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1.
Sci Total Environ ; 792: 148393, 2021 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-34465048

RESUMO

The ambient atmospheric PM2.5 concentrations in Anhui Province, China, which links the Yangtze River Delta region, China's fastest growing economy area, with the Beijing-Tianjin-Hebei (BTH) region, China's most polluted region, are influenced not only by local emissions, but also by changes in regional circulation. During the period 2013-2017, when China adopted a series of pollution abatement measures, there were still occasional pollution episodes with significant increases in PM2.5 concentrations. PM2.5 rise instead during the period 2013-2017 in Anhui (the Center of the Yangtze-Huaihe, YH), when pollution emissions continued to decrease? What is the controlling mechanism behind these? By analyzing elements such as ground-based PM2.5 concentration and the planetary boundary layer (PBL) structure affecting it as well as larger scale circulation, combined with the analysis of a parameterized index, one can find that aerosol pollution in the YH region can usually be classified into three types. (1) There is a short-term transport stage (TS) in the initial stage of pollution, then as the pollutant concentrations increase, the PBL height decreases, the temperature inversion is gradually formed or strengthened, the wind speed decreases and the relative humidity of the lower layer increases, forming a two-way feedback mechanism in the cumulative stage (CS). (2) Pollutant concentrations will not drop rapidly in the later stage of CS, while a short-term TS will occur again. (3) The explosive rise (ER) events are mainly affected by transportation in the YH. The first of these types tends to be accompanied by the emergence and maintenance of heavy pollution periods (HPEs), and some phases is accompanied by explosive rises (ERs) in PM2.5 that at least double in a short period of time. To sum up, deterioration of meteorological conditions explaining approximately 68% to the increase in PM2.5 in the ER.


Assuntos
Poluentes Atmosféricos , Poluição do Ar , Poluentes Atmosféricos/análise , Poluição do Ar/análise , China , Monitoramento Ambiental , Material Particulado/análise , Tempo (Meteorologia)
2.
Sci Total Environ ; 787: 147543, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34000526

RESUMO

This study utilized a long-term (2001-2018) aerosol optical component dataset retrieved from the Multiangle Imaging Spectroradiometer (MISR), Version 23, to perform comprehensive analyses of the global climatology of seasonal AODs, partitioned by aerosol types (including small-size, medium-size, large-size, spherical, and non-spherical). By dividing eight different AOD bins and performing trend analysis, the seasonal variability and trends in these type-segregated AODs, as well as in the frequency occurrences (FOs) for different AOD bins, globally and over 12 regions of interest, were also investigated. In terms of particle size, small-size aerosol particles (diameter < 0.7 µm) contribute the largest to global extinction in all three seasons except winter. A similar globally dominant role is exhibited by spherical aerosols, which contribute 68.5%, 73.3%, 71.6% and 70.2% to the global total AOD (TAOD) in spring, summer, autumn and winter, respectively, on a global average scale. FOs with different aerosol loading levels suggested that the seasonal FOs tend to decrease progressively with increasing aerosol loading, except for Level 1 (TAOD< 0.05). Examination of the seasonal distribution of FOs revealed that the FO at Level 1 (Level 2, 0.05 < TAOD< 0.15) is much larger in summer/winter (winter/autumn) than in spring/autumn (spring/summer) over most areas of the world. However, the FOs for Level 3 (0.15 < TAOD< 0.25) to Level 8 (TAOD> 1.0) generally exhibit greater intensity in spring/summer than in autumn/winter. Temporal trend analyses showed that the seasonal TAOD experiences a significant decline during 2001-2018 in most regions globally, except in South Asia, the Middle East, and North Africa. Opposite seasonal trends in the above regions are closely related to the increase in FOs in the range of 0.4 < TAOD< 1.0. The global average TAOD shows the most pronounced decline in spring, falling by -10.4% (P < 0.05). Examination of the trends in type-segregated AODs further revealed that the decreases in size-segregated (shape-segregated) AODs all contribute to the decrease in seasonal TAOD, with small-size AOD (spherical AOD) contributing most significantly.

