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Secondary organic aerosols (SOAs) account for a large fraction of atmospheric aerosol mass and play significant roles in visibility impairment by scattering solar radiation. However, comprehensive evaluations of SOA scattering abilities under ambient relative humidity (RH) conditions on the basis of field measurements are still lacking due to the difficulty of simultaneously direct quantifications of SOA scattering efficiency in dry state and SOA water uptake abilities. In this study, field measurements of aerosol chemical and physical properties were conducted in winter in Guangzhou (lasting about 3 months) using a humidified nephelometer system and aerosol chemical speciation monitor. A modified multilinear regression model was proposed to retrieve dry-state mass scattering efficiencies (MSEs, defined as scattering coefficient per unit aerosol mass) of aerosol components. The more oxidized oxygenated organic aerosol (MOOA) with an O/C ratio of 1.17 was identified as the most efficient light scattering aerosol component. On average, 34 % mass contribution of MOOA to total submicron organic aerosol mass contributed 51 % of dry-state organic aerosol scattering. The overall organic aerosol hygroscopicity parameter κOA was quantified directly through hygroscopicity closure, and hygroscopicity parameters of SOA components were further retrieved using a multilinear regression model by assuming hydrophobic properties of primary organic aerosols. The highest water uptake ability of MOOA among organic aerosol factors was revealed with κMOOA reaching 0.23, thus further enhancing the fractional contribution of MOOA in ambient organic aerosol scattering. In particular, the scattering abilities of MOOA were found to be even higher than those of ammonium nitrate under RH of %, which was identified as the most efficient inorganic scattering aerosol component, demonstrating that MOOA had the strongest scattering abilities in ambient air (average RH of 57 %) during winter in Guangzhou. During the observation period, secondary aerosols contributed dominantly to visibility degradation (∼70 %), with substantial contributions from MOOA (16 % on average), demonstrating significant impacts of MOOA on visibility degradation. The findings of this study demonstrate that more attention needs to be paid to SOA property changes in future visibility improvement investigations. Also, more comprehensive studies on MOOA physical properties and chemical formation are needed to better parameterize its radiative effects in models and implement targeted control strategies on MOOA precursors for visibility improvement.

Emission controls have substantially brought down aerosol pollution in China; however, aerosol mass reductions have slowed down in recent years in the Pearl River Delta (PRD) region, where secondary organic aerosol (SOA) formation poses a major challenge for air quality improvement. In this study, we characterized the roles of SOA in haze formation in urban Guangzhou in the PRD using year-long aerosol mass spectrometer measurements for the first time and discussed possible pathways of SOA formations. On average, organic aerosols (OA) contribute dominantly (50 %) to nonrefractory submicron aerosol mass (NR-PM1). The average mass concentration of SOA (including by less- and more-oxidized OA, LOOA and MOOA) contributed most to NR-PM1, reaching about 1.7 times that of primary organic aerosols (POA, including hydrocarbon-like and cooking-related OA) and accounting for 32 % of NR-PM1, even more than sulfate (22 %) and nitrate (16 %). Seasonal variations of NR-PM1 revealed that haze-formation mechanisms differed much among distinct seasons. Sulfate mattered more than nitrate in fall, while nitrate was more important than sulfate in spring and winter, with SOA contributing significantly to haze formations in all the seasons. Daytime SOA formation was weak in winter under low oxidant levels and air relative humidity, whereas prominent daytime SOA formation was observed in fall, spring and summer almost on a daily basis, suggesting important roles of photochemistry in SOA formations. Further analysis showed that the coordination of gas-phase photochemistry and subsequent aqueous-phase reactions likely played significant roles in quick daytime SOA formations. Obvious nighttime SOA formations were also frequently observed in spring, fall and winter, and it was found that daytime and nighttime SOA formations together had resulted in the highest SOA concentrations in these seasons and contributed substantially to severe haze formations. Simultaneous increases in nitrate with SOA after sunset suggested the important roles of NO3 radical chemistry in nighttime SOA formations, and this was further confirmed by a continuous increase in the NO+ / NO2+ fragment ratio that related to measured particulate nitrate after sunset. The findings of this study have promoted our understanding of haze pollution characteristics of the PRD and laid down future directions for investigations of SOA-formation mechanisms in urban areas of southern China that share similar emission sources and meteorological conditions.

