Aerosols In Beijing Research Articles

Dust Monitoring and Three-Dimensional Transport Characteristics of Dust Aerosol in Beijing, Tianjin, and Hebei

Dust Monitoring and Three-Dimensional Transport Characteristics of Dust Aerosol in Beijing, Tianjin, and Hebei

Seasonal variation and size distribution of aromatic acids in urban aerosols in Beijing, China

Aromatic acids are an integral component of organic acids in the atmosphere, contributing to the formation of climate-altering brown carbon (BrC). To better understand the sources and formation processes of aromatic acids, we collected size-segregated particulate matter samples in urban Beijing from April 2017 to January 2018, which were analyzed using solvent-extraction followed by gas chromatography/mass spectrometry. Phthalic acid (o-PhA) had the greatest average annual concentration, followed by terephthalic acid (p-PhA), 4-hydroxybenzoic acid (4-OHBA), dehydroabietic acid (DA), syringic acid (SA), 3-hydroxybenzoic acid (3-OHBA), isophthalic acid (m-PhA), and vanillic acid (VA). We identified distinct seasonal variations in aromatic acids, with o-PhA peaking in summer due to photochemical activity, while p-PhA and 4-OHBA elevated in autumn and summer, respectively, influenced by open waste and biomass burning. Wintertime variations in all aromatic acids were driven by complex meteorology and increased anthropogenic emissions, including rural biomass burning for cooking and heating. Particle size distribution of aromatic acids was affected by seasonal agricultural activities and dust storms, multiple emission sources, and formation mechanisms. The o-PhA has predominantly bimodal distribution, with diverse sources and complex formation mechanisms including gas- and aqueous-phase chemistry. The applicability of o-PhA as a tracer for specific secondary organic aerosols has been questioned due to its potential primary sources. The 3-OHBA, 4-OHBA, VA, SA, and DA exhibited bimodal or trimodal patterns during haze and non-haze periods across different particle size ranges. The seasonal variation in VA/SA and VA/4-OHBA ratios demonstrated the complexity of biomass burning types, influenced by season, particle size, meteorological conditions, and combustion sources.

Observation and Classification of Low-Altitude Haze Aerosols Using Fluorescence–Raman–Mie Polarization Lidar in Beijing during Spring 2024

Haze aerosols have a profound impact on air quality and pose serious health risks to the public. Due to its geographical location, Beijing experienced haze events in the spring of 2024. Lidar is an active remote sensing technology with a high spatiotemporal resolution and the ability to classify aerosols, and it is essential for effective haze monitoring. This study utilizes fluorescence–Raman–Mie polarization lidar with an emission wavelength of 355 nm, employing the δp-Gf method based on the particle depolarization ratio at 355 nm (δp355) and the fluorescence capacity (Gf), and combines meteorological data and backward-trajectory analysis to observe and classify low-altitude haze aerosols in Beijing during the spring of 2024. Notably, a mining dust event with strong fluorescence backscatter was detected. The haze aerosols were categorized into three types: pollution aerosols, desert dust, and mining dust. Their optical properties were summarized and compared. Desert dust showed a particle depolarization ratio range of 0.23–0.39 and a fluorescence capacity range from 0.18 × 10−4 to 0.63 × 10−4. Pollution aerosols had a larger fluorescence capacity but a lower depolarization ratio compared to desert dust, with a fluorescence capacity ranging from 0.55 × 10−4 to 1.10 × 10−4 and a depolarization ratio ranging from 0.10 to 0.17. Mining dust shared similar depolarization characteristics with desert dust but had a larger fluorescence capacity, ranging from 0.71 × 10−4 to 1.23 × 10−4, with a depolarization ratio range of 0.30–0.39. This study validates the effectiveness of the δp355-Gf method in classifying low-altitude haze aerosols in Beijing. Additionally, it offers a new perspective for more detailed dust classification using lidar. Furthermore, utilizing the δp355-Gf classification method and the δp355-Gf distributions of three typical aerosol samples, we developed a set of equations for the analysis of mixed aerosols. This method facilitates the separation and fraction analysis of aerosol components under various mixing scenarios. It enables the characterization of variations in the three types of haze aerosols at different altitudes and times, offering valuable insights into the interactions between desert dust, mining dust, and pollution aerosols in Beijing.

