Persistent Nonagricultural and Periodic Agricultural Emissions Dominate Sources of Ammonia in Urban Beijing: Evidence from ¹⁵N Stable Isotope in Vertical Profiles

Abstract

Ammonia (NH3) emission reduction is key to limiting the deadly PM2.5 pollution globally. However, studies of long-term source apportionment of vertical NH3 are relatively limited. On the basis of the one-year measurements of weekly vertical profiles of δ 15N–NH3 at 5 heights (2, 15, 102, 180, and 320 m) on a 325-m meteorological tower in urban Beijing, we found that vertical profiles of NH3 concentrations generally remained stable with height. δ 15N–NH3 increased obviously as a function of height in cold seasons (with heating) and decreased in warm seasons (with fertilization), indicating a stronger human-induced seasonal variation via regional transport at higher altitudes. Relatively stable δ 15N–NH3 near the ground surface suggested the strong local emission. The results of isotopic mixing model (SIAR) indicate that source apportionment using measured δ 15N–NH3 only would overestimate the contribution of agricultural emissions to NH3. By using an estimation of initial δ 15N–NH3, we found that nonagricultural sources contributed ∼72% of NH3 on average. Our study suggests that (i) both persistent nonagricultural and periodic agricultural emissions drive atmospheric NH3 concentration and its vertical distribution in urban Beijing; and (ii) source apportionment based on measured δ 15N–NH3 only likely underestimates fossil fuel source contribution, if the combined NH x isotope effects are not considered.

Atmospheric Ammonia in Beijing during the COVID-19 Outbreak: Concentrations, Sources, and Implications

“…Stable nitrogen isotope techniques were widely used to quantify the contributions of different sources to NH 3 in previous studies. 23 , 27 − 30 Our results indicated that δ 15 N-NH 3 was a more sensitive indicator than NH 3 concentrations to the changes in NH 3 emissions, suggesting isotope-based source apportionment of NH 3 could provide accurate and reliable evidence of the success of NH 3 emission controls, consequent air quality improvement, and further mitigation strategy design. However, further work is needed to improve δ 15 N-NH 3 collection techniques.…”

δ15N-stable isotope analysis of NHx: An overview on analytical measurements, source sampling and its source apportionment

“…+ (Chang et al, 2016;Liu et al, 2018;Chang et al, 2019;Wu et al, 2019a;Wu et al, 2019b;Bhattarai et al, 2020;Zhang et al, 2020a;Zhang et al, 2020b;Zhang et al, 2020c) in ambient atmosphere (see Supplementary data in Tables A1 and A2).…”

“…4.2 Uncertainty from measured/corrected δ 15 N(NH 3 ) values collected using passive samplers Previous studies (Chang et al, 2016;Felix et al, 2017;Chang et al, 2019;Berner and Felix, 2020;Zhang et al, 2020a;Zhang et al, 2020b) have shown that nonagricultural sources such as fossil fuel sources (e.g., vehicle exhaust) and urban waste volatilized sources (human excreta, solid waste and wastewater) are important source of NH 3 in urban areas of China and the USA (Table 2). This is without consideration of potential fractionation in δ 15 N(NH 3 ) values characterized for ambient NH 3 samples collected with passive diffusion samplers.…”

“…Their study and an earlier study from Felix et al (2014) highlighted the importance of fossil fuel related sources (e.g., vehicular exhaust, NH 3 slip from Selective Catalytic Reduction (SCR) equipped power plants, and coal combustion) based on isotope-based source apportionment of δ 15 N(NH 4 + ) and δ 15 N(NH 3 ) values, respectively. Thereafter a number of studies suggested that fossil fuel related sources may be an important source of NH 4 + and NH 3 in urban atmosphere in China based on source apportionment of δ 15 N(NH 4 + ) values (Liu et al, 2018;Pan et al, 2018a;Wu et al, 2019a;Wu et al, 2019b;Bhattarai et al, 2020;Wu et al, 2020;Xiao et al, 2020;Zhang et al, 2020c) and δ 15 N(NH 3 ) values (Chang et al, 2016;Chang et al, 2019;Bhattarai et al, 2020;Zhang et al, 2020a;Zhang et al, 2020b), respectively.…”

“…+ utilizing δ 15 N(NH 4 + ) values (e.g., Pan et al, 2018a;Wu et al, 2019a), and of ambient NH 3 utilizing δ 15 N(NH 3 ) values (e.g., Chang et al, 2019;Zhang et al, 2020a), respectively. However, there are some potential uncertainties in the current approach of isotope-based source apportionment of NH 4 + and NH 3 , which are highlighted in this study.…”