Urban Site In Shanghai Research Articles

Chemical Characteristics and Source Apportionment of Organic Aerosols in Urban Shanghai During Cold Season Based on High Time-resolution Measurements of Organic Molecular Markers

Organic aerosols (OA) are closely related to the formation of both PM2.5 and O3 in the atmosphere. In this study, a thermal desorption aerosol GC/MS (TAG) online system was adopted to measure hourly concentrations of 94 total organic molecular markers in PM2.5 at an urban site in Shanghai from November 6th to December 31st, 2021. Combined with air mass cluster analysis and other online measurement data, the chemical characteristics of OA under the influence of different air masses, oxidant levels, and relative humidity (RH) levels were investigated. The results showed that OA was characterized by higher mass percentages of primary organic molecular markers (e.g., saturated fatty acids, unsaturated fatty acids, and alkanes) under the influence of local air masses. Further, high loadings of biomass burning tracers were observed in OA under the influence of long-range transported air masses. In contrast, OA impacted by marine air masses was laden with significantly higher fractions of secondary organic molecular markers, such as dicarboxylic acids and hydroxyl dicarboxylic acids, which were formed from a wide range of volatile organic precursors through photochemical and aqueous-phase processing. With the application of the positive matrix factorization (PMF) model, seven total primary source factors and five secondary source factors were resolved for PM2.5 and OA during the observation. Among them, secondary nitrate was the highest contributor to PM2.5 mass with a mass percentage of 25.2%, whereas vehicle emissions were the top contributor (24.0%) to OA mass. Primary source factors, including coal combustion, vehicle emission, and cooking emission as well as their corresponding secondary source factors (e.g., secondary nitrate, secondary organic aerosols 2, etc.) showed elevated contributions in PM2.5 and OA with the increase in PM2.5 masses, indicating that more stringent controls of local emission sources (e.g., coal combustion, vehicle emission, and cooking emission) are needed to further lower PM2.5 pollution and improve air quality in Shanghai.

Identifying the O3 chemical regime inferred from the weekly pattern of atmospheric O3, CO, NOx, and PM10: Five-year observations at a center urban site in Shanghai, China

Ozone pollution is still considered a severe environmental problem in China despite the fact that great efforts have been devoted to monitoring and alleviating its impact by the Chinese government including the establishment of numerous observational networks. One of the issues most relevant to the design of emission reduction policies is to distinguish the O3 chemical regime. Here a method of quantifying the fraction of the radical loss versus NOx chemistry was applied to identify the O3 chemical regime inferred from the weekly pattern of atmospheric O3, CO, NOx, and PM10, which were monitored by Ministry of Ecology and Environment of China (MEEC). During spring and autumn, O3 and the total odd oxygen (Ox, Ox = O3 + NO2) weekend afternoon concentrations are both higher than the weekday values during 2015–2019 except in 2016, while CO and NOx weekend morning concentrations were generally both smaller than weekday values except 2017. Results from the calculated values of fraction of the radical loss by NOx chemistry relative to total radical loss (Ln/Q) suggested a volatile organic compound (VOC)-limited regime at this site in the spring of 2015–2019, as expected from the decreasing trend in NOx concentration and essentially constant CO after 2017. With respect to autumn, a shift from a transition regime during 2015–2017 to a VOC-limited regime in 2018 was found, which rapidly took place to a NOx-limited regime in 2019. No significant differences were detected in the Ln/Q values under different assumptions on photolysis frequencies both in spring and autumn mostly from 2015 to 2019, giving the same conclusion of determining the O3 sensitivity regime. This study develops a new method in determining the O3 sensitivity regime in the typical season in China and provides insight into efficient O3 control strategies in different seasons.

Size‐Resolved Atmospheric Phosphorus in Shanghai: Seasonal Variations, Sources and Dry Deposition

