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1.
In this experimental study, rate constants were measured for the reactions of ozone with 13 polycyclic aromatic hydrocarbons (PAHs) adsorbed on different types of particles. Graphite and silica were chosen to model, respectively, carbonaceous and mineral atmospheric particles. The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate PAH concentrations versus time. Second order rate constants were calculated considering the ozone gaseous concentration. At room temperature, rate constants varied, in the case of graphite particles, between (1.5 ± 0.5) × 10−17 and (1.3 ± 0.7) × 10−16 cm3 molecule−1 s−1 for chrysene and dibenzo[a,l]pyrene, respectively, and, in the case of silica particles, between (1.5 ± 0.3) × 10−17 and (1.4 ± 0.3) × 10−16 cm3 molecule−1 s−1 for fluoranthene and benzo[a]pyrene, respectively. Different granulometric parameters (particle size, pore size) and different PAH concentrations were tested in the case of silica particles. Heterogeneous reactions of ozone with particulate PAHs are shown to be more rapid than those occurring in the gas-phase, and may be competitive with atmospheric photodegradation.  相似文献   

2.
The contribution of emissions from agricultural facilities is rapidly becoming a major concern for local and regional air quality. Characterization of particle properties such as physical size distribution and chemical composition can be valuable in understanding the processes contributing to emissions and ultimate fate of particulate matter from agricultural facilities. A measurement campaign was conducted at an Iowa, deep-pit, three-barn swine finishing facility to characterize near-source ambient particulate matter. Size-specific mass concentrations were determined using minivol samplers, with additional size distribution information obtain using optical particle counters. Particulate composition was determined via ion chromatographic analysis of the collected filters. A thermal-CO2 elemental/organic carbon analyzer measured particulate carbon. The chemical composition and size distribution of sub-micron particles were determined via real-time aerosol mass spectrometry. Primary particulate was not found to be a major emission from the examined facility, with filter-based impactor samples showing average near-source increases (~15–50 m) in ambient PM10 of 5.8 ± 2.9 μg m−3 above background levels. PM2.5 also showed contribution attributable to the facility (1.7 ± 1.1 μg m−3). Optical particle counter analysis of the numerical size distributions showed bimodal distributions for both the upwind and downwind conditions, with maximums around 2.5 μm and below the minimum quantified diameter of 0.3 μm. The distributions showed increased numbers of coarse particles (PM10) during periods when wind transport came from the barns, but the differences were not statistically significant at the 95% confidence level. The PM10 aerosols showed statistically increased concentrations of sulfate, nitrate, ammonium, calcium, organic carbon, and elemental carbon when the samplers were downwind from the pig barns. Organic carbon was the major constituent of the barn-impacted particulate matter in both sub-micron (54%) and coarse size (20%) ranges. The AMS PM1 chemical speciation showed similar species increases, with the exception of and Ca+2, the latter not quantified by the AMS.  相似文献   

3.
Both aerosol and rainwater samples were collected and analyzed for ionic species at a coastal site in Southeast Asia over a period of 9 months (January–September 2006) covering different monsoons. In general, the occurrence and distribution of ionic species showed a distinct seasonal variation in response to changes in air mass origins. Real-time physical characterization of aerosol particles during rain events showed changes in particle number distributions which were used to assess particle removal processes associated with precipitation, or scavenging. The mean scavenging coefficients for particles in the range 10–500 nm and 500–10 μm were 7.0 × 10−5 ± 2.8 × 10−5 s−1 and 1.9 × 10−4 ± 1.6 × 10−5 s−1, respectively. A critical analysis of the scavenging coefficients obtained from this study suggested that the wet removal of aerosol particles was greatly influenced by rain intensity, and was particle size-dependent as well. The scavenging ratios, another parameter used to characterize particle removal processes by precipitation, for NH4 +, Cl−, SO4 2−, and NO3 − were found to be higher than those of Na+, K+, and Ca2+ of oceanic and crustal origins. This enrichment implied that gaseous species NH3, HCl, and HNO3 could also be washed out readily. These additional sources of ions in precipitation presumably counter-balanced the dilution effect caused by high total precipitation volume in the marine and tropical area.  相似文献   

