Unlocking the Mysterious of Nocturnal Aerosol Growth: An STXM/NEXAFS Investigation on New Delhi Aerosols

Abstract

Delhi, one of the most polluted regions in the world, encounters noteworthy emissions of both anthropogenic and natural particles, particularly during winter. However, there is a scarcity of information on these aerosols’ molecular composition, formation and growth. This is obvious not only in the day but particularly at night above the polluted areas such as Delhi. Studying nighttime atmospheric aerosols, including their chemical composition, properties, and behaviour, is hence fundamental to understanding and tending to this critical environmental challenge. The sampling was conducted in February and March 2023. Focus of the experiment is distinguishing numerous sources of pollutants and their development that influence the local air quality. The technique is based on scanning transmission X-ray microscopy (STXM) coupled with near-edge X-ray absorption fine structure (NEXAFS) techniques. STXM is an X ray microscopy technique that uses monochromatic X-rays focused on a sample to obtain an absorption image which is generated by scanning the sample. NEXAFS is a type of absorption spectroscopy, and its microscopy provides detailed, quantitative speciation and elemental analysis for an appropriate spectral range in a sample. This study identifies that the condensation of organic aerosols from biomass burning is a driving cause of the observed nocturnal growth and the decrease in nighttime temperatures and increase of relative humidity with biomass emissions drive the primary organic aerosol formations. NEXAFS spectroscopy discloses potassium, sulphur, and nitrogen-containing compounds, as well as carbonaceous particles containing considerable C=C double bonds and may be an indicator of soot or black carbon. This study is moreover crucial to encourage upgrading the understanding of composition, characteristics, sources of aerosols, and health concerns over Delhi, as well as to create mitigation measures fitted to local government agencies.