AbstractAtmospheric deposition is an important source for the P biological cycle, especially for P‐limited ecosystems. In the present study, 48 hr size‐segregated aerosol samples were collected at an urban site in Shanghai for one year from May 2019 to June 2020. Total phosphorus (TP) presented a bimodal distribution in four seasons, which was mainly contributed by mineral dust in the coarse mode, and was related to anthropogenic and combustion emissions in the fine mode. Dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) presented a bimodal distribution in spring and summer, and a unimodal distribution dominated by a fine mode in autumn and winter. Size distributions and correlation analysis showed that DIP in the fine and coarse modes originated from the acid processing of SO42‐ and NO3−, respectively, while DOP was mainly from biomass burning emissions. Positive Matrix Factor analysis showed that phosphorus (P) in atmospheric aerosols in Shanghai was mainly contributed by four sources, including crustal sources, sea‐salt, industry emissions and fossil fuel combustion, and biomass burning. Industry emissions and fossil fuel combustion, as well as biomass burning were important sources of TP in all particle sizes (50%–65%). Biomass burning was the most important source of DOP (>50%). The total deposition flux of total dissolved phosphorus (TDP) calculated based on the size‐weighted deposition velocity model averaged 75.2 ± 17.4 μg/m2/d. Assuming that all of TDP is bioavailable, TDP deposition can create a primary production of 8.0 mg C/m2/d, which can support 1.3%–4.4% of the new production in the East China Sea.

Organosulfates in atmospheric aerosols in Shanghai, China: seasonal and interannual variability, origin, and formation mechanisms

Abstract. Organosulfates (OSs) are ubiquitous in the atmosphere and serve as important tracers for secondary organic aerosols (SOAs). Despite intense research over the years, the abundance, origin, and formation mechanisms of OSs in ambient aerosols, particularly in regions with severe anthropogenic pollution, are still not well understood. In this study, we collected filter samples of ambient fine particulate matter (PM2.5) over four seasons in both 2015–2016 and 2018–2019 at an urban site in Shanghai, China, and comprehensively characterized the OS species in these PM2.5 samples using an ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometer equipped with an electrospray ionization (ESI) source (UPLC-ESI-QToFMS). Overall, we find that while the concentration of organic aerosols (OAs) decreased by 29 % in 2018–2019 compared to that in 2015–2016, mainly as a result of the reduction of anthropogenic pollutant emissions in eastern China, the annually averaged concentrations of 35 quantified OSs were similar in both years (65.5 ± 77.5 ng m−3, 0.57 % ± 0.56 % of OA in 2015–2016 vs. 59.4 ± 79.7 ng m−3, 0.66 % ± 0.56 % of OA in 2018–2019), suggesting an increased contribution of SOAs to OAs in 2018–2019 compared to 2015–2016. Isoprene- and monoterpene-derived OSs were the two most abundant OS families, on average, accounting for 36.3 % and 31.0 % of the quantified OS concentrations, respectively, during both sampling years, suggesting an important contribution of biogenic emissions to the production of OSs and SOAs in Shanghai. The abundance of biogenic OSs, particularly those arising from isoprene, exhibited strong seasonality (peaked in summer) but no significant interannual variability. In contrast, the quantified anthropogenic OSs had little seasonal variability and declined in 2018–2019 compared with those in 2015–2016. The C2 and C3 OS species that have both biogenic and anthropogenic origins contributed, on average, 19.0 % of the quantified OSs, with C2H3O6S−, C3H5O5S−, and C3H5O6S− being the most abundant species, together accounting for 76 % of the C2 and C3 OS concentrations in 2015–2016 and 2018–2019. 2-Methyltetrol sulfate (2-MTS, C5H11O7S−) and monoterpene-derived C10H16NO7S− were the most abundant OSs and nitrooxy OSs in summer, on average, contributing 31 % and 5 % of the quantified OSs, respectively, during the summertime of the sampling years. The substantially larger concentration ratio of 2-MTS to 2-methylglyceric acid sulfate (2-MAS, C4H7O7S−) in summer (6.8–7.8) compared to the other seasons (0.31–0.78) implies that low-NOx oxidation pathways played a dominant role in isoprene-derived SOA formation in summer, while high-NOx reaction pathways were more important in other seasons. We further find that the production of OSs was largely controlled by the level of Ox (Ox= O3+ NO2), namely the photochemistry of OS precursors, particularly in summer, though sulfate concentration, aerosol acidity, and aerosol liquid water content (ALWC) that could affect the heterogeneous chemistry of reactive intermediates leading to OS formation also played a role. Our study provides valuable insights into the characteristics and mechanisms of OS formation in a typical Chinese megacity and implies that the mitigation of Ox pollution can effectively reduce the production of OSs and SOAs in eastern China.

