Insights into the nitroaromatic compounds, formation, and light absorption contributing emissions from various...

Nitroaromatic compounds (NACs) are essential components of atmospheric organic aerosols. Coal combustion is a key source of atmospheric NACs. In this study, a triple-quadrupole liquid chromatography-mass spectrometry (LC-MS) system was used to identify ten individual NAC emitted in combustions of chunk coal and its briquette at different maturity levels. The Gaussian calculation was applied to quantify the absorption contribution of NACs to brown carbon (BrC). The emission factors (EFs) of total quantified NACs (ΣNACs) are 21.80-4429.55 μg/kg. 4-Nitrocatechol (4NC) is the most abundant NACs, accounting for 25.5-82.3 % of the ΣNACs and has the largest contribution to light absorption (0.34-29.23 %). The EFs for ΣNACs of chunk coal are 1.1-3.0 times those of its briquette, while the coal with volatile matter (VM) = 35.83 % shows the highest NAC emissions. The reaction pathway analysis demonstrates that NACs in briquette are generated through the pyrolysis of coal tar at an early stage of coal combustion, while volatile organic compounds (VOCs) that are emitted in chunk coal contribute greatly to the formations of NACs. The molecular properties analysis reveals that ΣNACs contribute 0.47-35.27 % to BrC light absorption. Anthracite coal (VM = 8.01 %) demonstrates the lowest light absorption coefficient (b_abs-365). Since bituminous coal (with VM = ~10 %-40 %) is popularly used for heating in rural China in winter, the results of this study could assist to evaluate the climate and environmental impacts on the NACs emission from coal combustion on a regional scale. Finally, the results highlighted that replacements of bituminous by clear fuel (such as chunk or briquette anthracite) could reduce NACs emission effectively.