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1.
Environ Sci Technol ; 56(9): 5390-5397, 2022 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-35442649

RESUMO

Urban greening has often been proposed as a cost-effective solution to improve environmental comfort, but may also deteriorate air quality. Quantifying these two opposing effects of urban greening is necessary to develop successful environmental policies for specific mega-city clusters. In this study, a high-resolution regional climate and air quality model (WRF-Chem, v4.0.3) was employed to test three scenarios aimed at quantifying the impact of land-use change and biogenic emissions from urban greening on regional climate and air quality. It was found that urban greening could effectively decrease the near-surface temperature by up to 0.45 °C, but the increased biogenic volatile organic compound (BVOC) emissions offset some of this cooling effect (by up to 65%). Land-use change due to urban greening dominated the improvement in human comfort but worsened diffusion conditions to result in the convergence of fine particulate matter in specific areas. The selection of low-emission tree species may be imperative, although increased emissions from urban greening will not change the sensitivity of ozone to precursors under the current scenario of anthropogenic emissions. This is because BVOC emissions due to urban greening will become a more important source of pollution with the development of clean energy and the popularity of low-carbon lifestyles.


Assuntos
Poluentes Atmosféricos , Poluição do Ar , Ozônio , Compostos Orgânicos Voláteis , Poluição do Ar/prevenção & controle , Monitoramento Ambiental , Política Ambiental , Poluição Ambiental , Humanos , Material Particulado
2.
Environ Sci Technol ; 56(8): 4828-4837, 2022 Apr 19.
Artigo em Inglês | MEDLINE | ID: mdl-35297613

RESUMO

Atmospheric nitrous acid (HONO) is a dominant precursor of hydroxyl (OH) radicals, and its formation mechanisms are still controversial. Few studies have simultaneously explored effects of different combustion processes on HONO sources. Hereby, synchronous HONO measurement in urban (BJ), suburban (XH) and rural (DBT) areas with different combustion processes is performed in the North China Plain in winter. A box model is utilized to analyze HONO formation mechanisms. HONO concentration is the highest at the DBT site (2.51 ± 1.90 ppb), followed by the XH (2.18 ± 1.95 ppb) and BJ (1.17 ± 1.20 ppb) sites. Vehicle exhaust and coal combustion significantly contribute to nocturnal HONO at urban and rural sites, respectively. During a stagnant pollution period, the NO+OH reaction and combustion emissions are more crucial to HONO in urban and rural areas; meanwhile, the heterogeneous reaction of NO2 is more significant in suburban areas. Moreover, the production rate of OH from HONO photolysis is about 2 orders of magnitude higher than that from ozone photolysis. Consequently, vehicle exhaust and coal combustion can effectively emit HONO, further causing environmental pollution and health risks. It is necessary to expand the implementation of the clean energy transition policy in China, especially in areas with substantial coal combustion.


Assuntos
Ácido Nitroso , Emissões de Veículos , China , Carvão Mineral , Radical Hidroxila
3.
Sci Total Environ ; 821: 153541, 2022 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-35101481

RESUMO

Under weak weather systems, pollutants circulate on plains and hillsides by means of oscillatory mountain-plain breezes (MPB). To investigate the impact of MPB on ambient volatile organic compounds (VOCs) on the northern edge of the North China Plain (NCP) region, synchronous online VOCs observations were first performed in the southwestern (Beijing, urban area) and northeastern (Xinglong, background area) of the dominant wind directions from September 11, 2020, to October 13, 2020. The results revealed that during the observation period, the average mixing ratios of TVOCs in Beijing and Xinglong were 32.5 ± 21.6 and 14.2 ± 8.6 ppbv, respectively, and a coincident temporal evolution trend of VOCs was observed at the two sites. Combined with the results of the backward trajectory, southerly air transport led to a significant increase in VOCs concentration, and southerly airflow was usually accompanied by apparent MPB circulation. Furthermore, the occurrence of MPB led to a sharp increase (1.5 times) in VOCs concentration in both Beijing and Xinglong. This study indicates that the periodic oscillation of the MPB leads to the large-scale pollution of "garbage out and garbage in", and the VOCs discharged by industry are the key to future control.


