Emissions of intermediate-volatility and semi-volatile organic compounds from domestic fuels used in Delhi, India

Abstract

Abstract. Biomass burning emits significant quantities of intermediate-volatility and semi-volatile organic compounds (I/SVOCs) in a complex mixture, probably containing many thousands of chemical species. These components are significantly more toxic and have poorly understood chemistry compared to volatile organic compounds routinely quantified in ambient air; however, analysis of I/SVOCs presents a difficult analytical challenge. The gases and particles emitted during the test combustion of a range of domestic solid fuels collected from across Delhi were sampled and analysed. Organic aerosol was collected onto Teflon (PTFE) filters, and residual low-volatility gases were adsorbed to the surface of solid-phase extraction (SPE) discs. A new method relying on accelerated solvent extraction (ASE) coupled to comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC–ToF-MS) was developed. This highly sensitive and powerful analytical technique enabled over 3000 peaks from I/SVOC species with unique mass spectra to be detected. A total of 15 %–100 % of gas-phase emissions and 7 %–100 % of particle-phase emissions were characterised. The method was analysed for suitability to make quantitative measurements of I/SVOCs using SPE discs. Analysis of SPE discs indicated phenolic and furanic compounds were important for gas-phase I/SVOC emissions and levoglucosan to the aerosol phase. Gas- and particle-phase emission factors for 21 polycyclic aromatic hydrocarbons (PAHs) were derived, including 16 compounds listed by the US EPA as priority pollutants. Gas-phase emissions were dominated by smaller PAHs. The new emission factors were measured (mg kg−1) for PAHs from combustion of cow dung cake (615), municipal solid waste (1022), crop residue (747), sawdust (1236), fuelwood (247), charcoal (151) and liquefied petroleum gas (56). The results of this study indicate that cow dung cake and municipal solid waste burning are likely to be significant PAH sources, and further study is required to quantify their impact alongside emissions from fuelwood burning.

Emissions of non-methane volatile organic compounds from combustion of domestic fuels in Delhi, India

“…The maximum error in this calibration approach was shown to be 21 % (Taipale et al, 2008). Peak assignment was assisted with results reported by previous burning studies and references therein (Brilli et al, 2014;Stockwell et al, 2015;Koss et al, 2018). The results may also contain other indistinguishable structural isomers not mentioned here.…”

“…Most species of similar functionality tracked each other. Stockwell et al (2015) demonstrated that benzene, phenol and furan could act as tracers for aromatic, phenolic and furanic species released from biomass burning. Figure 5a shows that heavier, more substituted phenolics appeared to be released at cooler temperatures.…”

“…The more recently developed technique of proton-transfer-reaction timeof-flight mass spectrometry (PTR-ToF-MS) has allowed for around 90 % of total measured NMVOC emissions in terms of mixing ratio from burning experiments to be speciated (Koss et al, 2018) and has also been used to study the formation of SOA (Bruns et al, 2016). The main disadvantages of the PTR-ToF-MS technique are its inability to speciate isomers, significant fragmentation of parent ions, only being able to detect species with a proton affinity greater than water and the formation of water clusters needing to be considered (Stockwell et al, 2015;Yuan et al, 2017). More recently, measurements have also been made using iodide chemical ionisation time-of-flight mass spectrometry (I − -CIMS), which is well suited to measuring acids and multifunctional oxygenates (Lee et al, 2014) as well as isocyanates, amides and organo-nitrate species released from biomass burning (Priestley et al, 2018).…”

“…Few studies measuring highly speciated NMVOC emission factors from fuels specific to India exist. Recent studies using PTR-ToF-MS to develop emission factors, which are more reflective of the range of species emitted from burning, have focussed largely on grasses, crop residues and peat (Stockwell et al, 2015) as well as fuels characteristic of the western US (Koss et al, 2018). A previous study measured emission factors of NMVOCs from cow dung cake using gas chromatography with flame ionisation detection (GC-FID) of 8-32 g kg −1 (EPA, 2000).…”

“…However, very few speciated NMVOC measurements were made, and the emission factors were similar to those measured using just GC (Fleming et al, 2018). Studies have also focussed on making detailed measurements, using a range of techniques, from the burning of municipal solid waste (Christian et al, 2010;Yokelson et al, , 2013Stockwell et al, 2015Stockwell et al, , 2016Sharma et al, 2019) and crop residues (Stockwell et al, 2015;Koss et al, 2018;Kumar et al, 2018).…”