Abstract
Abstract. Residential biomass burning for heating purposes is an important source of air pollutants during winter. Here we test the hypothesis that significant secondary organic aerosol production can take place even during winter nights through oxidation of the emitted organic vapors by the nitrate (NO3) radical produced during the reaction of ozone and nitrogen oxides. We use a mobile dual smog chamber system which allows the study of chemical aging of ambient air against a control reference. Ambient urban air sampled during a wintertime campaign during nighttime periods with high concentrations of biomass burning emissions was used as the starting point for the aging experiments. Biomass burning organic aerosol (OA) was, on average, 70 % of the total OA at the beginning of our experiments. Ozone was added in the perturbed chamber to simulate mixing with background air (and subsequent NO3 radical production and aging), while the second chamber was used as a reference. Following the injection of ozone, rapid OA formation was observed in all experiments, leading to increases in the OA concentration by 20 %–70 %. The oxygen-to-carbon ratio of the OA increased on average by 50 %, and the mass spectra of the produced OA was quite similar to the oxidized OA mass spectra reported during winter in urban areas. Furthermore, good correlation was found for the OA mass spectra between the ambient-derived emissions in this study and the nocturnal aged laboratory-derived biomass burning emissions from previous work. Concentrations of NO3 radicals as high as 25 ppt (parts per trillion) were measured in the perturbed chamber, with an accompanying production of 0.1–3.2 µg m−3 of organic nitrate in the aerosol phase. Organic nitrate represented approximately 10 % of the mass of the secondary OA formed. These results strongly indicate that the OA in biomass burning plumes can chemically evolve rapidly even during wintertime periods with low photochemical activity.
Highlights
Biomass burning from residential heating, agricultural fires, prescribed burning, and wildfires is a major source of atmospheric pollutants worldwide (Watson, 2002; Bond et al, 2004; Robinson et al, 2006)
Exp. 1 started during an early evening period with moderate to high concentrations of biomass burning organic aerosol (OA), volatile organic compounds (VOCs), and NOx (Table 1) and combined all the necessary elements to demonstrate the behavior of the system studied
The positive matrix factorization (PMF) analysis of the full campaign ambient data set suggested that 70 % of the OA at the time of filling originated from biomass burning (Kaltsonoudis et al, 2021)
Summary
Biomass burning from residential heating, agricultural fires, prescribed burning, and wildfires is a major source of atmospheric pollutants worldwide (Watson, 2002; Bond et al, 2004; Robinson et al, 2006). The mixing of ozone from the residual layer and the importance to nighttime chemistry was suggested in studies on nighttime oxidation of biogenic VOCs (Brown et al, 2009, 2013) Despite this important finding, the degree to which biomass burning plumes undergo nighttime aging and produce significant amounts of SOA remains poorly understood. The degree to which biomass burning plumes undergo nighttime aging and produce significant amounts of SOA remains poorly understood Lacking consideration of such nocturnal chemistry in transport models has been suggested as being a possible source of the underprediction of oxidized organic aerosol mass by a factor of 3–5 (Fountoukis et al, 2016; Tsimpidi et al, 2014) during wintertime in polluted areas with low photochemical activity. A dual atmospheric simulation chamber system is used to elucidate the formation of SOA during winter periods in urban areas with high biomass burning organic aerosol concentrations
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