Regional transport and urban emissions are important ammonia contributors in Beijing, China

Reduction potential of ammonia emissions and impact on PM2.5 in a megacity of central China

Ammonia control has attracted attention due to the possibility for fine particles (PM2.5) mitigation. Based on past decade ammonia emissions assessments and future predictions, this study seasonally evaluated the ammonia emissions reduction potential in 2025 and 2030 in Wuhan, a Central China megacity, according to the short-term and long-term predictable policies. Furthermore, combined with the reduction potential, PM2.5 components observation and thermodynamic model, the effectiveness of implementing ammonia emission control to reduce PM2.5 by 2025 and 2030 was explored seasonally. Results indicated that the total ammonia emissions are expected to decrease by 19.6-33.9% in 2025 and 2030 under positive reduction scenarios, or increase by 8.9-11.7% in the absence of any intervention. Livestock holds the largest potential for reducing ammonia emissions accounting for 46.4-52.5% of the total. Improvement of human excrement management in rural regions also contributes a 35-37% potential. Despite the implementation of exhaust requirements, ammonia emissions from vehicles in 2030 are expected to continue to increase by 55.3% and 23.5% under the regular (S1) and enhanced (S2) reduction strategy scenarios, respectively. Seasonally, the most potential source of ammonia reduction in spring, summer and fall remains livestock. While in winter, non-agricultural sources dominate the reduction potential. Further results indicated that by ammonia control is expected to decrease PM2.5 concentration up to 5% (less than 1 μg m-3) in 2025-2030. Despite the better effectiveness in winter, ammonia control won't be an effective way to reduce PM2.5 in Central China in future, from the management policies and areal ammonia-rich conditions.

Summertime Urban Ammonia Emissions May Be Substantially Underestimated in Beijing, China

Ammonia (NH3) is critical to the nitrogen cycle and PM2.5 formation, yet a great deal of uncertainty exists in its urban emission quantifications. Model-underestimated NH3 concentrations have been reported for cities, yet few studies have provided an explanation. Here, we explore reasons for severe WRF-Chem model underestimations of NH3 concentrations in Beijing in August 2018, including simulated gas-particle partitioning, meteorology, regional transport, and emissions, using spatially refined (3 km resolution) NH3 emission estimates in the agricultural sector for Beijing-Tianjin-Hebei and in the traffic sector for Beijing. We find that simulated NH3 concentrations are significantly lower than ground-based and satellite observations during August in Beijing, while wintertime underestimations are much more moderate. Further analyses and sensitivity experiments show that such discrepancies cannot be attributed to factors other than biases in NH3 emissions. Using site measurements as constraints, we estimate that both agricultural and non-agricultural NH3 emission totals in Beijing shall increase by ∼5 times to match the observations. Future research should be performed to allocate underestimations to urban fertilizer, power, traffic, or residential sources. Dense and regular urban NH3 observations are necessary to constrain and validate bottom-up inventories and NHx simulation.

The future air quality impact of electric vehicle promotion and coordinated charging in the Beijing-Tianjin-Hebei region

The synergetic benefit of air quality improvements together with greenhouse gas (GHG) mitigations from fleet electrification can be maximized if the power used for electric vehicles (EVs) is from renewables. The worth-noting mismatch between renewable power generation and EV fleet charging demand requires appropriate coordination strategy. Here, we analyze the environmental benefits from increased EVs penetration in Beijing-Tianjin-Hebei (BTH) regions by integrating various scenarios of fleet electrification with coordinated charging strategies to examine the air quality improvement and GHG abatement. The study found that fleet electrification could bring substantial reduction on urban PM_2.5 in BTH, especially in December by 0.8 ± 0.5 μg/m³. The coordinated charging strategy could further improve the air quality in BTH, albeit smaller than that of fleet electrification itself. PM_2.5 reduction benefit from EV adoption could be significantly more pronouncing when ammonia emission reduction was considered, by more than 0.3 μg/m³ in both December and July, validating the great significance of vehicle NH₃ emission control and the necessity of prioritizing the electrification of high ammonia emitting fleet. The outcome of this study helps to formulate the effective on-road transportation pollutant abatement strategies and offers technological support for policy makers to conduct more sensible sequence of future fleet electrification process.

