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Given the increasing complexity of the chemical composition of PM 2.5 , identifying and quantitatively assessing the contributions of pollution sources has played an important role in formulating policies to control particle pollution. This study provides a comprehensive assessment between PM 2.5 chemical characteristics, sources, and health risks based on sampling data conducted over 1 year (March 2018 to February 2019) in Nanjing. Results show that PM 2.5 exhibits a distinct variation across different seasons, which is primarily driven by emissions, meteorological conditions, and the chemical conversion of gaseous pollutants. First, the chemical mass reconstruction shows that secondary inorganic aerosols (62.5 %) and carbonaceous aerosols (21.3 %) contributed most to the PM 2.5 mass. The increasing oxidation rates of SO 2 and NO 2 from summer to winter indicate that the secondary transformation of gaseous pollutants is strongly positively correlated with relative humidity. Second, the positive matrix factorization (PMF) method shows that identified PM 2.5 sources include secondary inorganic aerosol source (SIS, 42.5 %), coal combustion (CC, 22.4 %), industry source (IS, 17.3 %), vehicle emission (VE, 10.7 %), fugitive dust (FD, 5.8 %), and other sources (1.3 %). The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the concentration-weighted trajectory (CWT) analysis are used to further explore different spatial distributions and regional transport of sources. The concentrations (10–11 µ g m -3) of SIS and CC distribute in Nanjing and central China in winter. The concentrations (8–10 µ g m -3) of IS and VE are potentially located north of Jiangsu, Anhui, and Jiangxi. Finally, the health risk assessment indicates that the carcinogenic and non-carcinogenic risks of toxic elements (Cr, As, Ni, Mn, V, and Pb) mainly come from IS, VE, and CC, which are within the tolerance or acceptable level. Although the main source of pollution in Nanjing is SIS at present, we should pay more attention to the health burden of vehicle emissions, coal combustion, and industrial processes. [ABSTRACT FROM AUTHOR]

Given the increasing complexity of the chemical composition of PM2.5, identifying and quantitatively assessing the contributions of pollution sources has played an important role in formulating policies to control particle pollution. This study provides a comprehensive assessment between PM2.5 chemical characteristics, sources, and health risks based on sampling data conducted over one year (March 2018 to February 2019) in Nanjing. Results show that PM2.5 exhibits a distinct variation across different seasons, which is primarily driven by emissions, meteorological conditions, and chemical conversion of gaseous pollutants. First, the chemical mass reconstruction shows that secondary inorganic aerosols (SIA, 62.5 %) and carbonaceous aerosols (21.3 %) contributed most to the PM2.5 mass. The increasing oxidation rates of SO2 and NO2 from summer to winter indicate that the secondary transformation of gaseous pollutants is strongly positively correlated with relative humidity. Second, the positive matrix factorization (PMF) method shows that identified PM2.5 sources include SIA (42.5 %), coal combustion (CC, 22.4 %), industry source (IS, 17.3 %), vehicle emission (VE, 10.7 %), fugitive dust (FD, 5.8 %) and other sources (1.3 %). The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the concentration-weighted trajectory (CWT) analysis are used to further explore different spatial distributions and regional transport of sources. High emissions (10-11 μg·m−3) of SIA and CC distribute in Nanjing and central China in winter. Moderate emissions (8-9 μg·m−3) of IS and VE are potentially located in the north of Jiangsu, Anhui, and Jiangxi. The PM2.5 pollution from long-range transport is attenuated by meteorological conditions and ocean air masses. Finally, the health risk assessment indicates that the carcinogenic and non-carcinogenic risks of toxic elements (Cr, As, Ni, Mn, V, and Pb) mainly come from IS, VE, and CC, which are within the tolerance or acceptable level. Although the main source of pollution in Nanjing is SIA at present, we should pay more attention to the health burden of vehicle emissions, coal combustion, and industrial processes. [ABSTRACT FROM AUTHOR]

