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Many studies have recently been done on understanding the sources and formation mechanisms of atmospheric aerosols at ground level. However, vertical profiles and sources of size-resolved particulate matter within the urban boundary layer are still lacking. In this study, vertical distribution characteristics of size-segregated particles were investigated at three observation platforms (ground level, 118 m, and 488 m) on the 610 m high Canton Tower in Guangzhou, China. Size-segregated aerosol samples were simultaneously collected at the three levels in autumn and winter. Major aerosol components, including water-soluble ions, organic carbon, and elemental carbon, were measured. The results showed that daily average fine-particle concentrations generally decreased with height. Concentrations of sulfate and ammonium in fine particles displayed shallow vertical gradients, and nitrate concentrations increased with height in autumn, while the chemical components showed greater variations in winter than in autumn. The size distributions of sulfate and ammonium in both seasons were characterized by a dominant unimodal mode with peaks in the size range of 0.44–1.0 µ m. In autumn, the nitrate size distribution was bimodal, peaking at 0.44–1.0 and 2.5–10 µ m, while in winter it was unimodal, implying that the formation mechanisms for nitrate particles were different in the two seasons. Our results suggest that the majority of the sulfate and nitrate is formed from aqueous-phase reactions, and we attribute coarse-mode nitrate formation at the measurement site to the heterogeneous reactions of gaseous nitric acid on existing sea-derived coarse particles in autumn. Case studies further showed that atmospheric aqueous-phase and heterogeneous reactions could be important mechanisms for sulfate and nitrate formation, which, in combination with adverse weather conditions such as temperature inversion and calm wind, led to haze formation during autumn and winter in the Pearl River Delta (PRD) region. [ABSTRACT FROM AUTHOR]

To grasp the key factors affecting particle mass scattering efficiency (MSE), particle mass and number size distribution, PM 2.5 and PM 10 and their major chemical compositions, and the particle scattering coefficient (bsp) under dry conditions were measured at an urban site in Guangzhou, southern China, during 2015–2016. On an annual average, 10±2 %, 48±7 % and 42±8 % of PM 10 mass were in the condensation, droplet and coarse modes, respectively, with mass mean aerodynamic diameters (MMADs) of 0.78±0.07 in the droplet mode and 4.57±0.42 µm in the coarse mode. The identified chemical species mass concentrations can explain 79±3 %, 82±6 % and 57±6 % of the total particle mass in the condensation, droplet and coarse mode, respectively. Organic matter (OM) and elemental carbon (EC) in the condensation mode, OM, (NH4)2SO4 , NH4NO3 , and crustal element oxides in the droplet mode, and crustal element oxides, OM, and CaSO4 in the coarse mode, were the dominant chemical species in their respective modes. The measured bsp can be reconstructed to the level of 91±10 % using Mie theory with input of the estimated chemically resolved number concentrations of NaCl, NaNO3 , Na2SO4 , NH4NO3 , (NH4)2SO4 , K2SO4 , CaSO4 , Ca(NO3)2 , OM, EC, crustal element oxides and unidentified fraction. MSEs of particle and individual chemical species were underestimated by less than 13 % in any season based on the estimated bsp and chemical species mass concentrations. Seasonal average MSEs varied in the range of 3.5±0.1 to 3.9±0.2 m 2 g -1 for fine particles (aerodynamic diameter smaller than 2.1 µm), which was mainly caused by seasonal variations in the mass fractions and MSEs of the dominant chemical species (OM, NH4NO3 , (NH4)2SO4) in the droplet mode. MSEs of the dominant chemical species were determined by their lognormal size-distribution parameters, including MMADs and standard deviation (σ) in the droplet mode. [ABSTRACT FROM AUTHOR]

