High contribution of anthropogenic combustion sources to atmospheric inorganic reactive nitrogen in South China evidenced by isotopes
Abstract. Due to the intense release of reactive nitrogen (Nr) from anthropogenic activity, the source layout of atmospheric nitrogen aerosol has changed. The inorganic nitrogen (NH4+ and NO3-) was essential part of atmospheric nitrogen aerosol and accounted for 69 %. To comprehensively clarify the level, sources, and environmental fate of NH4+ and NO3-, their concentrations and stable isotopes (δ15N) in fine particulate matters (PM2.5) were measured in a subtropical megacity of South China. N-NH4+ and N-NO3- contributed 45.8 % and 23.2 % to total nitrogen (TN), respectively. The source contributions of NH4+ and NO3- were estimated by δ15N, which suggested that anthropogenic combustion activities including coal combustion, biomass burning, and vehicles were dominant sources. Especially, biomass burning was the predominant source of NH4+ (27.9 %). Whereas, coal combustion was the dominant source of NO3- (40.4 %). This study emphasized the substantial impacts of human activities on inorganic Nr. With the rapid development of industry and transportation, nitrogen emissions will be even higher. The promotion of clean energy and efficient use of biomass would help reduce nitrogen emissions and alleviate air pollution.
Tingting Li et al.
Tingting Li et al.
High contribution of anthropogenic combustion sources to atmospheric inorganic reactive nitrogen in south China evidenced by isotopes https://doi.org/10.17632/yck5xy22w2.1
Tingting Li et al.
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The manuscript by Li et al. simultaneously reported concentrations and stable nitrogen isotope and oxygen isotopes compositions of atmospheric NO3- and concentrations and nitrogen isotopes compositions of atmospheric NH4+ in PM2.5 samples collected in Guangzhou from May 2017 to June 2018. Then, authors restrained nitrogen isotope fractionation values of the process of NH3 to formed NH4+ and NOx to formed NO3-. Finally, using the IsoSource model, authors quantified the relative contributions of major sources of NH3 and NOx to atmospheric NH4+ and NO3-, respectively. Authors found the focus of NH3 reduction should be on anthropogenic combustion sources especially on biomass burning, which might be responsible for the lag of the decline in deposition of air pollutions behind the reduction in emission. Additionally, despite a series of measures to reduce emissions of NOx, fossil fuels, as the main energy for production and living, will still inevitably emit a large amount of NOx. Authors emphasized that the emission of atmospheric inorganic nitrogen is largely related to anthropogenic combustion sources. The development and promotion of clean energy and efficient use of biomass are conducive to the deep reduction of atmospheric nitrogen. I believe that this result is meaningful and would make a substantial contribution to the field. The manuscript is generally well-organized in structure. If the following comments are adequately addressed, I believe the manuscript could be accepted to Atmospheric Chemistry and Physics.
(1) Lines 112-113: The author needs to provide the analytical accuracy of isotopes nitrogen and oxygen isotopes.
(2) Nitrogen isotope fractionation values of the process of NH3 to formed NH4+ and NOx to formed NO3- are key parameters for quantifying the relative contributions of major sources of NH3 and NOx to atmospheric NH4+ and NO3-. The calculation methods for the two parameters should be include in the text of manuscript. In addition, it is necessary to give readers detailed data of each parameter, especially the fractionation value.
(3) Authors should explain why these four sources are selected as main sources of atmospheric NO3- and these six sources are selected as main sources of atmospheric NH4+?
(4) Lines 176-178: Does the combustion of sugarcane leaf emit NH4+ directly or emit NH3 and then formed NH4+?
(5) Lines 236-237: The sources apportionment results of atmospheric NO3- in Figure c does not correspond to that in Figure b.
(6) Lines 272-273: Why does the author only consider the OH radical oxidation and N2O5 hydrolysis pathway to NO3-, and not consider other pathways? The author needs to explain.