Chemical Characterization and Source Apportionment of Organic Aerosols in the Coastal City of Chennai, India: Impact of Marine Air Masses on Aerosol Chemical Composition and Potential for Secondary Organic Aerosol Formation

Online chemical characterization of NR-PM1 (nonrefractory particulate matter <= 1 mu m) has been carried out using an ACSM (Aerosol Chemical Speciation Monitor) at a coastal urban site in Chennai, India. The average mass concentration of NR-PM1 during the campaign was 30.4 +/- 28.3 mu g/m(3) (arithmetic mean +/- standard deviation) with organics accounting for a major fraction of similar to 47.4% followed by sulfate (similar to 33.3%). Back trajectory analysis and STILT model simulations enabled the identification of a relatively clean period with prevailing air masses from ocean. During this period, the average NR-PM1 mass concentration was 7.1 +/- 2.8 mu g/m(3), which is similar to 5 times lower than that of the rest of the campaign (with air masses sampled from both continent and ocean) (33.3 +/- 29.1 mu g/m(3)). This reduction was primarily attributed to the dilution of local primary emissions due to cleaner marine influx. Comprehensive source apportionment for the organic fraction was performed using Positive Matrix Factorization (PMF). While equal contributions of primary (similar to 49%) and secondary (similar to 51%) organic factors were observed for the rest of the campaign, more oxidized-oxygenated organic aerosol (MO-OOA) factor dominated the OA and accounted for similar to 82% of the total OA mass during the clean period. Simultaneously, during the clean period a significant increase in the fraction of organic liquid water was observed. We studied the effect of marine influx on the enhanced secondary organic aerosol (SOA) fraction. In brief, our results demonstrate the significance of marine winds and meteorological conditions on the chemical composition and ambient aerosol mass burden at a coastal site. Further, this study emphasizes that marine influx can cause the dilution in local pollution and can demonstrate distinct chemical composition with impacts on local aerosol properties.

Automated summary

The online chemical characterization of NR-PM1 was conducted in Chennai, India using ACSM. A relatively clean period with marine air masses significantly reduced the mass concentration of NR-PM1, with organic aerosol dominating the composition. Chemical composition and aerosol properties at the coastal site were influenced by marine influx, leading to changes in the organic aerosol fraction and organic liquid water content.