Seasonal, Spatial, and Near-Surface Vertical Variability of Water-Soluble Carbon and Nitrogen in PM10 in Chennai, India

This study examines PM10 and water-soluble carbon and nitrogen at three Chennai street environments during campaigns ST2–ST4 and at nominal heights of 3, 16 and 37 m. The measurements comprise 76 PM10 observations, 75 determinations each of water-soluble organic carbon (WSOC) and water-soluble total nitrogen (WSTN), and 74 records of water-soluble inorganic nitrogen (WSIN). Mean PM10 was 65.32 µg m−3, WSOC was 2.53 µg C m−3, WSTN was 1.28 µg N m−3, and WSIN was 1.26 µg N m−3. WSOC decreased from 4.01 µg C m−3 in ST3 to 0.62 in ST4, while WSIN increased from 1.12 to 1.86 µg N m−3. The site contrast was pronounced for PM10, with the highest concentrations at Velachery, and for WSIN, which was highest on average at Arumbakkam. Campaign contrasts for WSOC and WSIN remained significant when site-days were treated as the sampling units, whereas vertical differences were not significant. Positive water-soluble nitrogen residuals were quantified as WSON+=max(0,WSTN−WSIN), which is distinguished from the signed nitrogen balance. Campaign meteorology differed in humidity, wind speed and boundary-layer height, consistent with contrasting dilution and aerosol-processing conditions. The combined observations reveal pronounced campaign and urban-site variability in soluble PM10 composition.