Examining the effect of dust events, festive fireworks, and the open-field biomass burning on carbonaceous aerosols and light absorption at a regional background location in Northern India

Abstract

<p>Fine particulate atmospheric aerosol (PM<sub>2.5</sub>) impact Earth’s radiative balance, regional air quality and is a major public health concern, especially in low and middle-income countries. Africa and Asia are the heaviest aerosol-laden regions in the world and have a high PM<sub>2.5 </sub>attributable burden of diseases. Open-field biomass burning (BB) is one of the leading contributors to PM<sub>2.5 </sub>in these countries, especially India, where high levels are reported even at the regional background locations [Maheswarkar et al., 2022]. BB events are often accompanied by dust events (during the <em>Rabi harvest season</em>) and fireworks on <em>Diwali </em>festival (during the <em>Kharif harvest season</em>), further deteriorating air quality. There is a need to better understand the impact of these episodic events on aerosol light absorption, chemical composition, and their interaction with the radiation budget. Hence, the primary objective of this study is to investigate the independent and mixed impact of episodic events like open-field BB, dust, and <em>Diwali</em> fireworks on aerosol light absorption and chemical composition. The 24-hour integrated samples were collected every other day during 2019 at Rohtak, a highly polluted regional background site in Northern India; aerosol light absorption and chemical species of PM<sub>2.5</sub> (elements, ions, and carbon fractions) were quantified as per COALESCE (CarbOnaceous AerosoL Emissions, Source apportionment and ClimatE Impacts) field monitoring and analysis protocols. Active fire count data (MODIS, NASA), reconstructed dust, back-trajectory analysis, and characteristic ratios are used to identify episodic events and examine the regional air quality. The data is normalized by ventilation coefficient (PBLH * wind speed) to understand the distinct impact of regional sources independent of meteorology. We find that open-field BB significantly (p<0.05) impacts the regional air quality during the post-monsoon <em>(Kharif</em>) as well as summer (<em>Rabi</em>) post-harvest season, the same period impacted by dust episodes and dilution effect, often unperceived despite reporting concentrations way above the national permissible limit. Light absorption at 880 and 370 nm (b<sub>abs-880</sub> and b<sub>abs-370</sub>) is significantly (p<0.05) higher for <em>Rabi</em> BB+Dust (95.62±37.49 and 164.84±70.71 Mm<sup>-1</sup>) than BB+nonDust (73.29±21.02 and 121.94±30.36 Mm<sup>-1</sup>) and nonBB+Dust period (75.45±15.94 and 125.64±28.05 Mm<sup>-1</sup>), respectively, indicating the mixed impact of both episodic events. Dust and open-field BB explain 5.8% and  8.6% (7.4% and 9.8%) variability in b<sub>abs-880  </sub>(b<sub>abs-370</sub>), respectively, out of 54.5% (61%), remaining explained by meteorology. Similarly, a significant increase is seen in b<sub>abs-880 ­</sub>and b<sub>abs-370 </sub>during <em>Diwali</em> (136.82±23.66 and 208.48±21.4 Mm<sup>-1</sup>, respectively) compared to the pre-<em>Diwali</em> period (93.74±21.61 and 162.51±35.93 Mm<sup>-1</sup>, respectively), both coinciding with BB days, which remain high (136.82±23.66 and 208.48±21.4 Mm<sup>-1</sup>) during the post<em>-Diwali</em> period. Higher fire counts over the Punjab-Haryana region and back-trajectory cluster analysis suggest downwind transport of BB and <em>Diwali</em> emissions at the receptor site during this period. Examination of the PM chemical composition of these episodic events is currently underway.</p>