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• NO3- concentrations in coarse particles show elevations in warm seasons. • Size distributions of semi-volatile species have a dependency on ambient temperatures. • Relative humidity plays a role in driving seasonal changes of PM size distributions. • Heterogeneous formations of secondary salts contribute ∼20% of speciated coarse PM. Size-segregated ambient particulate matter (PM) samples were collected seasonally in suburban Nanjing of east China from 2016 to 2017 and chemically speciated. In both fine (< 2.1 µm, PM 2.1) and coarse (> 2.1 µm, PM >2.1) PM, organic carbon (OC) accounted for the highest fractions (26.9% ± 10.9% and 23.1% ± 9.35%) of all measured species, and NO 3 − lead in average concentrations of water-soluble inorganic ions (WSIIs). The size distributions of measured components were parameterized using geometric mean diameter (GMD). GMD values of NO 3 −, Cl−, OC, and PM for the whole size range varied from < 2.1 µm in winter to > 2.1 μm in warm seasons, which was due to the fact that the size distributions of semi-volatile components (e.g., NH 4 NO 3 , NH 4 Cl, and OC) had a dependency on the ambient temperature. Unlike OC, elemental carbon (EC), and elements, NH 4 +, NO 3 −, and SO 4 2− exhibited an increase trend in GMD values with relative humidity, indicating that the hygroscopic growth might also play a role in driving seasonal changes of PM size distributions. Positive matrix factorization was performed using compositional data of fine and coarse particles, respectively. The secondary formation of inorganic salts contributing to the majority (> 70%) of fine PM and 20.2% ± 19.9% of speciated coarse PM. The remaining coarse PM content was attributed to a variety of dust sources. Considering that coarse and fine PM had comparable mass concentrations, more attention should be paid to local dust emissions in future air quality plans. [Display omitted] [ABSTRACT FROM AUTHOR]

This study seeks to understand the ambient levels, gas/particle partitioning, and sources of nonpolar organic molecular makers (OMMs) at a suburban site in Nanjing, China. Particle‐ and gas‐phase OMMs were collected using a medium volume sampler equipped with two quartz filters in series and a polyurethane foam (PUF)/XAD‐4/PUF (PXP) adsorbent sandwich. More than 100 pairs of filter and PXP samples were collected diurnally from September 2018 to September 2019. The concentration profiles of total n‐alkanes and polycyclic aromatic hydrocarbons were peaking at n‐C12–n‐C17 homologs (9.98 ± 5.43–38.4 ± 17.7 ng m−3) and naphthalene (92.5 ± 56.7 ng m−3), respectively, followed by decreasing concentrations with further increases in molecular weight. Three artifact correction methods with different pre‐assumptions on relative contributions of evaporation loss to backup filter measurements were used to separate particle‐ and gas‐phase OMMs. The resulting particle‐phase fractions showed significant differences for OMMs with vapor pressure <10−9 atm at 298.15 K. Absorptive gas/particle partitioning coefficients of OMMs were empirically calculated based on measurements and theoretically predicted for comparison. The results obtained under the three artifact correction methods suggested growing importance of evaporation loss with decreased vapor pressure. Positive matrix factorization (PMF) was performed for source apportionment using total (PMFtotal) and particle‐phase (PMFparticle) OMMs data, respectively. Besides eliminating the influence of gas/particle partitioning, the involvements of more volatile species and gaseous OMMs data improved the identification of specific emission sources, supporting the usage of total OMMs data over a wide vapor pressure range for PMF source apportionment. Key Points: The particulate fractions of organic molecular markers attained their minima in summer, when the total concentrations increasedEvaporation loss might be the main sampling artifact of particulate organics when the vapor pressure is lower than 10−10 atmTotal concentrations of organic molecular markers over a wide vapor pressure range should be used for positive matrix factorization analysis [ABSTRACT FROM AUTHOR]