Assuntos
Poluentes Atmosféricos , Ozônio , Compostos Orgânicos Voláteis , Poluentes Atmosféricos/análise , China , Monitoramento Ambiental/métodos , Ozônio/análise , Compostos Orgânicos Voláteis/análise , Vento
4.
Sci Total Environ ; 821: 153436, 2022 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-35092781

RESUMO

In addition to photochemical production and horizontal regional transport, surface O3 concentration can also likely be affected by vertical transport, which is not well known so far. The process analysis was conducted by using the Regional Atmospheric Modeling System Community Multiscale Air Quality (RAMS-CMAQ) model to investigate photochemical production and the vertical transport mechanism of boundary-layer O3 during a typical O3 pollution episode in the North China Plain (NCP), and further quantify the contribution of vertical transport to surface O3. The diurnal variations of vertical budgets of O3 and NO2 in the boundary layer at multiple sites showed that there were substantial differences in the vertical distribution of O3 production and transport between urban and suburban/rural areas. In urban areas, surface O3 is consumed by titration reaction to generate NO2, which is then transported to the upper boundary layer and produces O3 by photochemical reaction. With the development of the boundary layer, the upper-layer O3 stored in the residual layer at nighttime can be transported vertically to the surface as the turbulent diffusion intensifies the next morning. While in suburban and rural areas, the vertical transport is relatively weaker because the photochemical formation of O3 occurs in the whole boundary layer, although it decreases slightly with the altitude. Model simulation showed that 20.6-27.9% of urban surface O3 changes in the morning (09:00-10:00 LST) was attributable to the downward transport from the residual layer, while it is 15.0-22.1% at suburban site. The vertical transport from above the boundary layer contributed 24.0-63.6% to daytime urban surface O3 changes, which was weak in suburban areas. Differences and similarities in O3 formation and transport mechanism in urban and suburban regions revealed here highlight the importance of earlier control and regional collaboration.


Assuntos
Poluentes Atmosféricos , Poluição do Ar , Ozônio , Poluentes Atmosféricos/análise , Poluição do Ar/análise , Animais , China , Monitoramento Ambiental , Masculino , Ozônio/análise , Processos Fotoquímicos , Ovinos
5.
Sci Total Environ ; 814: 151953, 2022 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-34843782

RESUMO

We revealed that the absorption aerosol lying below or above the morning residual layer (MRL) promotes (stove effect, heating the MRL layer) or strongly inhibits (dome effect, heating the temperature inversion layer) the development of planetary boundary layer (PBL) after sunrise, while scattering aerosol exhibits similar suppression (surface or aloft umbrella effect) on the PBL regardless of its vertical location. However, the role of different type of aerosols (i.e., strong absorption aerosol and purely scattering aerosol) present from MRL to upper atmosphere remains lacking and therefore, needs to be further explored. Utilizing a large-eddy simulation model constrained by the in-situ observations in urban Beijing, we observed that the dome inhibition of absorption aerosols on PBL development becomes weaker as elevating the aerosol layer, and the effect (virtual dome effect) remains no change beyond a certain height, which is defined as the dome effective height z. This height z is highly related to the surface sensible heat flux. By comparison, the altitude of light-scattering aerosols relative to the MRL was less important. The scattering aerosols exhibit similar inhibition from MRL to upper atmosphere (aloft umbrella effect), but to a weaker extent than the virtual dome effect. The virtual dome effect and aloft umbrella effect play a leading role during some extremely polluted scenarios with deep aerosol layer, such as sandstorms and volcanic eruptions. Aerosol dome, virtual dome, and aloft umbrella effects, together with aerosol stove and surface umbrella effects, further advance the understanding on aerosol-PBL interactions, which is, more broadly, applied to interpret the impact of aerosol on PBL over other ecosystems as well as exoplanet atmospheres.


