Aerosols In Guangzhou Research Articles

Nitroaromatic Compounds from Secondary Nitrate Formation and Biomass Burning Are Major Proinflammatory Components in Organic Aerosols in Guangzhou: A Bioassay Combining High-Resolution Mass Spectrometry Analysis.

The limited characterization and detection capacity of unknown compounds hinder our understanding of the molecular composition of toxic compounds in PM2.5. The present study applied Fourier transform ion cyclotron resonance mass spectrometry coupled with negative and positive electrospray ionization sources (ESI-/ESI+ FT-ICR-MS) to probe the molecular characteristics and dynamic formation processes of the effective proinflammatory components in organic aerosols (OAs) of PM2.5 in Guangzhou for one year. We detected abundant proinflammatory molecules in OAs, mainly classified as CHON compounds (compounds composed of C, H, O, and N atoms) in elemental and nitroaromatic compounds (NACs) in structures. From the perspective of the formation process, we discovered that these proinflammatory molecules, especially toxic NACs, were largely driven by secondary nitrate formation and biomass burning (in emission source), as well as SO2 (in atmospheric evolution). In addition, our results indicated that the secondary processes had replaced the primary emission as the main contributing source of the toxic proinflammatory compounds in OAs. This study highlights the importance of community measures to control the production of nitroaromatic compounds derived from secondary nitrate formation and biomass burning in urban areas.

Characteristics, formation mechanisms, and sources of non-refractory submicron aerosols in Guangzhou, China

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.

Single particle diversity and mixing state of carbonaceous aerosols in Guangzhou, China

Many field studies have investigated the formation mechanisms of organic aerosol (OA) based on bulk analysis, yet the source and formation process of individual organic particles may be quite different due to the diversity of chemical composition and mixing state in single particles. Here we present the observation results of chemical composition and mixing state of carbonaceous single particles at an urban site in Guangzhou. The carbonaceous particles accounted for 74.6% of the total detected single particles, and were grouped into four types including elemental carbon-aged (EC-aged), elemental and organic carbon (ECOC), organic carbon-rich (OC-rich) and secondary ions-rich (SEC) particles. The formation of EC-aged particles was closely associated with the absorption of organics onto fresh EC particles from primary sources, and the further enrichment of organics in EC-aged particles resulted in the production of ECOC particles. In the daytime OC-rich and SEC particles were mainly produced from the photochemical reactions, while in the nighttime their sharp increases were found along with the enrichment of nitrate and organic nitrogen fragments, suggesting the heterogeneous formation of nitrate and organic nitrogen in OC-rich and SEC particles. The production rates of carbonaceous particles were also investigated in an episodic event, and the EC-aged particles showed the highest production rate compared to the other carbonaceous particles both in the daytime and nighttime, suggesting a significant role of EC in the formation and aging process of carbonaceous particles. The results from this work have revealed different formation processes and production rates of carbonaceous particles due to their diversity in mixing state, providing further insights into the formation mechanisms of OA in field studies.

Abundance and 14C-based source assessment of carbonaceous materials in PM2.5 aerosols in Guangzhou, South China

In this study, the carbonaceous aerosols were separated into organic carbon (OC), water soluble OC (WSOC), water soluble humic-like substances (HULIS), water soluble non-HULIS, water insoluble OC (WINSOC), and soot carbon (SC). Then the abundance and 14 C content of carbon fractions were determined to assess the contribution of contemporary versus fossil sources. The results showed that the OC fraction is the major carbon fraction, the OC sub-fractions such as WSOC, HULIS, non-HULIS, and WINSOC accounted for 39.5%–66.7%, 24.8%–43.2%, 11.9%–23.5%, and 31.3%–55.2% of total carbon (TC), respectively. The 14 C data show that the contribution of contemporary carbon ( f c ) to TC is 38.3%–63.5%, all carbon fractions were mixtures of carbon derived from contemporary and fossil sources. The f c values of OC (38.8%–63.9%) more than that (25.7%–46.6%) of SC in the same sample, indicated OC generally contained more contemporary carbon than SC. The WSOC and HULIS had relatively higher f c levels than the corresponding WINSOC and the f c values of WINSOC all less than 45%, indicated that the insoluble organic fractions in PM 2.5 samples were dominated by fossil fuel related sources. These results suggested that the contemporary and fossil contributions for different carbon fractions are different. In addition, the seasonal and spatial variations of contemporary and fossil contributions to carbon fractions indicated that the PM 2.5 samples collected during summer at background site (Maofengshan, MFS) and winter at urban site (Wushan, WS) have relative high contribution from contemporary sources, suggested the differences of primary and secondary sources at the two sites. • 14 C-based source assessment of carbonaceous materials in PM 2.5 aerosols. • All carbon fractions are mixtures of contemporary and fossil carbon. • The source of carbon fractions in aerosols is heterogeneous.

