Sources identification of ammonium in PM2.5 during monsoon season in Dhaka, Bangladesh

Strategic control of combustion-induced ammonia emissions: A key initiative for substantial PM2.5 reduction in Tianjin, North China Plain

Information on the temporal and spatial variations in the sources of ammonium salts (NH4+), a crucial alkaline component in PM2.5, is limited. Here, we simultaneously collected PM2.5 and gaseous ammonia (NH3) samples in both summer and winter from two sites in Tianjin: an urban site (Tianjin University, TJU) and a suburban site (Binhai New-region, BH). NH3 concentrations, the contents of major water-soluble inorganic ions in PM2.5, and the compositions of ammonium‑nitrogen isotopes (δ15N-NH4+) were measured. As a result, (NH4)2SO4 and NH4NO3 were the predominant forms of NH4+ in PM2.5 during summer and winter, respectively. However, the NH4NO3 concentrations were notably greater at TJU (6.2 ± 7.3 μg m-3) than at BH (3.8 ± 4.7 μg m-3) in summer, with no regional differences observed in winter. Both sites displayed almost half the contribution of c-NH3 (combustion-related NH3) to NH4+, differing from the finding of previous isotope-based studies. This discrepancy could be attributed to the combined effects of NHx isotope fractionation and seasonal δ15N value variations in NH3 sources. The contribution fractions of v-NH3 (volatile NH3) and c-NH3 exhibited similar patterns at both sites seasonally, probably caused by coal combustion for heating in winter and temperature fluctuations. However, the contribution fraction of c-NH3 was lower at BH than at TJU in summer but greater in winter than at TJU. In summer, NH4NO3 was unstable and limited its delivery to TJU from BH, and the high contribution of c-NH3 to NH4+ at TJU could be attributed to local vehicle emissions. In winter, the stable particulate NH4NO3 that formed from the c-NH3 in the upwind area could be transported to the downwind area, increasing the NH4+ concentration at BH. Our study provides valuable insights for devising emission mitigation strategies to alleviate the increasing burden of NH3 in the local atmosphere.

Nitrogen isotopes suggest agricultural and non-agricultural sources contribute equally to NH3 and NH4+ in urban Beijing during December 2018

Agricultural and non-agricultural sources emission contribute to atmospheric ammonia (NH₃) and particulate ammonium (NH₄⁺). However, our understanding on the sources of NH₃ and NH₄⁺ in PM_2.5 (particles smaller than 2.5 μm) during the winter period in the urban atmosphere is limited. Here, we measured the concentrations and stable nitrogen isotopic composition (δ¹⁵N) of NH₃ and NH₄⁺ in parallel during December 2018 in urban Beijing to assess the non-agricultural and agricultural sources contributions to NH₃ and NH₄⁺ in ambient air based on the Chemical Transport Model (CTM), a Bayesian isotope mixing model (SIMMR), and the δ¹⁵N signatures that we developed. Our study found weekly NH₄⁺ and NH₃ concentrations were on average 2.5 ± 1.4 μg m^-3 and 3.8 ± 1.7 μg m^-3, respectively during December 2018. Weekly concentration weighted δ¹⁵N(NH₄⁺) values ranged from 4.5‰ to 13.7‰ with an average value of 8.2 ± 3.9‰ during December 2018. After accounting for nitrogen isotopic fractionation from NH₃ gas to NH₄⁺ conversion, initial δ¹⁵N(NH₃) values ranged from -22.5‰ to -12.8‰ with an average value of -17.4 ± 3.5‰. Further, weekly measured δ¹⁵N(NH₃) values ranged from -22.2‰ to -10.2‰ (after correction) with an average value of -15.6 ± 5.3‰ during December 2018. Results from two different isotope-based method showed non-agricultural sources contributed 31.2%-63.1%, with an average value of 47.5 ± 14.6%, to NH₄⁺ and 32.3%-71.2%, with an average of 53.4 ± 16.1%, to ambient NH₃ during December 2018 in Beijing. Results from CMAQ-ISAM suggest non-agricultural sources contributed on average 66.2 ± 1.9% to ambient NH₄⁺ and 66.4 ± 1.9% to ambient NH₃ during December 2018. Results from this study suggest that agricultural and non-agricultural sources nearly equally contributed to NH₃ and NH₄⁺ in urban Beijing during December 2018 with an uncertainty range of 13%-19% between isotope-based methods and CTM method.

Long-Term Source Apportionment of Ammonium in PM2.5 at a Suburban and a Rural Site Using Stable Nitrogen Isotopes

Ammonia gas (NH3) is an important alkaline air pollutant and a precursor to particulate matter, and its source has been thought to be agricultural, but in recent years, nonagricultural sources have been suspected. In this study, stable nitrogen isotope ratios of ammonium (δ15N-NH4+) in fine particulate matter (PM2.5) were measured at a suburban site and a rural site in Japan. Then, the long-term sources of NH4+ were identified using the δ15N-NH3 and an isotopic mixing model. The results showed that the averaged contribution from nonagricultural sources was 67% at the suburban site and 78% at the rural site. We also reanalyzed NH3 data collected at the same location. The result showed that the averaged contribution of nonagricultural sources to NH3 was 39%. This result is reasonable because bottom-up estimates are close to the contribution, and the NH3 emissions are affected by warm season activities in the rural site. It was first found that the sources vary greatly, depending on the gas and particles. Back-trajectory results suggested that PM2.5 measured at the rural site was derived from the Asian continent. We inferred that the NH4+ had been formed on the continent and that these particles thus represent transboundary pollution.

Assessing the Relationship among Land Transfer, Fertilizer Usage, and PM2.5 Pollution: Evidence from Rural China

Concern for environmental issues is a crucial component in achieving the goal of sustainable development of humankind. Different countries face various challenges and difficulties in this process, which require unique solutions. This study investigated the relationship between land transfer, fertilizer usage, and PM_2.5 pollution in rural China from 2000 to 2019, considering their essential roles in agricultural development and overall national welfare. A cross section dependence test, unit root test, and cointegration test, among other methods, were used to test the panel data. A Granger causality test was used to determine the causal relationship between variables, and an empirical analysis of the impulse response and variance decomposition was carried out. The results show that the use of chemical fertilizers had a significant positive impact on PM_2.5 pollution, but the impact of land transfer on PM_2.5 pollution was negative. In addition, land transfer can reduce the use of chemical fertilizers through economies of scale, thus reducing air pollution. More specifically, for every 1% increase in fertilizer usage, PM_2.5 increased by 0.17%, and for every 1% increase in land transfer rate, PM_2.5 decreased by about 0.07%. The study on the causal relationship between land transfer, fertilizer usage, and PM_2.5 pollution in this paper is helpful for exploring environmental change—they are supplements and innovations which are based on previous studies and provide policy-makers with a basis and inspiration for decision-making.