Chongshu Zhu

Chemical profiles of urban fugitive dust PM2.5 samples in Northern Chinese cities

Urban fugitive dust PM2.5 samples were collected in 11 selected cities in North China, and 9 ions (SO4(2-), NO3(-), Cl(-), F(-), Na(+), NH4(+), K(+), Mg(2+), and Ca(2+)) and 22 elements (Si, Al, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr, Sn, Sb, Ba, and Pb) were determined to investigate chemical profiles of PM2.5. The coefficient of divergence (CD) was used to compare the similarities of the chemical profiles for fugitive dust among three regions in North China, and the results showed that their composition are quite similar. Total water soluble ions occupied 9.3% and 10.0% on average of road dust and construction dust, respectively, indicating that most of the materials in urban fugitive dust samples were insoluble. Ca(2+) was the most abundant cation and SO4(2-) dominated in anions. Soil dust loading was calculated to occupy 70.8% and 83.6% in road dust and construction dust, respectively. Ca, Si, Fe, and Al were the most abundant elements in all the samples, and Ca was absolutely the most abundant specie among the 22 detected elements in construction dust samples. Chemical species ratios were used to highlight the characteristics of urban fugitive dust by comparing with other types of aerosols. High Ca/Al ratio was a good marker to distinguish urban fugitive dust from Asian dust and Chinese loess. In addition, low K(+)/K and NO3(-)/SO4(2-), and high Zn/Al and Pb/Al ratios were good indicators to separate urban fugitive dust from desert dust, Chinese loess, or urban PM2.5 samples.

Comparison and implications of PM2.5 carbon fractions in different environments

The concentrations of PM₂.₅ carbon fractions in rural, urban, tunnel and remote environments were measured using the IMPROVE thermal optical reflectance (TOR) method. The highest OC1 and EC1 concentrations were found for tunnel samples, while the highest OC2, OC3, and OC4 concentrations were observed for urban winter samples, respectively. The lowest levels of most carbon fractions were found for remote samples. The percentage contributions of carbon fractions to total carbon (TC) were characterized by one peak (at rural and remote sites) and two peaks (at urban and tunnel sites) with different carbon fractions, respectively. The abundance of char in tunnel and urban environments was observed, which might partly be due to traffic-related tire-wear. Various percentages of optically scattering OC and absorbing EC fractions to TC were found in the four different environments. In addition, the contribution of heating carbon fractions (char and soot) indicated various warming effects per unit mass of TC. The ratios of OC/EC and char/soot at the sites were shown to be source indicators. The investigation of carbon fractions at different sites may provide some information for improving model parameters in estimating their radiative effects.

Two distinct patterns of seasonal variation of airborne black carbon over Tibetan Plateau.

Airborne black carbon (BC) mass concentrations were measured from November 2012 to June 2013 at Ranwu and Beiluhe, located in the southeastern and central Tibetan Plateau, respectively. Monthly mean BC concentrations show a winter (November-February) high (413.2ngm-3) and spring (March-June) low (139.1ngm-3) at Ranwu, but in contrast a winter low and spring high at Beiluhe (204.8 and 621.6ngm-3, respectively). By examining the meteorological conditions at various scales, we found that the monthly variation of airborne BC over the southeastern Tibetan Plateau (TP) was highly influenced by regional precipitation and over the hinterland by winds. Local precipitation at both sites showed little impact on the seasonal variation of airborne BC concentrations. Potential BC source regions are identified using air mass backward trajectory analysis. At Ranwu, BC was dominated by the air masses from the northeastern India and Bangladesh in both winter and spring, whereas at Beiluhe it was largely contributed by air masses from the south slope of Himalayas in winter, and from the arid region in the north of the TP in spring. The winter and spring seasonal peak of BC in the southern TP is largely contributed by emissions from South Asia, and this seasonal variation is heavily influenced by the regional monsoon. In the northern TP, BC had high concentrations during spring and summer seasons, which is very likely associated with more efficient transport of BC over the arid regions on the north of Tibetan Plateau and in Central Asia. Airborne BC concentrations at the Ranwu sampling site showed a significant diurnal cycle with a peak shortly after sunrise followed by a decrease before noon in both winter and spring, likely shaped by local human activities and the diurnal variation of wind speed. At the Beiluhe sampling site, the diurnal variation of BC is different and less distinct.

