China experienced severe haze pollution in January 2013. Here we have a detailed characterization of the sources and evolution mechanisms of this haze pollution with a focus on four haze episodes ...that occurred during 10–14 January in Beijing. The main source of data analyzed is from submicron aerosol measurements by an Aerodyne Aerosol Chemical Speciation Monitor. The average PM1 mass concentration during the four haze episodes ranged from 144 to 300 µg m−3, which was more than 10 times higher than that observed during clean periods. All submicron aerosol species showed substantial increases during haze episodes with sulfate being the largest. Secondary inorganic species played enhanced roles in the haze formation as suggested by their elevated contributions during haze episodes. Positive matrix factorization analysis resolved six organic aerosol (OA) factors including three primary OA (POA) factors from traffic, cooking, and coal combustion emissions, respectively, and three secondary OA (SOA) factors. Overall, SOA contributed 41–59% of OA with the rest being POA. Coal combustion OA (CCOA) was the largest primary source, on average accounting for 20–32% of OA, and showed the most significant enhancement during haze episodes. A regional SOA (RSOA) was resolved for the first time which showed a pronounced peak only during the record‐breaking haze episode (Ep3) on 12–13 January. The regional contributions estimated based on the steep evolution of air pollutants were found to play dominant roles for the formation of Ep3, on average accounting for 66% of PM1 during the peak of Ep3 with sulfate, CCOA, and RSOA being the largest fractions (> ~ 75%). Our results suggest that stagnant meteorological conditions, coal combustion, secondary production, and regional transport are four main factors driving the formation and evolution of haze pollution in Beijing during wintertime.
Key Points
Sources and evolution processes of a record‐breaking haze episodeLarge increase of coal combustion organic aerosol during haze episodesEstimation of regional contributions from steep increases of aerosol species
The May 12, 2008 Great Wenchuan Earthquake has resulted in more than 68,858 deaths and losses in the hundreds of billions RMB as of May 30, 2008, and these numbers will undoubtedly increase as more ...information becomes available on the extent of the event. Immediately after the earthquake, the China Earthquake Administration （CEA） responded quickly by sending teams of experts to the affected region, eventually including over 60 staff members from the Institute of Engineering Mechanics （IEM）. This paper reports preliminary information that has been gathered in the first 18 days after the event, covering seismicity, search and rescue efforts, observed ground motions, and damage and loss estimates. The extensive field investigation has revealed a number of valuable findings that could be useful in improving research in earthquake engineering in the future. Once again, this earthquake has shown that the vertical component of ground motion is as significant as horizontal ground motions in the near-source area. Finally, note that as more information is gathered, the numbers reported in this paper will need to be adjusted accordingly.
Fine particle (PM2.5) samples were collected simultaneously at three urban sites (Shanghai, Nanjing, and Hangzhou) and one rural site near Ningbo in the Yangtze River Delta (YRD) region, China, on a ...weekly basis from September 2013 to August 2014. In addition, high-frequency daily sampling was conducted in Shanghai and Nanjing for one month during each season. Severe regional PM2.5 pollution episodes were frequently observed in the YRD, with annual mean concentrations of 94.6 ± 55.9, 97.8 ± 40.5, 134 ± 54.3, and 94.0 ± 57.6 μg m−3 in Shanghai, Nanjing, Hangzhou, and Ningbo, respectively. The concentrations of PM2.5 and ambient trace metals at the four sites showed clear seasonal trends, with higher concentrations in winter and lower concentrations in summer. In Shanghai, similar seasonal patterns were found for organic carbon (OC), elemental carbon (EC), and water-soluble inorganic ions (K+, NH4+, Cl−, NO3−, and SO42-). Air mass backward trajectory and potential source contribution function (PSCF) analyses implied that areas of central and northern China contributed significantly to the concentration and chemical compositions of PM2.5 in Shanghai during winter. Three heavy pollution events in Shanghai were observed during autumn and winter. The modelling results of the Nested Air Quality Prediction Modeling System (NAQPMS) showed the sources and transport of PM2.5 in the YRD during the three pollution processes. The contribution of secondary species (SOC, NH4+, NO3−, and SO42-) in pollution event (PE) periods was much higher than in BPE (before pollution event) and APE (after pollution event) periods, suggesting the importance of secondary aerosol formation during the three pollution events. Furthermore, the bioavailability of Cu, and Zn in the wintertime PM2.5 samples from Shanghai was much higher during the pollution days than during the non-pollution days.
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Secondary aerosol formation is important and the bioavailability of trace metals is much higher during the pollution events.
