Jingchun Duan

Size distributions and sources of elements in particulate matter at curbside, urban and rural sites in Beijing

Size distributions of 29 elements in aerosols collected at urban, rural and curbside sites in Beijing were studied. High levels of Mn, Ni, As, Cd and Pb indicate the pollution of toxic heavy metals cannot be neglected in Beijing. Principal component analysis (PCA) indicates 4 sources of combustion emission, crust related sources, traffic related sources and volatile species from coal combustion. The elements can be roughly divided into 3 groups by size distribution and enrichment factors method (EFs). Group 1 elements are crust related and mainly found within coarse mode including Al, Mg, Ca, Sc, Ti, Fe, Sr, Zr and Ba; Group 2 elements are fossil fuel related and mostly concentrated in accumulation mode including S, As, Se, Ag, Cd, Tl and Pb; Group 3 elements are multi-source related and show multi-mode distribution including Be, Na, K, Cr, Mn, Co, Ni, Cu, Zn, Ga, Mo, Sn and Sb. The EFs of Be, S, Cr, Co, Ni, Cu, Ga, Se, Mo, Ag, Cd, Sb, Tl and Pb show higher values in winter than in summer indicating sources of coal combustion for heating in winter. The abundance of Cu and Sb in coarse mode is about 2-6 times higher at curbside site than at urban site indicating their traffic sources. Coal burning may be the major source of Pb in Beijing since the phase out of leaded gasoline, as the EFs of Pb are comparable at both urban and curbside sites, and about two times higher in winter than that in summer.

Source of atmospheric heavy metals in winter in Foshan, China

Foshan is a ceramics manufacturing center in the world and the most polluted city in the Pearl River Delta (PRD) in southern China measured by the levels of atmospheric heavy metals. PM2.5 samples were collected in Foshan in winter 2008. Among the 22 elements and ions analyzed, 7 heavy metals (Zn, V, Mn, Cu, As, Cd and Pb) were studied in depth for their levels, spatiotemporal variations and sources. The ambient concentrations of the heavy metals were much higher than the reported average concentrations in China. The levels of Pb (675.7 ± 378.5 ng/m(3)), As (76.6 ± 49.1 ng/m(3)) and Cd (42.6 ± 45.2 ng/m(3)) exceeded the reference values of NAAQS (GB3095-2012) and the health guidelines of the World Health Organization. Generally, the levels of atmospheric heavy metals showed spatial distribution as: downtown site (CC, Chancheng District)>urban sites (NH and SD, Nanhai and Shunde Districts)>rural site (SS, Shanshui District). Two sources of heavy metals, the ceramic and aluminum industries, were identified during the sampling period. The large number of ceramic manufactures was responsible for the high levels of atmospheric Zn, Pb and As in Chancheng District. Transport from an aluminum industry park under light north-west winds contributed high levels of Cd to the SS site (Shanshui District). The average concentration of Cd under north-west wind was 220 ng/m(3), 20.5 times higher than those under other wind directions. The high daily maximum enrichment factors (EFs) of Cd, Pb, Zn, As and Cu at all four sites indicated extremely high contamination by local emissions. Back trajectory analysis showed that the heavy metals were also closely associated with the pathway of air mass. A positive matrix factorization (PMF) method was applied to determine the source apportionment of these heavy metals. Five factors (industry including the ceramic industry and coal combustion, vehicle emissions, dust, transportation and sea salt) were identified and industry was the most important source of atmospheric heavy metals. The present paper suggests a control policy on the four heavy metals Cd, Pb, Zn, and Cu, and suggests the inclusion of As in the ceramic industry emission standard in the future.

Size distribution, characteristics and sources of heavy metals in haze episod in Beijing