To investigate the physical and chemical processes of fine particle matter (PM) at the mid-upper planetary boundary layer (PBL), we conducted 1-year continuous measurements of fine PM, the chemical composition of non-refractory submicron aerosol (NR-PM1), and some gas species (including sulfur dioxide, nitrogen oxides, and ozone) at an opening observatory (∼ 600 m) at the top of Shanghai Tower (SHT), which is China's first and the world's second highest building located in the typical financial central business district of Shanghai, China. This is the first report on the characteristics of fine particles based on continuous and sophisticated online measurements at the mid-upper level of the urban PBL. The observed PM2.5 and PM1 mass concentrations at SHT were 25.5 ± 17.7 and 17.3 ± 11.7 µg m−3, respectively. Organics, nitrate (NO3), and sulfate (SO4) occupied the first three leading contributions to NR-PM1 at SHT, accounting for 35.8 %, 28.6 %, and 20.8 %, respectively. The lower PM2.5 concentration was observed at SHT by 16.4 % compared with that near the surface during the observation period. It was attributed to the decreased nighttime PM2.5 concentrations (29.4 % lower than the surface) at SHT in all seasons due to the complete isolations from both emissions and gas precursors near the surface. However, daytime PM2.5 concentrations at SHT were 12.4 %–35.1 % higher than those near the surface from June to October, resulted from unexpected larger PM2.5 levels during early to middle afternoon at SHT than at the surface. We suppose the significant chemical production of secondary aerosols existed in the mid-upper PBL, because strong solar irradiance, adequate gas precursors (e.g., NOx), and lower temperature were observed at SHT, favorable for both photochemical production and gas-to-particle partitioning. This was further demonstrated by the significant increasing rate of oxygenated organic aerosols and NO3 observed at SHT during 08:00–12:00 in spring (7.4 % h−1 and 12.9 % h−1), fall (9.3 % h−1 and 9.1 % h−1), and summer (13.0 % h−1 and 11.4 % h−1), which cannot be fully explained by vertical mixing. It was noted that extremely high NO3 was observed at SHT both in daytime and nighttime in winter, accounting for 37.2 % in NR-PM1, suggesting the efficient pathway from heterogeneous and gas oxidation formation. Therefore, we highlight the priority of NOx reduction in Shanghai for the further improvement of air quality. This study reported greater daytime PM2.5 concentrations at the height of 600 m in the urban PBL compared with surface measurement, providing insight into their potential effects on local air quality, radiation forcing, and cloud and/or fog formations. We propose that the efficient production of secondary aerosol in the mid-upper PBL should be cognized and explored more comprehensively by synergetic observations in future.

International audience; While perceived waiting time can undermine user evaluation and cause application abandonment, there is little scientific research on waiting in mobile applications. This paper incorporates three mobile interactivity features (ubiquitous connectivity, active control, and responsiveness) into the model and examines the mediating role of cognitive absorption and the moderating role of perceived procedural justice between these features and perceived waiting time in a short-waiting application. The researchers empirically examine the model using data from 468 uses of the ride-sharing mobile application. The results reveal that mobile interactivity can directly and indirectly (via cognitive absorption) lead to more tolerance in perceived waiting time. The findings elicit several implications for theories and practice.