Ammonia control has received increasing attention as a measure to decrease particulate concentrations. Modeling analysis of observation data from central China over the period of September 2015 to August 2016 shows clear asymmetric responses of particulate pH and mass to ammonia emissions. With a change of ±80% of NHx (NH3 + NH4+), the corresponding ΔpH are +0.5 and −3.0, respectively, and the corresponding particulate NH4+ changes are +2.62% and −61.8%, respectively. This asymmetry implies that there is a Critical Total Ammonia Concentration, above which particulate pH and mass are insensitive to ammonia control. Analysis of the observation data suggests that the Critical Total Ammonia Concentration is −25%. The estimated cost for an NHx reduction of 25% is $140 – 320 million for Hubei province, which is the initial cost barrier before ammonia control can effectively affect particulate pH and mass in central China. This cost barrier will increase as NOx and SO2 emissions decrease. Key Points: Only after NHx reduction exceeds 25% can ammonia control effectively reduce the inorganic aerosol massMore NHx reduction will be required to reach the critical point of effective ammonia control as NOx and SO2 emissions decreaseA large enough NHx reduction (60%–80%) renders concurrent reduction of NOx emissions ineffective and even the effect of SO2 emission control is reduced [ABSTRACT FROM AUTHOR]

Elemental concentrations of ambient aerosols are commonly sampled over 12–24 h, and the low time resolution puts a great limit on current understanding about the temporal variations and source apportionment based on receptor models. In this work, hourly-resolved concentrations of eighteen elements in PM 2.5 at an urban site in Nanjing, a megacity in Yangtze River Delta of east China, were obtained by using a Xact 625 ambient metals monitor from 12/12/2016 to 12/31/2017. The influence of traffic activities was clearly reflected by the spikes of crustal elements (e.g., Fe, Ca, and Si) in the morning rush hour, and the firework burning and sandstorm events during the sampling periods were tracked by sharp enrichment of Ba, K and Fe, Ca, Si, Ti in PM 2.5 , respectively. To evaluate the advantage of hourly-resolved elements data in identifying impacts from specific emission sources, positive matrix factorization (PMF) analysis was performed with the 1-h data set (PMF 1-h) and 23-h averaged data (PMF 23-h), respectively. The 4- and 6-factor PMF 23-h solutions had similar factor profiles and consistent factor contributions as the corresponding PMF 1-h solutions. However, due to the limit in inter-sample variability, PMF analysis with 23-h average data misclassified some major (e.g., K, Fe, Zn, Ca, and Si) and trace (e.g., Pb) elements in factor profiles, resulting in different absolute factor contributions between PMF 23-h and PMF 1-h solutions. These results suggested the use of high time-resolved data to obtain valid and robust source apportionment results. Image 1 • PM 2.5 elements were measured with 1-h resolution at an urban site in Nanjing city. • Specific local emissions were reflected by the diurnal variations of PM 2.5 elements. • Two pollution episodes were tracked by sharp enrichment of distinct elements. • The 1-h measurements data were preferred over 23-h averages for source apportionment. This study suggests using high time-resolved measurements of PM 2.5 elements for receptor-based source apportionment to obtain robust results. [ABSTRACT FROM AUTHOR]

Intense new particle formation (NPF) events were observed in the coastal atmosphere during algae growth and farming season at Xiangshan gulf of the east China coast. High nucleation-mode iodine concentrations measured by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) confirmed that the NPF events were induced by iodine species. Our study provides important information on iodine speciation, size distributions, and its role in NPF in the context of heavy air pollution in China's coastal areas. For the first time, we identified 5 inorganic iodine species, 45 organic iodine compounds (35 molecular formulas), and a group of iodide–organic adducts in aerosols. The concentrations and size distributions of iodine species down to 10 nm were measured during the iodine-induced NPF, continental NPF, and non-NPF days at the coastal site and compared to those at an inland site. The iodine in the above four aerosol sample types were characterized by iodate, aromatic iodine compounds, iodoacetic acid or iodopropenoic acid, and iodide–organic adducts, respectively. Iodide and organic iodine compounds were found in the nucleation-mode particles; however, it is still not clear whether they contributed to nucleation or just new particle growth. Wild algae, as well as farmed algae, could be an important NPF source in China's coastal areas. [ABSTRACT FROM AUTHOR]

