Improved Inversion of Monthly Ammonia Emissions in China Based on the Chinese Ammonia Monitoring Network and Ensemble Kalman Filter.

Ammonia (NH3) emission inventories are an essential input in chemical transport models and are helpful for policy-makers to refine mitigation strategies. However, current estimates of Chinese NH3 emissions still have large uncertainties. In this study, an improved inversion estimation of NH3 emissions in China has been made using an ensemble Kalman filter and the Nested Air Quality Prediction Modeling System. By first assimilating the surface NH3 observations from the Ammonia Monitoring Network in China at a high resolution of 15 km, our inversion results have provided new insights into the spatial and temporal patterns of Chinese NH3 emissions. More enhanced NH3 emission hotspots, likely associated with industrial or agricultural sources, were captured in northwest China, where the a posteriori NH3 emissions were more than twice the a priori emissions. Monthly variations of NH3 emissions were optimized in different regions of China and exhibited a more distinct seasonality, with the emissions in summer being twice those in winter. The inversion results were well-validated by several independent datasets that traced gaseous NH3 and related atmospheric processes. These findings highlighted that the improved inversion estimation can be used to advance our understanding of NH3 emissions in China and their environmental impacts.

Laccase surface-display for environmental tetracycline removal: From structure to function.

Facing the increasingly prominent tetracycline pollution and the resulting environmental problems, how to find environmental and efficient treatment means is one of the current research hotspots. In this study, the laccase surface-display technology for tetracycline treatment was investigated. Via study, the type of anchoring protein had a minor influence on the laccase ability, while the type of laccase showed a major impact. Bacillus subtilis spore coat protein (CotA) exhibited higher laccase activity, stability, and efficiency in degrading tetracycline than Pleurotus ostreatus laccase 6 (Lacc6). The superiority of bacterial laccase over fungal laccase was elucidated from the perspective of crystal structure. Besides, a variety of technical means were used to verify the success of surface-display. pGSA-CotA surface-displayed bacteria exhibited good tolerance to high temperature, pH, and various heavy metals. Importantly, surface-displayed bacteria showed faster degradation efficiency and better treatment effects than the intracellular expression bacteria in tetracycline degradation. This implies that surface display technology has greater potential for laccase-mediated environmental remediation. Due to the adverse impacts of tetracycline on soil enzyme activity and microorganisms, our study found that pGSA-CotA surface-displayed bacteria can alleviate tetracycline stress in soil and partially activate the soil, thereby increasing soil enzyme activity and certain nitrogen cycling genes.

Elucidating the quantitative characterization of atmospheric oxidation capacity in Beijing, China.

The atmospheric oxidizing capacity (AOC) is the essential driving force of tropospheric chemistry, but its quantitative representation remains limited. This study presents the detailed evaluation of AOC in the megacity of Beijing based on newly developed indexes that represent the estimated oxidative capacity from the prospective of oxidation products (AOIe) and the potential oxidative capacity considering the oxidation rates of major reactants by oxidants (AOIp). A comprehensive suite of data taken from summer and winter field campaigns were used to create these two indexes and in the calculation of AOC. The AOC showed a clear seasonal pattern, with stronger intensity in summer compared to winter. The gaseous-phase oxidation products (O3 and NO2) dominated AOIe (~80%) during summertime at both sites, while the contribution of particle-phase oxidation products (sulfate, nitrate, and secondary organic aerosol) to AOIe increased in winter (~30%). As for AOIp in summer, the dominant contributor was alkenes (31.0%, urban) and CO (38.5%, suburban), whereas CO and NO2 dominated AOIp at both urban (68.8%) and suburban (61.0%) sites during wintertime. As expected, the dominant oxidant contributor to AOIp during the daytime was OH, while O3 was the second most important oxidant at both sites. The diurnal variations of normalized AOIe and AOIp were examined, revealing that they share the same daytime peak but showed significant bias during the nighttime. To explore the possible deviation in sources between AOIe and AOIp, a constrained photochemical box model and a constrained multiphase chemical box model were used to evaluate AOC budgets and their source apportionment. Our results suggest that unmeasured OVOC (oxygenated volatile organic compound) species and missed heterogeneous oxidation processes in the calculation of AOIp contributed substantially to the underestimation of AOC by this index, which should be taken into consideration in future studies of AOC.

Characteristics of fine particle explosive growth events in Beijing, China: Seasonal variation, chemical evolution pattern and formation mechanism.