The rapid urbanization in China is accompanied by increasingly serious air pollution. Particulate matter and ozone are the main air pollutants, and the study of their vertical distribution and correlation plays an important role in the synergistic air pollution control. In this study, we performed Lidar- and UAV-based observations in spring in Nanjing, China. The average concentrations of surface ozone and PM2.5 during the observation period are 87.78 µg m−3 and 43.48 µg m−3, respectively. Vertically, ozone reaches a maximum in the upper boundary layer, while the aerosol extinction coefficient decreases with height. Generally, ozone and aerosol are negatively correlated below 650 m. The correlation coefficient increases with altitude and reaches a maximum of 0.379 at 1875 m. Within the boundary layer, ozone and aerosols are negatively correlated on days with particulate pollution (PM2.5 > 35 μg m−3), while on clean days they are positively correlated. Above the boundary layer, the correlation coefficient is usually positive, regardless of the presence of particulate pollution. The UAV study compensates for Lidar detections below 500 m. We found that ozone concentration is higher in the upper layers than in the near-surface layers, and that ozone depletion is faster in the near-surface layers after sunset. [ABSTRACT FROM AUTHOR]

In this study, the concentrations and chemical components of size-fractionated particulate matter (PM) in Nanjing at the ground (Gulou, 20 m) and above the urban canopy (Zifeng, 380 m) were sampled and analyzed from 16 November to 12 December in 2016. Higher concentrations of PM10, PM10-2.1, and PM2.1 (108.3 ± 23.4 μg m−3, 47.3 ± 10.6 μg m−3, and 61.0 ± 18.8 μg m−3) were measured at Gulou than those (88.1 ± 21.1 μg m−3, 31.4 ± 6.7 μg m−3, and 56.7 ± 18.6 μg m−3) at Zifeng. The most abundant chemical components for size-fractionated PM were SO42−, NO3−, organic carbon (OC), NH4+, elemental carbon (EC), and crustal elements such as Al, Ca, Fe, and Mg, varying significantly on different particulate sizes. The concentrations of OC and EC were 7.46–19.60 μg m−3 and 3.44–5.96 μg m−3 at Gulou and were 8.34–18.62 μg m−3 and 2.86–4.11 μg m−3 at Zifeng, showing an equal importance in both fine and coarse particles. Nitrate, sulfate, and ammonium were more concentrated in PM2.1, contributing 11.30–13.76 μg m−3, 8.91–9.40 μg m−3, and 5.78–6.81 μg m−3, which was more than in PM10-2.1, which contributed 2.73–5.06 μg m−3, 2.16–3.81 μg m−3, and 0.85–0.87 μg m−3. In contrast, the crustal elements were larger in coarse particles and at the ground level, accounting for 18.6% and 15.3% of the total PM at Gulou and Zifeng. Source apportionment using the chemical mass balance (CMB) model EPA showed that the dominant three sources were secondary nitrate (18.2–24.9%), secondary sulfate (14.5–20.4%), and secondary organic aerosols (15.5–19.6%) for PM10, PM2.1, and PM1.1 at both Gulou and Zifeng during the entire sampling period. However, for PM10-2.1, the largest three contributors were secondary organic aerosols (18.3%), the coal-fired power plant (15.6%), and fugitive dust (14.4%), indicating dusts including construction dust, fugitive dust, and soil dust would contribute more at the ground. The results also showed that the concentrations of PM10, PM2.1, and PM1.1 were lower than the work carried out in the winter of 2010 at the same sampling site by 41.4%, 26.3%, and 24.8%, confirming the improvement of the air quality and the efficient control of PM pollutants. [ABSTRACT FROM AUTHOR]

