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A multiscale analysis of meteorological trends was carried out to investigate the impacts of the large-scale circulation types as well as the local-scale key weather elements on the complex air pollutants, i.e., PM

The atmospheric oxidizing capacity (AOC), reflecting the self-cleansing capacity of the atmosphere, plays an important role in the chemical evolution of secondary fine particulate matter (PM

Atmospheric particles are important reaction vessels for multiphase chemistry. We conducted a meta-analysis of previous field observations in various environments (includes ocean, urban and rural regions), showing that particle hygroscopicity inhomogeneity (PHI) is ubiquitous for the continental atmospheric particles, in which a considerable part of the particulate matters is hydrophobic (10%–33% on average). However, the effects of PHI in quantifying the uptake process of reactive gases are still unclear. Here, taking N2O5 uptake as an example, we showed that using a laboratory-based parameterization scheme without considering the PHI might result in a misestimation of uptake rate coefficient, especially under low ambient relative humidity (RH). Such misestimation may be caused by the differences of the uptake coefficients, as well as the proportion of surface area concentration (SA) between hydrophilic and hydrophobic particles. We suggested that the PHI should be well-considered in establishing the reactive traces gases heterogeneous uptake parameterizations.

Formaldehyde (HCHO) can possibly be taken by atmospheric particles due to its moderate solubility. Although previous model studies have proposed that uptake by particles was a large sink for HCHO, direct observation of HCHO partitioning and estimation of HCHO uptake coefficient (γ) for tropospheric conditions are still limited. In this work, online measurements of gaseous HCHO (HCHO

Volatile organic compounds (VOCs) play an important role in air pollution. In this study, we conducted comprehensive field observations to investigate wintertime air pollution in Beijing, Wangdu, and Dezhou in the Beijing-Tianjin-Hebei region during 2017 and 2018. The average VOC concentrations of the three sites were 35.6 ± 26.6, 70.9 ± 56.3, and 50.5 ± 40.0 ppbv, respectively. The species with the highest concentration were similar in all three sites and included ethane, ethylene, acetylene, acetone, and toluene. The VOC mixing ratios of the three sites showed synchronous growth during pollution episodes and were 1.2-2 times higher than those during clean periods. Moreover, the OH loss rates (LOH) during pollution episodes were 1.2-1.7 times that during clean periods. The crucial reactive species in the three sites were ethylene, propylene, and acetaldehyde, contributing approximately 70% to the total LOH during pollution periods. According to the source apportionment analysis, vehicle exhausts were the largest source of VOCs in Beijing, accounting for more than 50% of the total emissions. During the pollution episodes, Beijing's industrial emissions decreased, but the secondary and background sources increased. Coal combustion was significant (approximately 40%) in Wangdu and should therefore be prioritized in emission reduction policies. In Dezhou, industrial emissions had a considerable impact on the VOC mixing ratio during pollution periods and should therefore be prioritized. The backward trajectory analysis showed that VOCs from the southern region likely contribute to Beijing's VOC pollution, highlighting the importance of regional integration for air quality management.

Nitrate (NO3) radical is an important oxidant in the atmosphere as it regulates the NOx budget and impacts secondary pollutant formation. Here, a long-term observational dataset of NO3-related species at an urban site in Beijing was used to investigate changes in the NO3 budget and their atmospheric impacts during 2013–2019, in this period the Clean Air Actions Plan was carried out in China. We found that (1) changes in NO3 precursors (NO2 and O3) led to a significant increase in NO3 formation in the surface layer in winter but a decrease in summer; (2) a reduction in NOx promoted thermal equilibrium, favoring the formation of NO3 rather than dinitrogen pentoxide (N2O5). The simultaneous decrease in PM2.5, during these years, further weakened the N2O5 heterogeneous uptake; (3) a box model simulation revealed that both the reactions of NO3 with volatile organic compounds (VOC) and N2O5 uptake were weakened in summer, implying that the policy actions implemented help to moderate secondary aerosol formation caused by NO3 and N2O5 chemistry in summer; and (4) during winter, both NO3 + VOC and N2O5 uptake were enhanced. Specifically, for the N2O5 uptake, the rapid increase in NO3 production, or to some extent, NO3 oxidation capacity, far outweighed the negative shift effect, leading to a net enhancement of N2O5 uptake in winter, which indicates that the action policy implemented led to an adverse effect on particulate nitrate formation via N2O5 uptake in winter. This may explain the persistent winter particulate nitrate pollution in recent years. Our results highlight the systematic changes in the NO3 budget between 2013 and 2019 in Beijing, which subsequently affect secondary aerosol formation in different seasons.