4.
PM10 samples were collected over three years at Monzenmachi, the Japan Sea coast, the Noto Peninsula, Ishikawa, Japan from January 17, 2001 to December 18, 2003, using a high volume air sampler with quartz filters. The concentrations of the water-soluble inorganic ions in PM10 were determined with using ion chromatography. By analyzing the characteristics of these, the evidences were found that the Asian outflow had an obviously influence on the air quality at our study site. The results were as follows: the secondary pollutants SO42−, NO3− and NH4+ were the primary water-soluble inorganic ions at our study site. The monthly mean concentrations of SO42−, NH4+, NO3− and Ca2+ have prominent peak in spring due to the strong influence of the Asian continent outflow—these according to backward air trajectory analysis, the maximum of which were 6.09 for nss-SO42− in May, 2.87 for NO3− and 0.68 μg m−3 for nss-Ca2+ in April, respectively. Comparable to similar data reported from various points around East Asia, it had the characteristics of a polluted coastal area at our study site. The concentration of nss-Ca2+ in PM10 drastically increased when the Asian dust invaded, the mean value during the Asian dust days(AD) was 0.86 μg m−3, about 4 times higher than those of normal days (NAD). Meanwhile, the mean concentrations of nss-SO42−, NO3− and NH4+ in AD periods were higher than those in NAD periods which were 5.87, 1.76 and 1.82 μg m−3, respectively, it is due to the interaction between dust and secondary particles during the long-range transport of dust storms. Finally, according to the source apportionment with positive matrix factorization (PMF) method in this study, the major source profiles of PM10 at our study site were categorized as (1) marine salt, (2) secondary sulfate, (3) secondary nitrate and (4) crustal source.  相似文献   

5.
Ambient respirable particles (PM10; aerodynamic diameter ≤10 μm) collected in a tropical urban environment (Delhi, India) during December 2008-November 2009 were characterized with respect to 16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) and 8 major and trace metals (Fe, Mn, Cd, Cu, Ni, Pb, Zn and Cr). Concentrations of Σ16PAHs (annual mean: 74.7 ± 50.7 ng m−3, range 22.1–258.4 ng m−3) and most metallic species were at least an order of magnitude greater than values reported from similar locations worldwide. Seasonal variations in Σ16PAHs were significant (p < 0.001) with highest levels in winter while crustal and anthropogenic metals showed significant but mutually opposite seasonal dependence. Statistically significant associations were observed between chemical species and various meteorological parameters. The PAH profile was dominated by combustion-derived large-ring species (~85%) that were essentially local in origin. Principal component analysis–multiple linear regression (PCA-MLR) apportioned four sources: crustal dust (73%), vehicular emission (21%), coal combustion (4%) and industrial emission (2%) that was further validated by hierarchical cluster analysis (HCA). Temporal trend analysis showed that crustal sources were predominant in summer (p < 0.05) while the remaining sources were most active in winter. Summertime intrusions of Saharan dust were identified with the help of aerosol maps and air parcel backward trajectories. Inhalation cancer risk assessment showed that up to 3,907 excess cancer cases (357 for PAHs, 122 for Cd, 2040 for Cr (VI) and 1387 for Ni) are likely in Delhi considering lifetime inhalation exposure to these chemicals at their current concentrations.  相似文献   

6.
The kinetics of heterogeneous reactions of NO2 with 17 polycyclic aromatic hydrocarbons (PAHs) adsorbed on laboratory generated kerosene soot surface was studied over the temperature range (255–330) K in a low pressure flow reactor combined with an electron-impact mass spectrometer. The kinetics of soot-bound PAH consumption due to their desorption and reaction with NO2 were monitored using off-line HPLC measurements of their concentrations in soot samples as a function of reaction time, NO2 concentrations in the gas phase being analyzed by mass spectrometer. No measurable decay of PAHs due to the reaction with NO2 was observed under experimental conditions of the study (maximum NO2 concentration of 5.5 × 1014 molecule cm−3 and reaction time of 45 min), which allowed to determine the upper limits of the first-order rate constants for the heterogeneous reactions of 17 soot-bound PAHs with NO2: k < 5.0 × 10−5 s−1 (for most PAHs studied). Comparison of these results to previous studies carried on different carbonaceous substrates, showed that heterogeneous reactivity of PAHs towards NO2 is, probably, dependent on the substrate nature even for resembling, although different carbonaceous materials. Results show that particulate PAHs degradation by NO2 alone is of minor importance in the atmosphere  相似文献   