Unexpected moderate contribution of intermediate volatility organic compounds from gasoline vehicle emission to secondary organic aerosol formation in summer of Beijing

Intermediate volatility organic compounds (IVOCs) have been proposed to be important contributors to secondary organic aerosol (SOA) formation. In this study, we characterized ambient IVOCs in Beijing and performed a comprehensive closure study of ambient SOA production using top-down (photochemical-age-based parameterization method to apportion OA) and bottom-up (estimation of SOA from detailed speciation of IVOCs and VOCs) approaches. The IVOCs in Beijing were more oxidized and had a high abundance (62.5 ± 45.2 μg m−3), significantly higher than in the US. Unlike the US, the IVOCs in Beijing shows a hybrid characteristic of gasoline and vehicle exhausts and are influenced by complicated sources. A ∼ 80% SOA mass closure could be reached between the top-down and bottom-up methods, in which IVOCs was the dominant contributor (75.5%). Furthermore, we established a parametric method (SOA/CO vs. photochemical age) to estimate the contribution of vehicular SOA to ambient OA. Unexpectedly, the contributions of gasoline vehicles to ambient OA are only 7.3% for POA and 13.0% for SOA. Our results imply that IVOCs from other sources, e.g., diesel vehicles and cooking emissions, may be important precursors to secondary organic aerosol in Beijing. In addition, this study highlights the importance of comprehensively performing the molecular identification of IVOCs from different emissions in China. Plain language summarySecondary organic aerosol (SOA), formed by multigenerational oxidation of gas-phase compounds, represents a significant fraction of organic aerosol. However, current models often underestimate the measured SOA mass. One of the ubiquitous reasons is the missing measurement of the intermediate volatility organic compounds (IVOCs). Here we quantified and qualified the IVOCs in Beijing and performed a comprehensive SOA study using bottom-up and top-down methods. Besides, we estimate the SOA formation by gasoline vehicles. Unexpectedly, the contributions of gasoline vehicles to ambient OA are only 7.3% for POA and 13.0% for SOA, highlighting the importance of studying IVOCs from other sources, e.g., diesel exhausts and cooking emissions.

The characterization and quantification of viable and dead airborne biological particles using flow cytometry and double fluorescent staining

Primary biological aerosol particles (PBAPs) are important air pollutants because they are ubiquitous in the atmosphere; influence human health, air quality, atmospheric chemistry and physics; and play important roles in regulating atmospheric processes. In investigations of the effects of PBAPs in ambient environments, it is necessary to distinguish them from other particles. In this study, flow cytometry (FCM) was utilized in combination with permeant (SYBR Green dyes) and impermeant (Propidium Iodide, PI) nucleic acid fluorescent stains, to characterize and quantify the viable and dead airborne PBAPs in ambient aerosol in Beijing, China. The number concentrations of viable and dead PBAPs showed a consistent trend and correlated well with one another (R2 = 0.72, p < 0.01). However, no relationship was found between the number concentration of PBAPs and non-biological particles. The mean number concentrations of total particulate matter, dead PBAPs and viable PBAPs were 5.78 × 106 m−3, 1.11 × 106 m−3 and 7.09 × 105 m−3, respectively. The median PBAPs number concentrations (the sum of dead and viable) exhibited a seasonal cycle, i.e., highest in summer and autumn, lowest during winter and spring. Despite a lower median PBAPs number concentration during winter compared with other seasons, the viability peaked during winter, coinciding with the winter flu season. Stable synoptic conditions, polluted southwesterly air mass and long-range transported dust from the northwest desert region all contributed to the occurrence of explosive fluorescent PBAP episodes in Beijing, China.