Seasonal variation of aerosol compositions in Shanghai, China: Insights from particle aerosol mass spectrometer observations

The variations of non-refractory submicron aerosol (NR-PM1) were characterized using an high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and other online instruments measurements sampled at an urban site in Shanghai from 2016 to 2017. Spring (from 18 May to 4 June 2017), summer (from 23 August to 10 September 2017) and winter (from 28 November 2016 to 23 January 2017) seasons were chosen for detail investigating the seasonal variations in the aerosol chemical characteristics. The average PM1 (NR-PM1 + BC) mass concentration showed little difference in the three seasons in Shanghai. The average mass concentrations of total PM1 during spring, summer, and winter observations in Shanghai were 23.9 ± 20.7 μg/m3, 28.5 ± 17.6 μg/m3, and 31.9 ± 22.7 μg/m3, respectively. The seasonal difference on chemical compositions was more significant between them. Organic aerosol (OA) and sulfate were dominant contributor of PM1 in summer, whereas OA and nitrate primarily contribution to the increase of PM1 mass loading in spring and winter. As an abundant component in PM1 (accounting for 39%–49%), OA were resolved into two primary organic aerosol (POA) factors and two secondary aerosol (SOA) factors by using positive matrix factorization (PMF), of which OA was overwhelmingly dominated by the SOA (50–60%) across the three seasons in Shanghai. Correlation analysis with relative humidity and odd oxygen indicated that aqueous-phase processing and played an important role in more aged SOA formation in summer and winter. In spring, both aqueous-phase and photochemical processing contributed significantly to fresh SOA formation. Our results suggest the significant role of secondary particles in PM pollution in Shanghai and highlight the importance of control measures for reducing emissions of gaseous precursors, especially need to consider seasonal characteristics.

Impact of quarantine measures on chemical compositions of PM2.5 during the COVID-19 epidemic in Shanghai, China

The COVID-19 epidemic broke out in Wuhan, Hubei in December 2019 and in January 2020 and was later transmitted to the entire country. Quarantine measures during Chinese New Year effectively alleviated the spread of the epidemic, but they simultaneously resulted in a decline in anthropogenic emissions from industry, transportation, and import and export of goods. Herein, we present the major chemical composition of non-refractory PM2.5 (NR-PM2.5) and the concentrations of gaseous pollutants in an urban site in Shanghai before and during the quarantine period of the COVID-19 epidemic, which was Jan. 8―23 and Jan. 24―Feb. 8, respectively. The observed results show that the reduction in PM2.5 can be mainly attributed to decreasing concentrations of nitrate and primary aerosols. Nitrate accounted for 37% of NR-PM2.5 before the quarantine period when there was no emission reduction. During the quarantine period, the nitrate concentration decreased by approximately 60%, which is attributed to a reduction in the NOx concentration. Ammonium, as the main balancing cation, showed an approximately 45% simultaneous decrease in concentration. The concentrations of chloride and hydrocarbon-like organic aerosols from primary emissions also declined due to limited human activities. By contrast, sulphate and oxygenated organic aerosols showed a slight decrease in concentration, with their contributions increasing to 27% and 18%, respectively, during the quarantine period, which resulted in two pollution episodes with PM2.5 exceeding 100 μg/m3. This study provides a better understanding of the impact of quarantine measures on variations of the PM2.5 concentration and chemical compositions. Atmospheric oxidation capacities based on the oxidant (Ox = O3 + NO2) and oxidation ratios have been discussed for elucidating the source and formation of haze in an environment with lower anthropogenic emissions. With increasing contribution of secondary aerosols, lower NOx and nitrate concentrations did not completely avoid haze in Shanghai during the epidemic.

Simultaneous determination of nine atmospheric amines and six inorganic ions by non-suppressed ion chromatography using acetonitrile and 18-crown-6 as eluent additive

Atmospheric amines contribute to the nucleation and initial growth of new particles as well as secondary organic aerosol formation, influencing the radiative balance of the Earth's atmosphere. In this study, we develop an ion chromatography (IC) method for separating and quantifying the nine most abundant amines (methylaminium (MMAH+), dimethylaminium (DMAH+), trimethylaminium (TMAH+), ethylaminium (MEAH+), diethylaminium (DEAH+), propylaminium (MPAH+), butylaminium (MBAH+), ethanolaminium (MEOH+), and triethanolaminium (TEOH+)) from six common inorganic species in atmospheric aerosols. The retention times of the amines were altered by the addition of acetonitrile to the eluent because acetonitrile can reduce the adsorption of hydrophobic amines on the stationary phase. The developed method achieved the successful separation of DEAH+ and TMAH+ from inorganic cations, which often coelute with each other in established IC methods. The interference of K+ on the determination of MEAH+ was eliminated by the complexation of K+ with 18-crown-6, which prolonged the retention time of K+. Finally, 9 target amines and 6 common inorganic cations were separated, with a resolution Rs ≥ 1.2 for DEAH+ and MPAH+ and Rs > 1.5 for other species. The detection limits varied in the range of 0.34-1.48 ng for the 9 amines and 0.19-0.56 ng for the inorganic cations. The developed method was successfully applied for the determination of low molecular weight amines and inorganic cations in PM2.5 collected from an urban site in Shanghai and an isolated coast of Chongming Island. Eight amines were detected in the urban samples, in which MMAH+ and DMAH+ dominated. The average amine concentration in the urban aerosols was 76.3 ± 38.4 ng m−3, which is approximately 4-fold higher than those in the marine samples collected from the coast.