7.
Black carbon (BC) concentrations were measured in the southeast (SE) Tibetan Plateau along the valley of the Yarlung Tsangpo River during winter (between November, 2008 and January, 2009). The measured mean concentration (0.75 μg m−3) is significantly higher than the concentrations (0.004–0.34 μg m−3) measured in background and remote regions of the globe, indicating that Tibetan glaciers are contaminated by BC particles in the Plateau. Because BC particles play important roles for the climate in the Tibetan Plateau, the sources and causes of the BC contamination need to be understood and investigated. In this study, a mesocale dynamical model (WRF) with BC particle modules is applied for analyzing the measurement. The analysis suggests that the major sources for the contamination in the SE Plateau were mainly from the BC emissions in eastern Indian and Bangladesh. Because of the west prevailing winds, the heavy emissions in China had no significant effects on the SE Plateau in winter. Usually, the high altitude of the Himalayas acts a physical wall, inhibiting the transport of BC particles across the mountains to the plateau. This study, however, finds that the Yarlung Tsangpo River valley causes a 'leaking wall', whereby under certain meteorological conditions, BC particles are being transported up onto the glacier. This too causes variability of BC concentrations (ranging from 0.3 to 1.5 μg m−3) in a time scale of a few days. The analysis of the variability suggests that the “leaking wall” effect cannot occur when the prevailing winds were northwest winds, during which the BC transport along the valley of the Yarlung Tsangpo River was obstructed. As a result, large variability of BC concentration was observed due to the change of prevailing wind directions.  相似文献   

8.
Thin film methods and X ray energy dispersive technique were applied to analyze sulfate-containing particles in Beijing in order to examine their features and sources. Atmospheric aerosol particles were collected on electron mi-croscope meshes according to two size ranges: coarse particles (r>0.5μm) and fine particles (0.5μm≥r≥0.1μm) by using a two-stage impactor. It was found fiat more than seventy percent of the fine particles and about twenty percent of the coarse particles were sulfate-containing particles. These particles were formed mainly through heterogeneous nucleation. The element composition analyses revealed that the atmospheric aerosol particles in Beijing were domi-nated by crustal particles and construction dust.  相似文献   

9.
A continuous measurement of number size distributions and chemical composition of aerosol particles was conducted in Beijing in a dust storm event during 21-26 March 2001. The number concentration of coarse particles （ 〉2μm） increased more significantly than fine particles （ 〈2μm） during the dust storm due to dust weather, while the anthropogenic aerosols collected during the non-dust-storm period tended to be associated with fine particles. Elemental compositions were analyzed by using proton-induced X-ray emission （PIXE）. The results show that 20 elements in the dust storm were much higher than in the non-dust-storm period. The calculated soil dust concentration during the dust storm was, on average, 251.8μg m^-3, while it was only 52.1μg m^-3 on non-dust-storm days. The enrichment factors for Mg, A1, P, K, Ca, Ti, Mn, Fe, C1, Cu, Pb, and Zn show small variations between the dust storm and the non-dust-storm period, while those for Ca, Ni and Cr in the dust storm were much lower than those in the non-dust-storm period due to significant local emission sources. A high concentration and enrichment factor for S were observed during the dust storm, which implies that the dust particles were contaminated by aerosol particles from anthropogenic emissions during the long-range transport. A statistical analysis shows that the elemental composition of particles collected during the dust storm in Beijing were better correlated with those of desert soil colleted from desert regions in Inner Mongolia. Air mass back-trajectory analysis further confirmed that this dust storm event could be identified as streaks of dust plumes originating from Inner Mongolia.  相似文献   

10.
Airborne particulate matter in Saxony (Germany) was investigated at three different sites (central urban, urban outskirts, rural) during a winter (1999/2000) and a summer (2000) campaign. PM was collected simultaneously at all three sites using five-stage Berner impactors. Besides size-segregated chemical particle characterisation and mass closure source apportionment of the particle components, especially of the carbonaceous fraction was an aim of the study. Source apportionment was performed exclusively on the basis of experimental data without support of models considering a set of basic assumptions and logical deductions. The derived simple equations permit to differentiate the carbonaceous fraction in traffic, domestic heating (winter) and biogenic (summer) contributions.The total carbon (TC) in the smallest particle size range (Dpaer = 0.05-0.14μm) at the urban site, contributing 88% to the mass in that class, was completely attributed to traffic emissions. For the particle size range Dpaer = 0.42-1.2 μm (50-60% of the total mass) TC was attributed to traffic (67%) and domestic heating (33%) in winter and to traffic (82%) and biogenic origin (18%) in summer.Size-segregated determination of alkanes revealed that these compounds were mainly of biogenic origin in summer and of anthropogenic origin in winter considering the carbon preference index (CPIodd). Particulate PAHs found in winter samples originated mainly from domestic heating and not from traffic emissions.The method described cannot provide complete results, but the demonstrated source apportionment can be helpful to assess a given situation with regard to possible steps against the exceeding of the EU limit of the PM10 mass concentration of 50 μg m−3.  相似文献   