Assuntos
Poluentes Atmosféricos , Aerossóis/análise , Poluentes Atmosféricos/análise , Atmosfera , Ecossistema , Monitoramento Ambiental
6.
J Environ Sci (China) ; 112: 210-217, 2022 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-34955205

RESUMO

High loads of ground-level ozone have occurred with the implementation of the Air Pollution Prevention and Control Action Plan. However, the long temporal variation in precursor nonmethane hydrocarbons (NMHCs) has rarely been studied. In this study, we examined the evolution of NMHCs in Beijing based on ambient measurements from 2000 to 2019. The results indicated that the annual variation of ambient NMHCs during 2000 and 2019 could be divided into two stages. The mixing ratios of NMHCs rapidly rose during 2000 and 2009 (1.76 ppbv/year) but exhibited a downward trend from 2009 to 2019 at rate of 0.80 ppbv/yr. Moreover, the notable decrease in alkenes and aromatics after 2009 led to a sharp decrease in the propylene-equivalent concentration (PEC) (-0.80 ppbv/year). Implementation of emission reduction measures in Beijing have effectively reduced the contribution of vehicle-related sources, but the contribution of solvent usage and fuel consumption increased, which will become the focus of VOC control in Beijing in the future.


Assuntos
Poluentes Atmosféricos , Ozônio , Compostos Orgânicos Voláteis , Poluentes Atmosféricos/análise , Pequim , China , Monitoramento Ambiental , Hidrocarbonetos/análise , Ozônio/análise , Compostos Orgânicos Voláteis/análise
7.
J Environ Sci (China) ; 113: 300-310, 2022 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-34963539

RESUMO

Visibility observed at different altitudes is favorable to understand the causes of air pollution. We conducted 4-years of observations of visibility at 2.8 and 60 m and particulate matter (PM) concentrations from 2015 to 2018 in Shenyang, a provincial city in Northeast China. The results indicated that visibility increased with the increasing height in winter (especially at night), and decreased with height in summer (especially at the daytime). PM concentration exhibited opposite vertical variation to visibility, reflecting that visibility degrades with the increase of aerosol concentration in the air. The radiosonde meteorological data showed that weak turbulence in the planetary boundary layer (PBL) in winter favored aerosols' accumulation near the surface. Whereas in summer, unstable atmospheric conditions, upper-level moister environment, and regional transport of air pollutants resulted in the deterioration of upper-level visibility. Inter-annual variation in the two-level visibility indicated that the upper-level visibility improved more significantly than low-level visibility, much likely due to the reduction in emission of elevated point sources in Shenyang. Our study suggested that strengthening the control of surface non-point emissions is a promising control strategy to improve Shenyang air quality.


Assuntos
Poluentes Atmosféricos , Poluição do Ar , Aerossóis/análise , Poluentes Atmosféricos/análise , Poluição do Ar/análise , China , Monitoramento Ambiental , Material Particulado/análise , Estações do Ano
8.
Sci Total Environ ; 806(Pt 4): 150951, 2022 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-34656590

RESUMO

It is very important for air pollution prevention and control to accurately quantify atmospheric environment capacity (AEC) in the planetary boundary layer (PBL). This study developed a high temporal-resolution dynamic multi-box algorithm to estimate PM2.5 AEC with a PBL ceilometer and Doppler wind profile lidar in Beijing City. Compared with the traditional A-value method, two primary improvements are introducing the time coefficient and vertical multi-box assumption into the original box model. The algorithm can accurately calculate the PM2.5 AEC under different circulation patterns and predict the short-time dynamic change of AEC. The results show that the time coefficient effectively reduced the estimation errors when the initial PM2.5 concentration, horizontal wind speed and PBL heights change greatly with time, such situation is consistent with most circulation patterns. And the improvement of multi-box model is much more remarkable when the PM2.5 concentration and horizontal wind change greatly in the vertical direction, such as A, NE and W type circulations. The ideal AEC under polluted circulation patterns won't increase infinitely with wind speed and PBL height, generally less than 30 t/h. The horizontal advection has a much greater effect on expanding the capacity of PM2.5 than the vertical diffusion under clean circulation patterns, and the maximum value of ideal AEC can reach 50 t/h. The positive residual AEC under clean circulations indicates surplus capacity for PM2.5 because of vigorous turbulences, while weak diffusion and ventilation conditions under polluted circulations lead to negative residual AEC and insufficient capacity of atmosphere.