On-road mobile mapping of spatial variations and source contributions of ammonia in Beijing, China

Ammonia (NH₃) measurements were performed with a mobile platform deploying a cavity ring-down spectroscopy NH₃ analyzer in Beijing. The transect and loop sampling strategy revealed that the Beijing urban area is more strongly affected by NH₃ emissions than surrounding areas. Although average enhancements of on-road NH₃ were small compared to background levels, traffic emissions clearly dominated city enhancements of NH₃, carbon dioxide (CO₂), acetaldehyde and acetone. Increments of on-road NH₃ ranged between 5.1 ppb and 11.4 ppb in urban areas, representing an enhancement of 20.6 % to 47.9 % over the urban background. The vehicle NH₃:CO₂ emission ratio was 0.26 ppb/ppm, about a factor of 1.5 higher than the value derived from the available emission inventory. The obtained NH₃ emission factor was approximately 306.9 mg/kg. If the annual gasoline consumption in Beijing is accurate, annual NH₃ emissions from vehicles are estimated at 1.5 Gg. The influx and outflux of NH₃ in Beijing during monitoring periods fluctuated due to variations of wind direction (WD), wind speed (WS), and planetary boundary layer height (PBLH). Net fluxes at the 4^th Ring Road were larger than zero, suggesting that local emissions were important in urban Beijing. Negative net fluxes at the 6^th Ring Road reveal a large amount of NH₃ transported from agricultural regions south of Beijing lost during transport across the city, for example by deposition or particle formation in the city. Our analyses have important implications for regional NH₃ emission estimates and for improving vehicular NH₃ emission inventory allocations.

Spatial origin analysis on atmospheric bulk deposition of polycyclic aromatic hydrocarbons in Shanghai

Atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) onto soil threatens terrestrial ecosystem. To locate potential source areas geographically, a total of 139 atmospheric bulk deposition samples were collected during 2012-2019 at eight sites in Shanghai and its surrounding areas. A multisite joint location method was developed for the first time to locate potential source areas of atmospheric PAHs based on an enhanced three dimensional concentration weighted trajectory model. The method considered spatial and temporal variations of atmospheric boundary layer height and homogenized all results over the eight sites via geometric mean. Regional transport was an important contributor of PAH atmospheric deposition while massive local emissions may disturb the identification of potential source areas. Northwesterly winds were associated with elevated deposition fluxes. Potential source areas were identified by the multisite joint location method and included Hebei, Tianjin, Shandong and Jiangsu to the north, and Anhui to the west of Shanghai. PM and SO₂ data from the national ground monitoring stations confirmed the identified source areas of deposited PAHs in Shanghai.

Quantifying the Influence of a Burn Event on Ammonia Concentrations Using a Machine-Learning Technique

Although combustion is considered a common source of ammonia (NH3) in the atmosphere, field measurements quantifying such emissions of NH3 are still lacking. In this study, online measurements of NH3 were performed by a cavity ring-down spectrometer, in the cold season at a rural site in Xianghe on the North China Plain. We found that the NH3 concentrations were mostly below 65 ppb during the study period. However, from 18 to 21 November 2017, a close burn event (~100 m) increased the NH3 concentrations to 145.6 ± 139.9 ppb. Using a machine-learning technique, we quantified that this burn event caused a significant increase in NH3 concentrations by 411%, compared with the scenario without the burn event. In addition, the ratio of ∆NH3/∆CO during the burn period was 0.016, which fell in the range of biomass burning. Future investigations are needed to evaluate the impacts of the NH3 combustion sources on air quality, ecosystems, and climate in the context of increasing burn events worldwide.