Aerosols and ozone have significant influences on air qualities, human health, and climate changes. To further understand the characteristics and interactions among different urban air pollutants in the west Yangtze River Delta (YRD) region, continuous measurements of low-layer atmospheric particles and trace gases have been performed at an urban site in Nanjing from September 2016 to February 2017 in this study. In the urban area of the west YRD, the mean PM 10 and O3 concentrations are 86.3 µ g m -3 and 37.7 ppb, respectively, with significant seasonal and diurnal variations. Particles, which are dominated by fine aerosols, are relatively scattering. And most of their optical properties have similar variations to the aerosol concentrations. Results also show that the west YRD could still suffer severe air pollution, although the seasonal mean aerosol concentrations have decreased in recent years. Even in cold seasons, O3 could exceed the National Ambient Air Quality Standards for about 40 days during the sampling period. Most of polluted episodes are caused by local and subregional emissions. A case study for a typical O3 and PM 2.5 episode in December 2016 demonstrates that the episode was generally associated with regional transport and a stable weather system. Air pollutants were mostly transported from the western areas with high emissions, as well as with an anticyclone and high-pressure system in this region. Correlation analysis reveals that the interactions between O3 and PM are complex, with a combination of inhibition and promotion under different conditions. The inhibition effect might result from the reduction of photolysis frequency near the surface due to aerosols in addition to their positive correlations with precursors, while the promotion effect is from the formation of secondary aerosols under high concentrations of oxidants and solar radiation. However, the interaction between O3 and BC shows an inhibiting effect due to its chemical stability. This also indicated a VOC-sensitive regime for photochemical production of O3 in this region. This study further improves insight into the characteristics and interactions of main pollutants and may contribute to the improvement of the simulation and prediction of aerosols and gases in the urban area of the YRD. [ABSTRACT FROM AUTHOR]

To improve our understanding of the interplay among local and regional photochemical pollutants in the typical city of the Yangtze River Delta (YRD) region, the concurrent observation of O 3 and NO x concentrations at an urban and a suburban site in Nanjing during 2008 is presented. In general, the annual mean O 3 concentration is 2.35 ppbv lower in the downtown than at suburban due to higher NO x pollution levels correlated with heavy traffic. At both sites, O 3 shows a distinct seasonality with the spring maximum and the winter minimum, while the minimum concentration of NO x appears in summertime. Besides the chemical processes of O 3 sensitivity in the daytime and the NO x titration at night, meteorological conditions also play an essential role in these monthly and diurnal variations. The ozone weekend effect that can be attributed to the weekly routine of human activities is observed in the urban atmosphere of Nanjing as well, with O 3 concentrations 2.09 ppbv higher and NO x concentrations 6.20 ppbv lower on weekends than on weekdays. The chemical coupling of NO, NO 2 and O 3 is investigated to show that the OX-component (O 3 and NO 2 ) partitioning point occurs at about 35 ppbv for NO x , with O 3 being the dominant form at lower levels and NO 2 dominating at higher levels. And it is also discovered that the level of OX is made up of two contributions, including the regional contribution affected by regional background O 3 level and the local contribution correlated with the level of primary pollution. The diurnal peak of regional contribution appears 2–5 h after the peak of local contribution, implying that OX in Nanjing might prominently affected by the pollutants from a short distance. The highest regional contribution and the second highest local contribution lead to the spring peak of O 3 observed in Nanjing, whereas the highest local contribution and the moderate regional contribution make the O 3 concentrations in summer higher than those in autumn and winter. Our results reveal the important environment impacts from meteorological conditions and human activities in the YRD region, and can help to understand O 3 pollution in these polluted areas by just using the conventional observations. [ABSTRACT FROM AUTHOR]