Owing to the potential influence of light-absorbing organic carbon (OC), also termed "brown carbon" (BrC), on the planetary radiation budget, many studies have focused on its absorption in single-sized ranges of particulate matter (PM). However, the size distribution and organic tracer-based source apportionment of BrC absorption have not been extensively investigated. In this study, size-resolved PM samples were collected using multi-stage impactors from eastern Nanjing during each season in 2017. The light absorption of methanol-extractable OC at 365 nm (Abs 365 , Mm−1) was determined using spectrophotometry, and a series of organic molecular markers (OMMs) was measured using a gas chromatography-mass spectrometer. Fine PM with an aerodynamic diameter <2.1 μm (PM 2.1) dominated Abs 365 (79.8 ± 10.4%) of the total size ranges with maxima and minima in winter and summer, respectively. The distributions of Abs 365 shifted to larger PM sizes from winter to spring and summer due to lower primary emissions and increased BrC chromophores in dust. Except for low-volatility (p o,* L < 10−10 atm) polycyclic aromatic hydrocarbons (PAHs), the non-polar OMMs, including n- alkanes, PAHs, oxygenated PAHs, and steranes, showed a bimodal distribution pattern. Secondary products of biogenic precursors and biomass burning tracers presented a unimodal distribution peaking at 0.4–0.7 μm, while sugar alcohols and saccharides were enriched in coarse PM. Their seasonal variations in average concentrations reflected intense photochemical reactions in summer, more biomass burning emissions in winter, and stronger microbial activity in spring and summer. Positive matrix factorization was used for the source apportionment of Abs 365 in fine and coarse PM samples. Biomass burning contributed an average of 53.9% to the Abs 365 of PM 2.1 extracts. The Abs 365 of coarse PM extracts was associated with various dust-related sources where the aging processes of aerosol organics could occur. [Display omitted] • Fine particles dominated the light absorption of methanol extracts of total PM. • Low-volatile n- alkanes and steranes in coarse PM increased during warm periods. • Biomass burning contributed more than 50% to BrC absorption in fine PM. • Aging processes of organics in coarse particles could lead to BrC formation. [ABSTRACT FROM AUTHOR]

Atmospheric trace elements, especially metal species, are an emerging environmental and health concern with insufficient understanding of their levels and sources in Shanghai, the most important industrial megacity in China. Here we continuously performed a 1 year (from March 2016 to February 2017) and hourly resolved measurement of 18 elements in fine particles (PM2:5) at the Shanghai urban center with an Xact multi-metals monitor and several collocated instruments. Mass concentrations (mean±1σ; ngm-3) determined by Xact ranged from detection limits (nominally 0.1 to 20 ngm-3) to 15 µgm-3. Element-related oxidized species comprised an appreciable fraction of PM2:5 during all seasons, accounting for 8.3% on average. As a comparison, the atmospheric elements concentration level in Shanghai was comparable with that in other industrialized cities in East Asia but 1 or 2 orders of magnitude higher than at sites in North America and Europe. Positive matrix factorization (PMF) was applied to identify and apportion the sources of the elements in the PM2:5 mass. Five different factors were resolved (notable elements and relative contribution in parentheses): traffic-related (Ca, Fe, Ba, Si; 46%), shipping (V, Ni; 6%), nonferrous metal smelting (Ag, Cd, Au; 15%), coal combustion (As, Se, Hg, Pb; 18%) and ferrous metal smelting (Cr, Mn, Zn; 15%). The contribution from the exhaust and non-exhaust vehicle emissions, i.e., the traffic-related factor shows a strong bimodal diurnal profile with average concentration over 2 times higher during the rush hour than during nighttime. The shipping factor was firmly identified because V and Ni, two recognized tracers of shipping emissions, are almost exclusively transported from the East China Sea and their ratio (around 3.2) falls within the variation range of V= Ni ratios in particles emitted from heavy oil combustion. Interestingly, nearly half of the K was derived from coal combustion with high mineral affinity (elements associated with aluminosilicates, carbonates and other minerals in coal ash). The contributions of nonferrous metal smelting to the trace elements are consistent with a newly developed emission inventory. Although the precipitation scavenging effect on the mass concentration of the trace elements varied among different species and sources, precipitation could effectively lower the concentration of the trafficand coal combustion-related trace elements. Therefore, water spray to simulate natural types of precipitation could be one of the abatement strategies to facilitate the reduction of ambient PM2:5 trace elements in the urban atmosphere. Collectively, our findings in this study provide baseline levels and sources of trace elements with high detail, which are needed for developing effective control strategies to reduce the high risk of acute exposure to atmospheric trace elements in China's megacities. [ABSTRACT FROM AUTHOR]

