration. Measurements of nitrogen dioxide (NO2) show concentrations between 4 and 10 ppbv, which are substantially higher than the critical limit of surface O3 production.