Highly oxidized organic aerosols in Beijing: Possible contribution of aqueous-phase chemistry

The oxidation state of organic aerosol (OA) substantially influences the optical and hygroscopic properties, toxicity, and atmospheric lifetime of OA. Comprehensive field measurements have been carried out in Beijing to understand the possible mechanism relevant to the evolution of OA oxidation state in the ambient atmosphere. We found that OA was more oxidized in pollution events in autumn than in winter, evidenced by the higher ratios of OA/OC (2.50 ± 0.69) and f44/f43 (1.90 ± 0.54) in autumn than the corresponding values (1.80 ± 0.39 and 1.64 ± 0.45) in winter. Plumes with highly oxidized OA were identified to be transported from the southern regions of Beijing and strongly correlated with the high concentration of aerosol water content (AWC), which was dominantly affected by the high concentration of ammonium nitrate and the high RH. This suggests that aqueous-phase chemistry, as regulated by ammonium nitrate and RH, plays a crucial role in the formation of highly oxidized OA in Beijing.

Simultaneous Measurements of Carbonaceous Aerosol in Three Major Cities in the Beijing-Tianjin-Hebei Region, China

Simultaneous observations of carbonaceous aerosols in multiple cities are of great significance for a comprehensive understanding of the level of carbonaceous aerosol pollution in the Beijing-Tianjin-Hebei (BTH) region. In this study, PM2.5 samples were collected simultaneously in Beijing (BJ), Tianjin (TJ), and Shijiazhuang (SJZ) during the 2017–2018 heating season, and the contents of organic carbon (OC) and elemental carbon (EC) in the samples were measured. The mean mass concentrations were 10.15‒46.23 µg m–3 for OC, and 2.13‒10.42 µg m–3 for EC in three cities. SJZ had more serious carbonaceous aerosols pollution compared with BJ and TJ. The OC and EC levels in three cities, especially in Beijing, were significantly lower than those reported in previous studies, implying the effectivity of strict air pollution control measures in 2017. Based on the OC/EC minimum ratio method, the mass concentration of secondary organic carbon (SOC) was estimated, and SOC pollution in BJ was relatively light. Analysis of eight carbonaceous components showed that the gasoline vehicle exhaust sources made high contributions to the levels of carbonaceous aerosols in all three cities. Compared with SJZ, the carbonaceous aerosols in BJ and TJ were more affected by road dust pollution. Analysis of backward trajectory indicated that the carbonaceous aerosols in the three cities were affected by pollution transport from the BTH region and surrounding areas, in addition to local sources. In contrast to the other two cities, OC and EC in SJZ were greatly affected by short-distance air mass transport from Hebei Province.

Characteristics, evolution, and potential source regions of submicron aerosol in Beijing, China

Atmospheric fine particulate pollution has been a dramatically environmental concern in all seasons in the megacity Beijing in recent years. A long-term real-time monitoring campaign of non-refractory submicron aerosol (NR-PM1) at a southeastern urban site in Beijing from July 13, 2017 to May 26, 2018 using an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was carried out to investigate the characteristics and evolution processes of NR-PM1 and its potential source effects. The annual average concentration of NR-PM1 during the entire study period was 40.8 μg/m3, lower than that of NR-PM1 from July 2011 to June 2012, and its seasonal variation presented the order of autumn and spring > winter > summer. The average concentration of organic species Org in the entire study was 15.1 μg/m3 and accounted for 37% of NR-PM1, being consistently a significant component of NR-PM1 in the four seasons. The average concentrations of SO42− and NO3− were 8.6 and 11.1 μg/m3, respectively, accounting for 21% and 27% of NR-PM1, and NO3− and its contribution to NR-PM1 exceeded those of SO42−, suggesting that secondary nitrate became a more dramatic pollutant. Note that SO42− in summer accounted for 27% of NR-PM1, higher than those in the other seasons, indicating that secondary sulfate formation was greatly important in summer, however, NO3− in summer accounted for 22% of NR-PM1, lower than those in the other seasons, more likely due to relatively high temperature in summer being favorable for dissociation of nitrate. NH4+ and Cl− species presented lower mass concentrations and mass fractions, and the seasonal variation of NH4+ was similar to NO3−, yet Cl− presented a typical seasonal change related to intense fossil fuel combustion during the heating period in winter and biomass burning in autumn with an order of winter > autumn > spring > summer. All aerosol species exhibited different diurnal cycles, of which Org presented a bimodal mode, SO42− and Cl− showed a flatter diurnal pattern, however, NO3− and NH4+ displayed more similar single-peak patterns. The conversion of SO2 to SO42− presented an obvious seasonal variation with summer > autumn > spring > winter driven by different factors. The conversion of NO2 to NO3− also showed a significant seasonal change characterized by autumn > summer and spring > winter controlled by different factors. Relative humidity, temperature and wind speed during the study period were significant meteorological elements influencing NR-PM1 and its species, and heavy haze pollution episodes largely occurred under high relative humidity and low wind speed. High potential source regions influencing NR-PM1 pollution in Beijing in all seasons presented dramatically distributions related to wind directions.

