Abstract
N-containing aromatic compounds (NACs) are an important group of light-absorbing molecules in the atmosphere. They are often observed in combustion emissions, but their chemical formulas and structural characteristics remain uncertain. In this study, red oak wood and charcoal fuels were burned in cookstoves using the standard water boiling test (WBT) procedure. Submicron aerosol particles in the cookstove emissions were collected using quartz (Q f ) and polytetrafluoroethylene (PTFE) filter membranes positioned in parallel. A back-up quartz filter (Q b ) was also installed downstream of the PTFE filter to evaluate the effect of sampling artifact on NACs measurements. Liquid chromatography-mass spectroscopy (LC-MS) techniques identified seventeen NAC chemical formulas in the cookstove emissions. The average concentrations of total NACs in Q b samples (0.37 ± 0.31 - 1.79 ± 0.77 μg m-3) were greater than 50% of those observed in the Q f samples (0.51 ± 0.43 - 3.91 ± 2.06 μg m-3), and the Q b to Q f mass ratios of individual NACs had a range of 0.02 - 2.71, indicating that the identified NACs might have substantial fractions remaining in the gas-phase. In comparison to other sources, cookstove emissions from red oak or charcoal fuels did not exhibit unique NAC structural features, but had distinct NACs composition. However, before identifying NACs sources by combining their structural and compositional information, the gas-particle partitioning behaviors of NACs should be further investigated. The average contributions of total NACs to the light absorption of organic matter at λ = 365 nm (1.10 - 2.57%) in Q f and Q b samples (10.7 - 21.0%) are up to 10 times larger than their mass contributions (Q f 0.31 - 1.01%, Q b 1.08 - 3.31%), so the identified NACs are mostly strong light absorbers. To explain more sample extracts absorption, future research is needed to understand the chemical and optical properties of high molecular weight (e.g., MW > 500 Da) entities in particulate matter.
Highlights
In the developing world, 2.8 billion people burn solid fuels in household cookstoves for domestic activities such as heating and cooking (Bonjour et al, 2013)
The N-containing aromatic compounds (NACs) emissions from red oak burning are less likely influenced by the water-boiling test (WBT) phase, and the effect of fuel moisture content needs further investigation
Even if the NACs on quartzfiber backup filter (Qb) were totally derived from upstream filter evaporation, the adjusted average contributions of total NACs (Qf + Qb) to Abs365 of quartz-fiber filter (Qf) extracts were still lower than 5 % (1.59 %–4.01 %)
Summary
2.8 billion people burn solid fuels in household cookstoves for domestic activities such as heating and cooking (Bonjour et al, 2013). Unlike open BB (e.g., forest, grassland, and cropland fires) – one of the most important primary sources for organic aerosols (Bond et al, 2004) – the light absorption of BrC from household cookstove emissions is rarely investigated. BrC from wood combustion in cookstoves has a greater mass-specific absorption than that from open BB over the wavelength range of 300– 550 nm (Xie et al, 2018). These results suggest that cookstove emissions may be an important BrC source, which needs to be accounted for separately from open BB
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