In recent decade the ambient fine particle (PM

We present a comprehensive field campaign conducted in Beijing, September 2016, to elucidate the photochemical smog pollution, i.e. Ozone (O3). The observed daily maximum hydroxyl radical (OH) and hydroperoxy radical (HO2) concentrations were up to 1 × 107 cm-3 and 6 × 108 cm-3, respectively, indicating the active photochemistry in autumn Beijing. Photolysis of nitrous acid (HONO) and O3 contributed 1-2 ppbv h-1 to OH primary production during daytime. OH termination were dominated by the reaction with nitric oxide (NO) and nitrogen dioxide (NO2), which were in general larger than primary production rates, indicating other primary radical sources maybe important. The measurement of radicals facilitates the direct determination of local ozone production rate P (Ox) (Ox = O3 + NO2). The integrated P(Ox) reached 75 ppbv in afternoon (for 4 h) when planetary boundary layer was well developed. At the same time period, the observed total oxidant concentrations Ox, increased significantly by 70 ppbv. In addition, the Ox measurement showed compact increase in 12 stations both temporally and spatially in Beijing, indicating that active photochemical production happened homogenously throughout the city. The back-trajectory analysis showed that Beijing was isolated from the other cities during the episode, which further proved that the fast ozone pollution was contributed by local photochemical production rather than regional advection.

The Yangtze River Delta (YRD) urban agglomeration is one of the most developed regions in China. During recent decades, this region has experienced severe regional haze and photochemical smog pollution problems. In this study, we used a source-oriented chemical transport model to quantitatively estimate the effects of inter-city transport on fine particulate matter (PM

This study reports on the first continuous measurements of ambient OH and HO

Photolysis of nitrous acid (HONO) is one of the major sources for atmospheric hydroxyl radicals (OH), playing significant role in initiating tropospheric photochemical reactions for ozone (O

Cross-regional transport potentially contributes to PM

A field campaign was conducted from November to December 2017 at the campus of Peking University (PKU) to investigate the formation mechanism of the winter air pollution in Beijing with the measurement of hydroxyl and hydroperoxyl radical (OH and HO

The dicarbonyls glyoxal (Gly) and methylglyoxal (Mgly) are key tracers for the oxidation of volatile organic compounds (VOCs) in the atmosphere, but their atmospheric chemistry in remote forest environments is not well understood. A study was carried out during Jul. 31–Nov. 5 of 2016 at the summit of Mt. Tianjing (1690 m.a.s.l.), a remote mountaintop site in southern China, to measure the levels of Gly and Mgly and explore their sources and fate. During the study period, the average mixing ratios of Gly and Mgly were 509 ± 31 pptv and 340 ± 32 pptv, respectively, with the Gly/Mgly ratios averaging 1.8 ± 0.2. Both the dicarbonyl concentrations and the Gly/Mgly ratios were significantly higher than those observed in other background sites. Production yield calculations and meteorological data analysis indicate that high levels of Gly and Mgly observed at the study site were largely a combined result of rapid in-situ formation and regional transport by prevailing winds. On average, in-situ formation from precursors is estimated to account for 67% of the observed Mgly and about 9% of the observed Gly. There were significant changes in Gly and Mgly mixing ratios among different time periods when air masses from different source regions dominated, indicating contribution of regional transport to the observed dicarbonyl mixing ratios at the study site. Biogenic emissions in eastern China and anthropogenic emissions in the Pearl River Delta region were the two main sources responsible for the dicarbonyls observed at the site during most of the sampling period, but large-scale biomass burning in central China was also important in the late autumn, as supported by a backward trajectory analysis of fire spot data and the identification of biomass burning tracers. This study provides insights into the background atmospheric chemistry and the impact of biogenic and anthropogenic sources on the dicarbonyls speciation.