Increase of High Molecular Weight Organosulfate With Intensifying Urban Air Pollution in the Megacity Beijing

AbstractOrganosulfates (OSs), a key component of secondary organic aerosols (SOA), account for up to one third of organic matter in the atmosphere. However, high molecular weight (HMW, 500–800 Da) OSs in ambient aerosols are poorly characterized at a molecular level, due to experimental difficulties. With Fourier transform‐ion cyclotron resonance mass spectrometry (FT‐ICRMS), we are able to identify more than 8,000 OSs in wintertime aerosols in Beijing. We found that both the number and signal magnitudes of HMW OSs with low H/C and O/C ratios and degrees of unsaturation were greatly enhanced during hazy days, indicating that most HMW OSs were freshly formed during stagnant air pollution episodes. They are most likely to be the oxidation products of semivolatility to low‐volatility precursors (e.g., polycyclic aromatic hydrocarbons and fatty acids) and have showed a strong influence of anthropogenic emissions. The molecular corridor analysis suggests that the high abundance of HMW aromatic‐like and aliphatic OSs considerably decreases the volatility of organic aerosols in the urban atmosphere.

Pollution sources of atmospheric fine particles and secondary aerosol characteristics in Beijing

To investigate the secondary formation and pollution sources of atmospheric particles in urban Beijing, PM2.5 and its chemical components were collected and determined by URG-9000D ambient ion monitor (AIM) from March 2016 to January 2017. Among water-soluble ions (WSIs), NO3−, SO42- and NH4+ (SNA) had the largest proportion (77.8%) with the total concentration of 23.8 μg/m3. Moreover, as fine particle pollution worsened, the NO3−, SO42- and NH4+ concentrations increased basically, which revealed that secondary aerosols were the main cause of particle pollution in Beijing. Furthermore, the particle neutralization ratio (1.1), the ammonia to sulfate molar ratio (3.4) and the nitrate to sulfate molar ratio (2.2) showed that secondary aerosols are under ammonium-rich conditions with the main chemical forms of NH4NO3 and (NH4)2SO4, and vehicle emission could be the main anthropogenic source of secondary aerosols in Beijing. Source analysis further indicated that secondary aerosols, solid fuel combustion, dust and marine aerosol were the principal pollution sources of PM2.5, accounting for about 46.1%, 22.4% and 13.0%, respectively, and Inner Mongolia and Hebei Provinces could be considered as the main potential sources of PM2.5 in urban Beijing. In addition, secondary formation process was closely related with gaseous precursor emission amounts (SO2, NO2, NH3 and HONO), atmospheric ozone concentration (O3), meteorological conditions (temperature and relative humidity) and particle components. Sensitive analysis of the thermodynamic equilibrium model (ISORROPIA II) revealed that controlling total nitrate (TN) is the effective measure to mitigate fine particle pollution in Beijing.