Measurements of non-volatile aerosols with a VTDMA and their correlations with carbonaceous aerosols in Guangzhou, China

Abstract. Simultaneous measurements of aerosol volatility and carbonaceous matters were conducted at a suburban site in Guangzhou, China, in February and March 2014 using a volatility tandem differential mobility analyzer (VTDMA) and an organic carbon/elemental carbon (OC ∕ EC) analyzer. Low volatility (LV) particles, with a volatility shrink factor (VSF) at 300 °C exceeding 0.9, contributed 5 % of number concentrations of the 40 nm particles and 11–15 % of the 80–300 nm particles. They were composed of non-volatile material externally mixed with volatile material, and therefore did not evaporate significantly at 300 °C. Non-volatile material mixed internally with the volatile material was referred to as medium volatility (MV, 0.4 < VSF < 0.9) and high volatility (HV, VSF < 0.4) particles. The MV and HV particles contributed 57–71 % of number concentration for the particles between 40 and 300 nm in size. The average EC and OC concentrations measured by the OC ∕ EC analyzer were 3.4 ± 3.0 and 9.0 ± 6.0 µg m−3, respectively. Non-volatile OC evaporating at 475 °C or above, together with EC, contributed 67 % of the total carbon mass. In spite of the daily maximum and minimum, the diurnal variations in the volume fractions of the volatile material, HV, MV and LV residuals were less than 15 % for the 80–300 nm particles. Back trajectory analysis also suggests that over 90 % of the air masses influencing the sampling site were well aged as they were transported at low altitudes (below 1500 m) for over 40 h before arrival. Further comparison with the diurnal variations in the mass fractions of EC and the non-volatile OC in PM2.5 suggests that the non-volatile residuals may be related to both EC and non-volatile OC in the afternoon, during which the concentration of aged organics increased. A closure analysis of the total mass of LV and MV residuals and the mass of EC or the sum of EC and non-volatile OC was conducted. It suggests that non-volatile OC, in addition to EC, was one of the components of the non-volatile residuals measured by the VTDMA in this study.

The real part of the refractive indices and effective densities for chemically segregated ambient aerosols in Guangzhou measured by a single-particle aerosol mass spectrometer

Abstract. Knowledge on the microphysical properties of atmospheric aerosols is essential to better evaluate their radiative forcing. This paper presents an estimate of the real part of the refractive indices (n) and effective densities (ρeff) of chemically segregated atmospheric aerosols in Guangzhou, China. Vacuum aerodynamic diameter, chemical compositions, and light-scattering intensities of individual particles were simultaneously measured by a single-particle aerosol mass spectrometer (SPAMS) during the fall of 2012. On the basis of Mie theory, n at a wavelength of 532 nm and ρeff were estimated for 17 particle types in four categories: organics (OC), elemental carbon (EC), internally mixed EC and OC (ECOC), and Metal-rich. The results indicate the presence of spherical or nearly spherical shapes for the majority of particle types, whose partial scattering cross-section versus sizes were well fitted to Mie theoretical modeling results. While sharing n in a narrow range (1.47–1.53), majority of particle types exhibited a wide range of ρeff (0.87–1.51 g cm−3). The OC group is associated with the lowest ρeff (0.87–1.07 g cm−3), and the Metal-rich group with the highest ones (1.29–1.51 g cm−3). It is noteworthy that a specific EC type exhibits a complex scattering curve versus size due to the presence of both compact and irregularly shaped particles. Overall, the results on the detailed relationship between physical and chemical properties benefits future research on the impact of aerosols on visibility and climate.

Source apportionment using radiocarbon and organic tracers for PM2.5 carbonaceous aerosols in Guangzhou, South China: contrasting local- and regional-scale haze events.