Fine particle explosive growth (FPEG) events are frequently observed in heavy haze episodes in Beijing, the characteristics and formation mechanism of which remain not fully understood. In this study, a five year (2013-2017) online observation was conducted in Beijing and the chemical evolution pattern of FPEG events was analyzed to understand its formation mechanism. A total of 132 FPEG events were identified, and steadily decreased from 39 events in 2013 to 19 events in 2017. More than 70% of the FPEG events occurred in winter and autumn, which coincides with adverse weather conditions and enhanced primary emissions. Organic matter (OM) was the dominated components (~30%) in PM2.5, but it only accounted for 10% of total FPEG events as a driven factor, because its contribution usually decreased when the FPEG events developed. In contrast, the secondary inorganic species were the dominated driven factors, and sulfate-driven events accounted >50%. During the period of 2013-2017, the contribution from regional sources decreased significantly mainly due to the reduction of emissions from regional sources, while the contribution from local sources remained largely unchanged, indicating that the local secondary transformation played a leading role in promoting the FPEG events. The low nitrogen oxidation rates (NOR, 0.12 ±â€¯0.07) and the weak increase trend of NOR with elevated RH were observed, indicating the formation of which might be promoted by the homogenous reaction between HNO3 and NH3. In contrast, a significant increase in sulfur oxidation rate (SOR, 0.50 ±â€¯0.19) was observed when RH > 50%, suggesting enhanced heterogeneous oxidation of SO2 in FPEG events. In addition, our analysis suggest the S (IV) heterogeneous oxidation rates in FPEG events depend mainly on the aerosol liquid water content (ALWC) in addition to the aerosol acidity. This study provides observational evidence for understanding the formation mechanism of FPEG events in Beijing.

Characteristics of chemical composition and seasonal variations of PM2.5 in Shijiazhuang, China: Impact of primary emissions and secondary formation.

North China registers frequent air pollution episodes from high PM2.5 concentrations. Shijiazhuang is located at the intensive industrial zone of this region, but there is insufficient data on the chemical composition of PM2.5 and its sources in this city. In this study, the chemical and seasonal characteristics of PM2.5 in Shijiazhuang were investigated based on 12-h integrated PM2.5 measurements made over eight 1-month periods in each season between June 2014 and April 2016 (486 samples). The eight-season average concentration of PM2.5 was 138.8 µg m-3, and the major chemical components were secondary inorganic aerosol (SIA) species of sulfate, nitrate, and ammonium (41.5%), followed by organic matter (25.9%). The mass concentration and most of the chemical components of PM2.5 showed clear seasonal variation, with a winter-high and summer-low pattern. SO42- and NO3- were the dominant components at each pollution level in summer and autumn (18.1%-30.6% and 14.2%-27.0%, respectively). Sufficient gaseous oxidants (O3) concentrations and suitable meteorology conditions were observed in these two seasons. Highest SOR (0.61), SO42-/EC(10.8) and NOR (0.58), NO3-/EC (5.9) were found in summer and autumn, which indicated intense secondary transformation in these two seasons. Organic matter was the dominant species in winter, which increased from 17.1 µg m-3 for clean days (28.7% of PM2.5) to 169.1 µg m-3 (38.4% of PM2.5). The accumulation of primary emissions (coal combustion and biomass burning) was responsible for the increasing OM trend (especially for POC). The highest and leading proportion of mineral dust occurred in spring (20.3%-46.5%) as a result of higher wind speeds (up to 3 m/s). Potential source contribution function (PSCF) analyses implied that the border areas of Hebei, Henan and Shandong Provinces, together with the central area of Shanxi Province, contributed significantly to the PM2.5 pollution in Shijiazhuang, especially in autumn and winter.

Size-resolved aerosol water-soluble ions during the summer and winter seasons in Beijing: Formation mechanisms of secondary inorganic aerosols.

Size-segregated water-soluble ionic species (WSIs) were measured using an Anderson cascade impactor from Jul. to Aug. 2008 and from Dec. 2009 to Feb. 2010 in urban Beijing. The results showed that fine particles (PM2.1, Dp < 2.1 µm) accounted for ∼49% (summer) and ∼34% (winter) of the total particulate mass, and WSIs accounted for 23-82% of the mass concentration of PM2.1. Secondary inorganic aerosols (SIAs, the sum of SO42-, NO3- and NH4+) accounted for more than 30% of the fine particles, which were greatly elevated during particle pollution events (PM events), thereby leading to an alteration of the size distributions of SO42- and NO3- to nearly single fine-mode distributions peaking at 0.65-2.1 µm. This finding suggests that heterogeneous aqueous reactions were enhanced at high RH values. SIAs also increased during dust events, particularly for coarse mode SO42-, which indicated enhanced heterogeneous reactions on the dust surface. The positive matrix factorization (PMF) model was used to resolve the bulk mass size distributions into condensation, droplet, and coarse modes, representing the three major sources of the particles. The formation of SO42- was attributed primarily to in-cloud or aerosol droplet processes during summer (45%), and the heterogeneous reaction of SO2 on mineral dust surfaces was an important formation pathway during winter (45%). The formation pathways of NO3- in fine particles were similar to those of SO42-, where over 30% were formed by in-cloud processes. This work provides important field measurement-based evidence for understanding the formation pathway of secondary inorganic aerosols in the megacity of Beijing.