Assuntos
Poluentes Atmosféricos , Poluição do Ar , Poluentes Atmosféricos/análise , Poluição do Ar/análise , Algoritmos , China , Monitoramento Ambiental , Material Particulado/análise , Estações do Ano
9.
Sci Total Environ ; 806(Pt 4): 150950, 2022 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-34656595

RESUMO

The vertical distribution of carbonaceous aerosol impacts climate change, air quality and human health, but there is a lack of in-situ vertical observations of black (BC) and brown carbon (BrC). Thus, the characteristic of vertical profiles of BC concentration, particle number concentration (PNC), O3 concentration and optical absorption of BC and BrC were observed in a suburban site over North China Plain, where heavy pollution of PM2.5 and O3 always occurred in winter and summer, respectively. In winter, during a heavy pollution episode, the BC and PNC was near uniformly distributed within mixing layer (ML) (15.2 ± 6.7 µg m-3 and 678 ± 227 p cm-3, respectively) and decreased with altitude above the ML. The BC heating rate reached about 0.13 K h-1 during the heaviest pollution day. In summer, the BC concentration (2.9 ± 1.3 µg m-3) in ML during the middle O3 pollution events was higher than that (1.7 ± 0.6 µg m-3) during the light O3 pollution. The light absorption coefficients of BC at 880 nm and BrC at 375 nm measured in the early morning were lower than that in the daytime, and the contribution of BrC to total light absorption of carbonaceous aerosols was in the range of 27-47%. In addition, BC was effectively transported to high altitude than BrC in the daytime. The light absorption of secondary BrC in the daytime was higher 10-20% than that in the early morning. Simultaneously, the contribution of secondary BrC to the total BrC light absorption at 375 nm was range from 32% to 68% within 1000 m.


Assuntos
Poluentes Atmosféricos , Carbono , Aerossóis/análise , Poluentes Atmosféricos/análise , Carbono/análise , China , Monitoramento Ambiental , Humanos , Material Particulado/análise
10.
Huan Jing Ke Xue ; 42(10): 4602-4610, 2021 Oct 08.
Artigo em Chinês | MEDLINE | ID: mdl-34581102

RESUMO

To reveal the characteristics of photochemical pollution in North China, adsorbing columns with 2, 4-dinitrophenylhydrazine(DNPH) were used to sample carbonyl compounds in Shijiazhuang and Xinglong between May 2018 and April 2019. The samples were analyzed by high-performance liquid chromatography to understand the composition, volume fraction, source, ·OH loss rate, and ozone formation potential of the carbonyl compounds. A total of 13 carbonyl compounds containing carbonyl groups were determined, of which acetone, formaldehyde, and acetaldehyde were highest at(6.46±5.25)×10-9, (3.76±2.29×10-9), and(2.65±1.74)×10-9 in Shijiazhuang compared to(1.85±1.27)×10-9, (1.29±1.02)×10-9, and(0.72±0.48)×10-9 in Xinglong, respectively. The estimated maximum ozone formation potential(OFP) of formaldehyde was much higher than that of acetaldehyde; the C1/C2 and C2/C3 ozone formation potential(OFP) of formaldehyde was much higher than that of acetaldehyde; and the C1/C2 and C2/C3 values showed that vehicle exhaust and fossil fuel combustion were the main sources in Shijiazhuang in association with the higher level of industrialization. In Xinglong, the carbonyl compounds mainly originated from natural sources. Acetaldehyde(1.77 s-1), formaldehyde(1.57 s-1), and butyraldehyde(0.42 s-1) contributed most to L·OH in Shijiazhuang, and formaldehyde(0.53 s-1), acetaldehyde(0.47 s-1), and butyraldehyde(0.12 s-1) were the three main contributors to L·OH in Xinglong. The carbonyl compounds contributing most to O3 production were formaldehyde and acetaldehyde at(34.61×10-9 O3) and (16.73×10-9 O3) in Shijiazhuang, compared to (11.77×10-9 O3) and (4.47×10-9 O3) in Xinglong, respectively.