BSTRACT Primary (i.e. sugars and sugar-alcohols) and secondary (i.e. carboxylic acids) water-soluble organic compounds (WSOCs) in size-segregated aerosols from the urban and mountain atmosphere of China and from the marine atmosphere in the outflow region of East Asia were characterized on a molecular level. Levoglucosan is the most abundant compound among the quantified WSOCs in the urban and mountain atmosphere, whose concentration at the urban site was 1-2 orders of magnitude higher than that at the mountain and marine sites. In contrast, malic, succinic and phthalic acids were dominant among the measured WSOCs at the marine site. In the urban air, sugars except levoglucosan gave a bimodal size distribution with a large peak in fine range (<2.1 μm) and a small peak in coarse range (≥2.1 μm) during winter, being opposite to those in spring. In contrast, these WSOCs at the mountain and marine sites dominated in the coarse range but diminished and even disappeared in the fine range. Geometric mean diameters (GMDs) of the measured WSOCs in the fine mode at the urban site were larger in winter than in spring. Levoglucosan and carboxylic acids except for azelaic and benzoic acids showed a larger GMD in the coarse mode at the marine site probably due to an increased hygroscopic growth. [ABSTRACT FROM AUTHOR]

Abstract: Polar organic compounds and elements were quantified in PM10 aerosols collected in urban and rural areas of Baoji, an inland city of China, during winter and spring 2008. Concentrations of biomass burning markers and high molecular weight n-alkanoic acids (HMW, >C22:0) were heavily increased in winter. In contrast, sugars presented in higher levels in the spring, among which sucrose was the most abundant with an average of 219ngm−3 in winter and 473ngm−3 in spring respectively. This suggests enhanced biotic activity in the warm season, whereas no obvious trend was observed for sugar alcohols, concentrations of the three sugar alcohols in spring were only 0.94–2.3 times as those in winter, indicating a second pathway of their formation other than fungal spores in cold season. Major crustal elements (i.e., Fe, K, Mn and Ti) in PM10 aerosols were also observed in larger concentrations in spring samples than those in winter due to an enhancement of coarse particles from soil minerals. By using principal component analysis (PCA) and positive matrix factorization (PMF), sources and their contributions to the PM components were also investigated in this study. Four factors were extracted with both models, and the sources represented by different factors were based on the highest loaded marker species as follows: factor 1, soil and road dust (Fe, Sr and Ti); factor 2, biomass burning (levoglucosan, galactosan and syringic acid); factor 3, microbial emissions (fructose and sucrose); and factor 4, fossil fuel combustion and fungal spores influence (Pb, Zn, arabitol and mannitol). The high correlation between PM10 and factor 1 suggested that PM10 pollution in Baoji was dominated by soil and dust re-suspension. [Copyright &y& Elsevier]

Abstract: Normal alkanes and PAHs in atmospheric PM10 aerosols collected during 2008 winter and spring in Baoji, a mid-scale inland city of China, were determined on a molecular level. Concentrations of n-alkanes ranged from 232 to 3583 ng/m3 with an average of 1733 ng/m3 in winter and from 124 to 1160 ng/m3 with an average of 449 ng/m3 in spring, while PAHs in the PM10 samples were 594±405 and 128±82 ng/m3 in the two seasons. Molecular compositions showed that CPI (odd/even) values of n-alkanes were close to unity for all the samples especially in winter, and diagnostic ratios of PAHs (e.g., Phe/(Phe+Ant), CPAH/ΣPAHs and IcdP/(IcdP+BghiP)) were found similar to those in coal burning smoke with a strong linear relationship (R 2 ≥0.85) between PAHs and fossil fuel derived n-alkanes, demonstrating that coal burning is the main source of n-alkanes and PAHs in the city, especially in winter due to house heating. Concentrations of the determined compounds in Baoji are much higher than those in Chinese mega-cities, suggesting that air pollution in small cities in the country is more serious and need more attention. [Copyright &y& Elsevier]