We conducted a source apportionment and investigated the atmospheric behavior of carbonaceous aerosols during hazy and normal days using radiocarbon ((14)C) and biomass burning/secondary organic aerosol (SOA) tracers during winter in Guangzhou, China. Haze episodes were formed either abruptly by local emissions or through the accumulation of particles transported from other areas. The average contributions of fossil carbon to elemental carbon (EC), water-insoluble organic carbon, and water-soluble organic carbon were 71 ± 10%, 40 ± 6% and 33 ± 3%, respectively. High contributions of fossil carbon to EC (80-90%) were observed for haze samples that were substantially impacted by local emissions, as were the highest (lowest) ratios for NO3(-)/SO4(2-) (OC/EC), which indicates that these particles mainly came from local vehicle exhaust. Low contributions of fossil carbon to EC (60-70%) were found for haze particles impacted by regional transport. Secondary organic carbon (SOC) calculated using SOA tracers accounts for only ∼ 20% of the SOC estimated by (14)C, which is probably because some important volatile organic carbons are not taken into account in the SOA tracer calculation method and because of the large discrepancy in ambient conditions between the atmosphere and smog chambers. A total of 33 ± 11% of the SOC was of fossil origin, a portion of which could be influenced by humidity.

Attenuation of ultraviolet radiation reaching the surface due to atmospheric aerosols in Guangzhou

The UV attenuation due to atmospheric aerosols in Guangzhou was quantitatively assessed using surface ultraviolet radiation (UV, 295–385 nm) observation, sun photometer and radiation models. Observations showed that the annual average value of aerosol optical depth (AOD) was 1.19 in UV spectral region of 340 nm, the annual average occurrence frequency of aerosol optical depth AOD340 nm>1.0 was 55%, and the annual average attenuation rate of surface UV direct radiation of 340 nm was 68%. It was proven in the observation of surface UV radiation and model evaluation that annual average attenuation of UV due to atmosphere was 75%, and that reached 72% in the dry season (October, November, December and January); while average attenuation of UV due to atmospheric aerosols reached 62% in the dry season. It was indicated that very significant UV attenuations due to atmospheric aerosols existed in Guangzhou urban agglomeration, and at least half of UV radiation was attenuated due to atmospheric aerosols. Such large-amplitude attenuation will have a significant impact on urban ecosystem and species chemical cycles, especially photochemical reaction processes.

Simultaneous observation of seasonal variations of beryllium-7 and typical POPs in near-surface atmospheric aerosols in Guangzhou, China

Abstract Near-surface atmospheric aerosol samples were collected at the sampling frequency of 2–3 d per week for one year from August 2006 to August 2007 at a low latitude station in Tianhe District, Guangzhou, Guangdong Province of southern China. The samples were analyzed for cosmogenic nuclide 7Be and persistent organic pollutants, i.e. organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs). The annual average 7Be concentration was 2.59 mBq m−3, with the maximum occurred in May (8.45 mBq m−3) and minimum in late August and early September (0.07 mBq m−3). Winter and spring were the seasons in which the 7Be concentrations were high while summer and autumn were the lower 7Be seasons. Spring peaks in 7Be in the near-surface atmospheric aerosols may have associated with the “spring leak maximum” episode. The annual average ∑OCPs concentration was 345.6 pg m−3, ∑33PCBs 317.6 pg m−3, and ∑31PBDEs 609.0 pg m−3. The variation trends in the time-series of 7Be, OCPs, PCBs, and PBDEs in near-surface atmospheric aerosol showed both common features and differences. Significant correlations (R2 = 0.957 and 0.811. respectively, p = 0.01) were observed between the monthly average 7Be concentrations and those of ∑PCBs and ∑PBDEs in summer, autumn, and early winter. The difference between the seasonal variation features of OCPs and PCBs (and PBDEs) could be attributed to the different source functions and physical–chemical properties which could control the behaviors of these compounds in air–aerosol partitions as well as atmospheric transport.

Seasonal and spatial changes of free and bound organic acids in total suspended particles in Guangzhou, China

The concentrations and compositions of free and bound organic acids in total suspended particles from typical urban, suburban and forest park sites of Guangzhou were determined in this study. The free form of organic acids (solvent extractable) in aerosols in Guangzhou varied with site and season. The suburban samples contained the highest contents of alkanoic, alkenoic and dicarboxylic acids. These findings were consistent with a higher supply of hydrocarbons and NOx in the suburban area. However, concentrations of aromatic acids were similar in the urban, suburban and forest park sites. Generally, winter season samples of the acids from anthropogenic sources contained more organic acids than summer season samples due to stronger removal by wet deposition in the summer. For the acids from botanic sources, the summer season samples were higher. In addition to the free acids, bound acids (solvent non-extractable) mainly formed by esterification of free acids were also found in the samples. In general, bound acids were higher than free acids. Esterification is mainly controlled by the pKa of organic acids and the atmospheric pH value. This explains why aromatic and dicarboxylic acids occur mainly as bound forms and why the samples from urban sites contained high levels of bound acids as the pH of rain water can reach 4.53. Concentrations of alkanoic and alkenoic acids in the aerosols of Guangzhou were much higher than those in the other areas studied.