Assuntos
Poluentes Atmosféricos , Poluentes Atmosféricos/análise , Atmosfera , China , Monitoramento Ambiental , Emissões de Veículos/análise
11.
Environ Pollut ; 291: 118195, 2021 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-34555796

RESUMO

Controlling ammonia (NH3) emissions has been proposed as a strategy to mitigate haze pollution. To explore the role of NH3 in haze pollution in Sichuan Basin, where agricultural activities are intense, hourly in situ data of NH3, as well as nitric acid and secondary inorganic aerosols (SIAs) were gathered in Chengdu from April 2017 to March 2018. We found that NH3 had an annual mean concentration of 9.7 ± 3.5 (mean ± standard deviation) µg m-3, and exhibited seasonal variations (spring > summer > autumn and winter) due to changes in emission sources and meteorological conditions (particularly temperature). Chengdu's atmosphere is generally NH3-sufficient, especially in the warm seasons, implying that the formation of SIAs is more sensitive to the availability of nitric acid. However, an NH3 "sufficient-to-deficient" transition was found to occur during winter pollution periods, and the frequency of NH3 deficiency increased with the aggravation of pollution. Under NH3-deficient conditions, the nitrogen oxidation ratio increased linearly with the increase in free NH3, implying that NH3 contributes appreciably to the formation of nitrate and thus to high PM2.5 loadings. No relationships of NH3 with fossil fuel combustion-related pollutants were found. The NH3 emissions from farmland and livestock waste in the suburbs of Chengdu and regional transport from west of Chengdu probably contribute to the occurrence of high PM2.5 loading in winter and spring, respectively. These results suggest that to achieve effective mitigation of PM2.5 in Chengdu, local and regional emission control of NH3 and NOx synergistically would be effective.


Assuntos
Poluentes Atmosféricos , Poluição do Ar , Aerossóis/análise , Poluentes Atmosféricos/análise , Poluição do Ar/análise , Amônia/análise , China , Monitoramento Ambiental , Material Particulado/análise , Estações do Ano
12.
Sci Total Environ ; 799: 149438, 2021 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-34426343

RESUMO

Oxygenated volatile organic compounds (OVOCs) are important precursors of secondary air pollutants. However, knowledge of the vertical characteristics of OVOCs in the lower troposphere is lacking. Pairs of OVOCs samples were simultaneously collected via 2,4-dinitrophenylhydrazine (DNPH) near the ground and in the upper boundary layer (at 500 m in winter and 600 m in summer) with a tethered balloon in Shijiazhuang in January and June 2019. The samples were analyzed via high-performance liquid chromatography (HPLC), and 26 vertical profiles of 13 OVOCs were obtained in this study. In winter, the average concentrations of the total OVOCs (TOVOCs) in the upper boundary layer and near the ground were 7.9 ± 4.1 ppbv and 5.5 ± 2.8 ppbv, respectively; while in summer, the average concentrations were 7.1 ± 3.5 ppbv and 6.5 ± 2.7 ppbv, respectively. Acetone, formaldehyde and acetaldehyde were the three main components accounting for more than 80% of the TOVOCs. Significant vertical differences were observed before sunrise in winter and in the afternoon in summer. The TOVOCs concentration in the residual layer (8.4 ± 3.6 ppbv) was higher than that near the ground (6.0 ± 2.5 ppbv), while in the summer afternoon, the concentration in the upper mixing layer (ML) (9.5 ± 2.2 ppbv) was higher than that near the ground (5.8 ± 3.1 ppbv). OVOCs sources were examined with a positive matrix factorization (PMF) model. In winter, the small-molecule carbonyls (SMCs) in the upper boundary layer are mainly derived from secondary + long-lived species (68.4%) because volatile organic compounds at high concentrations were oxidized into OVOCs. In summer, the SMCs in the upper ML were mainly affected by elevated industrial point source emissions (42.9%). These data indicate that vertical gradient observations of SMCs are an important supplement to advance current air pollution research.


