Time-resolved distributions of bulk parameters, diacids, ketoacids and α-dicarbonyls and stable carbon and nitrogen isotope ratios of TC and TN in tropical Indian aerosols: Influence of land/sea breeze and secondary processes

Abstract To better understand the photochemical production and diurnal distributions of organic and inorganic aerosols in the tropical coastal Indian atmosphere, the aerosol (TSP) samples were collected every 3 h during 30–31 January, 14–15 February and 28–29 May 2007 from Chennai and studied for total carbon (TC) and nitrogen (TN) and their stable isotope ratios (δ 13 C TC and δ 15 N TN ), carbonaceous components, inorganic ions, diacids, ketoacids and α-dicarbonyls. Time-resolved distributions of bulk parameters, inorganic ions, and diacids and related compounds, except for few species, did not show any clear diurnal trend but showed peaks at 6–9 h during all the study periods, except for the peak at 15–18 h on 28 May. SO 4 2− , C 2  − C 6 diacids, ketoacids and α-dicarbonyls in February and on 29 May showed a diurnal trend. δ 13 C TC and δ 15 N TN stayed relatively constant during the study periods but showed 13 C depletion (in January) and 15  N enrichment when TC and TN peaked. Based on these results together with air mass trajectories, we found that the diurnal distributions of Chennai aerosols are mainly influenced by land/sea breeze and the aged (photochemically processed) air masses, although in situ photochemical production and nighttime chemistry of secondary aerosol species, particularly C 2 –C 4 diacids and SO 4 2− , are significant. The characteristics of seasonal variations of carbonaceous components, and diacids and related compounds and comparisons of δ 13 C TC and δ 15 N TN of Chennai aerosols with the isotopic signatures of the point sources inferred that biofuel/biomass burning in South and Southeast Asia are the major sources of aerosols (TSP).