To investigate the physical and chemical processes of fine particle matter (PM) at the mid-upper planetary boundary layer (PBL), we conducted 1-year continuous measurements of fine PM, the chemical composition of non-refractory submicron aerosol (NR-PM1), and some gas species (including sulfur dioxide, nitrogen oxides, and ozone) at an opening observatory (∼ 600 m) at the top of Shanghai Tower (SHT), which is China's first and the world's second highest building located in the typical financial central business district of Shanghai, China. This is the first report on the characteristics of fine particles based on continuous and sophisticated online measurements at the mid-upper level of the urban PBL. The observed PM2.5 and PM1 mass concentrations at SHT were 25.5 ± 17.7 and 17.3 ± 11.7 µg m−3, respectively. Organics, nitrate (NO3), and sulfate (SO4) occupied the first three leading contributions to NR-PM1 at SHT, accounting for 35.8 %, 28.6 %, and 20.8 %, respectively. The lower PM2.5 concentration was observed at SHT by 16.4 % compared with that near the surface during the observation period. It was attributed to the decreased nighttime PM2.5 concentrations (29.4 % lower than the surface) at SHT in all seasons due to the complete isolations from both emissions and gas precursors near the surface. However, daytime PM2.5 concentrations at SHT were 12.4 %–35.1 % higher than those near the surface from June to October, resulted from unexpected larger PM2.5 levels during early to middle afternoon at SHT than at the surface. We suppose the significant chemical production of secondary aerosols existed in the mid-upper PBL, because strong solar irradiance, adequate gas precursors (e.g., NOx), and lower temperature were observed at SHT, favorable for both photochemical production and gas-to-particle partitioning. This was further demonstrated by the significant increasing rate of oxygenated organic aerosols and NO3 observed at SHT during 08:00–12:00 in spring (7.4 % h−1 and 12.9 % h−1), fall (9.3 % h−1 and 9.1 % h−1), and summer (13.0 % h−1 and 11.4 % h−1), which cannot be fully explained by vertical mixing. It was noted that extremely high NO3 was observed at SHT both in daytime and nighttime in winter, accounting for 37.2 % in NR-PM1, suggesting the efficient pathway from heterogeneous and gas oxidation formation. Therefore, we highlight the priority of NOx reduction in Shanghai for the further improvement of air quality. This study reported greater daytime PM2.5 concentrations at the height of 600 m in the urban PBL compared with surface measurement, providing insight into their potential effects on local air quality, radiation forcing, and cloud and/or fog formations. We propose that the efficient production of secondary aerosol in the mid-upper PBL should be cognized and explored more comprehensively by synergetic observations in future.

Weekday/weekend mixing ratios of ozone (O3) and the O3 precursors of non-methane hydrocarbons (NMHCs) and nitrogen oxides (NOx) were recorded at the Guangzhou Panyu Atmospheric Composition Station (GPACS), a suburban site in Guangzhou, during the summer (June, July, and August) and autumn (September, October, and November) of 2011. In both summer and autumn, weekday/weekend O3 differences in the morning and at midday largely depend on how much the O3 precursors are affected by anthropogenic emissions. In the mornings (6:00–9:00 LT), pollutants (i.e. NOx and NMHCs) were more strongly influenced by vehicular emissions in autumn than in summer. In autumn, O3 titration and lower NOx on weekends in NMHCs-limited regimes lead to more rapid O3 production, which resulted in the O3 weekend effect during autumn morning. No O3 weekend effect occurred on summer mornings because O3 formation was in a NOx-limited regime, although O3 titration still existed. At midday (10:00–16:00 LT), the increase of biogenic NMHCs emissions reversed the sensitivity of O3 production from NMHCs-to NOx-sensitive. The weekday/weekend diurnal pattern of vehicular sources was the same at midday, more intense other human industrial activities in autumn not only gave rise to the higher mixing ratios of high-reactive anthropogenic NMHCs (e.g. aromatics) on weekdays, but also could affected the temperature in the city, leading to higher isoprene mixing ratio on weekdays. All these factors are likely to contribute to the O3 weekday effect in autumn. Meanwhile no weekday O3 effect occurred in summer due to the low-intensity industrial anthropogenic activities. Our results show that high-reactive NMHCs and NOx control can be effective for reducing peak O3 mixing ratios in Guangzhou. Further investigation based on numerical models is required to reach more robust conclusions.

Considering the importance of employees' environmental behavior to the greening and sustainable development of organizations, this research explored how environmental corporate social responsibility (CSR) transforms into employees' environmental citizenship behavior. Based on stimulus-organism-response (S–O-R) theory, this study establishes a theoretical model to explore the impact mechanism of environmental CSR on environmental citizenship behavior. The researchers collected 431 surveys from employees of manufacturing organizations to examine the research model. The results showed that environmental CSR can influence environmental citizenship behavior directly and indirectly (through environmental passion and empathy). CSR directed toward employees positively moderated the relationships between environmental passion and environmental citizenship behavior and the relationship between environmental empathy and environmental citizenship behavior. This research expands the micro-foundation of CSR and extends the research on the antecedents of employees' environmental behavior by revealing the social-psychological mechanism of environmental CSR's impact on environmental citizenship behavior and also provides specific suggestions for practice.