Based on detailed data on 102 volatile organic compounds (VOCs) measured continuously from 2016.10.9 to 2016.11.17 in Wuhan, the VOC characteristics, secondary organic aerosol (SOA) characteristics, SOA formation potential (SOAP), potential source regions, sources and contributions during different haze episodes were analyzed. The total VOC (TVOC) concentrations on clear days (visibility10 km), slight haze days (visibility of 5-10 km), and severe haze days (visibility5 km) were 34.87 ± 14.89 ppbv, 45.06 ± 26.69 ppbv, and 49.55 ± 24.82 ppbv, respectively. The SOAP on haze days (447.04 ± 253.85 ppbv) was significantly higher than that on clear days (300.62 ± 138.48 ppbv), and aromatics were the dominant contributors to SOA formation under different visibility conditions, accounting for approximately 97% of the total SOAP. The ratio of ethylbenzene to m/p-xylene (E/X) indicated that atmospheric photochemical reactions were slightly stronger on haze days. The ratio of toluene to benzene (T/B) indicated that vehicle exhaust had significant effects on VOCs, but no significant changes occurred during different haze episodes. The ratio of benzene, toluene, ethylbenzene and xylenes (BTEX) to CO indicated that VOCs from solvent usage in painting/coating and industrial emissions increased with increasing haze pollution. Based on backward trajectories and the potential source contribution function (PSCF), short-distance transport was the main source influencing VOC pollution, especially transport from the southwest. Seven sources were identified by positive matrix factorization (PMF): industrial sources, vehicular exhaust, solvent usage in painting/coating, fuel evaporation, liquefied petroleum gas (LPG) usage, biogenic sources and biomass burning. Moreover, solvent usage in painting/coating, vehicle exhaust and LPG usage were the most important sources that significantly aggravated VOC pollution during haze events. The results can provide references for local governments developing control strategies of VOCs during haze pollution events.

We present the in-situ measurements in Chengdu, a major city in south west of China, in September 2016. The concentrations of ozone and its precursor were measured at four sites. Although the campaign was conducted in early autumn, up to 100 ppbv (parts per billion by volume) daily maximum ozone was often observed at all sites. The observed ozone concentrations showed good agreement at all sites, which implied that ozone pollution is a regional issue in Chengdu. To better understand the ozone formation in Chengdu, an observation based model is used in this study to calculate the RO

Biomass burning emits large amounts of both trace gases and particles into the atmosphere. It plays a profound role in regional air quality and climate change. In the present study, an intensive campaign was carried out at an urban site in Beijing, China, in June 2014, which covered the winter wheat harvest season over the North China Plain (NCP). Meanwhile, two evident biomass-burning events were observed. A clear burst in ultrafine particles (below 100nm in diameter, PM1) and subsequent particle growth took place during the events. With the growth of the ultrafine particles, the organic fraction of PM1 increased significantly. The ratio of oxygen to carbon (O:C), which had an average value of 0.23±0.04, did not show an obvious enhancement, indicating that a significant chemical aging process of the biomass-burning aerosols was not observed during the course of events. This finding might have been due to the fact that the biomass-burning events occurred in the late afternoon and grew during the nighttime, which is associated with a low atmospheric oxidation capacity. On average, organics and black carbon (BC) were dominant in the biomass-burning aerosols, accounting for 60±10% and 18±3% of PM1. The high organic and BC fractions led to a significant suppression of particle hygroscopicity. Comparisons among hygroscopicity tandem differential mobility analyzer (HTDMA)-derived, cloud condensation nuclei counter (CCNc)-derived, and aerosol mass spectrometer-based hygroscopicity parameter (κ) values were consistent. The mean κ values of biomass-burning aerosols derived from both HTDMA and CCNc measurements were approximately 0.1, regardless of the particle size, indicating that the biomass-burning aerosols were less active. The burst in particle count during the biomass-burning events resulted in an increased number of cloud condensation nuclei (CCN) at supersaturation (SS)=0.2-0.8%.