To evaluate the impact of fine particulate matter (PM 2.5 ) size distribution on aerosol chemical and optical properties, dominant chemical components including water-soluble inorganic ions (WSII), organic carbon (OC) and elemental carbon (EC) in PM 1 and PM 2.5 , aerosol scattering coefficient (b sp ), and aerosol absorption coefficient (b ap ) were collected synchronously at an urban site in Guangzhou, south China during a typical summer month in 2009 and a winter month in 2010. PM 1 (sizes smaller than 1 μm) constituted 77% and 63% of PM 2.5 in summer and winter, respectively. From the reconstructed mass concentrations, the sum of SO 4 2 − , NO 3 − and NH 4 + (SNA) distributed more in PM 1 than in PM 1–2.5 (PM 2.5 minus PM 1 ) in summer and the opposite was found in winter, while carbonaceous aerosols distributed more in PM 1 in both summer and winter. With the aggravation of PM 2.5 pollution, the mass fraction of PM 1 /PM 2.5 increased for (NH 4 ) 2 SO 4 (AS), NH 4 NO 3 (AN) and EC but decreased for organic matter (OM) in summer, and the opposite was found in winter. B sp of PM 1 and PM 1–2.5 was estimated from the mass extinction efficiencies (MSEs) of the dominant chemical components, which showed good correlations ( R 2 = 0.99) with measured ones and those estimated using the IMPROVE formula. The fractional contributions of dominant chemical components to extinction coefficient (b ext ) were consistent with their respective mass size distributions, indicating the importance of chemically-resolved aerosol size distributions on aerosol optical properties and haze formation. [ABSTRACT FROM AUTHOR]

Though significant associations between particulate matter (PM) air pollution and cardiovascular diseases have been widely reported, it remains unclear what characteristics, such as particle size and chemical constituents, may be responsible for the effects. A time-series model was applied to examine the cardiovascular effects of particle size (for the period of 2009–2011) and chemical constituents (2007–2010) in Guangzhou, we controlled for potential confounders in the model, such as time trends, day of the week, public holidays, meteorological factors and influenza epidemic. We found significant associations of cardiovascular mortality with PM 10 , PM 2.5 and PM 1 ; the excess risk (ER) was 6.10% (95% CI: 1.76%, 10.64%), 6.11% (95% CI: 1.76%, 10.64%) and 6.48% (95% CI: 2.10%, 11.06%) for per IQR increase in PM 10 , PM 2.5 and PM 1 at moving averages for the current day and the previous 3 days (lag 03 ), respectively. We did not find significant effects of PM 2.5-10 and PM 1-2.5 . For PM 2.5 constituents, we found that organic carbon, elemental carbon, sulfate, nitrate and ammonium were significantly associated with cardiovascular mortality, the corresponding ER for an IQR concentration increase at lag 03 was 1.13% (95% CI: 0.10%, 2.17%), 2.77% (95% CI: 0.72%, 4.86%), 2.21% (95% CI: 1.05%, 3.38%), 1.98% (95% CI: 0.54%, 3.44%), and 3.38% (95% CI: 1.56%, 5.23%), respectively. These results were robust to adjustment of other air pollutants and they remained consistent in various sensitivity analyses by changing model parameters. Our study suggests that PM 1 and constituents from combustion and secondary aerosols might be important characteristics of PM pollution associated with cardiovascular mortality in Guangzhou. [ABSTRACT FROM AUTHOR]

To evaluate the effectiveness of the integrated control measures for reducing PM 2.5 (aerosol particles with an aerodynamic diameter of less than 2.5 μm) and hazy weather, day- and night-time PM 2.5 samples were collected at an urban site in Guangzhou during the 16th Asian Games period in November 2010. PM 2.5 samples were subject to chemical analysis for major water-soluble ions, organic carbon (OC), element carbon (EC), and biomass burning tracers–anhydrosugar levoglucosan (LG). In addition, aerosol scattering coefficient (b sp ) at dry condition and aerosol absorption coefficient (b ap ) and visibility at ambient condition were measured. The seven major control measures were effective for reducing PM 2.5 mass concentration and improving visibility during the Asian Games period. All monitored air pollutants except PM 2.5 satisfied the National Ambient Air Quality Standards (NAAQS). However, daily PM 2.5 concentrations still exceeded the NAAQS on 47% of the days and hazy weather also occurred on 80% of the days during this period. One factor causing the high frequency of hazy weather occurrence was the increased relative humidity during the Asian Games period. To avoid hazy weather occurrence, new PM 2.5 standard was recommended based on visibility calculations using three available aerosol hygroscopic curves previously obtained for this city. The recommended PM 2.5 standard was 63 μg m − 3 under dry condition and lower than 42 μg m − 3 under humid condition (RH ≥ 70%). These recommended values were much stricter than the NAAQS value of 75 μg m − 3 . To reach the new standard, more rigorous control measures for coal industries should be established in the Pearl River Delta (PRD) region. [ABSTRACT FROM AUTHOR]