Assuntos
Poluentes Atmosféricos , Compostos Orgânicos Voláteis , Poluentes Atmosféricos/análise , China , Monitoramento Ambiental , Gases , Compostos Orgânicos Voláteis/análise
13.
Sci Total Environ ; 788: 147740, 2021 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-34134376

RESUMO

Clarifying the relationship between meteorological factors and ozone can provide scientific support for ozone pollution prediction, but the effects of boundary layer meteorology, especially boundary layer height and turbulence, on ozone pollution are rarely studied. Here, ozone and its related meteorological factors were observed in summer in Shijiazhuang, a city with the most serious ozone pollution on the North China Plain. The forced and free convection boundary layers were classified using ground remote observations. After eliminating the forced convection condition, strong free convection conditions, exhibiting a high boundary layer height, high wind speed, strong turbulence and large-scale free convection velocity, were found to be beneficial for the aggravation of ozone pollution. Combined with the ozone profile detected by a tethered balloon, the ozone chemical budget was calculated using the differences in the column ozone concentrations between the morning and afternoon, and the results confirmed the impact of free convection intensity on ozone pollution. The change in ozone sensitivity from VOCs sensitivity to NOx sensitivity driven by strong free convection was the main reason for the deterioration of ozone pollution. This study clarified the impact of boundary layer meteorology on ozone and its sensitivity and has important practical significance for ozone pollution prevention and early warning.

14.
J Environ Sci (China) ; 104: 169-181, 2021 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-33985719

RESUMO

High values of ozone (O3) occur frequently in the dry spring season; thus, understanding the evolution characteristics of volatile organic compounds (VOCs) in spring is of great significance for preventing O3 pollution. In this study, a total of 101 VOCs from April 16 to May 21, 2019, were quantified using an online gas chromatography mass spectrometer/flame ionization detector (GCMS/FID). The results indicated that the observed concentration of total VOCs (TVOCs) was 30.4 ± 17.0 ppbv, and it was dominated by alkanes (44.3%), followed by oxygenated VOCs (OVOCs) (17.4%), halocarbons (12.7%), aromatics (9.5%), alkenes (8.2%), acetylene (5.3%) and carbon disulfide (2.5%). The average mixing ratio of VOCs showed obvious diurnal variation (high at night, low during daytime). We conducted a source apportionment study based on 32 major VOCs using positive matrix factorization (PMF), and coal + biomass burning (25.2%), diesel exhaust (16.0%), gasoline exhaust + evaporation (17.4%), secondary + long-lived species (16.7%), biogenic sources (4.3%), industrial emissions (9.3%) and solvent use (11.2%) were identified as major sources of VOCs. In addition to local emissions, most of the atmospheric VOCs were derived from long-distance air masses (65.7%), and the average mixing ratio of VOCs in the northwest direction was 29.4 ppbv. Combined with the results of the potential source contribution function (PSCF) indicate that research should focus on the local emissions of combustion, transportation sources and solvents usage to control atmospheric VOCs. Additionally, transmission of the northwest air mass is an important component that cannot be ignored during spring in Beijing.


