Seasonal Dynamics and Source Fingerprinting of Urban PM2.5 Carbonaceous Aerosols in the North-Western Himalayas

To explore spatio-temporal dynamics and source fingerprinting of carbonaceous aerosols (CAs), a systematic year-long study was conducted in the urban environment of Jammu region, North-Western Himalayas. PM2.5 samples were collected every third day using volume flow-controlled high-volume samplers simultaneously across five distinct land-use sites. Around 600 PM2.5 samples were analyzed for Organic Carbon (OC) and Elemental Carbon (EC) using a lab OC-EC aerosol analyzer while non-sea-salt-K+ (nss-K+) was measured using Ion Chromatography system. On annual basis, Total Carbon (TC), OC and EC contributed 32 ± 13%, 26 ± 10% and 5 ± 4% to PM2.5 respectively. Results of ANOVA applied on concentration datasets of various carbon forms revealed statistically significant (p < 0.05) spatio-temporal variations in the concentration and composition of CAs suggesting diverse emission sources. The EC-Tracer method-based estimation of Primary OC (POC) and Secondary OC (SOC) indicated the dominance of SOC, suggesting substantial contributions from gas-to-particle conversion. During the study period OC/EC ratios remained above 5, signifying prevalent biomass burning at all sites except kerbside and commercial sites during summer-monsoon [June–July–August (JJA)] and autumn [September–October–November (SON)] seasons. Strong correlations (R2 > 0.5) between nss-K+ and OC further underscored biomass burning as a significant source. Additionally, nss-K+/OC and nss-K+/EC ratios indicated that tropical wood, charcoal and agricultural residue were the dominant type of biomass burnt and contributed CAs during summer-monsoon (JJA), winter [December-January–February (DJF)] and spring [March–April-May (MAM)] as well as autumn (SON) seasons, respectively. Positive Matrix Factorization analysis revealed four major sources of PM2.5-CAs viz light motor vehicles (22–47%), heavy commercial vehicles/high-capacity engine emissions (28–49%), biomass burning (16–56%) and unidentified/tar burning (12–15%). The Potential Source Contribution Function (PSCF) and Concentration Weighted Trajectory (CWT) analysis showed that the north-western neighbouring countries remains the potential source regions of PM2.5-CAs in Jammu.