Recently, the occurrence of fog and haze over China has increased. The retrieval of trace gases from the multi-axis differential optical absorption spectroscopy (MAX-DOAS) is challenging under these conditions. In this study, various reported retrieval settings for formaldehyde (HCHO) and sulfur dioxide (SO2) are compared to evaluate the performance of these settings under different meteorological conditions (clear day, haze, and fog). The dataset from 1st December 2019 to 31st March 2020 over Nanjing, China, is used in this study. The results indicated that for HCHO, the optimal settings were in the 324.5–359 nm wavelength window with a polynomial order of five. At these settings, the fitting and root mean squared (RMS) errors for column density were considerably improved for haze and fog conditions, and the differential slant column densities (DSCDs) showed more accurate values compared to the DSCDs between 336.5 and 359 nm. For SO2, the optimal settings for retrieval were found to be at 307–328 nm with a polynomial order of five. Here, root mean square (RMS) and fitting errors were significantly lower under all conditions. The observed HCHO and SO2 vertical column densities were significantly lower on fog days compared to clear days, reflecting a decreased chemical production of HCHO and aqueous phase oxidation of SO2 in fog droplets. [ABSTRACT FROM AUTHOR]

China is an important emitter of light-absorbing carbonaceous aerosols (LACs), including black carbon (BC) and brown carbon (BrC). Currently, there are large uncertainties in model-estimated direct radiative forcing (DRF) of LACs, partially due to the poor understanding of the emissions and optical properties of LACs. In this study, we estimated the DRF of LACs over China during the implementation of the Air Pollution Prevention and Control Action Plan (APPCAP) using the global chemical transport model (GEOS-Chem) coupled with the Rapid Radiative Transfer Model of GCMs (RRTMG). We updated the refractive index of BC, includedbiomass burning (BB) sources, biofuel (BF) and coal combustion (CC) sources in the residential sector as BrC emission sources and the optical properties were updated, which were not fully considered in the previous model studies. Our results showed that model could reasonably capture the spatial and temporal variations of LACs in China with the correlation coefficients between model simulated and Aerosol Robotic Network (AERONET) observed daily absorption aerosol optical depth (AAOD) of LACs at 440 nm above 0.63 and the corresponding values of the normalized mean bias within ±30%. The simulated annual mean LACs AAOD at 440 nm in China was 0.016 (0.021) in 2017 (2014) and BrC contributed about 20% (21%). The estimated annual mean clear-sky LACs DRF at the top of the atmosphere in China was 1.02 W m−2 in 2017 and 1.38 W m−2 in 2014, and the contribution of BrC was about 10% and 11%, respectively, which was dominated by the BF sources (46% in 2017 and 44% in 2014) and the BB sources (38% in 2017 and 43% in 2014), with CC sources being low (16% in 2017 and 13% in 2014). The annual mean AAOD and DRF of LACs in China decreased by 0.005 and 0.36 W m−2 from 2014 to 2017, which were largely attributed to the reductions of anthropogenic emissions during the implementation of APPCAP. Our results would improve the understanding of the light absorption capacity and climate effects of LACs in China. • BrC from residential biofuel and coal combustion, and biomass burning sources was included. • DRF of LACs at TOA in China was simulated to be 1.02 W m−2 (1.38 W m−2) in 2017 (2014). • BrC contributed about 10% (11%) to the DRF of LACs at TOA in 2017 (2014). [ABSTRACT FROM AUTHOR]