Non-stop industries were the main source of air pollution during the 2020 coronavirus lockdown in the North China Plain

Despite large decreases of emissions of air pollution during the coronavirus disease 2019 (COVID-19) lockdown in 2020, an unexpected regional severe haze has still occurred over the North China Plain. To clarify the origin of this pollution, we studied air concentrations of fine particulate matter (PM_2.5), NO₂, O₃, PM₁₀, SO₂, and CO in Beijing, Hengshui and Baoding during the lockdown period from January 24 to 29, 2020. Variations of PM_2.5 composition in inorganic ions, elemental carbon and organic matter were also investigated. The HYSPLIT model was used to calculate backward trajectories and concentration weighted trajectories. Results of the cluster trajectory analysis and model simulations show that the severe haze was caused mainly by the emissions of northeastern non-stopping industries located in Inner Mongolia, Liaoning, Hebei, and Tianjin. In Beijing, Hengshui and Baoding, the mixing layer heights were about 30% lower and the maximum relative humidity was 83% higher than the annual averages, and the average wind speeds were lower than 1.5 m s^-1. The concentrations of NO₃ ^-, SO₄ ^2-, NH₄ ⁺, organics and K⁺ were the main components of PM_2.5 in Beijing and Hengshui, while organics, K⁺, NO₃ ^-, SO₄ ^2-, and NH₄ ⁺ were the main components of PM_2.5 in Baoding. Contrary to previous reports suggesting a southerly transport of air pollution, we found that northeast transport caused the haze formation.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10311-021-01314-8.

Indoor NH3 variation and its relationship with outdoor NH3 in urban Beijing

Online measurements of indoor and outdoor ammonia (NH₃ ) were conducted at a university building in Haidian District, Beijing, to investigate their variation characteristics, indoor-outdoor differences, influencing factors, and possible contribution of indoor NH₃ to atmospheric NH₃ . Indoor NH3 mixing ratios varied greatly among the rooms of the same building. Indoor NH₃ mixing ratio peaked at 1.43 ppm in a toilet. Both indoor and outdoor NH₃ mixing ratios exhibited higher values during summer and lower values during winter and correlated significantly with relative humidity and temperature. Moreover, their daily mean mixing ratios were significantly correlated with each other. But indoor and outdoor NH₃ in cold months exhibited quite different diurnal variations. During the measurement period, indoor NH₃ mixing ratios were substantially higher than those outdoors, by an average factor of 3.1 (1.0-6.6). This indicates that indoor NH₃ could be a source of outdoor atmospheric NH₃ . The contribution of indoor NH₃ to atmospheric NH₃ was estimated at 0.7 ± 0.5 Gg NH₃ -N·a^-1 , accounting for approximately 1.0 ± 0.7% of total emissions in Beijing and being comparable to industry, biomass combustion, and soil emissions, but lower than transportation emissions. The influence of COVID-19 control measures caused indoor and outdoor NH₃ mixing ratios to decrease by 22.8% and 19.3%, respectively-attributable to decreased human activity and traffic flow.

Ammonia exposure causes the disruption of the solute carrier family gene network in pigs

Ammonia is the main harmful gas in livestock houses. However, the toxic mechanism of ammonia is still unclear. Therefore, we examined the effects of ammonia exposure on different tissues of fattening pigs by histological analysis and transcriptome techniques in this study. The results showed that there were varying degrees of pathological changes in liver, kidney, hypothalamus, jejunum, lungs, spleen, heart and trachea of fattening pigs under ammonia exposure. Notably, the extent of damage in liver, kidney, jejunum, lungs, hypothalamus and trachea was more severe than that in heart and spleen. Transcriptome results showed that ammonia exposure caused changes in 349, 335, 340, 229, 120, 578, 407 and 115 differentially expressed genes in liver, kidney, spleen, lung, trachea, hypothalamus, jejunum and heart, respectively. Interestingly, the changes in solute vector (SLC) family genes were found in all 8 tissues, and the verified gene results (SLC11A1, SLC17A7, SLC17A6, SLC6A4, SLC22A7, SLC25A3, SLC28A3, SLC7A2, SLC6A6, SLC38A5, SLC22A12, SLC34A1, SLC26A1, SLC26A6, SLC27A5, SLC22A8 and SLC44A4) were consistent with qRT-PCR results. In conclusion, ammonia exposure can cause pathological changes in many tissues and organs of fattening pigs and changes in the SCL family gene network. Importantly, the SCL family is involved in the toxic mechanism of ammonia. Our findings will provide a new insight for better assessing the mechanism of ammonia toxicity.