Zhuzi Zhao

Pyrolysis of tire powder: influence of operation variables on the composition and yields of gaseous product

The pyrolysis of tire powder was studied experimentally using a specially designed pyrolyzer with high heating rates. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined at temperatures between 500 and 1000 °C under different gas phase residence times. It is found that the gas yield goes up while the char and tar yield decrease with increasing temperature. The gaseous product mainly consists of H2, CO, CO2, H2S and hydrocarbons such as CH4, C2H4, C2H6, C3H6, C3H8, C4H8 and C4H6 with a little other hydrocarbon gases. Its heating value is in the range of 20 to 37 MJ/Nm3. Maximum heating value is achieved at a temperature between 700 and 800 °C. The product distribution ratio of gas, tar and char is about 21:44:35 at 800 °C. The gas yield increases with increasing gas residence time when temperature of the residence zone is higher than 700 °C. The gas heating value shows the opposite trend when the temperature is higher than 800 °C. Calcined dolomite and limestone were used to explore their effect on pyrolyzed product distribution and composition of the gaseous product. It is found that both of them affect the product distribution, but the effect on tar cracking is not obvious when the temperature is lower than 900 °C. It is also found that H2S can be absorbed effectively by using either of them. About 57% sulfur is retained in the char and 6% in the gas phase. The results indicated that high-energy recovery could not be achieved if fuel gas is the only target product. In view of this, multi-use of the pyrolyzed product is highly recommended.

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.

Atmospheric levels and cytotoxicity of polycyclic aromatic hydrocarbons and oxygenated-PAHs in PM2.5 in the Beijing-Tianjin-Hebei region

The chemical composition of PM2.5 and cellular effects from exposure to fine aerosol extracts were studied for samples collected in Beijing, Tianjin, Shijiazhuang, and Hengshui, China in winter 2015. Effects of priority polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs) in PM2.5 on cell cultures were a major focus of the study. Total quantified PAHs and OPAHs at Shijiazhuang and Hengshui were higher than at Beijing and Tianjin, and benz(a)anthracene, chrysene and 1,8-naphthalic anhydride were the most abundant species. Exposure to PM2.5 extracts caused a concentration-dependent decline in cell viability and a dose-dependent increase in nitric oxide production. Two cytokines, tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6), also increased when A549 test cells were exposed to PM2.5 extracts. PAHs and OPAHs in PM2.5 can potentially cause cell damage and induce cytotoxicity and pro-inflammatory responses: benzo(a)anthracene-7,12-dione was highly correlated with NO production, dibenz(a,h)anthracene and 1,4-chrysenequinone were correlated with TNF-α production, and 1-naphthaldehyde was significantly correlated with IL-6 production. The study provides a new approach for evaluating relationships between air-quality and cell toxicity with respect to specific chemicals.

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.

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.

Variation in Day-of-Week and Seasonal Concentrations of Atmospheric PM2.5-Bound Metals and Associated Health Risks in Bangkok, Thailand

While effective analytical techniques to promote the long-term intensive monitoring campaign of particulate heavy metals have been well established, efforts to interpret these toxic chemical contents into policy are lagging behind. In order to ameliorate the interpretation of evidence into policies, environmental scientists and public health practitioners need innovative methods to emphasize messages concerning adverse health effects to state and local policymakers. In this study, three different types of health risk assessment models categorized by exposure pathways. Namely, ingestion, dermal contact, and inhalation were quantitatively evaluated using intensive monitoring data of 51 PM2.5-bound metals that were collected on three consecutive days, from 17 November 2010 to 30 April 2011 in the heart of Bangkok. Although different exposure pathways possess different magnitudes of risk for each PM2.5-bound metal, it can be concluded that ingestion of dust causes more extensive risk to residents compared with inhalation and dermal contact. The investigation of enrichment factors reveals the overwhelming influences of vehicular exhausts on 44 selected metal concentrations in Bangkok. These findings are in agreement with previous studies that highlight the role of public transportation and urban planning in air pollution control.

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.

Chemical characterization of PM 2.5 from a southern coastal city of China: applications of modeling and chemical tracers in demonstration of regional transport

An intensive sampling campaign of airborne fine particles (PM2.5) was conducted at Sanya, a coastal city in Southern China, from January to February 2012. Chemical analyses and mass reconstruction were used identify potential pollution sources and investigate atmospheric reaction mechanisms. A thermodynamic model indicated that low ammonia and high relative humidity caused the aerosols be acidic and that drove heterogeneous reactions which led to the formation of secondary inorganic aerosol. Relationships among neutralization ratios, free acidity, and air-mass trajectories suggest that the atmosphere at Sanya was impacted by both local and regional emissions. Three major transport pathways were identified, and flow from the northeast (from South China) typically brought the most polluted air to Sanya. A case study confirmed strong impact from South China (e.g., Pearl River Delta region) (contributed 76.8% to EC, and then this result can be extended to primary pollutants) when the northeast winds were dominant. The Weather Research Forecasting Black carbon model and trace organic markers were used to apportion local pollution versus regional contributions. Results of the study offer new insights into the atmospheric conditions and air pollution at this coastal city.