3.
Sci Total Environ ; 760: 143394, 2021 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-33221018

RESUMO

Submicron particle matter (PM1) that rapidly reaches exceedingly high levels in several or more hours in the North China Plain (NCP) has been threating~400 million individuals' health for decades. The precise cause of the rapid rise in PM1 remains uncertain. Based on sophisticated measurements in PM1 characterizations and corresponding boundary-layer (BL) meteorology in the NCP, it demonstrates that this rising is mainly driven by BL meteorological variability. Large increases in near-ground inversions and decreases in vertical heat/momentum fluxes during the day-night transition result in a significant reduction in mixing space. The PM1 that is vertically distributed before accumulates at the near-ground and then experiences a rapid rise. Besides meteorological variability, a part of the rise in organics is ascribed to an increase of coal combustion at midnight. The daily-based accumulation of PM1 is attributed to day-to-day vertical meteorological variability, particularly diminishing mixing layer height exacerbated by aerosol-radiation feedback. Resolved by a multiple linear regression model, BL meteorological variability can explain 71% variances of PM1. In contrast, secondary chemical reactions facilitate the daily-based accumulation of PM1 rather than the rapid rise. Our results show that BL meteorological variability plays a dominant role in PM1 rising and day-to-day accumulation, which is crucial for understanding the mechanism of heavy pollution formation.

4.
Sci Total Environ ; 749: 142208, 2020 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-33370901

RESUMO

NH3, SO2, NOx and the inorganic ions of PM2.5 in winter 2009, 2014 and 2016 were examined to investigate the change in NH3 and aerosol chemistry in Beijing, China. NH3 concentrations showed an increase by 59% on average, in contrast to the decrease of SO2 by 63% from winter 2009 to 2016. The mean mass ratio of NH3/NHx was 0.83 ± 0.12 in 2016, which is higher than those obtained in 2009 and 2014, implying more NHx remaining as free NH3 in 2016 winter. Our findings suggest that vehicles exhaust emissions are an important NH3 source in urban central atmosphere of Beijing in winter. Despite the observed NOx presenting declining trends from 2014 to 2016, nitrate concentrations even exhibited a significant increasing trend, which may be largely attributable to high NH3 levels. An in-depth analysis of measured NH3 and aerosol species in a heavy pollution episode in December 2016, combined with the acidity predicted by ISORROPIA II model demonstrated abundant NH3 most of the time in air, where NH3 is not only a precursor for NH4+ but also effect the neutralization of SO42- and NO3- in PM2.5. With high RH and low photochemical activity, elevated NO3- concentration was attributed to an enhanced heterogeneous conversion of NOx to HNO3 to form NH4NO3 in pollution transport stage. The decrease in NOx from high level and the increase in NH3, with peaks of SO42- occurring were observed in pollution cumulative stage. The aqueous-phase oxidation of SO2 by NO2 to sulfate might play an important role with high pH values. Our results suggested that the simultaneous control of NH3 emissions in conjunction with SO2 and NOx emissions would be more effective in reducing particulate matter PM2.5 formation.

5.
Sci Total Environ ; 716: 136892, 2020 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-32036150

RESUMO

The monthly average PM2.5 concentration decreased from 127.15 µg m-3 in December 2016 to 85.54 µg m-3 in December 2017 (approximately 33%) in Central and Eastern China (33°N-41°N, 113°E-118°E). This decrease is attributed to the combined impacts of meteorology and emission sources changes, though the question of which is more important has raised great concerns. Four sensitivity experiments based on the Global-Regional Assimilation and Prediction System coupled with the Chinese Unified Atmospheric Chemistry Environment (GRAPES-CUACE) model, together with comparative analysis of the observed meteorological conditions and emission inventory between 2016 and 2017, are used to evaluate the relative contributions of meteorology and emission to the substantial reductions of PM2.5 concentration from December 2016 to December 2017. The results show that the meteorological conditions and emission in December 2017 were both beneficial to the PM2.5 decrease in Central and Eastern China. Regarding the entire region, 21.9% of the PM2.5 decrease was a result of the favorable meteorological conditions, and 78.1% of the decrease was a result of emission reductions, showing the distinct contributions of emission reductions on the air quality. The relative contributions of meteorology varied from 12.2% to 50.9% to the PM2.5 decrease from December 2016 to December 2017, while the emission contributed 49.1% to 87.8%, in different cities depending on geographical location and topography. Meteorology showed the largest contributions to the PM2.5 decrease from 2016 to 2017 in Beijing (BJ), which caused the greatest total decrease of PM2.5 compared to that of other cities. In addition, in Central and Eastern China, the dominant factors of the decrease of PM2.5 were favorable meteorological conditions (accounting for 98.2%) during clear periods and emission reductions (accounting for 72.5-81.2%) during pollution periods.