Although existing research generally has found that corporate social responsibility (CSR) has a positive impact on organizations and individuals, researchers should still be alert to the potential risks it may bring. This study will explore why employee-oriented corporate social responsibility (employee-oriented CSR) triggers unethical pro-organizational behavior (UPB). Based on the social identity theory, this study establishes a moderated mediation model to explore the impact mechanism of employee-oriented CSR on UPB. We collected survey data from 298 employees of manufacturing organizations to test our research model. The regression statistics results indicate that employee-oriented CSR can indirectly (via perceived insider status (PIS)) affect employees’ UPB. Moreover, ethical climate rules negatively moderate the relationship between PIS and UPB, and negatively moderate the indirect effect of employee-oriented CSR on UPB. This study promotes a full understanding of the impact of CSR, expands the micro-foundation of CSR, and extends the research on the antecedents of employees’ UPB by revealing the social-psychological mechanism of employee-oriented CSR impact UPB, and also gives specific suggestions to put into practice.

Submicron aerosols (PM1) have more serious effect on the visibility, air quality, human health and climate change compared to coarse particles (particle size between 2.5 and 10 μm). There is practical significance in understanding the formation mechanisms and sources of these particles. In this study, we conducted real-time measurements on the composition of non-refractory submicron aerosols (NR-PM1) in Guangzhou from 20 October to 1 December, 2016, using a quadripole aerosol chemical speciation monitor (Q-ACSM). Overall, the composition of NR-PM1 was dominated by organics (48.2%), followed by nitrate (NO3−, 20.3%), sulfate (SO42−, 17.4%), ammonium (NH4+, 11.4%), and chloride (Cl−, 2.7%). The high contribution of NO3− and NO3−/SO42− mass ratios were observed in high-PM episodes, suggesting that NOx emission control should be a priority in mitigating PM-pollution in South China. Primary organic aerosols (POA) accounted for 51% of organics as the campaign average, and POA contribution increased with PM concentrations especially during high PM episodes, indicating that local emissions played a very important role in high-PM pollution. The conversion of SO2 to SO42− and aqueous, heterogeneous production may not be the dominant source of SO42− in NR-PM1, while regional transport is likely to be the main source during high-sulfate episodes. The formation of NO3− in this study was related to gas-phase reactions of NO2 (photochemical reaction) during daytime, and heterogeneous reactions (hydrolysis reaction of N2O5) during the nighttime. Gas-phase reactions would be less important for nitrate formation during severe polluted events. Particle acidity analyses showed that particles were generally acidic and the NH4+ was not enough to fully neutralise the NO3− and SO42−, the existing forms of SO42− could be (NH4)2SO4, NH4HSO4 or (NH4)3H(SO4)2. Controlling the emissions of NH3 to reduce the NH4+ concentration can probably be a feasible direction in the future in Guangzhou if the problem of agriculture and aerosol acidity can be solved. Wind rose plots and back-trajectory analyses also demonstrated that local emission was more important to the formation of NO3− and regional transport was more conducive to the increase of SO42− concentration.

Ozone has become the main factor affecting the air quality in the Pearl River Delta (PRD) in recent years, and a clear understanding source of ozone pollution is a top priority of ozone pollution prevention. However, the vertical distribution of tropospheric ozone in the PRD is poorly understood. Based on daily ozone sounding data obtained in Yangjiang (111°58'00" E, 21°50'00" N), Guangdong Province, from 18 November tjo 3 December 2013, the detailed vertical distribution of tropospheric ozone and its influencing factors were determined and compared with weekly autumn ozone profile data obtained at the Hong Kong Observatory (HKO) and corresponding tropospheric column ozone (TCO) datasets from the Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) onboard satellite AURA. Overall, the ozone profiles observed in Yangjiang are in accordance with those of the HKO in terms of the vertical structure. The TCO values are 34.2 ± 4.0 and 34.3 ± 4.6 DU, respectively, that are, 4 DU higher than those of satellite data, indicating that the OMI/MLS product underestimates the TCO level in the PRD region. The Yangjiang ozone profiles indicate significant variations in the ozone vertical structure and concentration during the observation period. A significant ozone peak permanently occurs in the lower troposphere at 1.1 ± 0.4 km above the surface. The vertical structural difference is mainly reflected in the presence of low-ozone strata (below 30 ppbv) near the tropopause and ozone peaks and high-ozone stratification in the middle and upper troposphere. The average ozone peak concentrations in the lower, middle, and upper troposphere are 65.2 ± 9.9, 57.8 ± 7.7, 71.8 ± 13.6 ppbv, respectively, which are higher than the average ground-level ozone concentration (48.9 ± 9.4 ppbv). Based on the analysis of the profile characteristics, weather conditions, and backward trajectories, it can be concluded that the low-ozone strata near the tropopause are caused by the regional transport of the tropical air mass from the tropical cyclone storm area. Potential vorticity analysis shows that stratosphere-troposphere exchange (STE) is the main reason for the formation of the ozone peaks and its varying concentrations in the middle and upper troposphere. Photochemical reactions represent the main factor affecting the ozone concentration in the lower troposphere. The STE is also an important factor affecting the ozone in the lower troposphere, leading to an increase in the surface ozone concentration by ~10.9 ppbv.