Assuntos
Poluentes Atmosféricos , Compostos Orgânicos Voláteis , Poluentes Atmosféricos/análise , Pequim , China , Monitoramento Ambiental , Estações do Ano , Compostos Orgânicos Voláteis/análise
15.
Sci Total Environ ; 782: 146845, 2021 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-33848867

RESUMO

High ozone concentrations promote the formation of nitrate in the nocturnal residual layer (RL), but this phenomenon has not been confirmed by direct observation. In this study, ozone, water-soluble ions in PM2.5 and the corresponding meteorological factors in the stable boundary layer, RL and mixing layer were observed by portable instruments carried on a tethered balloon over the North China Plain. The ozone concentration significantly increased in the RL compared to that in the stable boundary layer, while particulate nitrate significantly decreased, except in the clouds. Unfavorable environmental conditions, i.e., high temperature, low relative humidity, low aerosol surface area, and weak particle acidity, are not conducive to dinitrogen pentoxide uptake and hydrolysis to form particulate nitrate in the RL, and are conducive to the volatilization of nitrate to a gaseous state. Thus, our observations differed from traditional reports and confirmed that the morning peak of particulate nitrate at ground level is not related to the downward transport of nitrate from the RL. In addition, evidence for nitrate formation in cloudy weather is provided, and the possible impact on ozone is discussed.

16.
Sci Total Environ ; 783: 146976, 2021 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-33866162

RESUMO

An aerosol mass spectrometer (AMS) was used to measure the chemical composition of non-refractory submicron particles (NR-PM1) in Beijing from 2012 to 2013. The average concentration of NR-PM1 was 56 µg·m-3, with higher value of 106 µg·m-3 when Beijing was influenced by air masses from south in winter. Organics was the primary chemical component with a concentration of 26 µg·m-3, accounting for 46% of the total NR-PM1. The ratio of NO3-/SO42- was utilized to identify the relative contribution of stationary and traffic related resource to PM pollution. When NR-PM1 concentration was between 50 and 200 µg·m-3, NO3-/SO42-was larger than 1, indicating traffic resource contributed more than stationary resource during the aerosol growth. A new method was developed to calculate aerosol extinction coefficient (σ) as a function of aerosol optical depth (AOD) and the mixing layer height (MLH). σ derived from the new method showed a statistically significant correlation with that obtained from traditional method, which was calculated using visibility (y = 0.99x + 85 R2 = 0.69). Multiple linear regressions in dependence of chemical component were performed to evaluate light extinction apportionment. Under the overall condition, NR-PM1 contributed about 88% to the whole aerosol light extinction; organics, ammonium chloride, ammonium nitrate, ammonium sulfate, black carbon contributed 30%, 6%, 24%, 26% and 6% of the NR-PM1 light extinction, respectively. By further comparing the light extinction apportionment under the different dominated air masses, we concluded that the organics and ammonium sulfate contributed more in polluted days (36% and 23%) than that in clean days (21% and 21%). Mass ratio (MR) between NR-PM1 and black carbon (MR = massNR-PM1/massBC) was used to identify black carbon aging degree, and the result showed that aerosol mass extinction efficiency increased rapidly after MR reached about 7 in the process of black carbon aging.

17.
Sci Total Environ ; 771: 145306, 2021 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-33736127

RESUMO

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.