6.
Environ Sci Technol ; 54(3): 1344-1352, 2020 02 04.
Artigo em Inglês | MEDLINE | ID: mdl-31766848

RESUMO

The Beijing government implemented a number of clean air action plans to improve air quality in the last 10 years, which contributed to changes in the concentration of fine particles and their compositions. However, quantifying the impacts of these interventions is challenging as meteorology masks the real changes in observed concentrations. Here, we applied a machine learning technique to decouple the effect of meteorology and evaluate the changes in the chemistry of nonrefractory PM1 (particulate matter less than 1 µm) in winter 2007, 2016, and 2017 as a result of the clean air actions. The observed mass concentrations of PM1 were 74.6, 90.2, and 36.1 µg m-3 in the three winters, while the deweathered concentrations were 74.2, 78.7, and 46.3 µg m-3, respectively. The deweathered concentrations of PM1, organics, sulfate, ammonium, chloride, SO2, NO2, and CO decreased by -38, -46, -59, -24, -51, -89, -16, and -52% in 2017 in comparison to 2007. On the contrary, the deweathered concentration of nitrates increased by 4%. Our results indicate that the clean air actions implemented in 2017 were highly effective in reducing ambient concentrations of SO2, CO, and PM1 organics, sulfate, ammonium, and chloride, but the control of nitrate and PM1 organics remains a major challenge.


Assuntos
Poluentes Atmosféricos , Poluição do Ar , Pequim , China , Monitoramento Ambiental , Tamanho da Partícula , Material Particulado
7.
Sci Total Environ ; 688: 642-652, 2019 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-31254830

RESUMO

Persistent heavy aerosol pollution episodes (HPEs) often occur in the central and eastern regions of China during the wintertime. When PM2.5 mass concentration cumulates to a certain extent that normally exceeds 100 µg m-3, the PM2.5 pollution will then further worsen the meteorological conditions in boundary layer (BL), resulting in significant two-way feedback between the cumulative PM2.5 pollution and worsened meteorological conditions. In the less polluted northwest area of China, whether there is significant two-way feedback phenomenon mentioned above after the accumulation of PM2.5 mass concentration has always been an issue of concern for understanding the full picture of meteorological causes of HPEs in China. Here, measurements of PM2.5 concentration, meteorological data and an integrated pollution-linked meteorological index (PLAM) are used to characterize the relationship between meteorological elements and PM2.5 concentration in persistent HPEs from 1 December 2016 to 10 January 2017 in Lanzhou and Urumqi. In early stage of the HPEs formation, the general 500 hPa circulation situations are normally high-pressure ridge or zonal westerly airflow patterns, associating with worsened meteorological conditions. At this time, with the decrease of BL height, the mass concentration of PM2.5 also increases as the pollutants mix in a relatively small space as compared to the clean period. When PM2.5 cumulates to a certain extent (above 75 µg m-3 in Lanzhou and above 100 µg m-3 in Urumqi), there are often obvious inversion and humidification in the near-surface. The inversion is mainly caused by the accumulation of the PM2.5 concentration, which indicates that even in northwest China, where anthropogenic activities are less affected and PM2.5 pollution is less serious, the cumulative PM2.5 can nonetheless worsen meteorological conditions. The worsened meteorological conditions, which are quantified by the PLAM index, dominate the changes in PM2.5 in the explosive growth of persistent HPEs (accounted for 50-85%).