Fossil and Non-fossil Fuel Sources of Organic and Elemental Carbonaceous Aerosol in Beijing, Shanghai, and Guangzhou: Seasonal Carbon Source Variation

ABSTRACT We measured the radiocarbon isotope signals in various fractions of carbonaceous aerosols sampled across four seasons (Oct 2013–Jul 2014) in three megacities of China, viz., Beijing, Shanghai, and Guangzhou. The contributions of fossil fuel (FF) and non-fossil fuel (NF) to the carbonaceous aerosol were estimated based on the radiocarbon content in the organic carbon (OC), water-soluble organic carbon (WSOC), water-insoluble organic carbon (WIOC), and elemental carbon (EC). Although NF generated the primary share (> 55%) during autumn in all of the cities, the seasonal contributions of the sources differed by location during the rest of the year. During winter, FF emissions constituted the majority of the carbonaceous pollution (64%) in Beijing, probably as a result of increased coal combustion for heating. On average, the EC, WSOC, and WIOC generated by FF composed ~10%, 35%, and 19% of the total carbon (TC). Overall, NF was identified as the largest source of carbonaceous aerosol in Guangzhou (63%), whereas FF was the largest source, contributing slightly more than NF, in Shanghai (54%). During spring and summer, FF played a greater role than NF in Beijing (~55%) and Guangzhou (~63%); additionally, based on our limited number of samples, it contributed 71% in Shanghai during the latter season, with a significant portion due to fuel combustion (i.e., industrial, vehicular, fishing-boat, and large-vessel emissions).

Multi-method determination of the below-cloud wet scavenging coefficients of aerosols in Beijing, China

Abstract. Wet scavenging is one of the most efficient processes for removing aerosols from the atmosphere. This process is not well constrained in chemical transport models (CTMs) due to a paucity of localized parameterization regarding the below-cloud wet scavenging coefficient (BWSC). Here we conducted field measurements of the BWSC during the Atmospheric Pollution and Human Health Beijing (APHH-Beijing) campaign of 2016. Notably, the observed BWSC values based on the updated aerosol mass balance agree well with another estimation technique, and they fall in a range of 10−5 s−1. The measurement in this winter campaign, combined with that in summer of 2014, supported an exponential power distribution of BWSCs with rainfall intensity. The observed parameters were also compared with both the theoretical calculations and modeling results. We found that the theoretical estimations can effectively characterize the observed BWSCs of aerosols with sizes smaller than 0.2 µm and larger than 2.5 µm. However, the theoretical estimations were an order of magnitude lower than observed BWSCs within 0.2–2.5 µm, a domain size range of urban aerosols. Such an underestimation of BWSC through a theoretical method has been confirmed not only in APHH-Beijing campaign but also in all the rainfall events in summer of 2014. Since the model calculations usually originated from the theoretical estimations with simplified scheme, the significantly lower BWSC could well explain the underprediction of wet depositions in polluted regions as reported by the Model Inter-Comparison Study for Asia (MICS-Asia) and the global assessment of the Task Force on Hemispheric Transport of Atmospheric Pollutants (TF-HTAP). The findings highlighted that the wet deposition module in the CTMs requires improvement based on field measurement estimation to construct a more reasonable simulation scheme for BWSC, especially in polluted regions.

The impact of aerosols on photolysis frequencies and ozone production in Beijing during the 4-year period 2012–2015

Abstract. During the period 2012–2015, photolysis frequencies were measured at the Peking University site (PKUERS), a site representative of Beijing. We present a study of the effects of aerosols on two key photolysis frequencies, j(O1D) and j(NO2). Both j(O1D) and j(NO2) display significant dependence on aerosol optical depth (AOD; 380 nm) with a non-linear negative correlation. With the increase in AOD, the slopes of photolysis frequencies vs. AOD decrease, which indicates that the capacity of aerosols to reduce the actinic flux decreases with AOD. The absolute values of slopes are equal to 4.2–6.9×10-6 and 3.4×10-3 s−1 per AOD unit for j(O1D) and j(NO2) respectively at a solar zenith angle (SZA) of 60∘ and AOD smaller than 0.7, both of which are larger than those observed in a similar, previous study in the Mediterranean. This indicates that the aerosols in Beijing have a stronger extinction effect on actinic flux than absorptive dust aerosols in the Mediterranean. Since the photolysis frequencies strongly depended on the AOD and the SZA, we established a parametric equation to quantitatively evaluate the effect of aerosols on photolysis frequencies in Beijing. According to the parametric equation, aerosols lead to a decrease in seasonal mean j(NO2) by 24 % and 30 % for summer and winter, respectively, and a corresponding decrease in seasonal mean j(O1D) by 27 % and 33 %, respectively, compared to an aerosol-free atmosphere (AOD =0). Based on an observation campaign in August 2012, we used a photochemical box model to simulate the ozone production rate (P(O3)). The simulation results shows that the monthly mean daytime net ozone production rate is reduced by up to 25 % due to the light extinction of aerosols. Through further in-depth analysis, it was found that particulate matter concentrations maintain a high level under the condition of high concentrations of ozone precursors (volatile organic compounds, VOCs, and NOx), which inhibits the production of ozone to a large extent. This phenomenon implies a negative feedback mechanism in the atmospheric environment of Beijing.