11.
Secondary aerosol formation was studied at Allahabad in the Indo-Gangetic region during a field campaign called Land Campaign-II in December 2004 (northern winter). Regional source locations of the ionic species in PM10 were identified by using Potential Source Contribution Function (PSCF analysis). On an average, the concentration of water soluble inorganic ions (sum of anions and cations) was 63.2 μgm−3. Amongst the water soluble ions, average NO3− concentration was the highest (25.0 μgm−3) followed by SO42− (15.8 μgm−3) and NH4+ (13.8 μgm−3) concentrations. These species, contributed 87% of the total mass of water soluble species, indicating that most of the water soluble PM10 was composed of NH4NO3 and (NH4)2SO4/NH4HSO4 or (NH4)3H(SO4)2 particles. Further, the concentrations of SO42−, NO3−, and NH4+ aerosols increased at high relative humidity levels up to the deliquescence point (∼63% RH) for salts of these species suggesting that high humidity levels favor the conversion and partitioning of gaseous SO2, NOx, and NH3 to their aerosol phase. Additionally, lowering of ambient temperature as the winter progressed also resulted in an increase of NO3− and NH4+ concentrations, probably due to the semi volatile nature of ammonium nitrate. PSCF analysis identified regions along the Indo-Gangetic Plain (IGP) including Northern and Central Uttar Pradesh, Punjab, Haryana, Northern Pakistan, and parts of Rajasthan as source regions of airborne nitrate. Similar source regions, along with Northeastern Madhya Pradesh were identified for sulfate.  相似文献   

12.
Polychlorinated biphenyls (PCBs) as Σ21 congeners, were investigated in atmospheric bulk deposition over one year, along a northern transect of France, including 5 sites from the Atlantic coast to the east of Paris. Evidence was obtained for an easterly rise of the PCB concentrations, from 3 to 76 ng L−1. The PCB patterns were depleted in low chlorinated congeners in rural areas whereas at urban sites, the profiles were typical of local sources. The seasonal variations of concentrations were mainly controlled by the temperature. Next, at Paris, PCB distribution between the gaseous and the particulate phases was studied, considering seasonal parameters and different fate processes. Their distribution showed a prevalence of congeners in the gaseous phase (0.15–1.17 ng m−3) which occurrence decreased from 93 to 68% with the rise of congener chlorination level. In the particulate phase, they ranged from 0.01 to 0.27 ng m−3, only. Rainwater concentrations ranged from 3.1 to 13.1 ng L−1. A total rain water/air washout ratio was determined and showed a negative correlation with those reported in the literature. That might be attributed to the importance of particle scavenging. The annual bulk deposition ranged from 8 to 29 μg m−2. A decreasing trend of PCB atmospheric levels over the last fifteen years was confirmed in the studied area.  相似文献   

13.
A comprehensive study on the chemical compositions of rainwater was carried out from June 2007 to December 2008 in Guiyang, a city located on the acid rain control zone of southwest China. All samples were analyzed for pH, major anions (F−, Cl−, NO3−, SO42−), major cations (K+, Na+, Ca2+, Mg2+, NH4+), Sr2+ and Sr isotope. The pH increase is due to the result of neutralization caused by the alkaline dust which contain large amount of CaCO3. It was observed that Ca2+ was the most abundant cation with a volume-weighted mean (VWM) value of 217.6 μeq/L (52.7–1928 μeq/L), accounting for 66% (39%–88%) of the total cations. SO42− was the most abundant anion with VWM value of 237.8 μeq/L (49.6-1643 μeq/L). SO42− and NO3− were dominant among the anions, accounting for 66%–97% of the total measured anions. The Sr concentrations vary from 0.01 to 0.92 μmol/L, and strontium isotopic ratios vary in the range of 0.707684–0.710094, with an average of 0.708092. The elements ratios and the 87Sr/86Sr ratios showed that the solutes of rainwater mainly come from weathering of carbonate and secondary dust input. Moreover, urbanization results in the calcium-rich dust increased and the high concentrations of alkaline ions (mainly Ca2+) have played an important role to neutralize the acidity of rainwater, leading to the increase of arithmetic pH mean value by 0.5 units since 2002. It is worth noting that the emission of SO2 and NOx from the automobile exhaust is increasing and is becoming another important precursor of acid rain now.  相似文献   