Absorbing aerosols can significantly modulate short-wave solar radiation in the atmosphere, affecting regional and global climate. The aerosol absorption coefficient (AAC) is an indicator that assesses the impact of absorbing aerosols on radiative forcing. In this study, the near-surface AAC and absorption Ångström exponent (AAE) in the urban area of Nanjing, China, are characterized on the basis of measurements in 2012 and 2013 using the seven-channel Aethalometer (model AE-31, Magee Scientific, USA). The AAC is estimated with direct and indirect corrections, which result in consistent temporal variations and magnitudes of AAC at 532 nm. The mean AAC at 532 nm is about 43.23 ± 28.13 M m−1 in the urban area of Nanjing, which is much lower than that in Pearl River Delta and the same as in rural areas (Lin'an) in Yangtze River Delta. The AAC in the urban area of Nanjing shows strong seasonality (diurnal variations); it is high in cold seasons (at rush hour) and low in summer (in the afternoon). It also shows synoptic and quasi-2-week cycles in response to weather systems. Its frequency distribution follows a typical log-normal pattern. The 532 nm AAC ranging from 15 to 65 M m−1 dominates, accounting for more than 72 % of the total data samples in the entire study period. Frequent high pollution episodes, such as those observed in June 2012 and in winter 2013, greatly enhanced AAC and altered its temporal variations and frequency distributions. These episodes are mostly due to local emissions and regional pollution. Air masses flowing from northern China to Nanjing can sometimes be highly polluted and lead to high AAC at the site. AAE at 660/470 nm from the Schmid correction (Schmid et al., 2006) is about 1.56, which might be more reasonable than from the Weingartner correction (Weingartner et al., 2003). Low AAEs mainly occur in summer, likely due to high relative humidity (RH) in the season. AAC increases with increasing AAE at a fixed aerosol loading. The RH–AAC relationship is more complex. Overall, AAC peaks at RH values of around 40 % (1.3 < AAE < 1.6), 65 % (AAE < 1.3 and AAE > 1.6), and 80 % (1.3 < AAE < 1.6).

An online coupled regional climate-chemistry model called RegCCMS is used to investigate the interactions between anthropogenic aerosols and the East Asian summer monsoon (EASM) over East Asia. The simulation results show that the mean aerosol loading and optical depth over the region are 17.87 mg/m2 and 0.25, respectively. Sulfate and black carbon (BC) account for approximately 61.2% and 7.8% of the total aerosols, respectively. The regional mean radiative forcing (RF) is approximately −3.64, −0.55, and +0.88 W/m2 at the top of the atmosphere for the total aerosol effect, the total aerosol direct effect, and the BC direct effect, respectively. The surface direct RF of BC accounts for approximately 31% of the total RF of all aerosols. Because of the total aerosol effect, both the energy budgets and air temperature are considerably reduced in the region with high aerosol loadings, leading to decreases in the land-ocean air temperature gradient in summer. The total column-absorbed solar radiation and surface air temperature decrease by 8.4 W/m2 and 0.31 K, respectively. This cooling effect weakens horizontal and vertical atmospheric circulations over East Asia. The wind speed at 850 hPa decreases by 0.18 m/s, and the precipitation decreases by 0.29 mm/d. The small responses of solar radiation, air temperature, and atmospheric circulations to the BC warming effect are opposite to those of the total aerosol effect. The BC-induced enhancement of atmospheric circulation can increase local floods in south China, while droughts in north China may worsen in response to the BC semidirect effect. The total aerosol effect is much more significant than the BC direct effect. The East Asian summer monsoon becomes weaker due to the total aerosol effect. However, this weakness could be partially offset by the BC warming effect. Sensitivity analyses further indicate that the influence of aerosols on the EASM might be more substantial in years when the southerlies or southwesterlies at 850 hPa are weak compared with years when the winds are strong. Changes in the EASM can induce variations in the distribution and magnitude of aerosols. Aerosols in the lower troposphere over the region can increase by 3.07 and 1.04 µg/m3 due to the total aerosol effect and the BC warming effect, respectively.