Sources apportionment and carcinogenic risk of polycyclic aromatic hydrocarbons in gas phase of urban Shanghai: Based on high volume solid phase extraction (Hi-volume SPE).

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants, posing potentially serious threats to human health. This study analyzed compositional characteristics, sources, and carcinogenic risks of PAHs in the atmospheric gas phase at an urban site in Shanghai, East China. Seventy-four gas phase samples were collected during the warm months of May-October 2018 using a high-volume solid phase extraction (Hi-volume SPE) technique. The total concentration of sixteen priority PAHs (ΣPAHs) was in the range of 5.54-182.05ngm-3 (average 34.47ngm-3) and the total of seven carcinogenic PAHs (ΣCPAHs) was in range of 0.03-1.49ngm-3 (average 0.48ngm-3), accounting for 1.47% of ΣPAHs and indicating low carcinogenic potential. Redundancy analyses indicated positive correlations between ΣPAHs and air quality, and ΣCPAHs and average high temperature, and a negative correlation between ΣPAHs and wind speed. Four possible sources, namely petroleum and petrogenic sources, traffic emissions, coal combustion, and mixed gasoline and coal combustion sources, were identified by positive matrix factorization (PMF), accounting for 62.84%, 19.31%, 10.15%, and 7.69% of ΣPAHs, respectively. The overall lifetime lung cancer risk (LLCR) through inhalation of PAHs was estimated to be at a low risk level of 1.61×10-5. The LLCR based on PMF apportionment decreased in the order of mixed gasoline and coal combustion sources (47.07%)>traffic emissions (35.10%)>petroleum and petrogenic sources (11.06%)>coal combustion (6.74%). This study demonstrates the effectiveness of Hi-volume SPE in collecting and analyzing atmospheric gas phase PAHs.

Observation Constrained Aromatic Emissions in Shanghai, China

AbstractAromatics in the atmosphere are a large contributor to ozone and secondary organic aerosol formation and have an adverse impact on human health. Observation‐based emissions are urgently needed for air quality management and decision making due to the large uncertainties in the emissions inventories. Atmospheric aromatics were continuously observed at one urban site in Shanghai of China in 2015, which were compared with the simulations of the Community Multiscale Air Quality (CMAQ) model. Large differences were found in the temporal variations between the model and measurements, corroborating with previous studies that the current bottom‐up emission inventories are highly biased. We corrected the aromatic emissions biases of the emission inventories using the observations with the CMAQ simulations, with the assumption that the response relationship of the emissions input and aromatic concentrations was reasonable on a monthly basis in CMAQ simulations, suggesting that the results are dependent on the model performance. The resulting aromatic emissions exhibited clear monthly variations, increasing from 5.5 ± 2.1 Gg month−1 in February to 17.4 ± 7.7 Gg month−1 in July, being different from the flat monthly pattern in the current bottom‐up emissions inventory. Toluene, xylenes, and ethylbenzene dominated aromatic emissions, accounting for ~74% on average but with considerable monthly variations, which was different from the nearly uniform value of 77% throughout the whole year in the emissions inventory. These highly temporally resolved and speciated in situ aromatics measurements provide observation‐based constraints on aromatic emissions, which cannot be obtained from satellite measurements. This study proposes a top‐down emission estimation method constrained by ambient measurements.