Molecular Characterization and Seasonal Variation in Primary and Secondary Organic Aerosols in Beijing, China

AbstractBiomass burning (BB) aerosols, primary biological aerosol particles, and secondary organic aerosols, are critical components of particulate matter in the atmosphere. In this study, saccharides, lignin/resin acids, biogenic secondary organic aerosols tracers, aromatic acids, and hydroxyacids/polyacids were measured in total suspended particles collected from April 2012 to March 2013 at an urban site in Beijing using gas chromatography/mass spectrometry. The concentration of levoglucosan was elevated during 18–20 June. The high ratio of levoglucosan to mannosan and low ratio of galactosan to mannosan in June demonstrated the influence of wheat straw combustion in the North China Plain via long‐rang transport. Sucrose, glucose, and fructose were more abundant in April, the spring bloom season. The maximum trehalose content (298 ng/m3) occurred during a dust storm (27–29 April) with the highest stable carbon isotope ratio (δ13C, −21.2‰) of total carbon. Fungal spore tracers (arabitol and mannitol) peaked in summer. The largest concentrations of the oxidization products of isoprene and α/β‐pinene also occurred in summer. However, the β‐caryophyllene tracer was much more abundant on long‐lasting haze days in winter and was positively related to levoglucosan. The contributions of biogenic primary sources (plant debris, fungal spores, and BB) to organic carbon were estimated to be in range of 2.64–35.2% (11.8%), with BB being the predominant source. Biogenic secondary sources (isoprene, α‐pinene, and β‐caryophyllene) and anthropogenic secondary source (naphthalene) accounted for 0.23–10.9% (3.36%) of organic carbon with large contributions in summer and winter, respectively.

Primary biogenic and anthropogenic sources of organic aerosols in Beijing, China: Insights from saccharides and n-alkanes

Sugars and n-alkanes are important organic constituents of atmospheric fine particulate matter (PM2.5). For better understanding their sources and seasonal variations in urban atmosphere, sugar compounds (anhydrosugars, sugars and sugar alcohols) and homologue n-alkanes (C18–C37) were studied in PM2.5 samples collected from September 2013 to July 2014 in Beijing, China. In general, all measured compounds showed the lowest levels in summer. Higher concentrations of sugar compounds and n-alkanes were observed in winter, probably due to elevated combustion emissions (e.g., coal, biofuel and agricultural residue burning) and stable meteorological conditions during heating season. Levoglucosan was the major sugar species in all seasons particularly in autumn and winter, highlighting the significant contribution of biomass burning to fine organic aerosols throughout the whole year especially in cold seasons. Plant waxes contributed to n-alkanes the most in late spring (54.5%) and the least in winter (11.6%); while fossil fuel combustion had the largest contribution in winter (385 ng m−3). The weak odd-carbon predominance of n-alkanes in wintertime aerosols also suggests fossil fuel combustion as the important source of organic aerosols in the heating season. Soil resuspension, fossil fuel combustion and biomass burning, and secondary sources are the main sources of OC in PM2.5 at Beijing. The seasonal variation in source contributions indicates that meteorological condition is a key factor in controlling PM2.5 levels. Furthermore, dust storms in spring can strongly enhance the atmospheric level of fine organic matter in Beijing.

