Impact of the mixing boundary layer on the relationship between PM2.5 and aerosol optical thickness

The purpose of this paper is to study the relationship between columnar aerosol optical thickness and ground-level aerosol mass. A set of Sun photometer, elastic backscattering lidar and TEOM measurements were acquired during April 2007 in Lille, France. The PM2.5 in the mixed boundary layer is estimated using the lidar signal, aerosol optical thickness, or columnar integrated Sun photometer size distribution and compared to the ground-level station measurements. The lidar signal recorded in the lowest level (240 m) is well correlated to the PM2.5 (R² = 0.84). We also show that the correlation between AOT-derived and measured PM2.5 is significantly improved when considering the mixed boundary layer height derived from the lidar. The use of the Sun photometer aerosol fine fraction volume does not improve the correlation.     

Source apportionment of Phoenix PM2.5 aerosol with the Unmix receptor model

The multivariate receptor model Unmix has been used to analyze a 3-yr PM2.5 ambient aerosol data set collected in Phoenix, AZ, beginning in 1995. The analysis generated source profiles and overall average percentage source contribution estimates (SCEs) for five source categories:gasoline engines (33 +/- 4%), diesel engines (16 +/- 2%), secondary SO4(2-) (19 +/- 2%), crustal/soil (22 +/- 2%), and vegetative burning (10 +/- 2%). The Unmix analysis was supplemented with scanning electron microscopy (SEM) of a limited number of filter samples for information on possible additional low-strength sources. Except for the diesel engine source category, the Unmix SCEs were generally consistent with an earlier multivariate receptor analysis of essentially the same data using the Positive Matrix Factorization (PMF) model. This article provides the first demonstration for an urban area of the capability of the Unmix receptor model.     

Simple model for estimating dry deposition velocity of ozone and its destruction in a polluted nocturnal boundary layer

Determining the destructions of both ozone and odd oxygen, O_x, in the nocturnal boundary layer (NBL) is important to evaluate the regional ozone budget and overnight ozone accumulation. This work develops a simple method to determine the dry deposition velocity of ozone and its destruction at a polluted nocturnal boundary layer. The destruction of O_x can also be determined simultaneously. The method is based on O₃ and NO₂ profiles and their surface measurements. Linkages between the dry deposition velocities of O₃ and NO₂ and between the dry deposition loss of O_x and its chemical loss are constructed and used. Field measurements are made at an agricultural site to demonstrate the application of the model. The model estimated nocturnal O₃ dry deposition velocities from 0.13 to 0.19 cm s^?1, very close to those previously obtained for similar land types. Additionally, dry deposition and chemical reactions account for 60 and 40% of the overall nocturnal ozone loss, respectively; ozone dry deposition accounts for 50% of the overall nocturnal loss of O_x, dry deposition of NO₂ accounts for another 20%, and chemical reactions account for the remaining 30%. The proposed method enables the use of measurements made in typical ozone field studies to evaluate various nocturnal destructions of O₃ and O_x in a polluted environment.     

Seasonal variations of monosaccharide anhydrides in PM1 and PM2.5 aerosol in urban areas

The concentrations of monosaccharide anhydrides (levoglucosan, mannosan, galactosan) in PM1 and PM2.5 aerosol samples were measured in Brno and ?lapanice in the Czech Republic in winter and summer 2009. 56 aerosol samples were collected together at both sites to investigate the different sources that contribute to aerosol composition in studied localities. Daily PM1 and PM2.5 aerosol samples were collected on pre-fired quartz fibre filters.The sum of average atmospheric concentration of levoglucosan, mannosan and galactosan in PM1 aerosol in ?lapanice and Brno during winter was 513 and 273 ng m^?3, while in summer the sum of average atmospheric concentration of monosaccharide anhydrides (MAs) was 42 and 38 ng m^?3, respectively. The sum of average atmospheric concentration of MAs in PM1 aerosol formed 71 and 63% of the sum of MA concentration in PM2.5 aerosol collected in winter in ?lapanice and Brno, whereas in summer the sum of average atmospheric concentration of MAs in PM1 aerosol formed 45 and 43% of the sum of MA concentration in PM2.5 aerosol in ?lapanice and Brno, respectively.In winter, the sum of MAs contributed significantly to PM1 mass ranging between 1.37% and 2.67% of PM1 mass (Brno – ?lapanice), while in summer the contribution of the sum of MAs was smaller (0.28–0.32%). Contribution of the sum of MAs to PM2.5 mass is similar both in winter (1.37–2.71%) and summer (0.44–0.55%).The higher concentrations of monosaccharide anhydrides in aerosols in ?lapanice indicate higher biomass combustion in this location than in Brno during winter season. The comparison of levoglucosan concentration in PM1 and PM2.5 aerosol shows prevailing presence of levoglucosan in PM1 aerosol both in winter (72% on average) and summer (60% on average).The aerosol samples collected in ?lapanice and Brno in winter and summer show comparable contributions of levoglucosan, mannosan and galactosan to the total amount of monosaccharide anhydrides in both aerosol size fractions. Levoglucosan was the most abundant monosaccharide anhydride with a relative average contribution to the total amount of MAs in the range of 71–82% for PM1 aerosols and 52–79% for PM2.5 aerosols.     