14.
The non-polar organic composition of airborne particulate matter was analysed over a two year period in an urban area under oceanic climate conditions (Errenteria, Basque Country, Spain). In addition, the distribution of polycyclic aromatic hydrocarbons (PAH) among different aerosol particle sizes was determined. Clues as to the origin of various particle types were gained by using scanning electron microscopy to view the morphology of the particulates in each size fraction. Samples were collected on glass fibre filters and analysed by means of soxhlet extraction and gas chromatography (either with a flame ionization detector or coupled to a mass spectrometry). In general, total PAH levels were moderate (0.96–50 ng m− 3) as compared to other studies conducted in Europe, and showed clear seasonal variation with maxima in winter and minima in summer. Vehicular traffic was identified as a major source of PAHs in the study area. Regarding particle size, a bimodal distribution was observed. The large sized particles exhibited an apparent seasonal variation with higher concentrations in winter than in summer. The dependences between particle size, PAH distribution and meteorological variables were studied with multivariate statistics. Three main sources of organic compounds were identified: combustion, vegetation, and atmospheric oxidation.  相似文献   

15.
The results of one year’s monitoring in Srednja Bijambarska Cave (Bosnia and Herzegovina) are presented and discussed. Temporal variations of the carbon dioxide (CO2) concentration are controlled by the switching between two ventilation regimes driven by outside temperature changes. A regression model with a simple perfectly mixed volume applied to a cave sector (“Music hall”) resulted in an estimate of ventilation rates between 0.02 h−1 and 0.54 h−1. Carbon dioxide input per plan surface unit is estimated by the model at around 50 × 10−6 mh−1 during the winter season and up to more than 1000 × 10−6 mh−1 during the first temperature falls at the end of summer (0.62 μmoles m−2 s−1 and 12.40 μmoles m−2 s−1 for normal conditions respectively). These values have been found to be related to the cave ventilation rate and dependent on the availability of CO2 in the surrounding environment. For airflow close to zero the values of CO2 input per plan surface have a range in the order of magnitude of a few units × 10−6 mh−1. Based on two experiments, the anthropogenic contribution from cave visitors has been calculated, at between 0.35 lCO2 min−1 person−1 and 0.45 lCO2min−1person−1.  相似文献   

16.
In this study, a regional air quality model system (RAQMS) was applied to investigate the spatial distributions and seasonal variations of atmospheric aerosols in 2006 over East Asia. Model validations demonstrated that RAQMS was able to reproduce the evolution processes of aerosol components reasonably well. Ground-level PM10 (particles with aerodynamic diameter ≤10 μm) concentrations were highest in spring and lowest in summer and were characterized by three maximum centers: the Taklimakan Desert (～1000 μg m-3), the Gobi Desert (～400 μg m-3), and the Huabei Plain (～300 μm-3) of China. Vertically, high PM10 concentrations ranging from 100 μg m-3 to 250 μg m-3 occurred from the surface to an altitude of 6000 m at 30o--45oN in spring. In winter, the vertical gradient was so large that most aerosols were restricted in the boundary layer. Both sulfate and ammonium reached their highest concentrations in autumn, while nitrate reached its maximum level in winter. Black carbon and organic carbon aerosol concentrations reached maximums in winter. Soil dust were strongest in spring, whereas sea salt exerted the strongest influence on the coastal regions of eastern China in summer. The estimated burden of anthropogenic aerosols was largest in winter (1621 Gg) and smallest in summer (1040 Gg). The sulfate burden accounted for ～42% of the total anthropogenic aerosol burden. The dust burden was about twice the anthropogenic aerosol burden, implying the potentially important impacts of the natural aerosols on air quality and climate over East Asia.  相似文献   

