Seasonal and vertical characteristics of particulate and elemental concentrations along diverse street canyons in South India.

Abstract

The impact of street geometries on vertical dispersion of PMs (PM2.5 and PM10) in (1) non-street canyon (NSC), (2) street canyon (SC), and (3) street canyon with viaduct (SCV) was studied during four seasons. The chemical composition of the species was analysed for source apportionment. The mass concentration of PMs in canyons was in the order of SCV > SC > NSC, implicating the canyon effect. Independent of height, most of the PM concentrations in SC and SCV violated the National Ambient Air Quality Standards (NAAQS) and exceeded the World Health Organization (WHO) guidelines in all three street geometries. The vertical concentration trend of PMs was significant during winter and summer seasons in NSC and SC. The vertical trend of both PMs was significant during summer and monsoon seasons in SCV. The seasonal change in PMs' vertical trend was influenced by atmospheric stability, wind velocities associated with street morphology, and emission sources. The ratio of PM2.5/PM10 indicated the dominance of PM10 in all three locations. Among the estimated species, Fe (crustal and vehicle) and Na (sea salt and crustal) were abundant in PM2.5 and PM10, respectively. Estimation of enrichment factor (EF) revealed that most of the emission sources were anthropogenic in PM2.5 and natural in PM10. Principal component analysis (PCA) showed crustal/soil dust, vehicular emission, and sea salt to the common source profile for PMs. Specific contribution of smoking activity contributed to Be and Tl in PM2.5, which may be considered a site-specific source.