Chemosphere - Global Change Science最新文献

Dry fall aerosol particulate matter was collected in the western rural area of Bahrain. The collection was carried out using an open beaker trap of deionized water placed on the roof of an 8 m high building in seven villages representing the area under study. The water-soluble matter was analyzed for its chemical components by ion chromatography. The data obtained were in good correlation with the meteorological and surface features of Bahrain. The sizes of 108 randomly chosen particles, measured with a photomicrographic microscope, ranged between 6 and 230 μm. The latter value gives an indication that most of these particles were soil-derived.

A one-dimensional model is used to study the effect of stratospheric ozone depletion (SOD) on the net production of ozone in the troposphere over various chemical coherent regions. It is found that in addition to the concentration of NO_x, the response of the net ozone production to SOD is also determined by the concentrations of non-methane hydrocarbons (NMHCs), ozone and water vapor. The threshold NO_x concentration, at which the response to SOD of the net ozone production changes from negative to positive, depends on the chemical regime and varies during a day, but it is typically about 1 ppb in a 24-hour average. The net ozone production in the boundary layer over polluted rural areas is most likely decreased due to SOD over a NO_x-limited region and increased over an NMHCs-limited region. In an NO_x-limited region the decrease in the net ozone production is the largest at high relative humidity. In cases with an increase in the net ozone production due to SOD, the increase is most favored at low relative humidity for the same NO_x and NMHCs conditions.

A passive integrative mercury sampler (PIMS) based on a sealed polymeric membrane was effective for the collection and preconcentration of Hg⁰. Because the Hg is both oxidized and stabilized in the PIMS, sampling intervals of weeks to months are possible. The effective air sampling rate for a 15×2.5 cm device was about 2 l-equivalents/day (0.002 m³/day) and the detection limit for 4-week sampling was about 2 ng/m³ for conventional ICP-MS determination without clean-room preparation. Sampling precision was ⩽5% RSD for laboratory exposures, and 5–10% RSD for field exposures. These results suggest that the PIMS could be useful for screening assessments of Hg contamination and exposure in the environment, the laboratory, and the workplace. The PIMS approach may be particularly useful for applications requiring unattended sampling for extended periods at remote locations. Preliminary results indicate that sampling for dissolved gaseous mercury (DGM) and potentially other neutral mercury species from water is also feasible. Rigorous validation of the sampler performance is currently in progress.

Concentration profiles of C₂–C₆ non-methane hydrocarbons (NMHCs) were obtained in metropolitan Taipei, Taiwan based on 50 air samples collected simultaneously during an evening traffic rush hour. Although motor vehicle exhaust contributes most of the measured hydrocarbons in the city, levels of propane and butane are significant, and do not correlate well with typical NMHCs emitted from vehicle exhaust, suggesting that the leakage from liquefied petroleum gas (LPG) is the primary source. Natural gas (NG) leakage was also investigated using ethane as a tracer, and a similar profile to propane was observed, suggesting that the use of LPG and NG in metropolitan Taipei is not exclusive but rather complementary. The reactivity of ethane, propane, iso-and n-butanes released from NG and LPG was estimated to be about 5–6% of the total reactivity summed from C₂–C₆ NMHCs, compared to their mass fraction of about 27%. The profiles computed from simultaneous sampling provide a direct view of NMHC distributions in Taipei metropolitan area, and are useful to indicate source strength with respect to geographic locations. The principle component analysis, however, can reveal relative importance of various sources in a particular location or area.

Monosaccharide derivatives from the breakdown of cellulose are the major organic components of smoke particles emitted to the atmosphere from biomass burning. In urban areas a related biopolymer, chitin, may contribute markers to smoke from grilling/charring of crustacean seafood. 1,6-Anhydro-2-acetamido-2-deoxyglucose and the related degradation products from chitin can be utilized as specific and general indicator compounds for the presence of emissions from charring/burning of crustaceans in samples of atmospheric fine particulate matter. This enables the potential assessment of such cooking emissions in urban and rural areas. There are other compounds (e.g., thermal alteration derivatives from proteins and nucleic acids) which are additional key indicators in smoke from charring/burning of chitin. 1,6-Anhydro-2-acetamido-2-deoxyglucose is proposed as a specific indicator for chitin in biomass burning emissions. It is emitted at similarly high concentrations and emission rates as levoglucosan from cellulose burning that it should be detectable in certain indoor and urban atmospheres.