Abstract: Molecular compositions and size distributions of water-soluble organic compounds (WSOC, i.e., sugars, sugar-alcohols and carboxylic acids) in particles from urban air of Nanjing, China during a severe haze event caused by field burning of wheat straw were characterized and compared with those in the summer and autumn non-haze periods. During the haze event levoglucosan (4030 ng m−3) was the most abundant compound among the measured WSOC, followed by succinic acid, malic acid, glycerol, arabitol and glucose, being different from those in the non-haze samples, in which sucrose or azelaic acid showed a second highest concentration, although levoglucosan was the highest. The measured WSOC in the haze event were 2–20 times more than those in the non-hazy days. Size distribution results showed that there was no significant change in the compound peaks in coarse mode (>2.1 μm) with respect to the haze and non-haze samples, but a large difference in the fine fraction (<2.1 μm) was found with a sharp increase during the hazy days mostly due to the increased emissions of wheat straw burning. Molecular compositions of organic compounds in the fresh smoke particles from wheat straw burning demonstrate that sharply increased concentrations of glycerol and succinic and malic acids in the fine particles during the haze event were mainly derived from the field burning of wheat straw, although the sources of glucose and related sugar-alcohols whose concentrations significantly increased in the fine haze samples are unclear. Compared to that in the fresh smoke particles of wheat straw burning an increase in relative abundance of succinic acid to levoglucosan during the haze event suggests a significant production of secondary organic aerosols during transport of the smoke plumes. [Copyright &y& Elsevier]

In this study, collocated samples of particulate matter with aerodynamic diameter less than 2.5 μm (PM 2.5) were collected every sixth day on quartz filters (Q f) at a suburban site in northern Nanjing, China for one year. A backup quartz filter (Q b) was installed behind Q f to estimate positive artifacts. The analysis of gravimetric mass, water-soluble inorganic ions (WSIIs), total organic (OC) and elemental carbon (EC), water-soluble OC (WSOC), total nitrogen (WSTN) and organic nitrogen (WSON) were performed on both Q f and Q b. Due to the high mass loadings on Q f (17.9 ± 7.82 mg filter−1, 4.71–38.5 mg filter−1), the collocated precision of gravimetric mass and dominant species (NH 4 +, NO 3 −, SO 4 2−, OC, and EC) is better than that from previous work. Except K+, EC, and WSON, all other target components were detected on Q b with average Q b /Q f ratios ranging from 3.02 ± 3.48–21.7 ± 22.4%. The final concentrations and uncertainties of PM 2.5 components were determined based on duplicate Q f –Q b data. The results suggest that using an error fraction of 10% will underestimate the uncertainty of less concentrated species (e.g., Ca2+ and Mg2+) in PM 2.5. Due to the evaporation loss of semi-volatile materials from the Q f , the Q f –Q b calculation would lead to an estimate of the lower limit for particulate NH 4 +, NO 3 −, and OC. Synchronized hourly data of PM 2.5 mass and components were obtained at downtown Nanjing. The comparisons of gravimetric versus reconstructed PM 2.5 and filter-based versus continuous measurements of PM 2.5 components indicate that a substantial fraction of the unexplained gravimetric PM 2.5 can be attributed to aerosol water. Image 1 • Collocated precision of PM 2.5 components depends largely on filter loadings. • Besides OC adsorption, quartz filter sampling is also subject to surface reactions. • Assuming a constant error fraction of 10% is appropriate for PM 2.5 major components. • Water content contributes a substantial fraction of the unexplained gravimetric PM 2.5. [ABSTRACT FROM AUTHOR]

The influence of atmosphere pollution on human health is receiving more and more concerns as strengthened anthropogenic activity had brought excessive pollutant into the atmosphere. To date, the quantitative estimation about the contribution of atmosphere on the accumulation of heavy metal in the edible cereal parts induced by anthropogenic forcing is scarce. Taking the Yangtze River Delta area, China as an example, this study estimates quantitatively the influence of atmosphere on the concentration of heavy metal in the aboveground wheat tissues induced by anthropogenic industrial activity at the regional scale. The results show that the aboveground wheat tissues in the southern Yangtze River Delta area accumulated much more heavy metals than that in the northern area, although there is no significant difference in the geological and climate conditions, soil types, agricultural manages, wheat cultivar and soil heavy metals concentrations (even heavy metals concentrations in wheat root) between the southern area and northern area. The mean concentrations of Pb, Zn, Cu and Cd in wheat grain in southern area have exceeded the thresholds of contamination levels. The present study suggests that the influence of atmosphere on the accumulation of Hg, Cd, Pb, Zn, Cu, Ni and Cr in the aboveground wheat tissues is greatly significant when high amounts of pollutant are measured in the atmosphere. Based on translocation coefficient of the element, it is estimated that atmospheric pollution induced by anthropogenic forcing might lead to the concentration of heavy metals in wheat straw and grain increase by approximately 100% and 354% (Hg), 64% and 293% (Pb), 122% and 160% (Cr), 50% and 38% (Cd) and 14% and 41% (Cu), respectively. • Contribution of atmosphere on heavy metal in wheat is estimated quantitatively. • Excessive heavy metal in wheat was found in south of Yangtze River Delta, China. • Anthropogenic air pollution greatly enhances heavy metal accumulation in wheat. • Anthropogenic forcing can increase Hg concentration in wheat grain by about 3 times. [ABSTRACT FROM AUTHOR]