Water-soluble inorganic ions (WSIIs) are major components of PM 2.5 , and play a prominent role in atmospheric acidification. In January 2019, a large-scale persistent particle pollution episode occurred in the Yangtze River Delta (YRD) region of China. High time resolution on-line monitoring of WSIIs in PM 2.5 were conducted at the Atmospheric Environment Vertical Observation Station of Nanjing University by using In-situ Gas and Aerosol Compositions Monitor. From January 1 to 13, the mean concentration of WSIIs was 76.7 ± 48.2 μg·m−3. WSIIs accounted for 64.2% of PM 2.5 concentration. Sulfate, nitrate and ammonium (SNA) were the major components of WSIIs, and accounted for 25.5%, 45.6% and 26.3%, respectively. The values of NO 3 −/SO 4 2− increased from 1.37 to 2.86, indicating that the contribution of mobile sources to fine particle pollution was significantly enhanced than that of stationary sources. The main factors affecting the values of sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) were gaseous precursor concentrations, relative humidity and air temperature. The values of SOR and NOR exceeded 0.1, implying the secondary transformation processes played critical roles during this pollution episode. To investigate the potential source areas of WSIIs in PM 2.5 , the Principal Component Analysis - Multiple Linear Regression (PCA-MLR) analysis and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model were used. By using PCA-MLR, it was found that the main pollution sources in Nanjing were secondary transformation (58%), manmade dust (26%) and biomass combustion (16%). Based on the backward trajectory calculation, the potential source contribution function (PSCF) analysis and the concentration weighted trajectory (CWT) analysis, it was revealed that the air pollutants mainly came from the local sources in and around Nanjing. With the aggravation of pollution, the contribution of regional transport to PM 2.5 concentrations decreased and the contribution of local emissions increased. Among the main components of WSIIs in Nanjing, NH 4 + was mainly caused by agricultural activities, and generally came from Jiangsu, eastern Henan, southern Shandong, and northeastern Anhui. SO 4 2− was mainly derived from coal burning in the nearby industrial areas or from the north through the long-distance transmission. NO 3 − mainly concentrated in the local areas, which was greatly affected by human activities. The weighted concentration weighted trajectory (WCWT) peak values of NH 4 + and SO 4 2− were about 10 μg·m−3, while that of NO 3 − was more than 20 μg·m−3, which further indicated that the local emission of NO 3 − was the main potential source. The findings can contribute to understand the behavior of WSIIs and their roles in the wintertime haze event, reveal potential source areas for the corresponding components, and enlighten beneficial suggestions for particle pollution prevention and control in high polluted areas. • High time resolution observation of WSIIs were carried out in Nanjing, China. • Characteristics of different WSIIs composition during a wintertime haze were analyzed. • Potential pollution components and areas were identified by the principal component analysis and backward trajectory calculation. • Secondary transformation of SNA was the main potential source. • Local emission was the main potential source contributor. [ABSTRACT FROM AUTHOR]

Aerosol optical properties at Gulou station in Nanjing, China were measured and analyzed from April 2011 to April 2012. The annual median of aerosol optical depth (hereafter called as AOD) at 440 nm was 0.73 and the corresponding annual median of angstrom exponent (hereafter called as AE) between 440 nm and 870 nm was 1.28. The monthly median of AOD 440nm presented a seasonal variation, which revealed a maximum in August (1.22) and a minimum in February (0.51), while the monthly median of AE showed a minimum in May (0.79) and a maximum in December (1.42). AOD and AE accumulated mainly between 0.40–0.90 (68%) and 1.20–1.50 (68%) respectively in Nanjing. The observation data showed that high AODs (>1.00) were clustered in the fine mode growth wing and the coarse mode. Comparison was made between two typical cases under different weather conditions and the results showed that Nanjing is influenced by the dust aerosol from Northwest China and Mongolia under dust weather in spring and the anthropogenic aerosol from local emission and surrounding industrialization region under haze weather. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols are important absorbing components that can impact the regional climate and environment. To better understand the effects of BC, long-term variations in BC concentrations and the relationships between BC and other air pollutants were investigated in urban Nanjing in the Yangtze River Delta (YRD) based on near-nine-year observations using a seven-channel aethalometer (AE-31). The BC concentrations in YRD city had substantial seasonal and diurnal variations, which are higher in winter (rush hours) and lower in summer (at noon). They had a significant declining trend since 2013 when the Action Plan for Air Pollution Prevention and Control was carried out, which was reduced by at least 45% from 2013 to 2019, and the same applies to heavy pollution episodes. The aerosol absorption coefficient (AAC) had temporal variations similar to those of the BC concentration because BC was the dominant component of absorbing aerosols (>80% at 550 nm). Investigations also indicated that the average contributions of BC from biomass burning (BC bb) and fossil fuel (BC ff) to the total BCs concentration could be of equal importance. However, the ratios of BC bb to the total BCs in colder seasons were much higher than those in summer. Nevertheless, both BC bb and BC ff might significantly contribute to the high BC loadings during particulate pollution episodes. Further comparisons showed that BCs had substantial positive correlations with CO and PM 2.5. The relationships between BC and CO imply that the sources of fossil fuel BC aerosols in Nanjing might mainly came from the combustion of industrial coal and gasoline vehicles. An extremely high BC loading or higher BC/PM 2.5 ratio always corresponded to a lower O 3 concentration, implying that BC might have a substantial influence on O 3 formation. • The interannual variation trend of black carbon is revealed in an urban area of China. • BC from biomass and fossil fuel combustion in the Yangtze River Delta region are qualified. • BC might have a potential influence on tropospheric ozone formation. [ABSTRACT FROM AUTHOR]