Continuous monitoring, compositions analysis and the implication of regional transport for submicron and fine aerosols in Beijing, China

A comprehensive observation was conducted to reveal the characteristics of submicron and fine aerosols and their chemical components in Beijing in autumn. The potential source contribution function (PSCF) and concentration weighted trajectory (CWT) model, Weather Research & Forecasting (WRF) and Comprehensive Air Quality Model with Extension (CAMx) were applied to identify the impacts of emissions from surrounding areas on PM2.5 concentrations in Beijing for different study episodes. These results showed that the monthly average concentration of non-refractory submicron aerosols (NR-PM1) was 60.20 ± 53.48 μg/m3, with organics being the major fraction (42.33%), followed by NO3− (22.87%), SO42− (18.70%), NH4+ (12.24%) and Cl− (3.86%). The PSCF and CWT analysis indicated common high source regions was located in the western Shandong, northern Henan and southern Hebei, and the distribution of the source areas usually varied with species during different episodes. The regional source apportionment results revealed that 52.36% of surface PM2.5 in Beijing was contributed by surrounding sources in terms of monthly mean and the outside contribution increased to 64.56% during the haze days, indicating the strong influence of regional transport on Beijing haze pollution. Note that the PM2.5 inflows for Beijing mainly came from Baoding and Langfang, and outflows towards Chengde and Zhangjiakou, identifying two key transport pathways: the southwest-northeast pathway and the southeast-northwest pathway. The PM2.5 inflow fluxes from surroundings were much higher than outflows from Beijing, leading to the peaking PM2.5 pollution, with the highest concentrations occurring from 00:00 to 11:00 LT, 14 October 2016. Based on the net PM2.5 fluxes and their vertical distributions, we discovered the PM2.5 transport mainly occurred at 400–800 m during the entire episode, while at 600–1000 m for a heavy pollution episode, both followed by the southwest-northeast pathway. However, the PM2.5 fluxes were far lower for a clean episode, and followed by the northwest-southeast pathway.

The organic molecular composition, diurnal variation, and stable carbon isotope ratios of PM2.5 in Beijing during the 2014 APEC summit

Organic tracers are useful for investigating the sources of carbonaceous aerosols but there are still no adequate studies in China. To obtain insights into the diurnal variations, properties, and the influence of regional emission controls on carbonaceous aerosols in Beijing, day-/nighttime PM2.5 samples were collected before (Oct. 15th – Nov. 2nd) and during (Nov. 3rd – Nov. 12th) the 2014 Asia-Pacific Economic Cooperation (APEC) summit. Eleven organic compound classes were analysed using gas chromatography/mass spectrometry (GC/MS). In addition, the stable carbon isotope ratios (δ13CTC) of total carbon (TC) were detected using an elemental analyser/isotope ratio mass spectrometry (EA/irMS). Most of the organic compounds were more abundant during the night than in the daytime, and their concentrations generally decreased during the APEC. These features were associated with the strict regional emission controls and meteorological conditions. The day/night variations of δ13CTC were smaller during the APEC than those before the APEC the summit, suggesting that regionally transported aerosols are potentially played an important role in the loading of organic aerosols in Beijing before the APEC summit. The source apportionment based on the organic tracers suggested that biomass burning, plastic and microbial emissions, and fossil fuel combustion were important sources of organic aerosols in Beijing. Furthermore, a similar contribution of biomass burning to OC before and during the APEC suggests biomass burning was a persistent contributor to PM2.5 in Beijing and its surroundings.

High Contribution of Nonfossil Sources to Submicrometer Organic Aerosols in Beijing, China.