Combining technology with finance is the focus of supporting economic structure adjustment, and environmental benefits are also the proper meaning of the policy. Using the panel data of 274 cities in China from 2006 to 2017, this paper examines the impact of the Science and Technology Finance Policy (STFP) on carbon emission intensity in pilot cities and the transmission mechanisms through the difference-in-differences method and further explores the impact of STFP on the carbon emission intensity in neighboring cities. The results show that (1) STFP has significantly reduced carbon emission intensity in pilot cities and has dynamic effects, which gradually increase over time. There is significant heterogeneity in the carbon emission reduction effect of STFP, which produces stronger policy effects in first and second-tier cities and cities with higher information levels. (2) STFP achieves carbon emission reduction effects through three main pathways: the total factor productivity improvement effect, innovative elements agglomeration effect, and industrial structure optimization effect. (3) The STFP and national e-commerce demonstration policy have an interactive effect, and the two jointly contribute to the reduction in carbon emission intensity. From the perspective of a spatial effect, STFP has a radiation effect; that is, STFP not only reduces local carbon emission intensity but also curbs the carbon emission intensity in neighboring areas.

Hourly PM 2.5 speciation data have been widely used as an input of positive matrix factorization (PMF) model to apportion PM 2.5 components to specific source-related factors. However, the influence of constant source profile presumption during the observation period is less investigated. In the current work, hourly concentrations of PM 2.5 water-soluble inorganic ions, bulk organic and elemental carbon, and elements were obtained at an urban site in Nanjing, China from 2017 to 2020. PMF analysis based on observation data during specific pollution (firework combustion, sandstorm, and winter haze) and emission-reduction (COVID-19 pandemic) periods was compared with that using the whole 4-year data set (PMF whole ). Due to the lack of data variability, event-based PMF solutions did not separate secondary sulfate and nitrate. But they showed better performance in simulating average concentrations and temporal variations of input species, particularly for primary source markers, than the PMF whole solution. After removing event data, PMF modeling was conducted for individual months (PMF month ) and the 4-year period (PMF 4-year ), respectively. PMF month solutions reflected varied source profiles and contributions and reproduced monthly variations of input species better than the PMF 4-year solution, but failed to capture seasonal patterns of secondary salts. Additionally, four winter pollution days were selected for hour-by-hour PMF simulations, and three sample sizes (500, 1000, and 2000) were tested using a moving window method. The results showed that using short-term observation data performed better in reflecting immediate changes in primary sources, which will benefit future air quality control when primary PM emissions begin to increase., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The Comprehensive Air-quality Model with extensions (CAMx) was used to explore the sensitivity of PM 2.5 and O 3 concentrations to four selected meteorological factors: wind speed, temperature, water vapor mixing ratio (Q), and planetary boundary layer height (PBLH) during two pollution episodes over the North China Plain (NCP). We also investigated the impact pathways of different meteorological factors on the formation of PM 2.5 and O 3. It is found that PM 2.5 was more sensitive to the selected meteorological factors in the southeastern NCP, where high anthropogenic emissions and severe air pollution occur. Large variations were observed along the Taihang Mountains, where the height of the terrain changes dramatically. The sensitivity of O 3 to wind speed, PBLH, temperature, and Q was mainly determined by the inhibition effects of PM 2.5 in winter, while in summer, the complex chemical reactions were dominant. Significant diurnal variations of process analysis (PA) results were observed