In this study, samples of size-fractionated particulate matter were collected continuously using a 9-size interval cascade impactor at an urban site in Nanjing, before, during and after the Asian Youth Games (AYG), from July to September of 2013, and the Youth Olympic Games (YOG), from July to September of 2014. First, elemental concentrations, water-soluble ions including Cl − , NO 3 − , SO 4 2 − , NH 4 + , K + , Na + and Ca 2 + , organic carbon (OC) and elemental carbon (EC) were analysed. Then, the source apportionment of the fine and coarse particulate matter was carried out using the chemical mass balance (CMB) model. The average PM 10 concentrations were 90.4 ± 20.0 μg/m 3 during the 2013 AYG and 70.6 ± 25.3 μg/m 3 during the 2014 YOG. For PM 2.1, the average concentrations were 50.0 ± 12.8 μg/m 3 in 2013 and 34.6 ± 17.0 μg/m 3 in 2014. Investigations showed that the average concentrations of particles declined significantly from 2013 to 2014, and concentrations were at the lowest levels during the events. Results indicated that OC, EC, sulfate and crustal elements have significant monthly and size-based variations. The major components, including crustal elements, water-soluble ions and carbonaceous aerosol accounted for 75.3–91.9% of the total particulate mass concentrations during the sampling periods. Fugitive dust, coal combustion dust, iron dust, construction dust, soil dust, vehicle exhaust, secondary aerosols and sea salt have been classified as the main emissions in Nanjing. The source apportionment results indicate that the emissions from fugitive dust, which was the most abundance emission source during the 2013 AYG, contributed to 23.0% of the total particle mass. However, fugitive dust decreased to 6.2% of the total particle mass during the 2014 YOG. Construction dust (14.7% versus 7.8% for the AYG and the YOG, respectively) and secondary sulfate aerosol (9.3% versus 8.0% for the AYG and the YOG, respectively) showed the same trend as fugitive dust, suggesting that the mitigation measures of controlling particles from the paved roads, construction and industry worked more efficiently during the YOG. [ABSTRACT FROM AUTHOR]

Although China is a big carbon dioxide (CO 2 ) emitter, in situ measurements of atmospheric CO 2 are sparse in urban China. The mixing ratio of carbon dioxide (CO 2 ) and its influencing factors in urban Nanjing were investigated in this study, from the 18th of January to the 31st of December 2011. The annual average mixing ratio of CO 2 was 406.5 ± 20.0 ppmv over the study period. The signal analysis using the fast Fourier transform (FFT) algorithm showed that CO 2 had different cycles as a result of multiple controlling factors. The seasonal and intra-seasonal fluctuations of CO 2 were mainly caused by the terrestrial biospheric uptake and emission and atmospheric oscillation. The weekly variation of CO 2 was largely influenced by traffic volume. The diurnal cycle of CO 2 presented a bimodal pattern in winter (DJF) probably due to the rush hour emissions. The seasonal mean CO 2 /CO correlation slope varied from 0.024 ppmv/ppbv to 0.029 ppmv/ppbv, comparable to the fossil fuel combustion emission ratio. The diurnal pattern of CO 2 /CO was irregular, indicating random anthropogenic emissions in an urban area. Firework setting was a large source of CO 2 during the Spring Festival holiday. The backward trajectories by the HYSPLIT model showed that the local anthropogenic emissions contributed the most to the high CO 2 mixing ratio in the urban area. [ABSTRACT FROM AUTHOR]