Daily PM2.5 samples were collected in Guangzhou — the largest megacity in South China, for a period of one month in each season during 2009–2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC) and elemental carbon (EC) in PM2.5 were determined, and aerosol scattering coefficient (bsp) was synchronously measured. The daily PM2.5 mass concentrations ranged from 21.0 to 213.6μgm−3 with an annual average of 76.8±41.5μgm−3. The highest seasonal average PM2.5 was observed in winter (103.3±50.1μgm−3) and the lowest in summer (38.6±15.7μgm−3). Annual average PM2.5 mass scattering efficiency (MSE) was 3.5±0.9m2 g−1, with obvious seasonal variations in sequence of autumn (4.5±0.2m2 g−1)>winter (3.9±0.5m2 g−1)>spring (3.0±0.4m2 g−1)>summer (2.3±0.3m2 g−1). To determine the relationship between bsp and the chemical components of PM2.5, bsp was reconstructed in each season using the original IMPROVE formula with a modification of including sea salt aerosols. The estimated bsp using this method was 22±28% smaller on annual average compared to the measurements. Multiple linear regression of measured bsp against (NH4)2SO4, NH4NO3, OM (Organic Mass), SS (Sea Salt), FS (Fine Soil), and CM (Coarse Mass) were also performed in all the four seasons. The estimated bsp from using the regression equation was 4±12% larger than the measured values. On average, (NH4)2SO4, NH4NO3, OM, SS, FS and CM accounted for 50±11%, 18±10%, 19±5%, 5±4%, 3±2% and 5±6%, respectively, of the estimated bsp. [ABSTRACT FROM AUTHOR]

The objective of this study was to reconstruct light extinction coefficients ( b) according to chemical composition components of particulate matter up to 2.5 µm in size (PM). PM samples were collected at the monitoring station of the South China of Institute of Environmental Science (SCIES, Guangzhou, China) during January 2010, and the online absorbing and scattering coefficients were obtained using an aethalometer and a nephelometer. The measured values of light absorption coefficient by particle ( b) and light scattering coefficient by particle ( b) significantly correlated ( R > 0.95) with values of b and b that were reconstructed using the Interagency Monitoring of Protected Visual Environments (IMPROVE) formula when RH was <70%. The measured bext had a good correlation ( R > 0.83) with the calculated bext under ambient RH conditions. The result of source apportionment of b showed that ammonium sulfate [(NH)SO] was the largest contributor (35.0%) to b, followed by ammonium nitrate (NHNO, 22.9%), organic matter (16.1%), elemental carbon (11.8%), sea salt (4.7%), and nitrogen dioxide (NO, 9.6%). To improve visibility in Guangzhou, the effective control of secondary particles like sulfates, nitrates, and ammonia should be given more attention in urban environmental management. [ABSTRACT FROM AUTHOR]

To explore the controlling factors for mass absorption efficiency (MAE) of elemental carbon (EC) in fine particles (PM 2.5), major chemical compositions in size-segregated aerosol samples and bulk PM 2.5 samples and light absorption coefficient (b ap) of PM 2.5 samples under dry condition were measured during four seasons in an urban environment in Guangzhou of south China. On seasonal average, absorption Ångström exponent (AAE) in the wavelength range of 370–880 nm measured by a transmissometer or in the range of 370–950 nm measured by an aethalometer ranged from 0.95 to 1.02 and from 1.01 to 1.14, respectively. The estimated EC MAE at 550 nm in PM 2.5 were 10.1 ± 1.0, 8.9 ± 0.7, 9.1 ± 1.0 and 9.1 ± 0.7 m2 g−1 in spring, summer, autumn and winter, respectively, which were evidently higher than the value of 7.5 m2 g−1 for "pure EC". More than 61% of EC mass in PM 2.1 was distributed in the droplet mode (0.43–2.1 μm), which should be related to hygroscopic growth of aged EC particle as well as external mixing with coating materials. No significant correlations were found between EC MAE and mass fraction of EC or mass ratio of (SO 4 2-+NO 3 −+OC)/EC in the droplet mode. The deliquescence of aerosol was primarily determined by NH 4 NO 3 , and the high EC MAE was mainly related to high nitrate mass concentration and positive ΔRH (ambient relative humidity minus deliquescence relative humidity of NH 4 NO 3). [Display omitted] • Elemental carbon was mainly originated from vehicle emissions in urban Guangzhou. • EC was mainly distributed in the droplet mode largely due to external mixing. • The estimated EC MAE at 550 nm was evidently higher than that for pure EC. • Enhanced EC MAE was mainly caused by aerosol deliquescence by nitrate. [ABSTRACT FROM AUTHOR]