Size segragated samples were collected during high polluted winter haze days in 2006 in Beijing, China. Twenty nine elements and 9 water soluble ions were determined. Heavy metals of Zn, Pb, Mn, Cu, As, Cr, Ni, V and Cd were deeply studied considering their toxic effect on human being. Among these heavy metals, the levels of Mn, As and Cd exceeded the reference values of National Ambient Air Quality Standard (GB3095-2012) and guidelines of World Health Organization. By estimation, high percentage of atmospheric heavy metals in PM2.5 indicates it is an effective way to control atmospheric heavy metals by PM2.5 controlling. Pb, Cd, and Zn show mostly in accumulation mode, V, Mn and Cu exist mostly in both coarse and accumulation modes, and Ni and Cr exist in all of the three modes. Considering the health effect, the breakthrough rates of atmospheric heavy metals into pulmonary alveoli are: Pb (62.1%) > As (58.1%) > Cd (57.9%) > Zn (57.7%) > Cu (55.8%) > Ni (53.5%) > Cr (52.2%) > Mn (49.2%) > V (43.5%). Positive matrix factorization method was applied for source apportionment of studied heavy metals combined with some marker elements and ions such as K, As, SO4(2-) etc., and four factors (dust, vehicle, aged and transportation, unknown) are identified and the size distribution contribution of them to atmospheric heavy metals are discussed.

Long-term trends of chemical characteristics and sources of fine particle in Foshan City, Pearl River Delta: 2008-2014.

Foshan is a major international ceramic center and the most polluted city in the Pearl River Delta (PRD). Here we present the results of the first long-term PM2.5 (particles <2.5μm) sampling and chemical characterization study of the city. A total of 2774 samples were collected at six sites from 2008 to 2014, and analyzed for water soluble species, elements and carbonaceous species. The major constituents of PM2.5 were sulfate, OC (Organic Carbon), nitrate, ammonium and EC (Elemental Carbon), which accounted for 50%-88% of PM2.5. PM2.5 and the most abundant chemical species decreased from 2008 to 2011, but rebounded in 2012-2013. After 2008, the chemical composition of PM2.5 changed dramatically due to the implementation of pollution control measures. From 2008 to 2011, SO4(2-) and NO3(-) were the two largest components; subsequently, however, OC was the largest component. The respective contributions of SO4(2-), NO3(-) and OC to the sum of water soluble species and carbonaceous species were 30.5%, 22.9% and 19.9% in 2008; and 20.2%, 16.5% and 30.2% in 2014. Distinct differences in nitrate and sulfate, and in mass ratio [NO3(-)]/[SO4(2-)] imply that mobile sources tended to more important in Foshan during 2012-2014. The results indicate that pollution control measures implemented during 2008-2014 had a large effect on anthropogenic elements (Pb, As, Cd, Zn and Cu) and water soluble species, but little influence on crustal elements (V, Mn, Ti, Ba and Fe) and carbonaceous species. The PMF method was used for source apportionment of PM2.5. Industry (including the ceramic industry and coal combustion), vehicles and dust were the three most important sources and comprised 39.2%, 20.0% and 18.4% of PM2.5 in 2008, respectively. However, secondary aerosols, vehicles and industry were the three most important sources and comprised 29.5%, 22.4% and 20.4% of PM2.5 in 2014, respectively. During the seven year study interval, the contributions of primary sources (industry and dust) decreased significantly, but secondary sources increased dramatically. Industry, dust and vehicles contributed 36.6μgm(-3), 13.9μgm(-3), and 9.2μgm(-3) to the reduction of PM2.5, respectively.

Harmonizing Aerosol Carbon Measurements between Two Conventional Thermal/Optical Analysis Methods

Although total carbon (TC) can be consistently quantified by various aerosol carbon measurement methods, the demarcation of TC into organic carbon (OC) and elemental carbon (EC) has long been inconsistent. The NIOSH and IMPROVE protocols are most widely used for thermal/optical analysis (TOA), but current knowledge rests in the description that the NIOSH protocol usually gives lower EC values than does the IMPROVE protocol. This study seeks to explore the possibility of quantitatively linking the difference between the two TOA protocols. Residential coal-burning samples that had been collected and analyzed following the NIOSH protocol in previous studies were directly reanalyzed following the IMPROVE protocol for this study. A comparison of each pair of NIOSH and IMPROVE EC values reveals the dynamic relation between the two protocols, which can be expressed as a regression equation, y=(1-x)/(1+4.86x2) (R2=0.96), where the independent x is the EC/TC ratio R(EC/TC) for the IMPROVE protocol, and the dependent y is the difference between IMPROVE and NIOSH REC/TC relative to IMPROVE REC/TC. This regression equation may be the first effort in formulating the relationship between the two TOA protocols, and it is very helpful in harmonizing inconsistent TOA measurements, for example, source characterization, ambient monitoring, and atmospheric modeling.

