Characteristics of Haze Pollution Events During Biomass Burning Period at an Upwind Site of Delhi

The National Capital Region (NCR) of Delhi frequently experiences severe haze episodes during the post-monsoon and winter months, driven by long-range transport of biomass burning aerosols, local emissions, and unfavorable meteorological conditions. However, observational studies tracing these pollution episodes along the pathway to Delhi are lacking. This study investigates haze pollution at an upwind site in Sonipat using advanced instrumentation during October 25 to 15 November 2023, encompassing biomass burning and Diwali events. Sudden spikes in pollutants caused severe haze, temporary reductions in pollution due to rainfall, and a resurgence of haze during Diwali. Two major haze episodes were identified, with particulate matter (PM<inf>2.5</inf>) levels exceeding 300 μg/m³. Organics dominated composition based PM<inf>2.5</inf> (C-PM<inf>2.5</inf>) followed by Black Carbon (BC), jointly accounting for ∼80% of total mass during all the episodes, with secondary inorganics contributed minimally. Limited day-night variations and low inorganics contribution suggested minimal photochemical activity and secondary formation. Elevated levels of biomass burning tracers and emission ratios indicated aged, oxidized aerosols from crop residue burning in Punjab and Haryana, supported by fire count data and 72-hr backward trajectory analysis. Regional meteorology, including a shallow atmospheric boundary layer (ABL) and low wind speeds, hindered pollutant dispersion, leading to accumulation and prolonged haze. By integrating emission analysis, meteorological factors, and transport dynamics, this study provides critical insights into haze formation, emphasizing the need for targeted mitigation strategies, such as stricter crop residue burning controls and improved emission management, to address haze pollution and its health risks effectively.