The Yangtze River Delta (YRD) region has experienced a rapid urbanization process accompanied with economic development during last decades. To investigate impacts of urbanization on regional climate and air quality, two-month (January and July 2010) simulations with two different land-use scenarios (USGS and MODIS land-use types) are conducted using the Advanced Weather Research and Forecasting/Chemistry (WRF/Chem) modeling system in this study. Results show that the conversion of vegetated and irrigated cropland into urban type significantly changes 2-m temperature and 10-m wind speed, which are obtained from differences of two simulations based on significance t-test at 95% confidence level. Changes of land-use cause an increase in 2-m temperature with maximum (minimum) value of 2.3 °C (0.9 °C) over urbanized area, a decrease in 10-m wind speed with magnitude of 0.6–1.2 m s−1 for both the two months. Planetary boundary layer height (PBLH) differences show a maximum increase of 425 m during daytime in July, and the increases are about 100 m during nighttime for both January and July. Urbanization reduces near-surface PM10 concentration due to increase of PBLH, with maximum decrease of 57.6 μg m−3 during nighttime in July. The biggest increase of O3 is around 6.8 ppb during daytime in July and the difference is about 1.7–2.3 ppb in January. Vertical profiles show that PM10 concentrations decrease due to increase of mixing height during both daytime and nighttime. While for O3 concentration, urbanization causes an increase during daytime due to higher air temperature and decrease of wind speed and leads to a decrease during nighttime. Overall, influences of urbanization on climate and air quality are important and significant over YRD region, which must be considered in any climate and air quality assessment.

As a short-lived climate forcing agent, black carbon (BC) aerosol plays an important role in climate change, atmospheric environment, and human health. In this study, continuous measurements of BC and trace gases were made at an urban site in Nanjing, Yangtze River Delta (YRD) of China in 2012. The annual mean BC concentration in Nanjing was found to be 4157 ± 2626 ng/m3, with a range of 221–24,686 ng/m3. The value was much lower than that in most megacities of China and also lower than that in LinAn, a rural site in YRD. BC concentrations in Nanjing showed strong seasonality, high in spring and autumn and low in summer. The concentrations also varied diurnally, high at rush hours and low in the afternoon. The diurnal cycles of BC loadings in winter to spring 2012 were similar to those in 2011 in magnitude and shape. BC concentrations followed a typical lognormal pattern, with over 75% of data samples between 1000 and 6000 ng/m3. The maximum frequency occurred in low BC concentrations in summer and high BC concentrations in other seasons. In Nanjing, high levels of BC were mainly caused by local and regional emissions. Low levels of BC were mostly associated with winds from northern and eastern directions of Nanjing. BC and CO varied similarly with season, having a correlation coefficient over 0.7 in most seasons. Annual mean ΔBC/ΔCO was about 7 ng/m3/ppb, implying that the sources of the BC likely came from combustions of bio-fuel, industry-coal, and vehicle-gasoline. Serious pollution episodes with high levels of BC were detected in early June at the site. Analysis suggested that the episodes were due to biomass burning in northwestern region of Nanjing. During this period, ΔBC/ΔCO reached about 9.7 ng/m3/ppb and much higher BC levels were found at mid-night.