Gas-to-particle conversion of atmospheric ammonia and sampling artifacts of ammonium in spring of Beijing

PM2.5 and gaseous pollutants (SO2, HNO2, HNO3, HCl, and NH3) were simultaneously collected by Partisol® Model 2300 Sequential Speciation Sampler with denuder-filter pack system in the spring of 2013 in Beijing. Water-soluble inorganic ions and gaseous pollutants were measured by Ion Chromatography. Results showed that the concentrations of NH3, NH4+ and PM2.5 had similar diurnal variation trends and their concentrations were higher at night than in daytime. The results of gas-to-particle conversion revealed that [NH3]:[NH4+] ratio was usually higher than 1; however, it was less than 1 and the concentration of NH4+ increased significantly during the haze episode, indicating that NH3 played an important role in the formation of fine particle. Research on the sampling artifacts suggested that the volatilization loss of NH4+ was prevalent in the traditional single filter-based sampling. The excess loss of HNO3 and HCl resulted from ammonium-poor aerosols and semivolatile inorganic species had severe losses in the clean day, whereas the mass of NH4+ was usually overestimated during the single filter-based sampling due to the positive artifacts. Correlation analysis was used to evaluate the influence of meteorological conditions on the volatilization loss of NH4+. It was found that the average relative humidity and temperature had great effects on the loss of NH4+. The loss of NH4+ was significantly under high temperature and low humidity, and tended to increase with the increasing of absorption of gaseous pollutants by denuder. The total mass of volatile loss of NH4+, NO3− and Cl− could not be ignored and its maximum value was 12.17 μg m−3. Therefore it is important to compensate sampling artifacts for semivolatile inorganic species.

Chemical characterization of humic-like substances (HULIS) in PM2.5 in Lanzhou, China.

Evaporative light scattering detection (ELSD) was applied to quantify HULIS (humic-like substances) for the first time in 2012 winter and 2013 summer at an urban site in Lanzhou. Water soluble organic carbon (WSOC), water soluble inorganic ions, and carbonaceous species (OC/EC) were also analyzed. The results show that OM (Organic Matter=OC×1.6, constituting 45.8% to PM2.5) was the most abundant species, followed by SNA (SO42-+NO3-+NH4+, constituting 23.4% to PM2.5). The chemical species were in the order of: OC>EC>SO42->NO3->NH4+>Cl->Ca2+>K+. The annual average concentration of HULIS was 4.70μg/m-3 and HULISc (carbon content of HULIS) contributed 6.19% to PM2.5 and 45.6% to WSOC, indicating that HULIS was the most important components of WSOC. The concentration of HULIS was 2.14±0.80μg/m3 in summer and 7.24±2.77μg/m3 in winter, respectively. The concentrations of HULIS were relatively low and stable in summer, while high and varied dramatically in winter. The abundance of HULISc in WSOC shows a more concentrated distribution in Lanzhou, with a range between 0.28-0.57. The ratios of HULIS/K+ were 6.25±1.41 and 6.14±1.96 in summer and winter, respectively, suggesting there were other significant sources in addition to biomass burning emissions. HULIS and WSOC exhibited similar seasonal variation and had a strong positive correlation. In addition to the good relationship (0.89) between HULIS and Cl- in winter, the great enhancement of HULIS with significantly high Cl- and relatively low K+ in winter indicated that residential coal burning was probably an important HULIS source in winter. Correlation and back trajectory analysis suggested that biomass burning and secondary formation were also important HULIS sources and the contribution of HULIS from dust could be neglected. Adverse meteorological conditions were also important factors for the accumulation of HULIS in winter.