Abstract: Visibility, Air Pollution Index (API) and meteorological parameters over Nanjing during 2004 are analyzed using multiple statistic methods to study the characterization of visibility and relevant affecting factors. The mean value of visibility during the study year is 8.8km, with 57.9% of daily average less than 10km. Annual average visibility exhibits a significant diurnal variation with minimum of 6.6km at 07:00 Local Time (LT) and maximum of 10.7km at 16:00 LT. Seasonal variations is weak: 9.2km in spring (March–May), 9.8km in summer (June–August), 8.2km in autumn (September–November), and 8.1km in winter (December–February), respectively. No significant weekend effect in visibility is found. Moreover, wavelet analysis reveals the significant periodic variations in visibility, with major periods of synoptic scale (2–8days), and quasi-two-week scale (8–17days). Using a high pass filtering technique to eliminate the seasonal trend, correlation analysis and principal component analysis (PCA) are carried out to investigate the relations between visibility and relevant factors and to understand the dominated processes/causes to the synoptic changes in visibility. Our results highlight the significant impact of synoptic weather on air pollution and visibility in Nanjing. [Copyright &y& Elsevier]

The vertical structure of ozone (O 3) and fine particulate matter (FPM) as well as their interactions are important for understanding the atmospheric chemistry process and their impact on climate. Through a ground-based lidar observation during April 18th-May 22nd 2017 and surface measurement during March 1st-May 31st 2017, this study obtained the vertical distribution of O 3 and aerosol extinction coefficient with their correlations during the springtime in the lower troposphere (LT) in Nanjing, eastern China. Surface average O 3 and PM 2.5 concentrations in spring were 39.89 ppb and 41.93 μg m−3. O 3 generally increased with height in the LT, while aerosol extinction coefficient decreased. The correlation between O 3 and aerosol extinction coefficient was −0.32 at 300 m, and 0.34 at 1747.5 m. An on-line coupled model Weather Research and Forecasting with Chemistry (WRF-Chem) was used to analyze the effect of aerosol's radiation feedback on ozone. Aerosol reduced the surface downward shortwave radiation by −25.66 W m−2, and increased the upwelling shortwave radiation at the top of atmosphere by 3.19 W m−2 in urban Nanjing. The photolysis rate of NO 2 and O1D were reduced by −1% and −0.7% near surface and increased by 0.3% and 0.2% at upper LT. Aerosol-included effect also led to a more stable planet boundary layer (PBL), with −0.24 °C and −0.05 m s−1 changes in temperature and wind speed at surface. However, the temperature and wind speed increased by 0.18 °C and 0.13 m s−1 at 1760 m, respectively. O 3 decreased by −3.70% at surface and increased by 0.89% at 2870 m. This study showed that aerosol can affect ozone through altering photolysis rate and atmospheric stability. Aerosol's radiation feedback has a complex effect on the vertical structure of ozone, which leads to ozone decrease near the surface and increase above the aerosol layer. • The vertical structure and the correlation of O 3 and PM 2.5 were analyzed. • O 3 increases with height in the lower troposphere, while aerosol decreases. • PM 2.5 reduces surface O 3 by reducing photolysis rate and increasing PBL stability. • PM 2.5 and O 3 are positive correlated at higher altitudes. [ABSTRACT FROM AUTHOR]