17.
Cascade impactor samples were collected over the Alaskan Arctic during the first three research flights of AGASP-II. These samples were analyzed using analytical electron microscopy to determine the morphology, mineralogy and elemental composition of individual particles. For analytical considerations, a typical impactor sample was run for approximately 20 min, thus giving excellent time resolution of discrete events.Samples collected during flights 201 and 202 consisted of stratospheric aerosol and lower-altitude haze samples. Stratospheric samples were characterized by moderate loadings of H2SO4 droplets with relatively few particles of other types. Samples collected in tropospheric haze layers generally exhibited light-to-moderate particle loadings. H2SO4 was again the most prevalent species, with crustal and anthropogenic particles also observed. One sample taken over south-central Alaska near the end of flight 203 showed high concentrations of solid crustal particles, with relatively little associated H2SO4. Giant particles larger than 5 m were occasionally observed in this aerosol. The composition of this material closely matches that of bulk ash from the Mt. Augustine volcano, which erupted 9–13 days before collection of this sample. This brings forth the possibility that pockets of ash-rich aerosol existed over parts of south and central Alska during the AGASP-II field mission. There is no evidence that these volcanic aerosols were present in the AGASP study area north of the Brooks Range.  相似文献   

18.
Using a single drop experiment, the uptake of NO3 radicals on aqueous solutions of the dye Alizarin Red S and NaCl was measured at 293 K. Uptake coefficients in the range (1.7–3.1) ⋅ 10− 3 were measured on Alizarin Red S solutions. The uptake coefficients measured on NaCl solutions were in the range of (1.1–2.0) ⋅ 10−3 depending on the salt concentration. Both experiments lead to a consistent result for the mass accommodation coefficient of αNO3 = (4.2− 1.7+2.2)⋅ 10−3. The product H(Dl kCl−II)0.5 for the NO3 radical was determined to be (1.9 ± 0.2) M atm− 1 cm s−0.5 M−0.5 s−0.5 by fitting the uptake data for the NaCl solutions to the so-called resistance model. The yield of the chemical NO3 radical source was characterized using UV-VIS and FT-IR spectroscopy. The amount of gas-phase NO3 radicals measured at elevated humidities was less than expected. Instead, a rise of the gas-phase HNO3 concentration was found indicating a conversion of gas-phase NO3 radicals to gas-phase HNO3 on the moist reactor walls.  相似文献   

19.
Dispersion estimates with a Gaussian plume model are often incorrect because of particle settling (β), deposition (γ) or the vertical gradient in diffusivity (K v (z) = K 0 + μz). These “non-Gaussian” effects, and the interaction between them, can be evaluated with a new Hankel/Fourier method. Due to the deepening of the plume downwind and reduced vertical concentration gradients, these effects become more important at greater distance from the source. They dominate when distance from the source exceeds L β = K 0 U/β 2, L γ  = K 0 U/γ 2 and L μ = K 0 U/μ 2 respectively. In this case, the ratio β/μ plays a central role and when β/μ = 1/2 the effects of settling and K gradient exactly cancel. A general computational method and several specific closed form solutions are given, including a new dispersion relation for the case when all three non-Gaussian effects are strong. A more general result is that surface concentration scales as C(x) ~ γ −2 whenever deposition is strong. Categorization of dispersion problems using β/μ, L γ and L μ is proposed.  相似文献   

20.
The joint impact of UV-B radiation and temperature on photodegradation of polycyclic aromatic hydrocarbons (PAHs) sorbed to an organic solvent was assessed in this study. This approach was experimentally performed in a laboratory investigation by means of comparison of two different environments: Atlantic (Lancaster, UK) and Mediterranean (Tarragona, Catalonia, Spain) climatic conditions. The concentration of 10 PAHs contained in a tetradecane solution was compared under two different temperatures (10 and 20°C) and UV-B doses (6.5 and 22.5 kJ m−2 day−1). No photodegradation was observed for the heaviest hydrocarbons (benzo(a)anthracene, chrysene, benzo(a)pyrene, dibenzo(g,h,i)perylene and coronene). In general terms, the half-life of PAHs was highly dependent on their molecular weight. Significant faster photodegradation rates were detected specially for light PAHs. It indicates that a synergistic effect occurred when both temperature and UV-B dose increased. This synergism might have a great implication on the long-range transport of environmental organic pollutants taking into account that low-latitude areas are the hottest and most irradiated of the planet.  相似文献   

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