Chemical characteristics and source apportionment of PM2.5 in Lanzhou, China

Daily PM2.5 samples were collected during winter 2012 and summer 2013 at an urban site in Lanzhou and were analyzed for chemical compounds including water soluble inorganic ions (WSIN), trace elements, water soluble organic carbon (WSOC), carbonaceous species (OC/EC), polycyclic aromatic hydrocarbons (PAHs), and humic-like substances (HULIS). The seasonal-average reconstructed PM2.5 mass was 120.5μgm-3 in winter and 34.1μgm-3 in summer. The top three groups of species in PM2.5 were OC (35.4±13.9μgm-3), WSIN (34.89±14.21μgm-3), and EC (13.80±5.41μgm-3) in winter and WSIN (11.25±3.25μgm-3), OC (9.74±3.30μgm-3), and EC (4.44±2.00μgm-3) in summer. EC exceeded SO42- on most of the days. Several anthropogenic produced primary pollutants such as PAHs, Cl-, Pb, Cd and OCpri were 4-22 times higher in winter than summer. Carcinogenic substances such as Arsenic, BaP, Pb, and Cd in PM2.5 exceeded the WHO guideline limits by 274%, 153%, 23% and 7%, respectively. Positive Matric Factorization analysis identified seven source factors including steel industry, secondary aerosols, coal combustion, power plants, vehicle emissions, crustal dust, and smelting industry, which contributed 7.1%, 33.0%, 28.7%, 3.12%, 8.8%, 13.3%, and 6.0%, respectively, to PM2.5 in winter, and 6.7%, 14.8%, 3.1%, 3.4%, 25.2%, 11.6% and 35.2% in summer. Smelting industry and steel industry were identified for the first time as sources of PM2.5 in this city, and power plant was distinguished from industrial boiler and residential coal burning.

Characteristics of atmospheric non-methane hydrocarbons during haze episode in Beijing, China

This study firstly focused on non-methane hydrocarbons (NMHCs) during three successive days with haze episode (16–18 August 2006) in Beijing. Concentrations of alkanes, alkenes, aromatic hydrocarbons, and ethyne all peaked at traffic rush hour, implying vehicular emission; and alkanes also peaked at non-traffic rush hour in the daytime, implying additional source. Especially, alkanes and aromatics clearly showed higher levels in the nighttime than that in the daytime, implying their active photochemical reactions in the daytime. Correlation coefficients (R2) showed that propane, n-butane, i-butane, ethene, propene, and benzene correlated with ethyne (R2 = 0.61–0.66), suggesting that their main source is vehicular emission; 2-methylpentane and n-hexane correlated with i-pentane (R2 = 0.61–0.64), suggesting that gasoline evaporation is their main source; and ethylbezene, m-/p-xylene, and o-xylene correlated with toluene (R2 = 0.60–0.79), suggesting that their main source is similar to that of toluene (e.g., solvent usage). The R2 of ethyne, i-pentane, and toluene with total NMHCs were 0.58, 0.76, and 0.60, respectively, indicating that ambient hydrocarbons are associated with vehicular emission, gasoline evaporation, and solvent usage. The sources of other hydrocarbons (e.g., ethane) might be natural gas leakage, biogenic emission, or long-range transport of air pollutants. Measured higher mean B/T ratio (0.78 ± 0.27) was caused by the more intensive photochemical activity of toluene than benzene, still indicating the dominant emission from vehicles.

Pollutional characteristics and sources analysis of polycyclic aromatic hydrocarbons in atmospheric fine particulate matter in Lanzhou City

Polycyclic aromatic hydrocarbons (PAHs) are a group of important toxic compounds. In order to detect the pollutional characteristics of atmospheric PAHs in Fine Particulate Matter (PM2.5), a total of 60 PM2.5 samples were collected in Lanzhou City during the winter of 2012 and summer of 2013. The GC/MS measurement results of the samples demonstrated the averagely total mass concentrations of the most significant 16 homologues of PAHs were (191.79±88.29) ng·m-3 and (8.94±4.34) ng·m-3 in winter and summer respectively, indicating a higher pollution level in winter. In winter, the snowfall was the most important meteorological factor for the decrease of PAHs mass concentration in PM2.5. The percentages of PAHs with 4 rings were the highest in both winter (51.40%) and summer (49.94%) in Lanzhou. The percentage of PAHs with 5-6 rings in summer (41.04%) was higher than that in winter (24.94%). However, the percentage of PAHs with 2-3 rings in summer (9.03%) was lower than that in winter (23.67%). Based on the analysis of characteristic ratios, we concluded that the PAHs in atmospheric PM2.5 in Lanzhou were mainly sourced from coal and vehicle emissions in winter, especially the diesel vehicles. The absolute contributions of all possible PAHs pollution sources were insignificant in summer, with relatively higher contribution from gasoline vehicles.