Chemical Characterization and source apportionment of PM2.5 over an upwind site of Delhi during Biomass Burning and Diwali Festival period

Each year Delhi experiences extremely poor air quality in the post-monsoon season due to large scale stubble burning in the upwind states of Punjab and Haryana, excessive firecracker uses during the Diwali festival, and unfavorable meteorological conditions such as shallow inversions over emission sources. Numerous studies have reported severe haze episodes in Delhi, often linking them to long-range transport of biomass burning aerosols from these upwind regions. In the present study, we investigate the variability in chemical composition of  non-refractory PM_2.5 using a Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) and black carbon (BC) aerosols using an Aethalometer AE31 at an upwind side of Delhi-NCR in Sonipat, Haryana (28.9° N, 77.1° E) during the stubble burning period and Diwali time (25 Oct 2023 to 15 Nov 2023). We quantified the mass concentrations of biomass burning tracer species, such as levoglucosan, mannosan, and potassium (K⁺), along with other chemical constituents. The daily average concentrations of levoglucosan, mannosan and K⁺ in NR-PM_2.5 were 1.28 ± 1.27, 0.02 ± 0.01 and 5.38±4.57 μg m⁻³, respectively. Preliminary analysis indicates higher concentration of biomass burning tracers, carbonaceous aerosols, and secondary inorganic aerosols during nighttime as compared to daytime. The daily average mass concentrations of Organics are 108±48.5 and 70.2±49.7 μg m⁻³, and BC are 18.8±86.0 μg m⁻³ and 24.0±10.2 μg m⁻³ during biomass burning and Diwali festival period, respectively. Additionally, we are conducting source apportionment analysis using models such as Positive Matrix Factorization (PMF) to identify various sources contributing to PM2.5 concentrations over the region. More results with greater details will be presented.