Size-fractionated water-soluble ions during autumn and winter: Insights into volatile ammonium formation mechanisms in Shanghai, a megacity of China

Abstract Size-fractionated aerosols were collected by a Micro-Orifice Uniform Deposit Impactor at an urban site in Shanghai during the autumn and winter of 2014. The results showed that the average concentration of PM1.8 increased from 49 μg m−3 in autumn to 74 μg m−3 in winter. By contrast, the relative contribution of the water-soluble inorganic species decreased from 40% in autumn to 31% in winter. This finding suggests that the increase of organic matter (OM) greatly contributed to the deterioration of particle pollution in winter. Compared to autumn, the concentration of sulfate decreased whereas the concentration of NH4Cl increased significantly and became an important constituent of the fine particles in winter. The formation of nitrate in autumn became significant at [NH4+]/[SO42−] > 2, indicating that H2SO4 was fully neutralized by NH3 to form (NH4)2SO4. Our results showed that the regression between [NO3−]/[SO42−] and [NH4+]/[SO42−] drawn an unrealistic nitrate formation mechanism when the particulate NH4Cl was abundant. Replacing [NO3−] with {[NO3−]+[Cl−]} in the regression between [NO3−]/[SO42−] and [NH4+]/[SO42−], it is established that (NH4)2SO4 is preferentially formed before the excess available NH3 can react with HNO3 and HCl to form NH4NO3 and NH4Cl during wintertime. The concentrations of particulate sulfate and nitrate were not positively correlated with the ambient relative humidity, indicating that heterogeneous reactions on wet particles were not the key to haze formation in Shanghai during winter. Our results suggest that more studies are needed to understand the complex haze formation mechanisms in China.

Evaluation of the Surface Urban Energy and Water Balance Scheme (SUEWS) at a Dense Urban Site in Shanghai: Sensitivity to Anthropogenic Heat and Irrigation

Abstract The Surface Urban Energy and Water Balance Scheme (SUEWS) is used to investigate the impact of anthropogenic heat flux QF and irrigation on surface energy balance partitioning in a central business district of Shanghai. Diurnal profiles of QF are carefully derived based on city-specific hourly electricity consumption data, hourly traffic data, and dynamic population density. The QF is estimated to be largest in summer (mean daily peak 236 W m−2). When QF is omitted, the SUEWS sensible heat flux QH reproduces the observed diurnal pattern generally well, but the magnitude is underestimated compared to observations for all seasons. When QF is included, the QH estimates are improved in spring, summer, and autumn but are poorer in winter, indicating winter QF is overestimated. Inclusion of QF has little influence on the simulated latent heat flux QE but improves the storage heat flux estimates except in winter. Irrigation, both amount and frequency, has a large impact on QE. When irrigation is not considered, the simulated QE is underestimated for all seasons. The mean summer daytime QE is largely overestimated compared to observations under continuous irrigation conditions. Model results are improved when irrigation occurs with a 3-day frequency, especially in summer. Results are consistent with observed monthly outdoor water use. This study highlights the importance of appropriately including QF and irrigation in urban land surface models—terms not generally considered in many previous studies.

High-resolution modeling of gaseous methylamines over a polluted region in China: source-dependent emissions and implications of spatial variations

Abstract. Amines have received increasing attention in recent years because of their potential role in new particle formation in the atmosphere and their impact on aerosol chemistry. High concentrations of amines are expected to be limited to the vicinity of source regions due to their short lifetime, highlighting the necessity of having a better understanding of contributions of emissions from different source types. This study presents the first high-resolution model simulation of concentrations of methylamines on a regional scale over the Yangtze River Delta region in East China. The WRF-Chem with nested grids is used in model simulations. In contrast to the very limited existing modeling studies that assumed a fixed ratio (FR) of amines to total ammonia emission, we derive source-dependent ratios (SDR) that distinguish C1-amine (CH3NH2), C2-amines (C2H7N), C3-amines (C3H9N) emissions from five different source types (agriculture, residential, transportation, chemical industry, and other industry). The amines-to-ammonia mass emission ratios, estimated from previous measurements, are 0.026, 0.0015, 0.0011, 0.0011, and 0.0011 for C1-amine; 0.007, 0.0018, 0.0015, 0.01, and 0.0009 for C2-amines; and 0.0004, 0.0005, 0.00043, 0.0006, and 0.0004 for C3-amines for chemical–industrial, other industrial, agricultural, residential, and transportational sources, respectively. The simulated concentrations of C1-, C2-, and C3-amines, based on both FR and SDR, have been compared with field measurements at a suburban site in Nanjing and at an urban site in Shanghai, China. SDR substantially improves the ability of the model in capturing the observed concentrations of methylamines. Concentrations of C1-, C2-, and C3-amines in the surface layer in the Yangtze River Delta region are generally in the range of 2–20, 5–50, and 0.5–4 pptv. Vertically, the concentrations of C1-, C2-, and C3-amines decrease quickly with altitude, dropping by a factor of ∼10 from the surface to ∼900 hPa. Results from the present study are critical to evaluating potential roles of amines in nucleation and chemical processes in polluted air.