Non-refractory submicron aerosol (NR-PM1) species measured by an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) along with collocated gaseous species are used to investigate the impacts of ...relative humidity (RH) on aerosol composition and evolution processes during wintertime in Beijing, China. Aerosol species exhibit strong, yet different RH dependence between low and high RH levels. At low RH levels (<50%), all aerosol species increase linearly as a function of RH, among which organics present the largest mass increase rate at 11.4 μg m−3/10% RH. Because the particle liquid water predicted by E-AIM model is very low and the temperature is relatively constant, the enhancement of aerosol species is primarily due to the decrease of wind speed. While the rates of increase for most aerosol species are reduced at high RH levels (>50%), sulfate presents an even faster increasing rate, indicating the significant impact of liquid water on sulfate production. The RH dependence of organic aerosol (OA) components is also quite different. Among OA components, coal combustion OA (CCOA) presents the largest enhancement in both mass concentration and contribution as a function of RH. Our results elucidate the important roles of liquid water in aerosol processing at elevated RH levels, in particular affecting sulfate and CCOA via aqueous-phase reaction and gas-particle partitioning associated with water uptake, respectively. It is estimated that aqueous-phase processing can contribute more than 50% of secondary inorganic species production along with an increase of aerosol particle acidity during the fog periods. However, it appears not to significantly enhance secondary organic aerosol (SOA) formation and the oxidation degree of OA.
•The RH impacts on aerosol composition and processes in Beijing were examined.•The RH shows the largest impact on sulfate and coal combustion OA during wintertime.•Aqueous processing appears not to significantly enhance SOA production and oxidation degree.
The rapidly spread coronavirus disease (COVID-19) has limited people's outdoor activities and hence caused substantial reductions in anthropogenic emissions around the world. However, the air quality ...in some megacities has not been improved as expected due to the complex responses of aerosol chemistry to the changes in precursors and meteorology. Here we demonstrate the responses of primary and secondary aerosol species to the changes in anthropogenic emissions during the COVID-19 outbreak in Beijing, China along with the Chinese New Year (CNY) holiday effects on air pollution by using six-year aerosol particle composition measurements. Our results showed large reductions in primary aerosol species associated with traffic, cooking and coal combustion emissions by 30–50% on average during the CNY, while the decreases in secondary aerosol species were much small (5–12%). These results point towards a future challenge in mitigating secondary air pollution because the reduced gaseous precursors may not suppress secondary aerosol formation efficiently under stagnant meteorological conditions. By analyzing the long-term measurements from 2012 to 2020, we found considerable increases in the ratios of nitrate to sulfate, secondary to primary OA, and sulfur and nitrogen oxidation capacity despite the overall decreasing trends in mass concentrations of most aerosol species, suggesting that the decreases in anthropogenic emissions have facilitated secondary formation processes during the last decade. Therefore, a better understanding of the mechanisms driving the chemical responses of secondary aerosol to the changes in anthropogenic emissions under complex meteorological environment is essential for future mitigation of air pollution in China.
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•Different responses of primary and secondary species to the COVID-19 outbreak•30–50% decreases in primary aerosol species during the Chinese New Year holiday•Much smaller changes in secondary species compared with primary aerosol species•Large increases in sulfur and nitrogen oxidation capacity during the last decade
Earthen sites are easily eroded by the natural environment, resulting in many micro-cracks on the surface. To explore the effects of environmental effects such as drying shrinkage and freeze-thaw on ...surface cracking, orthogonal tests that imposed these effects on the Zhouqiao site were conducted. Using range analysis, image processing technology, surface strength measurement and microstructure characteristic analysis, this paper explores the effects of soil thickness, water content, dry shrinkage, freeze-thaw cycles and other factors on the morphological characteristics of the site's surface cracks. The results show that under the action of dry shrinkage, the thickness of soil layer is the primary factor affecting the cracking of earthen soil. The thinner the thickness of soil layer, the lower the moisture content, and the more serious the cracking. The initial moisture content is the most disadvantageous factor affecting the reduction of the surface strength of the earthen soil. The strength around the soil sample is lower than that inside, and there are more cracks. Under the action of freezing and thawing, the main factors affecting the cracking and surface strength reduction of earthen soil are the initial water content and soil layer thickness, and the thicker the soil layer, the smaller the crack development and the lower the surface strength. Scanning electron microscope results show that under dry shrinkage and freeze-thaw conditions, the internal cracks of the soil samples exhibit different shape characteristics. Intergranular cracks appear most often under dry shrinkage conditions, and isolated cracks appear most often in the soil samples from the freeze-thaw cycle test. The cracks caused by these two types of external environment factors damage the earthen soil. According to the tension failure model and the definition of the first frost heaving theory, it can be determined that when the micro pore force F and the maximum frost heaving pressure P
are greater than the cohesion of the soil sample, the soil sample will germinate cracks.
