Combustion-related activities dominate atmospheric ammonia in the Pearl River Delta region, China

Abstract

Ammonia (NH₃) is a key precursor of fine particulate matter (PM_2.5) in the air; however, its emission sources at different heights remain poorly understood in the Pearl River Delta (PRD) region of China. In this study, we simultaneously collected PM_2.5 samples at three atmospheric heights (ground, 118 m, and 488 m) based on the atmospheric observatories of Canton Tower, the tallest structure in the PRD region. Our results showed that the average NH₄⁺ concentrations were 2.7 ± 1.4, 3.0 ± 1.8, and 2.6 ± 1.7 μg/m³ at the ground site, 118 m, and 488 m during the sampling campaign, with no significant difference (p > 0.05) among the three heights. However, the stable nitrogen isotope composition values in NH₄⁺ (δ¹⁵N-NH₄⁺) displayed a significant correlation with height (p < 0.05). We further calculated the initial δ¹⁵N-NH₃ values and performed source apportionments using the Bayesian Isotope Mixture Model. The results indicated that the mean contributions of agriculture, waste, vehicle, biomass burning, NH₃ slip, and coal combustion were 9.9% ± 4.4%, 8.3% ± 5.5%, 29% ± 8.0%, 16% ± 2.2%, 25% ± 6.0%, and 12% ± 3.4%, respectively, at the ground site during the sampling campaign. By contrast, the contributions of sources at 488 m remained relatively stable due to the limited influence of local activities. Overall, our study highlights the dominant role of combustion sources in NH₃ emissions in the PRD region, with their contribution being highly dependent on atmospheric height.

Graphical abstract

Keywords

Ammonia / Stable nitrogen isotope / Source apportionment / Canton Tower / PRD region

Highlight

	● The NH4+ concentrations showed no significant differences at different altitudes.
	● The δ15N-NH4+ values decreased with increasing altitude in urban areas.
	● Combustion source was the largest emitter for NH3 in the PRD region.
	● The contributions of different sources to NH3 vary with height.

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