Particle Size Distributions of Oxidative Potential of Lung-Deposited Particles: Assessing Contributions from Quinones and Water-Soluble Metals

Redox-active species in ambient particulate matter (PM) cause adverse health effects through the production of reactive oxygen species (ROS) in the human respiratory tract. However, respiratory deposition of these species and their relative contributions to oxidative potential (OP) have not been described. Size-segregated aerosols were collected during haze and nonhaze periods using a micro-orifice uniform deposit impactor sampler at an urban site in Shanghai to address this issue. Samples were analyzed for redox-active species content and PM OP. The average dithiothreitol (DTT) activity of haze samples was approximately 2.4-fold higher than that of nonhaze samples and significantly correlated with quinone and water-soluble metal concentrations. The size-specific distribution data revealed that both water-soluble OPvDTT (volume-normalized OP quantified by DTT assay) and OPmDTT (mass-normalized OP) were unimodal, peaking at 0.56-1 and 0.1-0.32 μm, respectively, due to contributions from accumulation-mode quinones and water-soluble metals. We further estimated that transition metals (mainly copper and manganese) contributed 55 ± 13% of the DTT activity while quinones accounted for only 8 ± 3%. Multiple-path particle dosimetry calculations estimated that OP deposition in the pulmonary region was mainly from accumulation-mode transition metals despite quinones having the highest DTT activity. This behavior is primarily attributed to the efficiency of deposition of transition metals in the pulmonary region being approximately 1.2-fold greater than that of quinones. These results reveal that accumulation-mode transition metals are significant contributors to the OP of deposited water-soluble particles in the pulmonary region of the lung.

Insights into the formation of secondary organic carbon in the summertime in urban Shanghai

To investigate formation mechanisms of secondary organic carbon (SOC) in Eastern China, measurements were conducted in an urban site in Shanghai in the summer of 2015. A period of high O3 concentrations (daily peak > 120 ppb) was observed, during which daily maximum SOC concentrations exceeding 9.0 μg/(C·m3). Diurnal variations of SOC concentration and SOC/organic carbon (OC) ratio exhibited both daytime and nighttime peaks. The SOC concentrations correlated well with Ox (= O3 + NO2) and relative humidity in the daytime and nighttime, respectively, suggesting that secondary organic aerosol formation in Shanghai is driven by both photochemical production and aqueous phase reactions. Single particle mass spectrometry was used to examine the formation pathways of SOC. Along with the daytime increase of SOC, the number fraction of elemental carbon (EC) particles coated with OC quickly increased from 38.1% to 61.9% in the size range of 250–2000 nm, which was likely due to gas-to-particle partitioning of photochemically generated semi-volatile organic compounds onto EC particles. In the nighttime, particles rich in OC components were highly hygroscopic, and number fraction of these particles correlated well with relative humidity and SOC/OC nocturnal peaks. Meanwhile, as an aqueous-phase SOC tracer, particles that contained oxalate-Fe(III) complex also peaked at night. These observations suggested that aqueous-phase processes had an important contribution to the SOC nighttime formation. The influence of aerosol acidity on SOC formation was studied by both bulk and single particle level measurements, suggesting that the aqueous-phase formation of SOC was enhanced by particle acidity.

Characteristics of size-resolved atmospheric inorganic and carbonaceous aerosols in urban Shanghai