In view of its impact on the earth’s climate, methane despite its low atmospheric concentration, has assumed importance in recent years. Natural wetlands are one of the major sources for methane emission to the atmosphere. This study was carried out to find out the seasonal fluctuation in CH₄ fluxes from water bodies and the difference in the methane efflux from vegetated and unvegetated surfaces of natural and man-made water bodies as well as to investigate the edaphic factors controlling the methane production and emission. The results revealed that there were seasonal fluctuations in methane emission from both the natural and man-made water bodies. Evidently, CH₄ emission from the vegetated surface was many times higher than that from the unvegetated surface of the same water body, indicating the importance of vegetation in methane transport from sediments to atmosphere. Study of several edaphic factors like pH, redox potential, temperature and organic carbon of 10 water bodies, including 5 man-made ponds showed that all these factors largely determined CH₄ production in the sediment as reflected by its emission from water bodies.

Oceanic measurements made to determine the fluxes of methyl chloride between the sea surface and atmosphere have pointed to the possibility of significant errors in literature values for the solubility of this gas in seawater. In this work the Henry's Law constant for CH₃Cl in seawater has been measured as $\text{ln}\text{H=8.83−2866/T}$, where T is the absolute temperature. Also reported are solubilities for CH₂Cl₂, CHCl₃, C₂HCl₃ and C₂Cl₄. The influence of the new value for CH₃Cl on estimates of its global oceanic source to the atmosphere is discussed. The net flux of CH₃Cl from the ocean to the atmosphere is estimated to be in the range: 6.4–8 × 10⁹ moles yr⁻¹ (0.3–0.4 T g yr⁻¹).

Fluxes of N₂O from four paddy soils, two upland soils, two orchard soils, and two hardwood forest soils located at central and southern parts of Taiwan were measured between 1994 and 1997 using a static close chamber technique. Daily emissions and variations in rate of N₂O fluxes from paddy and orchard soils were larger than those from fallow upland and hardwood forest soils. Daily coefficients of variation of these measurements ranged from 4% to 350%. The range of daily N₂O fluxes were listed in the following order : the highest amount observed in upland soils, paddy soils, orchard soils, and hardwood forest soils. The largest N₂O flux was detected from upland soil collected at Chishan which was 324.6 g N₂O-N ha⁻¹ day⁻¹ with a daily mean flux around 57.7 g N₂O-N ha⁻¹. In all test soils, based on annual measurements, the mean temporal coefficients of variation ranged from 14.8 to 130.9%, and the largest was detected in paddy soils. The results also indicate that the mean annual amounts of N₂O released into the atmosphere was 11.3, 5.6, 4.5 and 3.4 kg N₂O-N ha⁻¹ yr⁻¹ from upland, paddy, orchard, and hardwood forest soils, respectively. It was calculated that the total amounts of emission of N₂O from those agroecosystems and hardwood forest soils of central and southern parts of Taiwan, together having a total area of 970 965 ha, was about 5944 tons N₂O-N per year.

Although campfires are typically enjoyable events, people are exposed to high concentrations of gaseous and particulate pollutants. The combustion conditions of wood burned in campfires are different from those of indoor wood burning in stoves or fireplaces. Typically, wood logs, twigs, and branches with their leaves or needles are burned in campfires, whereas mostly wood logs are burned in indoor settings. Consequently, the molecular source profiles for organic particulate matter emissions may be different from a campfire. For human exposure assessment, there is a need to fingerprint the organic compound compositions in campfire wood smoke. Here we present the detailed biomarker composition of conifer wood smoke from a campfire. The major biomarkers emitted are dehydroabietic acid, the resin acids (pimaric, iso-pimaric, sandaracopimaric and abietic acids), retene, pimanthrene, methylcyclopentenophenanthrene and β-sitosterol, with levoglucosan and lignin phenolics such as vanillic acid in the polar fraction. PAH are minor components. A marker and PAH profile has been generated which can be utilized for tracing emissions from campfire burning and evaluating personal exposure risk.

A sampling technique was developed to sample floodwater and soil solution from wetland ricefields for the determination of dissolved CH₄. The method was compared with the soil core method used in the measurement of entrapped CH₄. This was done to assess if dissolved CH₄ determination could be an alternative to soil-entrapped CH₄ measurements since the latter is time-consuming, laborious and destructive in nature.

The dynamics of both dissolved CH₄ and entrapped CH₄ follow the same seasonal pattern. They have the same degree of spatial and temporal variability. However, the sampling procedure developed for the determination of dissolved CH₄ is relatively simple, easy and convenient compared to that for soil-entrapped CH₄ measurements. It also allows in-situ solution sampling at different soil depths. Therefore, it is recommended that dissolved CH₄ measurements can be an alternative to soil-entrapped CH₄ determinations.