Source apportionment of organic carbon (OC) and elemental carbon (EC) from PM1 (particulate matter with a diameter equal to or smaller than 1 μm) in Beijing, China was carried out using radiocarbon (14C) measurement. Despite a dominant fossil-fuel contribution to EC due to large emissions from traffic and coal combustion, nonfossil sources are dominant contributors of OC in Beijing throughout the year except during the winter. Primary emission was the most important contributor to fossil-fuel derived OC for all seasons. A clear seasonal trend was found for biomass-burning contribution to OC with the highest in autumn and spring, followed by winter and summer. 14C results were also integrated with those from positive matrix factorization (PMF) of organic aerosols from aerosol mass spectrometer (AMS) measurements during winter and spring. The results suggest that the fossil-derived primary OC was dominated by coal combustion emissions whereas secondary OC was mostly from fossil-fuel emissions. Taken together with previous 14C studies in Asia, Europe and USA, a ubiquity and dominance of nonfossil contribution to OC aerosols is identified not only in rural/background/remote regions but also in urban regions, which may be explained by cooking contributions, regional transportation or local emissions of seasonal-dependent biomass burning emission. In addition, biogenic and biomass burning derived SOA may be further enhanced by unresolved atmospheric processes.

Characterization of organic aerosol in Beijing by laser desorption ionization coupled with Fourier Transform Ion Cyclotron Resonance Mass spectrometry

In order to resolve the organic compositions in the atmospheric aerosol which is significant for understanding the formation mechanism of particulate matter and their harm for human health, a direct laser desorption ionization (LDI) coupled with Fourier Transform Resonance Mass (FT-ICR MS) was utilized for characterizing the aerosol particles collected in Beijing during winter. A lot of organic compounds can be detected by direct laser desorption ionization of the aerosol particular with different size collected on aluminum foil without complicated sample pretreatment process. In addition, semi quantification of the organic compounds can be achieved with solvent extraction procedure. It was found that the ubiquitous polycyclic aromatic hydrocarbons (PAHs) contaminants in the aerosol could serve as matrix, which helps the detection of many kinds of compounds including highly saturated amphiphilic long alkyl chain compounds (carbon number>16), like aliphatic amines in positive ion mode and organosulfates in negative ion mode. Based on the accurate mass measurement results, elemental compositions of over 1500 peaks in the mass spectrum were derived, and we categorized them into five groups according to their elemental compositions in order to provide helpful information for tracing the pollution source. It is demonstrated that abundant information about the organic components in the atmospheric aerosol can be provided by direct LDI FT-ICR MS method, and these information will largely facilitate further studies on origin and formation process of the aerosol.

Seasonal Trends of Atmospheric PAHs in Five Asian Megacities and Source Detection Using Suitable Biomarkers

The most prevalent pollutant, polycyclic aromatic hydrocarbons (PAHs) is now plenteously distributed in the global atmosphere. We recently quantified 36 polycyclic aromatic hydrocarbons (PAHs) associated with aerosols (particulate matter: PM) in five Asian cities: Tokyo (Japan), Beijing (China), Kolkata (India), Hanoi (Vietnam), and Kuala Lumpur (Malaysia). Average atmospheric PAH concentrations (Σ12 PAHs-ng m^(–3)) increased in the order of Kuala Lumpur (2.99) ≈ Tokyo (3.95) ＜ Hanoi (7.99) ＜＜ Kolkata (63.5) ＜＜ Beijing (142.8). The most abundant PAHs in PM samples in these cities were chrysene, benz[a]anthracene, benzofluoranthenes, benzo[a]pyrene, and benzo[e]pyrene. We used the PAH compositions, especially the relative abundances of alkylated PAHs, and hopanes to determine vehicle exhaust-derived PAHs, and levoglucosan as a tracer for biomass burning, especially from wood combustion. Vehicle exhaust contributed to atmospheric PAHs in all cities, indicated by higher ratios of (C_(30)17α)/total PAHs and MPAHs/PAHs than coal and wood combustion products. Coal combustion contributed also in winter aerosols in Beijing, indicated by higher abundance of β isomers i.e., 17β21β (H)-C30hopane (C_(30)17β) and 17β21β (H)-C_(29)hopane (C_(29)17β) signifying mass use of coal for heating. The ratio of levoglucosan/PAHs was high in Kuala Lumpur and Hanoi, suggesting greater inputs of PAHs from biomass burning there.