Size-segregated aerosol particles were collected with a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI) at an urban site in Shanghai, China for four non-consecutive months representing four seasons from 2015 to 2016. Chemical composition, including water-soluble ions as well as organic carbon (OC), elemental carbon (EC) and secondary organic carbon (SOC) of size-resolved (0.056–18 μm) atmospheric aerosols in four seasons and in different polluted cases were studied. The size distributions of sulfate, nitrate and ammonium (SNA) and carbonaceous aerosol (OC, EC and SOC) were discussed and the potential sources of PM1.8-associated secondary species (SO42−, NO3−, SNA and SOC) in different seasons were identified by potential source contribution function (PSCF) model. Results showed that atmospheric ultrafine and fine particle pollution in Shanghai were very serious during the study period. Most of the water-soluble ions tended to be enriched in fine particles, especially being abundant in the droplet mode in polluted cases. Compared with sulfate, size distributions of nitrate and ammonium presented more significant seasonal variations and showed distinctive characteristics in polluted days. Abundant nitrate was concentrated in fine particles in cold seasons (spring and winter), whereas it was enriched in coarse mode during summer and autumn. The droplet mode sulfate with high concentration did not result in the aggravation of air pollution, while the nucleation mode sulfate may have made a great contribution to the air pollution in urban Shanghai. It was also found that the formation of air pollution in urban Shanghai had a significant link with nitrate and ammonium, especially with nitrate and ammonium in condensation mode and droplet mode, and the contribution of sulfate to the pollution formation in Shanghai would somehow be surpassed by the increasing nitrate and ammonium. OC and EC concentrations from spring to winter were found to be 11.10, 7.10, 12.30, 20.16, and 3.73, 2.84, 4.63, 7.10 μg m−3, respectively, distinctly presenting the summer minima and winter maxima in this study. The maximum OC/EC was in the droplet mode and the minimum was in the nucleation mode for both clean and polluted days. The great contribution of SOC to OC in droplet mode and the occurrence of PM pollution necessarily had an important bearing on the SOC formation in droplet mode particles. Particle acidity may play a key role in secondary organic aerosol formation and the particles with the size of 0.056–0.1 μm was the most sensitive particles to acid catalysis in SOA formation. The similar PSCF results of PM1.8-associated SOC to those of SO42−, NO3− and SNA indicated possible connections between the formation of SOC and secondary inorganic species in PM.

Comparison of PM2.5 carbonaceous pollutants between an urban site in Shanghai and a background site in a coastal East China Sea island in summer: concentration, composition and sources.

Nine paired samples of atmospheric particulate matter with an aerodynamic diameter less than or equal to 2.5 μm (PM2.5) were collected concurrently from an urban site in Shanghai, China and a background site in Huaniao Island (HNI) in the coastal East China Sea (ECS) between July 21 and 29, 2011. The samples were analyzed for 16 United States Environmental Protection Agency (USEPA) priority polycyclic aromatic hydrocarbons (PAHs), n-alkanes (20 species, C14-C33), hopanes (10 species, C29-C32), and steranes (12 species, C27-C29). These two sites, approximately 66 km apart, are both on the pathway of land-based pollutants as they are transported to the ECS by seasonal winds. As expected, concentrations in Shanghai were higher (average: 8.4 and 67.8 ng m-3 for the 16 PAHs and n-alkanes, respectively) than those in HNI (average: 1.8 and 8.5 ng m-3, respectively). The dominant contributor to the 16 PAHs in Shanghai was 5-6-ring PAHs (60.0%), whereas 2-3-ring PAHs contributed the most (72.5%) in HNI. Plant waxes contributed 45.7% and 25.9% of the n-alkanes in Shanghai and HNI, respectively, implying a relatively greater contribution from petroleum residues to the n-alkanes in HNI. Principal component analysis (PCA) and the compositions of hopanes and steranes highlighted a prominent contribution from traffic emissions to carbonaceous PM2.5 aerosols. This study provides comprehensive details about the sources, formation, and transport of pollutants from eastern China to the coastal ECS.

Radiation Fluxes in a Business District of Shanghai, China

AbstractRadiative fluxes are key drivers of surface–atmosphere heat exchanges in cities. Here the first yearlong (December 2012–November 2013) measurements of the full radiation balance for a dense urban site in Shanghai, China, are presented, collected with a CNR4 net radiometer mounted 80 m above ground. Clear-sky incoming shortwave radiation K↓ (median daytime maxima) ranges from 575 W m−2 in winter to 875 W m−2 in spring, with cloud cover reducing the daily maxima by about 160 W m−2. The median incoming longwave radiation daytime maxima are 305 and 468 W m−2 in winter and summer, respectively, with increases of 30 and 15 W m−2 for cloudy conditions. The effect of air quality is evident: haze conditions decrease hourly median K↓ by 11.3%. The midday (1100–1300 LST) clear-sky surface albedo α is 0.128, 0.141, 0.143, and 0.129 for winter, spring, summer, and autumn, respectively. The value of α varies with solar elevation and azimuth angle because of the heterogeneity of the urban surface. In winter, shadows play an important role in decreasing α in the late afternoon. For the site, the bulk α is 0.14. The Net All-Wave Radiation Parameterization Scheme/Surface Urban Energy and Water Balance Scheme (NARP/SUEWS) land surface model reproduces the radiation components at this site well, which is a promising result for applications elsewhere. These observations help to fill the gap of long-term radiation measurements in East Asian and low-latitude cities, quantifying the effects of season, cloud cover, and air quality.

