Characterization of carbonaceous species of ambient PM2.5 in Beijing, China

One-week integrated fine particulate matter (i.e., particles <2.5 microm in diameter; PM2.5) samples were collected continuously with a low-flow rate sampler at a downtown site (Chegongzhuang) and a residential site (Tsinghua University) in Beijing between July 1999 and June 2000. The annual average concentrations of organic carbon (OC) and elemental carbon (EC) at the urban site were 23.9 and 8.8 microg m(-3), much higher than those in some cities with serious air pollution. Similar weekly variations of OC and EC concentrations were found for the two sampling sites with higher concentrations in the winter and autumn. The highest weekly variations of OC and EC occurred in the winter, suggesting that combustion sources for space heating were important contributors to carbonaceous particles, along with a significant impact from variable meteorological conditions. High emissions coupled with unfavorable meteorological conditions led to the max weekly carbonaceous concentration the week of November 18-25, 1999. The weekly mass ratios of OC:EC ranged between 2 and 4 for most samples and averaged 2.9, probably suggesting that secondary OC (SOC) is present most weeks. The range of contemporary carbon fraction, based on the C14 analyses of eight samples collected in 2001, is 0.330-0.479. Estimated SOC accounted for approximately 38% of the total OC at the two sites. Average OC and EC concentrations at Tsinghua University were 25% and 18%, respectively, higher than those at Chegongzhuang, which could be attributed to different local emissions of primary carbonaceous particles and gaseous precursors of SOC, as well as different summer photochemical intensities between the two locations.     

Volatilization of ketones

Volatilization fluxes of seven ketones were measured over a range of temperatures. Gas-film coefficients were calculated from these volatilization fluxes and related to the gas-film coefficient for the evaporation of water. These relations, when combined with an equation for estimating the gas-film coefficient for evaporation of water from a canal, permit estimating gas-film coefficients for the volatilization of ketones from streams and rivers.     

Current concepts and applications of air quality simulation models

Current air quality simulation models (AQSM) based on the continuity equation employ the gradient transport approximation and neglect the effect of turbulent fluctuation on chemical reactions. The implications of these approximations are examined, and an alternative statistical, Lagrangian approach applicable to nonreactive pollutants is also discussed.Practically, the working equations of AQSMs are derived from either the Gaussian principle or the conservation-of-mass principles, in conjunction with the semi-empirical parameterizatio of meteorological and photochemical aspects of the problem. The main features of the treatment of the meteorology and current concepts of the photochemical smog mechanism are examined. Some applications of AQMSs, e.g., predictions of future trends of urban carbon monoxide concentrations and photochemical smog, derivation of the relationship between ambient oxidant levels and precursor emission, and estimation of hydrocarbon reactivity for photochemical smog formation, are presented.     

Enhanced decomposition of NO on the alkalized PdO/Al2O3 catalyst

Experimentally, decomposition of NO on the alkalized Pd/Al2O3 catalyst is remarkably enhanced at 825-1000 K. The enhancement in N2 yield may be due to the additional basic sites on the alkalized catalyst that can trap NO molecules. However, at T > 1000 K, due to the fact that the absorbed oxygen in subsurface or bulk of Pd was involved in the formation and desorption of oxygen molecules, yield of oxygen was enhanced.     

Contrasting effects of silicates on cadmium uptake by three dicotyledonous crops grown in contaminated soil

The effects of several silicates (talcum powder (TP), calcium silicate (CS), sodium silicate (SS), and potassium silicate (PS)), in comparison with other amendments (quicklime (QL) and potassium dihydrogen phosphate (PDP)) on cadmium (Cd) uptake by three dicotyledonous crops (Amaranthus hypochondriacus L. Cv. ‘K112’, Amaranthus tricolor L., and Brassica oleracea var. albiflora Kuntze) were investigated in Cd–contaminated soil. The effects of both application methods of amendments (singly and combined) and timing of application were also evaluated. Sodium silicate was the most effective in reducing crop Cd uptake and translocation, which was diminished by 51 % in roots, 53 % in stems, and 72 % in leaves on average. Application of CS amendment showed greater efficiency than PDP amendment in decreasing Cd uptake by crops and resulted in increased biomass. Potassium silicate only slightly decreased shoot Cd concentration. Combination of PDP and SS was able to overcome the inhibitory effect of SS on crop yield while decreasing Cd concentrations in roots, stems and leaves of the tested crops by average rates of 52, 65, and 68 % respectively. Applications of SS and PS significantly reduced the root-to-shoot Cd transfer factor. We found that Si accumulation in crops was not associated with lower Cd concentration, indicating that Si in crops may play a major role in alleviating metal stress rather than inhibiting crop Cd accumulation. We suggested that the inhibitive effect of silicates on crops Cd uptake was majorly attributed to the properties of the silicates, those were their specific effects on soil pH and cations, which increased Cd adsorption by soil and suppressed Cd uptake from soil solution by increasing the relative dissolved concentrations of competing cations.     