The lockdown measures due to COVID-19 affected the industry, transportation and other human activities within China in early 2020, and subsequently the emissions of air pollutants. The decrease of ...atmospheric NO2 due to the COVID-19 lockdown and other factors were quantitively analyzed based on the surface concentrations by in-situ observations, the tropospheric vertical column densities (VCDs) by different satellite retrievals including OMI and TROPOMI, and the model simulations by GEOS-Chem. The results indicated that due to the COVID-19 lockdown, the surface NO2 concentrations decreased by 42% ± 8% and 26% ± 9% over China in February and March 2020, respectively. The tropospheric NO2 VCDs based on both OMI and high quality (quality assurance value (QA) ≥ 0.75) TROPOMI showed similar results as the surface NO2 concentrations. The daily variations of atmospheric NO2 during the first quarter (Q1) of 2020 were not only affected by the COVID-19 lockdown, but also by the Spring Festival (SF) holiday (January 24–30, 2020) as well as the meteorology changes due to seasonal transition. The SF holiday effect resulted in a NO2 reduction from 8 days before SF to 21 days after it (i.e. January 17 - February 15), with a maximum of 37%. From the 6 days after SF (January 31) to the end of March, the COVID-19 lockdown played an important role in the NO2 reduction, with a maximum of 51%. The meteorology changes due to seasonal transition resulted in a nearly linear decreasing trend of 25% and 40% reduction over the 90 days for the NO2 concentrations and VCDs, respectively. Comparisons between different datasets indicated that medium quality (QA ≥ 0.5) TROPOMI retrievals might suffer large biases in some periods, and thus attention must be paid when they are used for analyses, data assimilations and emission inversions.
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•NO2 in China decreased by 42% and 26% in February and March 2020 due to COVID-19.•The NO2 VCDs by satellites were consistent with the surface NO2 concentrations.•Spring Festival holiday led to a NO2 decrease in 30 days with a maximum of 37%.•COVID-19 led to a NO2 decrease from 6 days after SF with a maximum of 51%.•NO2 concentrations and VCDs decreased by 25% and 40% in 90 days due to meteorology.
China is one of the regions with highest PM2.5 concentration in the world. In this study, we review the spatio-temporal distribution of PM2.5 mass concentration and components in China and the effect ...of control measures on PM2.5 concentrations. Annual averaged PM2.5 concentrations in Central-Eastern China reached over 100μgm−3, in some regions even over 150μgm−3. In 2013, only 4.1% of the cities attained the annual average standard of 35μgm−3. Aitken mode particles tend to dominate the total particle number concentration. Depending on the location and time of the year, new particle formation (NPF) has been observed to take place between about 10 and 60% of the days. In most locations, NPF was less frequent at high PM mass loadings. The secondary inorganic particles (i.e., sulfate, nitrate and ammonium) ranked the highest fraction among the PM2.5 species, followed by organic matters (OM), crustal species and element carbon (EC), which accounted for 6–50%, 15–51%, 5–41% and 2–12% of PM2.5, respectively. In response to serious particulate matter pollution, China has taken aggressive steps to improve air quality in the last decade. As a result, the national emissions of primary PM2.5, sulfur dioxide (SO2), and nitrogen oxides (NOX) have been decreasing since 2005, 2006, and 2011, respectively. The emission control policies implemented in the last decade could result in noticeable reduction in PM2.5 concentrations, contributing to the decreasing PM2.5 trends observed in Beijing, Shanghai, and Guangzhou. However, the control policies issued before 2010 are insufficient to improve PM2.5 air quality notably in future. An optimal mix of energy-saving and end-of-pipe control measures should be implemented, more ambitious control policies for NMVOC and NH3 should be enforced, and special control measures in winter should be applied. 40–70% emissions should be cut off to attain PM2.5 standard.
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•In 2013, only 4.1% of the Chinese cities attained the annual average PM2.5 standard.•Secondary inorganic aerosol ranked the highest fraction among PM2.5 species.•National emissions of primary PM2.5 and SO2 have been decreasing since 2005/2006, so as NOX since 2011.•Emission controls make important contributions to decreasing trends in PM2.5 concentrations in megacities.•40–70% emission reduction in the future is needed to attain the PM2.5 standard.
We review and synthesize the current state of knowledge regarding acid deposition and its environmental effects across Asia. The extent and magnitude of acid deposition in Asia became apparent only ...about one decade after this issue was well described in Europe and North America. In addition to the temperate zone, much of eastern and southern Asia is situated in the tropics and subtropics, climate zones hitherto little studied with respect to the effects of high loads of acid deposition. Surface waters across Asia are generally not sensitive to the effects of acid deposition, whereas soils in some regions are sensitive to acidification due to low mineral weathering. However, soil acidification was largely neutralized by such processes as base cation deposition, nitrate (NO3−) denitrification, and sulfate (SO42−) adsorption. Accompanying the decrease in S deposition in recent years, N deposition is of increasing concern in Asia. The acidifying effect of N deposition may be more important than S deposition in well drained tropical/subtropical soils due to high SO42− adsorption. The risk of regional soil acidification is a major threat in Eastern Asia, indicated by critical load exceedance in large areas.
•Here review more recent studies on acid deposition in Asia, especially in Eastern Asia.•Surface waters are generally not sensitive to acid deposition in comparison with soils.•Soil acidification is not very serious because of base cation deposition, N denitrification, and SO42− sorption.
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