Variations in surface ozone and NOx at Kannur: a tropical, coastal site in India

Continuous measurements of surface ozone (O-3), NOx (NO + NO2) and meteorological parameters have been made in Kannur (11.9 A degrees N, 75.4 A degrees E, 5 m asl), India from November 2009 to October 2010. It was observed that O-3 and NOx showed distinct diurnal and seasonal variabilities at this site. The annual average diurnal profile of O-3 showed a peak of (30.3 A +/- 10.4) ppbv in the late afternoon and a minimum of (3.2 A +/- 0.7) ppbv in the early morning. The maximum value of O-3 mixing ratio was observed in winter (44 A +/- 3.1) ppbv and minimum during monsoon (18.46 A +/- 3.5) ppbv. The rate of production of O-3 was found to be higher in December (10.1 ppbv/h) and lower in July (1.8 ppbv/h) during the time interval 0800-1000 h. A correlation coefficient of 0.52 for the relationship between O-3 and [NO2]/[NO] reveals the role of NO2 photolysis that generates O-3 at this site. The correlation between O-3 and meteorological parameters indicate the influence of seasonal changes on O-3 production. Investigations were further extended to explore the week day weekend variations in O-3 mixing ratio at an urban site reveals the enhancement of O-3. The variations of O-3 mixing ratio with seasonal air mass flows were elucidated with the aid of backward air trajectories. This study also indicates how vapor phase organic species present in the ambient air at this location may influence the complex chemistry involving (VOCs) that enhances the production of O-3 at this location.