under various meteorological conditions. Higher temperature generally enhance heterogeneous chemistry and transport of NO 3 - through the top boundary layer during night-time in winter, however, in summer, the heterogeneous chemistry of NO 3 - and NH 4 + during daytime were the major pathways to the increased PM 2.5 due to increased temperature. Moreover, temperature alter PM 2.5 concentrations through affecting vertical diffusivity and relative humidity, and alter O 3 concentrations by affecting the gas phase chemistry and mass fluxes through the top boundary layer. Q mainly affects the rate of chemical reactions of PM 2.5 and O 3 . The different impact pathways suggest that it is essential to consider variations in meteorological factors, in addition to the direct impacts of wind speed and PBLH, more attention should be paid to the complex impacts of temperature and Q, when developing emission control strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In this study, hourly concentrations of PM 2.5 water-soluble inorganic ions, bulk organic carbon (OC), and elemental carbon (EC) were monitored from 1/1/2017 to 12/31/2017 and validated using filter-based offline analysis at an urban site in Nanjing, China. Compared with 2013 or before, the annual average of PM 2.5 concentration (36.5 ± 32.9 μg m -3 ) in 2017 decreased by more than 40%, NO 3 - (12.8 ± 11.4 μg m -3 ) became the most abundant water-soluble ion instead of SO 4 2- (9.29 ± 6.07 μg m -3 ), and the relative contribution of OC (5.92 ± 3.40 μg m -3 ) and EC (2.95 ± 1.53 μg m -3 ) to bulk PM 2.5 (24.9 ± 9.31%) increased substantially, indicating the effectiveness of the control policy for reducing gaseous precursor emissions. Based on the diurnal variations of water-soluble ions and gaseous pollutants, NH 4 + , SO 4 2- , and NO 3 - were secondarily formed and NH 4 NO 3 dominated the composition of ammonium salts in PM 2.5 . The diurnal changes of OC, EC, and OC/EC ratios reflected prominent influences from local traffic patterns. Positive matrix factorization was performed using hourly data of PM 2.5 components (PMF 1-h ), of which the results were justified by comparing to those using 23-h averaged data (PMF 23-h ). Given that the secondary ion formation was still the dominant source (68.2%) of PM 2.5 , and the average PM 2.5 concentration in urban Nanjing remained higher than Tier II limit (35 μg m -3 ) of the Chinese National Ambient Air Quality Standard, controlling emissions of PM 2.5 precursor gases should be continued after the completion of Air Pollution Prevention and Control Action Plan in 2017., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Elemental concentrations of ambient aerosols are commonly sampled over 12-24 h, and the low time resolution puts a great limit on current understanding about the temporal variations and source apportionment based on receptor models. In this work, hourly-resolved concentrations of eighteen elements in PM 2.5 at an urban site in Nanjing, a megacity in Yangtze River Delta of east China, were obtained by using a Xact 625 ambient metals monitor from 12/12/2016 to 12/31/2017. The influence of traffic activities was clearly reflected by the spikes of crustal elements (e.g., Fe, Ca, and Si) in the morning rush hour, and the firework burning and sandstorm events during the sampling periods were tracked by sharp enrichment of Ba, K and Fe, Ca, Si, Ti in PM 2.5 , respectively. To evaluate the advantage of hourly-resolved elements data in identifying impacts from specific emission sources, positive matrix factorization (PMF) analysis was performed with the 1-h data set (PMF 1-h ) and 23-h averaged data (PMF 23-h ), respectively. The 4- and 6-factor PMF 23-h solutions had similar factor profiles and consistent factor contributions as the corresponding PMF 1-h solutions. However, due to the limit in inter-sample variability, PMF analysis with 23-h average data misclassified some major (e.g., K, Fe, Zn, Ca, and Si) and trace (e.g., Pb) elements in factor profiles, resulting in different absolute factor contributions between PMF 23-h and PMF 1-h solutions. These results suggested the use of high time-resolved data to obtain valid and robust source apportionment results., (Copyright © 2019 Elsevier Ltd. All rights reserved.)