DISTRIBUTION OF CARBONACEOUS AEROSOL DURING SPRING 2005 OVER THE HORQIN SANDLAND IN NORTHEASTERN CHINA

The objective of this study was to characterize the elemental carbon and organic carbon (EC and OC, respectively) content of aerosol particles (PM2.5) collected at Tongliao, a site in the Horqin Sandland of northeastern China. During spring 2005, the PM2.5 mass concentration was 126±71 μg·m−3, with higher dust concentrations during five dust storms than on non-dusty days (255±77 vs. 106±44 μg·m−3). The average OC and EC concentrations in PM2.5 determined by a thermal/optical reflectance method were 15.7±7.3 μg·m−3 and 3.3±1.7 μg·m−3, respectively, and carbonaceous aerosol accounted for 9.9% of the PM2.5 mass during dust storms compared to 21.7% on normal days. The average ratios of OC to EC during dust storms were similar to those on non-dusty days, and the correlation coefficient between OC and EC was high, 0.86. The high OC/EC ratios, the distributions of eight carbon fractions, and the strong relationship between K with OC and EC indicate that rural biomass burning was the dominant contributor to the regional carbonaceous aerosol.

Spectral dependence of aerosol light absorption at an urban and a remote site over the Tibetan Plateau

We present a study of aerosol light absorption by using a 7-wavelength Aethalometer model AE33 at an urban site (Lhasa) and a remote site (Lulang) in the Tibetan Plateau. Approximately 5 times greater aerosol absorption values were observed at Lhasa (53±46Mm-1 at 370nm and 20±18Mm-1 at 950nm, respectively) in comparison to Lulang (15±19Mm-1 at 370nm and 4±5Mm-1 at 950nm, respectively). Black carbon (BC) was the dominant light absorbing aerosol component at all wavelengths. The brown carbon (BrC) absorption at 370nm is 32±15% of the total aerosol absorption at Lulang, whereas it is 8±6% at Lhasa. Higher value of absorption Ångström exponent (AAE, 370-950nm) was obtained for Lulang (1.18) than that for Lhasa (1.04) due to the presence of BrC. The AAEs (370-950nm) of BrC were directly extracted at Lulang (3.8) and Lhasa (3.3). The loading compensation parameters (k) increased with wavelengths for both sites, and lower values were obtained at Lulang than those observed at Lhasa for all wavelengths. This study underlines the relatively high percentage of BrC absorption contribution in remote area compared to urban site over the Tibetan Plateau.

Development of source profiles and their application in source apportionment of PM 2.5 in Xiamen, China

Ambient PM2.5 samples were collected at four sites in Xiamen, including Gulangyu (GLY), Hongwen (HW), Huli (HL) and Jimei (JM) during January, April, July and October 2013. Local source samples were obtained from coal burning power plants, industries, motor vehicles, biomass burning, fugitive dust, and sea salt for the source apportionment studies. The highest value of PM2.5 mass concentration and species related to human activities (SO42–, NO3–, Pb, Ni, V, Cu, Cd, organic carbon (OC) and elemental carbon (EC)) were found in the ambient samples from HL, and the highest and lowest loadings of PM2.5 and its components occurred in winter and summer, respectively. The reconstructed mass balance indicated that ambient PM2.5 consisted of 24% OM (organic matter), 23% sulfate, 14% nitrate, 9% ammonium, 9% geological material, 6% sea salt, 5% EC and 10% others. For the source profiles, the dominant components were OC for coal burning, motor vehicle, biomass burning and sea salt; SO42– for industry; and crustal elements for fugitive dust. Source contributions were calculated using a chemical mass balance (CMB) model based on ambient PM2.5 concentrations and the source profiles. GLY was characterized by high contributions from secondary sulfate and cooking, while HL and JM were most strongly affected by motor vehicle emissions, and biomass burning and fugitive dust, respectively. The CMB results indicated that PM2.5 from Xiamen is composed of 27.4% secondary inorganic components, 20.8% motor vehicle emissions, 11.7% fugitive dust, 9.9% sea salt, 9.3% coal burning, 5.0% biomass burning, 3.1% industry and 6.8% others.

A 10-year observation of PM 2.5 -bound nickel in Xi’an, China: Effects of source control on its trend and associated health risks

This study presents the first long term (10-year period, 2004–2013) datasets of PM2.5-bound nickel (Ni) concentration obtained from the daily sample in urban of Xi’an, Northwestern China. The Ni concentration trend, pollution sources, and the potential health risks associated to Ni were investigated. The Ni concentrations increased from 2004 to 2008, but then decreased due to coal consumption reduction, energy structure reconstruction, tighter emission rules and the improvement of the industrial and motor vehicle waste control techniques. With the comparison of distributions between workday and non-workday periods, the effectiveness of local and regional air pollution control policies and contributions of hypothetical Ni sources (industrial and automobile exhausts) were evaluated, demonstrating the health benefits to the populations during the ten years. Mean Ni cancer risk was higher than the threshold value of 10−6, suggesting that carcinogenic Ni still was a concern to the residents. Our findings conclude that there are still needs to establish more strict strategies and guidelines for atmospheric Ni in our living area, assisting to balance the relationship between economic growth and environmental conservation in China.