18.
Environ Sci Technol ; 55(8): 4542-4552, 2021 04 20.
Artigo em Inglês | MEDLINE | ID: mdl-33769806

RESUMO

Vertical measurements are essential for the characterization of aerosol and boundary layer interactions; yet, our knowledge of vertical profiles of primary and secondary aerosol species in megacities is limited. Here, we conducted comprehensive vertical measurements of aerosol particle composition on a 325 m meteorological tower with two aerosol chemical speciation monitors in winter in urban Beijing. The simultaneous measurements at ground level, 140, and 240 m illustrated similar aerosol bulk composition at these three heights. However, the vertical ratios varied significantly among different aerosol species. Particularly, the vertical ratios of the aqueous phase and photochemical-related secondary organic aerosol (SOA) (aqOOA/OOA) decreased significantly, accompanied by the increases in ratios of secondary to primary OA, highlighting different chemical properties of OA between ground level and aloft, and the large impacts of vertical changes in meteorology and gaseous precursors on SOA formation. The vertical changes in NO3/SO4 ratios, however, were mostly insignificant, likely due to the low relative humidity and aerosol water content that inhibited nocturnal heterogeneous reactions in the residual layer. Considerable increases in the ratios of 240 m to ground level in the early morning were also observed for most aerosol species, demonstrating impact of residual layer on the air pollution of 2nd day.


Assuntos
Poluentes Atmosféricos , Aerossóis/análise , Poluentes Atmosféricos/análise , Pequim , Monitoramento Ambiental , Meteorologia
19.
J Environ Sci (China) ; 102: 207-215, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33637245

RESUMO

Atmospheric extinction is impacted by the chemical composition of particles. To better understand the chemical composition of PM2.5 (particles with diameters of less than 2.5 µm) and its relationship with extinction, one-month sampling campaigns were carried out in four different seasons from 2013 to 2014 in Jinan, China. The seasonal average concentrations of PM2.5 were 120.9 (autumn), 156.6 (winter), 102.5 (spring), and 111.8 µg/m3 (summer). The reconstructed PM2.5 chemical composition showed that sulfate, nitrate, chlorine salt, organic matter (OM), mineral dust, elemental carbon (EC) and others accounted for 25%, 14%, 2%, 24%, 22%, 3% and 10%, respectively. The relationship between the chemical composition of PM2.5 and visibility was reconstructed by the IMPROVE method, and ammonium sulfate, ammonium nitrate, OM and EC dominated the visibility. Seven main sources were resolved for PM2.5, including secondary particles, coal combustion, biomass burning, industry, motor vehicle exhaust, soil dust and cooking, which accounted for 37%, 21%, 13%, 13%, 12%, 3% and 1%, respectively. The contributions of different sources to visibility were similar to those to PM2.5. With increasing severity of air pollution, the contributions of secondary particles and coal combustion increased, while the contribution of motor vehicle exhaust decreased. The results showed that coal combustion and biomass burning were still the main sources of air pollution in Jinan.


Assuntos
Poluentes Atmosféricos , Material Particulado , Aerossóis/análise , Poluentes Atmosféricos/análise , China , Monitoramento Ambiental , Material Particulado/análise , Estações do Ano , Emissões de Veículos/análise
20.
Sci Total Environ ; 768: 144538, 2021 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-33453527

RESUMO

Nitrate-driven aerosol pollution frequently occurs during winter over the North China Plain (NCP). Extensive studies have focused on inorganic nitrate formation, but few have focused on organic nitrates in China, precluding a thorough understanding of the nitrogen cycle and nitrate aerosol formation. Here, the inorganic (NO3,inorg) and organic nitrate (NO3,org) formation regimes under aerosol liquid water (ALW) and aerosol acidity (pH) influences were investigated during winter over the NCP based on data derived from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The campaign-averaged concentration of the total nitrate was 5.3 µg m-3, with a 13% contribution from NO3,org, which exhibited a significantly decreased contribution with increasing haze episode evolution. The diurnal cycles of NO3,inorg and NO3,org were similar, with high concentrations during the nighttime at a high ALW level, revealing the important role of aqueous-phase processes. However, the correlations between the aerosol pH and NO3,inorg (R2 = 0.13, P < 0.01) and NO3,org (R2 = 0.63, P < 0.01) during polluted periods indicated a contrasting effect of aerosol pH on inorganic and organic nitrate formation. Our results provide a useful reference for smog chamber studies and promote a better understanding of organic nitrate formation via anthropogenic emissions.

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