8.
Sci Total Environ ; 685: 239-247, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31174121

RESUMO

A humidified nephelometer system was deployed to measure the aerosol scattering coefficients at RH < 30% and RH in the range of 40 to 85% simultaneously in megacity Beijing in March 2018. The aerosol optical properties and aerosol hygroscopicity of two sizes (PM10 and PM1) during the pollution period, dust period and a new particle formation event (NPF) were analyzed. During the pollution period, the scattering and absorption coefficients increased dramatically with the accumulation of pollutants, while scattering Ångström exponent (SAE), submicron scattering fraction (Rsp), submicron absorption fraction (Rap) decreased, as well as single scattering albedo (SSA) rose slightly, which indicated the increasing contribution of larger particle to scattering and absorption, and enhanced the scattering ability of aerosols. The average PM10 mass scattering efficiency is 3.86 ±â€¯1.19 m2 g-1 with a range of 2.05-5.74 m2 g-1 during the pollution period, and 0.40 ±â€¯0.05 m2 g-1 during the dust period. Rsp at wavelength of 550 nm varied from 55.8% to 89.3% during the measurement period, with the average of 64.8% ±â€¯5.2% and 73.1% ±â€¯6.8% during the pollution period and dust period, respectively, which suggests that the aerosol scattering coefficient is mainly affected by fine particles. The average PM10 and PM1 aerosol scattering hygroscopic growth factors f(80%) are 1.75 ±â€¯0.05 and 1.75 ±â€¯0.04 during the pollution period, 1.14 ±â€¯0.09 and 1.15 ±â€¯0.06 during the dust period, 1.59 ±â€¯0.05 and 1.60 ±â€¯0.06 during the NPF event period, respectively. Aerosol scattering hygroscopic growth factors showed a strong correlation with the scattering Ångström exponent which suggests the hygroscopicity is much stronger for fine particles (SAE > 1.5) than the coarse particles (SAE < 1.0).

9.
Sci Total Environ ; 664: 140-147, 2019 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-30739849

RESUMO

Heavy aerosol pollution episodes (HPEs) in Beijing are worsened by the two-way feedback mechanism between unfavorable meteorological conditions and cumulative aerosols. In Winter 2017/18, mean PM2.5 mass concentration substantially decreased by 62% from 113 µg m-3 in Winter 2016/17 to 43 µg m-3. With reduced PM2.5 levels, the meteorological feedback on PM2.5 was relatively weak in Winter 2017/18. However, the weakening degree and its contributions to PM2.5 reduction are still uncertain. In this study, we investigated the change in the aerosol-induced modification of atmospheric stratification by combining PM2.5 data, radiosonde observations, and ERA-Interim reanalysis data, and then estimated the weakened meteorological feedback effect on PM2.5 change using machine learning. During polluted days, near-ground cooling bias, specific humidity (SH) increase, and relative humidity (RH) enhancement in Winter 2017/18 merely account for 38%, 65%, and 36% of the meteorological modification caused by aerosols in Winter 2016/17, respectively. Using machine learning algorithms with three most related variables, we found that during polluted days, the PM2.5 increase due to the meteorological feedback in Winter 2017/18 was merely 49% of that in Winter 2016/17. Effective pollution control and more favorable meteorological conditions have resulted in an additional benefit in PM2.5 reduction.

10.
Sci Total Environ ; 630: 46-52, 2018 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-29471190

RESUMO

Winter is a season of much concern for aerosol pollution in China, but less concern for pollution in the summertime. There are even less concern and larger uncertainty about interdecadal changes in summer aerosol pollution, relative influence of meteorological conditions, and their links to climate change. Here we try to reveal the relation among interdecadal changes in summer's most important circulation system affecting China (East Asian Summer Monsoon-EASM), an index of meteorological conditions (called PLAM, Parameter Linking Air Quality and Meteorological Elements, which is almost linearly related with aerosol pollution), and aerosol optical depth (AOD) in the middle and lower reaches of the Yangtze River (M-LYR) in central eastern China during summertime since the 1960's. During the weak monsoon years, the aerosol pollution load was heavier in the M-LYR and opposite in the strong monsoon years mainly influenced by EASM and associated maintenance position of the anti-Hadley cell around 115°E. The interdecadal changes in meteorological conditions and their associated aerosol pollution in the context of such climate change have experienced four periods since the 1960's, which were a relatively large decreased period from 1961 to 1980, a large rise between 1980 and 1999, a period of slow rise or maintenance from 1999 to 2006, and a relatively rapid rise between 2006 and 2014. Among later three pollution increased periods, about 51%, 25% and 60% of the aerosol pollution change respectively come from the contribution of worsening weather conditions, which are found to be greatly affected by changes in EASM.

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