Concentrations and compositions of PAHs and oxygenated PAHs (OPAHs) in four size ranges of ambient particles (< 1.1, 1.1–3.3, 3.3–9.0 and > 9.0 μm) collected in Xi'an and Guangzhou, two megacities of China, during the winter and summer of 2013 were measured and compared with those in 2003. The TSP-equivalent concentrations of Σ14PAHs in Xi'an and Guangzhou are 57 ± 20 and 18 ± 23 ng m − 3 in winter, 5–10 times higher than those in summer. PAHs in both cities are dominated by 5- and 6-ring congeners in summer. In contrast, they are dominated by 4- and 5-ring congeners in winter, probably due to enhanced gas-to-particle phase partitioning of the semi-volatile PAHs. TSP-equivalent Σ7OPAHs during winter are 54 ± 15 and 23 ± 32 ng m − 3 in Xi'an and Guangzhou and dominated by 5-ring OPAHs. Size distribution results showed that the fine modes (< 3.3 μm) of PAHs and OPAHs in both cities are dominated by 4- and 5-ring congeners in winter and 5- and 6-ring congeners in summer. Relative abundances of 3-ring PAHs and OPAHs increased along with an increase in particle sizes, accounting for from about 1% of the total PAHs or OPAHs in the smallest particles (< 1.1 μm) to > 90% of the total in the largest particles (> 9.0 μm). The toxicity of PAH assessment indicated that atmospheric particles in Xi'an and Guangzhou during winter are much more toxic than those during summer and fine particles are more toxic than coarse particles. Compared to those in 2003, fine particulate PAHs and OPAHs in both cities during winter decreased by 50–90%, most likely due to the replacement of coal by natural gas in the country. [ABSTRACT FROM AUTHOR]

Ambient fine particulate matter (PM 2.5) levels in South China have been decreasing in the past decade, but the decreasing rates differed between its major chemical components, e.g., with much small rates for carbonaceous aerosols than for secondary inorganic aerosols. To investigate the sources of carbonaceous aerosols in this region, a comprehensive campaign was carried out in urban Guangzhou in the winter of 2019–2020 using a combination of various instruments. Data generated from this campaign include hourly total carbon (TC), black carbon (BC), criteria air pollutants and meteorological parameters, 4-hourly particle-bound elements, and chemically-resolved daily PM 2.5. Similar diurnal patterns were observed for TC, CO and NO 2 , suggesting TC was very likely related to vehicle exhaust emission. Secondary organic carbon (SOC) estimated using the Minimum R squared (MRS) method accounted for 35 ± 17% of OC, indicating strong atmospheric oxidation capacity. Four major source factors for carbonaceous aerosols were identified by positive matrix factorization (PMF) model, including coal combustion, traffic emissions, soil dust and ship emissions, which accounted for 37 ± 23%, 39 ± 23%, 14 ± 10% and 10 ± 13%, respectively, of TC mass concentration, 38 ± 24%, 38 ± 23%, 14 ± 10% and 10 ± 12%, respectively, of OC mass concentration, and 29 ± 21%, 43 ± 22%, 14 ± 11% and 14 ± 15%, respectively, of EC mass concentration. Among these sources, traffic emission was the most important one, suggesting the necessity for promoting clean energy vehicles and relieving urban traffic congestion. • Total carbon accounted for nearly 30% of PM 2.5 during the campaign. • High SOC/OC ratio was related with high ozone concentration. • Traffic emission is the most important source of total carbon. [ABSTRACT FROM AUTHOR]