Continuous measurements of atmospheric aerosols were made in Nanjing, a megacity in China, from 18 January to 18 April, 2011 (Phase 1) and from 22 April 2011 to 21 April 2012 (Phase 2). Aerosol characteristics, optical properties, and direct radiative forcing (DRF) were studied through interpretations of these measurements. We found that during Phase 1, mean PM2.5, black carbon (BC), and aerosol scattering coefficient (Bsp) in Nanjing were 76.1 ± 59.3 μg m−3, 4.1 ± 2.2 μg m−3, and 170.9 ± 105.8 M m−1, respectively. High pollution episodes occurred during Spring and Lantern Festivals when hourly PM2.5 concentrations reached 440 μg m−3, possibly due to significant discharge of fireworks. Temporal variations of PM2.5, BC, and Bsp were similar to each other. It is estimated that inorganic scattering aerosols account for about 49 ± 8.6% of total aerosols while BC only accounted for 6.6 ± 2.9%, and nitrate was larger than sulfate. In Phase 2, optical properties of aerosols show great seasonality. High relative humidity (RH) in summer (June, July, August) likely attributed to large optical depth (AOD) and small Angstrom exponent (AE) of aerosols. Due to dust storms, AE of total aerosols was the smallest in spring (March, April, May). Annual mean 550-nm AOD and 675/440-nm AE were 0.6 ± 0.3 and 1.25 ± 0.29 for total aerosols, 0.04 ± 0.02 and 1.44 ± 0.50 for absorbing aerosols, 0.48 ± 0.29 and 1.64 ± 0.29 for fine aerosols, respectively. Annual single scattering albedo of aerosols ranged from 0.90 to 0.92. Real time wavelength-dependent surface albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS) was used to assess aerosol DRFs. Both total and absorbing aerosol DRFs had significant seasonal variations in Nanjing and they were the strongest in summer. Annual mean clear sky TOA DRF (including daytime and nighttime) of total and absorbing aerosols was about −6.9 and +4.5 W m−2, respectively. Aerosol DRFs were found to be sensitive to surface albedo. Over brighter surfaces, solar radiation was more absorbed by absorbing aerosols and less scattered by scattering aerosols.

A Regional Climate Chemistry Modeling System that employed empirical parameterizations of aerosol-cloud microphysics was applied to investigate the spatial distribution, radiative forcing (RF), and climate effects of black carbon (BC) over China. Results showed high levels of BC in Southwest, Central, and East China, with maximum surface concentrations, column burden, and optical depth (AOD) up to 14 μg m−3, 8 mg m−2, and 0.11, respectively. Black carbon was found to result in a positive RF at the top of the atmosphere (TOA) due to its direct effect while a negative RF due to its indirect effect. The regional-averaged direct and indirect RF of BC in China was about +0.81 and −0.95 W m−2, respectively, leading to a net RF of −0.15 W m−2 at the TOA. The BC indirect RF was larger than its direct RF in South China. Due to BC absorption of solar radiation, cloudiness was decreased by 1.33 %, further resulting in an increase of solar radiation and subsequently a surface warming over most parts of China, which was opposite to BC’s indirect effect. Further, the net effect of BC might cause a decrease of precipitation of −7.39 % over China. Investigations also suggested large uncertainties and non-linearity in BC’s indirect effect on regional climate. Results suggested that: (a) changes in cloud cover might be more affected by BC’s direct effect, while changes in surface air temperature and precipitation might be influenced by BC’s indirect effect; and (b) BC second indirect effect might have more influence on cloud cover and water content compared to first indirect effect. This study highlighted a substantial role of BC on regional climate changes.

Long-range transport of dust aerosol has severe impact on the atmospheric environment over vast areas. In this study, the features of a severe dust storm and its transport characteristics were investigated during the period from 28 April to 5 May 2011 in East Asia. The combined impact on Nanjing was studied with the observational PM10, PM2.5, visibility and meteorological data, and the numerical models of HYSPLIT and WRF/Chem. This dust storm was caused by a cyclone on 28 April over arid and semiarid areas in Mongolia and China, and then transported to broad downwind areas including northern, central, and eastern parts of China, the Korean Peninsula, and Japan. Among the available data, the highest hourly PM10 concentration reached 3.916 mg/m3 at Jinchang site near the source area. In East China, the coastal cities had poorer air quality than inland ones for two days. Dust aerosol arrived at Nanjing from the northwest, and then north, owing to the movement of synoptic system, mixed with local anthropogenic emissions, resulting in the highest PM10 concentration of 0.767 mg/m3 with PM2.5 level reaching 0.222 mg/m3. As the dust storm gradually turned eastward, the dust aerosol went over the seas in the east of the continent and then flowed back to Nanjing. Numerical simulations showed that dust aerosol affecting East China was mainly transported below the altitude of 2.5 km. The vertical profiles of PM10 and PM2.5 concentrations showed maxima at the altitude between 0.2 km and 1.3 km.