Composition and source of saccharides in aerosols in Guangzhou, China

The total suspended particles (TSP) collected during 2002 to 2003 in Wushan district and Liwan district in Guangzhou were analyzed for the saccharide compositions using gas chromatography-mass spectrometry (GC/MS) and N,O-bis-(trimethylsilye)trifluoroacetamide (BSTFA) derivatization. The results showed that the saccharides were composed of anhydrosaccharides consisting of levoglucosan, mannosan, galactosan and 1,6-anhydro-β-glucofuranose, and primary saccharides with sucrose as the most abundant, followed by α-and β-glucose, α-and β-fructose, mycose, and saccharide polyols. The highest saccharide levels occurred in autumn. The anhydrosaccharides came from biomass burning, whereas primary saccharides were the result of resuspention of surface soil dust associated with the agricultural activities and the decay of the falling leaves.

Heavy metals and Pb isotopic composition of aerosols in urban and suburban areas of Hong Kong and Guangzhou, South China—Evidence of the long-range transport of air contaminants

Rapid urbanization and industrialization in South China has placed great strain on the environment and on human health. In the present study, the total suspended particulate matter (TSP) in the urban and suburban areas of Hong Kong and Guangzhou, the two largest urban centres in South China, was sampled from December 2003 to January 2005. The samples were analysed for the concentrations of major elements (Al, Fe, Mg and Mn) and trace metals (Cd, Cr, Cu, Pb, V and Zn), and for Pb isotopic composition. Elevated concentrations of metals, especially Cd, Pb, V and Zn, were observed in the urban and suburban areas of Guangzhou, showing significant atmospheric trace element pollution. Distinct seasonal patterns were observed in the heavy metal concentrations of aerosols in Hong Kong, with higher metal concentrations during the winter monsoon period, and lower concentrations during summertime. The seasonal variations in the metal concentrations of the aerosols in Guangzhou were less distinct, suggesting the dominance of local sources of pollution around the city. The Pb isotopic composition in the aerosols of Hong Kong had higher 206Pb/ 207Pb and 208Pb/ 207Pb ratios in winter, showing the influence of Pb from the northern inland areas of China and the Pearl River Delta (PRD) region, and lower 206Pb/ 207Pb and 208Pb/ 207Pb ratios in summer, indicating the influence of Pb from the South Asian region and from marine sources. The back trajectory analysis showed that the enrichment of heavy metals in Hong Kong and Guangzhou was closely associated with the air mass from the north and northeast that originated from northern China, reflecting the long-range transport of heavy metal contaminants from the northern inland areas of China to the South China coast.

Chemical Composition and Sources of PM10 and PM2.5 Aerosols in Guangzhou, China

Aerosol samples of PM10 and PM2.5 are collected in summertime at four monitoring sites in Guangzhou, China. The concentrations of organic and elemental carbons (OC/EC), inorganic ions, and elements in PM10 and PM2.5 are also quantified. Our study aims to: (1) characterize the particulate concentrations and associated chemical species in urban atmosphere (2) identify the potential sources and estimate their apportionment. The results show that average concentration of PM2.5 (97.54 microg m(-3)) in Guangzhou significantly exceeds the National Ambient Air Quality Standard (NAAQS) 24-h average of 65 microg m(-3). OC, EC, Sulfate, ammonium, K, V, Ni, Cu, Zn, Pb, As, Cd and Se are mainly in PM2.5 fraction of particles, while chloride, nitrate, Na, Mg, Al, Fe, Ca, Ti and Mn are mainly in PM2.5-10 fraction. The major components such as sulfate, OC and EC account for about 70-90% of the particulate mass. Enrichment factors (EF) for elements are calculated to indicate that elements of anthropogenic origins (Zn, Pb, As, Se, V, Ni, Cu and Cd) are highly enriched with respect to crustal composition (Al, Fe, Ca, Ti and Mn). Ambient and source data are used in the multi-variable linearly regression analysis for source identification and apportionment, indicating that major sources and their apportionments of ambient particulate aerosols in Guangzhou are vehicle exhaust by 38.4% and coal combustion by 26.0%, respectively.