Chemical characteristics of fine particles and their impact on visibility impairment in Shanghai based on a 1-year period observation

In this work, a one-year observation focusing on high time resolution characteristics of components in fine particles was conducted at an urban site in Shanghai. Contributions of different components on visibility impairment were also studied. Our research indicates that the major components of PM2.5 in Shanghai are water-soluble inorganic ions and carbonaceous aerosol, accounting for about 60% and 30% respectively. Higher concentrations of sulfate (SO42−) and organic carbon (OC) in PM2.5 occurred in fall and summer, while higher concentrations of nitrate (NO3−) were observed in winter and spring. The mass concentrations of Cl− and K+ were higher in winter. Moreover, NO3− increased significantly during PM2.5 pollution episodes. The high values observed for the sulfate oxidizing rate (SOR), nitrate oxidizing rate (NOR) and secondary organic carbon (SOC) in OC indicate that photochemical reactions were quite active in Shanghai. The IMPROVE (Interagency Monitoring of Protected Visual Environments) formula was used in this study to investigate the contributions of individual PM2.5 chemical components to the light extinction efficient in Shanghai. Both NH4NO3 and (NH4)2SO4 had close relationships with visibility impairment in Shanghai. Our results show that the reduction of anthropogenic SO2, NOx and NH3 would have a significant effect on the improvement of air quality and visibility in Shanghai.

Seasonal variation of carbonaceous pollutants in PM2.5 at an urban ‘supersite’ in Shanghai, China

Multiple PM2.5 samples collected through different seasons from October 2011 to August 2012 at an urban site in Shanghai, China were analyzed for carbonaceous pollutants. Data from this site, a 'super' air quality monitoring station at Fudan University, has been used by researchers to investigate the formation mechanism of haze episodes. The characteristics and concentrations of organic carbon (OC), elemental carbon (EC), n-alkanes, as well as relative abundances of hopanes, in these samples were determined. The concentrations showed a pronounced annual cycle with higher values in cold seasons (spring and winter, mean: 8.6 μg/m(3), 3.3 μg/m(3) and 136.4 ng/m(3) for OC, EC and n-alkanes, respectively) and lower values in warm seasons (fall and summer, mean: 6.6 μg/m(3), 2.6 μg/m(3) and 73.8 ng/m(3) for OC, EC and n-alkanes, respectively). EC generally displayed a common source with that of OC in all seasons. Petroleum residue was the major source of n-alkanes, contributing 71.4% to the targeted C14-C33n-alkanes over four seasons. Principal components analysis and the composition of hopanes showed that emissions from vehicle exhaust contributed more carbonaceous aerosols than coal combustion. These data could provide important information for measures to reduce carbonaceous pollutant emissions and improve air quality in Shanghai, and other urban centers across China.

Chemical composition of PM2.5 and meteorological impact among three years in urban Shanghai, China

Air pollution is a major environmental concern in Yangtze River Delta (YRD) region in East China. Here we presented 3-year on-line measurements of PM2.5 chemical components from January 2011 to December 2013 at an urban site in Shanghai of YRD region. The 3-year average of PM2.5 mass concentration was 47 μg/m3, 34% higher than the second grade of China National Ambient Air Quality Standards for PM2.5 annual concentration. Monthly patterns of PM2.5 mass concentration and chemical components were observed, which were mainly influenced by the meteorological conditions through long-range transport and ventilation, and by the secondary species transformation. Significant year-to-year differences of PM2.5 characterization were observed during 2011–2013, and it can be attributed to the differences of regional transport as well as the wet deposition by precipitation. Generally, air mass from the western YRD region caused the most polluted air in Shanghai, while, air masses from the East China Sea had the lowest particle pollution because of marine time background air, and those from the surrounding region of Bo Hai in the north of China caused the moderate PM2.5 pollution in Shanghai. A large decrease of PM2.5 mass concentration, ∼44%, was observed for the fifteen years. In terms of chemical components, persistent decrease was observed for element carbon with a decrease of 70% but not for organic carbon, and the significant decrease of secondary inorganic ions was observed before year of 2008 but the persistent increase started after that.