Synchronized online measurements of gas- and particle- phase organics including non-methane hydrocarbons (NMHCs), oxygenated volatile organic compounds (OVOCs) and submicron organic matters (OM) were conducted in November 2010 at Heshan, Guangdong provincial supersite, China. Several biomass burning events were identified by using acetonitrile as a tracer, and enhancement ratios (EnRs) of organics to carbon monoxide (CO) obtained from this work generally agree with those from rice straw burning in previous studies. The influences of biomass burning on NMHCs, OVOCs and OM were explored by comparing biomass burning impacted plumes (BB plumes) and non-biomass burning plumes (non-BB plumes). A photochemical age-based parameterization method was used to characterize primary emission and chemical behavior of those three organic groups. The emission ratios (EmRs) of NMHCs, OVOCs and OM to CO increased by 27-71%, 34-55% and 67% in BB plumes, respectively, in comparison with non-BB plumes. The estimated formation rate of secondary organic aerosol (SOA) in BB plumes was found to be 24% faster than non-BB plumes. By applying the above emission ratios to the whole PRD, the annual emissions of VOCs and OM from open burning of crop residues would be 56.4 and 3.8Gg in 2010 in PRD, respectively.

To evaluate the effectiveness of the integrated control measures for reducing PM 2.5 (aerosol particles with an aerodynamic diameter of less than 2.5 μm) and hazy weather, day- and night-time PM 2.5 samples were collected at an urban site in Guangzhou during the 16th Asian Games period in November 2010. PM 2.5 samples were subject to chemical analysis for major water-soluble ions, organic carbon (OC), element carbon (EC), and biomass burning tracers–anhydrosugar levoglucosan (LG). In addition, aerosol scattering coefficient (b sp ) at dry condition and aerosol absorption coefficient (b ap ) and visibility at ambient condition were measured. The seven major control measures were effective for reducing PM 2.5 mass concentration and improving visibility during the Asian Games period. All monitored air pollutants except PM 2.5 satisfied the National Ambient Air Quality Standards (NAAQS). However, daily PM 2.5 concentrations still exceeded the NAAQS on 47% of the days and hazy weather also occurred on 80% of the days during this period. One factor causing the high frequency of hazy weather occurrence was the increased relative humidity during the Asian Games period. To avoid hazy weather occurrence, new PM 2.5 standard was recommended based on visibility calculations using three available aerosol hygroscopic curves previously obtained for this city. The recommended PM 2.5 standard was 63 μg m − 3 under dry condition and lower than 42 μg m − 3 under humid condition (RH ≥ 70%). These recommended values were much stricter than the NAAQS value of 75 μg m − 3 . To reach the new standard, more rigorous control measures for coal industries should be established in the Pearl River Delta (PRD) region.

Objectives Several studies reported acute mortality and morbidity effects of exposure to carbon monoxide (CO); which, however, has been least studied in Chinese population at regional scale. Methods We conducted a time-series analysis assessing mortality effects of CO in four cities located in the Pearl River Delta (PRD) of China, a labor and resource intensive city cluster, using daily mortality and air pollution data (2006–2008). Generalized linear model with Poisson regression incorporating natural spline functions was used to analyze the effects of exposure to ambient CO on total (nonaccidental), cardiovascular and respiratory mortality. Effect estimates were determined first for individual cities, and then focused for the mega-city Guangzhou. Results We found exposure to CO was significantly associated with increased mortality in the mega-city of Guangzhou and medium-sized industrial city of Foshan. In specific, per 0.5 ppm increase in the average lag 1–2 (previous two days) exposure to CO was associated with 3.04% [95% confidence interval (CI), 2.18–3.90%], 3.62% (95% CI, 2.20–5.06%) and 3.72% (95% CI, 1.71–5.76%) increases in excessive risks (ERs) of total, cardiovascular and respiratory mortality, in Guangzhou. Further, we observed significant heterogeneity in mortality effects of exposure to CO among the four PRD cities of different development levels: stronger mortality effects were found in larger, more developed and industrialized cities. Conclusions Exposure to ambient CO is associated with significant increases in total, cardiovascular and respiratory mortality in Chinese population. CO is an established biologic toxicant, whereas the effects and possible mechanisms of exposure to ambient level of CO and co-pollutants warrant further investigation.

