Abstract
Abstract. Air quality in rural India is impacted by residential cooking and heating with biomass fuels. In this study, emissions of CO, CO2, and 76 volatile organic compounds (VOCs) and fine particulate matter (PM2.5) were quantified to better understand the relationship between cook fire emissions and ambient ozone and secondary organic aerosol (SOA) formation. Cooking was carried out by a local cook, and traditional dishes were prepared on locally built chulha or angithi cookstoves using brushwood or dung fuels. Cook fire emissions were collected throughout the cooking event in a Kynar bag (VOCs) and on polytetrafluoroethylene (PTFE) filters (PM2.5). Gas samples were transferred from a Kynar bag to previously evacuated stainless-steel canisters and analyzed using gas chromatography coupled to flame ionization, electron capture, and mass spectrometry detectors. VOC emission factors were calculated from the measured mixing ratios using the carbon-balance method, which assumes that all carbon in the fuel is converted to CO2, CO, VOCs, and PM2.5 when the fuel is burned. Filter samples were weighed to calculate PM2.5 emission factors. Dung fuels and angithi cookstoves resulted in significantly higher emissions of most VOCs (p<0.05). Utilizing dung–angithi cook fires resulted in twice as much of the measured VOCs compared to dung–chulha and 4 times as much as brushwood–chulha, with 84.0, 43.2, and 17.2 g measured VOC kg−1 fuel carbon, respectively. This matches expectations, as the use of dung fuels and angithi cookstoves results in lower modified combustion efficiencies compared to brushwood fuels and chulha cookstoves. Alkynes and benzene were exceptions and had significantly higher emissions when cooking using a chulha as opposed to an angithi with dung fuel (for example, benzene emission factors were 3.18 g kg−1 fuel carbon for dung–chulha and 2.38 g kg−1 fuel carbon for dung–angithi). This study estimated that 3 times as much SOA and ozone in the maximum incremental reactivity (MIR) regime may be produced from dung–chulha as opposed to brushwood–chulha cook fires. Aromatic compounds dominated as SOA precursors from all types of cook fires, but benzene was responsible for the majority of SOA formation potential from all chulha cook fire VOCs, while substituted aromatics were more important for dung–angithi. Future studies should investigate benzene exposures from different stove and fuel combinations and model SOA formation from cook fire VOCs to verify public health and air quality impacts from cook fires.
Highlights
Parts of rural India are comprised of densely populated villages with ambient ozone and PM2.5 levels that affect air quality for inhabitants (Bisht et al, 2015; Ojha et al, 2012; Reddy, 2012)
We found that our Emission factors (EFs) were always higher for dung–chulha compared to brushwood–chulha, which was not always the case in Stockwell et al (2016)
By examining the EFs reported in the supporting information section of Stockwell et al (2016), we found that the disagreement resulted from the way the final recommended EFs were obtained from the measurements
Summary
Parts of rural India are comprised of densely populated villages with ambient ozone and PM2.5 levels that affect air quality for inhabitants (Bisht et al, 2015; Ojha et al, 2012; Reddy, 2012). In the rural area of Anantapur in southern India, monthly mean ozone levels varied between 29 ppbv (parts per billion by volume) in August during the monsoon season and 56 ppbv in April (Reddy, 2012). While measurements of O3 and PM2.5 in rural India are relatively scarce, it has become clear that household combustion is a major contributor to ambient levels of these pollutants. Over the last half decade, several researchers have, through independent studies, come to the conclusion that a significant fraction (22 %–52 %) of ambient PM2.5 is directly emitted from residential cooking and heating (Butt et al, 2016; Chafe et al, 2014; Conibear et al, 2018; GBD MAPS Working Group, 2018; Guttikunda et al, 2016; Klimont et al, 2017; Lelieveld et al, 2015; Silva et al, 2016)
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