Black carbon aerosol and its radiative impact at a high-altitude remote site on the southeastern Tibet Plateau

Aerosol black carbon (BC) was measured with an Aethalometer™ at Lulang, a high-altitude station in southeastern Tibetan Plateau (TP), from July 2008 to August 2009. Daily mean BC loadings varied from 57.7 to 5368.9 ng m−3 (grand average ± standard deviation = 496.5 ± 521.2 ng m−3), indicating a significant BC burden even at free tropospheric altitudes. BC loadings were highest during the pre-monsoon and lowest during the monsoon, and peaks in BC were coincident with high atmospheric boundary layers. Daily peaks in BC occurred from 08:00–10:00 local time with minor fluctuations at other times. The BC mass absorption efficiency (MAE) was calculated from elemental carbon concentrations obtained from a thermal/optical reflectance method and absorption coefficients from the Aethalometer™, and values ranged from 6.1–31.7 m2 g−1 (average = 16.6 ± 5.7 m2 g−1). Strong variations in the MAEs during the monsoon can be ascribed to large uncertainties due to low BC and babs, and possibly coatings on the BC. High MAEs during pre-monsoon pollution events were likely due to internal mixing during transport. The mean direct surface radiative forcing (DRF) estimated from a radiation model was −19.9 (±7.4) for the full aerosol population and −3.9 (±1.8) W m−2 for a BC only scenario. The BC DRF during a case study (−36.0 W m−2) was much stronger than the typical, and the BC contribution to the forcing was higher (~50%) than usual (~20%). These results show that BC can at times account for a relatively large fraction of the aerosol surface heating over the southeast TP, which may affect both climate and hydrological cycles.

Light absorption properties of brown carbon over the southeastern Tibetan Plateau

We present a study of the light-absorbing properties of water-soluble brown carbon (WS-BrC) and methanol-soluble brown carbon (MeS-BrC) at a remote site (Lulang, 3326m above sea level) in the southeastern Tibetan Plateau during the period 2015-2016. The light absorption coefficients at 365nm (babs365) of WS-BrC and MeS-BrC were the highest during winter and the lowest during monsoon season. MeS-BrC absorbs about 1.5 times higher at 365nm compared to WS-BrC. The absorption at 550nm appears lower compared to that of 365nm for WS-BrC and MeS-BrC, respectively. Higher average value of the absorption Ångström exponent (AAE, 365-550nm) was obtained for MeS-BrC (8.2) than that for WS-BrC (6.9). The values of the mass absorption cross section at 365nm (MAC365) indicated that BrC in winter absorbs UV-visible light more efficiently than in monsoon. The results confirm the importance of BrC in contributing to light-absorbing aerosols in this region. The understanding of the light absorption properties of BrC is of great importance, especially in modeling studies for the climate effects and transport of BrC in the Tibetan Plateau.

Morphologies and elemental compositions of local biomass burning particles at urban and glacier sites in southeastern Tibetan Plateau: Results from an expedition in 2010

Many studies indicate that the atmospheric environment over the southern part of the Tibetan Plateau is influenced by aged biomass burning particles that are transported over long distances from South Asia. However, our knowledge of the particles emitted locally (within the plateau region) is poor. We collected aerosol particles at four urban sites and one remote glacier site during a scientific expedition to the southeastern Tibetan Plateau in spring 2010. Weather and backward trajectory analyses indicated that the particles we collected were more likely dominated by particles emitted within the plateau. The particles were examined using an electron microscope and identified according to their sizes, shapes and elemental compositions. At three urban sites where the anthropogenic particles were produced mainly by the burning of firewood, soot aggregates were in the majority and made up >40% of the particles by number. At Lhasa, the largest city on the Tibetan Plateau, tar balls and mineral particles were also frequently observed because of the use of coal and natural gas, in addition to biofuel. In contrast, at the glacier site, large numbers of chain-like soot aggregates (~25% by number) were noted. The morphologies of these aggregates were similar to those of freshly emitted ones at the urban sites; moreover, physically or chemically processed ageing was rarely confirmed. These limited observations suggest that the biomass burning particles age slowly in the cold, dry plateau air. Anthropogenic particles emitted locally within the elevated plateau region may thus affect the environment within glaciated areas in Tibet differently than anthropogenic particles transported from South Asia.