The 2008 Summer Olympic Games will be held in Beijing; however, summer is the season in which Beijing is marked by frequent high-O(3) episodes. Observation analysis reveals that the urban plume is transported by a southerly wind and undergoes chemical reaction during propagation, resulting in the common occurrence of high O(3) concentrations in the urban downwind area; this is the typical scenario of the formation of high summertime O(3) levels over the Beijing area. The typical high-O(3) episode is well reproduced by the 3-dimensional air-quality model CMAQ-MADRID (Community Multi-scale Air-Quality Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution). Radical cycle analysis reveals that the Beijing urban area was in a VOC-limited regime for O(3) formation, while the urban downwind area changed gradually to a NO(x)-limited condition. The urban downwind area, Dingling, is readily affected by intrusion of the urban plume. Detailed process analysis indicated that although the O(3) peaks reached the same level on 26 and 27 June 2000, the dominant process contributing to the O(3) increase was different on each day. On 26 June, the major contributor to the O(3) peak at Dingling was the arrival of high O(3) levels with propagation of the urban plume; in contrast, on 27 June O(3) precursors were transported rapidly to the urban downwind area by strong transportation processes that occurred earlier than those on the previous day, resulting in O(3) production by local photochemistry becoming the major contributor to the high-O(3) episode.

Beijing is a rapidly developing city with severe and unique air pollution problems. Organic matter is the most abundant fraction in fine particles in Beijing, occupying 30-50% of the total mass, indicating its key role in air pollution control. However, detailed chemical characterization of particulate organic matter in Beijing has never been reported. In this study, fine particles in the urban atmosphere in Beijing were investigated for its organic components by GC/MS technique. Over 100 individual organic compounds were identified and quantified in 25 PM2.5 samples from the summer, autumn and winter of 2002-2003. Alkanes, fatty acids, dicarboxylic acids, polycyclic aromatic hydrocarbons and some important tracer compounds (hopanes, levoglucosan and steroids) were the major constituents with the sum of their concentrations of 502, 1471 and 1403 ng m(-3) in summer, autumn and winter, respectively. Different organic compounds presented apparently different seasonal characteristics, reflecting their different dominant emission sources, such as coal combustion, biomass burning and cooking emission. The abundance and origin of these organic compounds are discussed to reveal seasonal air pollution characteristics of Beijing.

In this study, the hourly variations of the mass concentrations of PM10, SO2, NO(x) and O3 at three sampling sites were observed in Beijing during dust storm occurrence period in April 2000. The PM2.5 samples were simultaneously collected. By comparing the hourly variations of the pollutant concentrations before, during and after dust storm event and haze pollution episode, the variation characteristics of the mass concentrations of PM10, SO2, NO(x) and O3 during dust storm events were presented. The results show that the mass concentration of PM10 reached 1500 microg m(-3) during dust storm events on April 6 and 25, 2000, which was 5-10 times that of the non-dust weather conditions, and this period of high mass concentration of PM10 lasted for about 14 h, and then the concentration level prior to the dust event was recovered in 6-h time period. Due to the strong wind, the concentrations of SO2, NO(x), NO2 and O3 during dust storm period were maintained at low levels, which was significantly different from those on non-dust storm and haze pollution conditions. A lot of coarse particles as well as a very large amount of fine particles were contained in the atmospheric particulates during dust storm period, and the concentration level of PM2.5 was comparable to that during haze pollution episode. During the dust storm period, the PM2.5 concentration was approximately 230 microg m(-3), accounting for 30% of the total PM10 mass concentration, was four times that of non-dust weather conditions, and the crustal elements constituted about 66.4% of the chemical composition of PM2.5 while sulfate and nitrate contributed much less, which was quite different from the chemical composition of PM2.5 primarily constituted by sulfate, nitrate and organics on haze pollution day.