Source apportionment of emissions from light-duty gasoline vehicles and other sources in the United States for ozone and particulate matter

Federal Tier 3 motor vehicle emission and fuel sulfur standards have been promulgated in the United States to help attain air quality standards for ozone and PM_2.5 (particulate matter with an aerodynamic diameter <2.5 μm). The authors modeled a standard similar to Tier 3 (a hypothetical nationwide implementation of the California Low Emission Vehicle [LEV] III standards) and prior Tier 2 standards for on-road gasoline-fueled light-duty vehicles (gLDVs) to assess incremental air quality benefits in the United States (U.S.) and the relative contributions of gLDVs and other major source categories to ozone and PM_2.5 in 2030. Strengthening Tier 2 to a Tier 3-like (LEV III) standard reduces the summertime monthly mean of daily maximum 8-hr average (MDA8) ozone in the eastern U.S. by up to 1.5 ppb (or 2%) and the maximum MDA8 ozone by up to 3.4 ppb (or 3%). Reducing gasoline sulfur content from 30 to 10 ppm is responsible for up to 0.3 ppb of the improvement in the monthly mean ozone and up to 0.8 ppb of the improvement in maximum ozone. Across four major urban areas—Atlanta, Detroit, Philadelphia, and St. Louis—gLDV contributions range from 5% to 9% and 3% to 6% of the summertime mean MDA8 ozone under Tier 2 and Tier 3, respectively, and from 7% to 11% and 3% to 7% of the maximum MDA8 ozone under Tier 2 and Tier 3, respectively. Monthly mean 24-hr PM_2.5 decreases by up to 0.5 μg/m³ (or 3%) in the eastern U.S. from Tier 2 to Tier 3, with about 0.1 μg/m³ of the reduction due to the lower gasoline sulfur content. At the four urban areas under the Tier 3 program, gLDV emissions contribute 3.4–5.0% and 1.7–2.4% of the winter and summer mean 24-hr PM_2.5, respectively, and 3.8–4.6% and 1.5–2.0% of the mean 24-hr PM_2.5 on days with elevated PM_2.5 in winter and summer, respectively.

Implications: Following U.S. Tier 3 emissions and fuel sulfur standards for gasoline-fueled passenger cars and light trucks, these vehicles are expected to contribute less than 6% of the summertime mean daily maximum 8-hr ozone and less than 7% and 4% of the winter and summer mean 24-hr PM_2.5 in the eastern U.S. in 2030. On days with elevated ozone or PM_2.5 at four major urban areas, these vehicles contribute less than 7% of ozone and less than 5% of PM_2.5, with sources outside North America and U.S. area source emissions constituting some of the main contributors to ozone and PM_2.5, respectively.     

Determination of four fluoroquinolone antibiotics in tap water in Guangzhou and Macao

Four fluoroquinolone antibiotics (norfloxacin, ciprofloxacin, lomefloxacin, and enrofloxacin) in tap water in Guangzhou and Macao were analyzed using high performance liquid chromatography fluorescence detection. The results showed that all target antibiotics were detected in high rate both in Guangzhou (77.5%) and Macao (100%), ranging from 1.0 to 679.7 ng/L (SD ≤ 37.6) in Guangzhou, and from 2.0 to 37.0 ng/L (SD ≤ 2.5) in Macao. The fluoroquinolone antibiotics pollution in tap water widely distributes in Guangzhou and Macao. In addition, the effect of rainfall on concentration of fluoroquinolone antibiotics in south China was also investigated. Our result indicates that the antibiotic concentration in tap water in Guangzhou tends to obviously reduce at the beginning of rainy season, even decreases below the limit of quantification immediately. Thus, it was clarified that the heavy rain in south China has the function of reducing the fluoroquinolone antibiotics concentrations in tap water.     

Characterization of Activated Carbon Fiber Filters for Pressure Drop,Submicrometer Particulate Collection,and Mercury Capture

ABSTRACT

The use of activated carbon fiber (ACF) filters for the capture of particulate matter and elemental Hg is demonstrated. The pressure drop and particle collection efficiency characteristics of the ACF filters were established at two different face velocities and for two different aerosols: spherical NaCl and combustion-generated silica particles. The clean ACF filter specific resistance was 153 kg m^-2 sec^-1. The experimental specific resistance for cake filtration was 1.6 × 10⁶ sec^-1 and 2.4 × 10⁵ sec^-1 for 0.5- and 1.5-μm mass median diameter particles, respectively. The resistance factor R was approximately 2, similar to that for the high-efficiency particulate air filters. There was a discrepancy in the measured particle collection efficiencies and those predicted by theory. The use of the ACF filter for elemental Hg capture was illustrated, and the breakthrough characteristic was established. The capacity of the ACF filter for Hg capture was similar to other powdered activated carbons.     

镉胁迫对万寿菊生长及生理生态特征的影响

通过水培实验,研究了不同Cd浓度(0、0.1、0.5、1、2和5 mg/L)胁迫对万寿菊生长及生理生化指标的影响.研究表明,低浓度Cd(＜0.5 mg/L)胁迫下,万寿菊的生长末受到显著影响,说明万寿菊对低浓度Cd有一定的耐性.而Cd浓度超过0.5 mg/L时,万寿菊的相对生长速率较对照明显降低(P＜0.05),最高可...     

安徽地震活动期的划分与地震活动趋势的研究

20世纪以来安徽与中国大陆地震活动呈同步活跃关系。本文对安徽的地震活动周期进行了划分 ,并用综合统计分析方法进行安徽未来地震活动趋势研究 ,结果表明 :安徽目前正处在一个相对较弱的地震活动期 ,该活动期约在 2 0 0 6年前后结束 ,估计发生地震的最大震级为 5级左右 ,可能主要是 4～ 5级地震活动。