Seasonal effect on ammonia nitrogen removal by constructed wetlands treating polluted river water in southern Taiwan

A pilot-scale constructed wetland (CW) system, combining a free water surface wetland and a subsurface wetland in series, was used to purify highly polluted river water. The concentrations of constituents varied seasonally. The effects of season-dependent parameters, such as temperature, mass loading rate and inflow salinity, on the removal of ammonia nitrogen (AN) in the wetland system were examined at a constant hydraulic loading rate, based on data from June 1998 to February 2000. AN removal of the CW varied cyclically with the seasons. The removal efficiency and the first-order volumetric removal rate constant (k(V)) increased exponentially with water temperature, yielding a high temperature coefficient (theta). However, the mass removal rate decreased exponentially as temperature increased. These contradictory results made the actual effect of temperature uncertain. The inhibition of high water salinity on AN removal was also unclear because k(V) (as well as k(V20)) and mass removal rate were inversely proportional to salinity. However, mass loading rate (MLR) predominantly affected both the removal efficiency and the mass removal rate of AN, both of which were factors that explicitly determined seasonality. A power equation, k(V20)' alpha MLR(-n), was proposed to correct the variation of the mass loading rate in estimating k(V) and thus in designing a constructed wetland.     

Trends in arsenic levels in PM10 and PM2.5 aerosol fractions in an industrialized area

Arsenic is a toxic element that affects human health and is widely distributed in the environment. In the area of study, the main Spanish and second largest European industrial ceramic cluster, the main source of arsenic aerosol is related to the impurities in some boracic minerals used in the ceramic process. Epidemiological studies on cancer occurrence in Spain points out the study region as one with the greater risk of cancer. Concentrations of particulate matter and arsenic content in PM₁₀ and PM_2.5 were measured and characterized by ICP-MS in the area of study during the years 2005–2010. Concentrations of PM₁₀ and its arsenic content range from 27 to 46 μg/m³ and from 0.7 to 6 ng/m³ in the industrial area, respectively, and from 25 to 40 μg/m³ and from 0.7 to 2.8 ng/m³ in the urban area, respectively. Concentrations of PM_2.5 and its arsenic content range from 12 to 14 μg/m³ and from 0.5 to 1.4 ng/m³ in the urban background area, respectively. Most of the arsenic content is present in the fine fraction, with ratios of PM_2.5/PM₁₀ in the range of 0.65–0.87. PM₁₀, PM_2.5, and its arsenic content show a sharp decrease in recent years associated with the economic downturn, which severely hit the production of ceramic materials in the area under study. The sharp production decrease due to the economic crisis combined with several technological improvements in recent years such as substitution of boron, which contains As impurities as raw material, have reduced the concentrations of PM₁₀, PM_2.5, and As in air to an extent that currently meets the existing European regulations.     

Internal acid buffering in San Joaquin Valley fog drops and its influence on aerosol processing

Although several chemical pathways exist for S(IV) oxidation in fogs and clouds, many are self-limiting: as sulfuric acid is produced and the drop pH declines, the rates of these pathways also decline. Some of the acid that is produced can be buffered by uptake of gaseous ammonia. Additional internal buffering can result from protonation of weak and strong bases present in solution. Acid titrations of high pH fog samples (median pH=6.49) collected in California's San Joaquin Valley reveal the presence of considerable internal acid buffering. In samples collected at a rural location, the observed internal buffering could be nearly accounted for based on concentrations of ammonia and bicarbonate present in solution. In samples collected in the cities of Fresno and Bakersfield, however, significant additional, unexplained buffering was present over a pH range extending from approximately four to seven. The additional buffering was found to be associated with dissolved compounds in the fogwater. It could not be accounted for by measured concentrations of low molecular weight (C₁–C₃) carboxylic acids, S(IV), phosphate, or nitrophenols. The amount of unexplained buffering in individual fog samples was found to correlate strongly with the sum of sample acetate and formate concentrations, suggesting that unmeasured organic species may be important contributors. Simulation of a Bakersfield fog episode with and without the additional, unexplained buffering revealed a significant impact on the fog chemistry. When the additional buffering was included, the simulated fog pH remained 0.3–0.7 pH units higher and the amount of sulfate present after the fog evaporated was increased by 50%. Including the additional buffering in the model simulation did not affect fogwater nitrate concentrations and was found to slightly decrease ammonium concentrations. The magnitude of the buffering effect on aqueous sulfate production is sensitive to the amount of ozone present to oxidize S(IV) in these high pH fogs.     

Characterization and sources assignation of PM2.5 organic aerosol in a rural area of Spain

The results from a year-long study of the organic composition of PM2.5 aerosol collected in a rural area influenced by a highway of Spain are reported. The lack of prior information related to the organic composition of PM2.5 aerosol in Spain, concretely in rural areas, led definition of the goals of this study. As a result, this work has been able to characterize the main organic components of atmospheric aerosols, including several compounds of SOA, and has conducted a multivariate analysis in order to assign sources of particulate matter. A total of 89 samples were taken between April 2004 and April 2005 using a high-volume sampler. Features and abundance of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), alcohols and acids were separately determined using gas chromatography/mass spectrometry and high performance liquid chromatography analysis. The Σn-alkane and ΣPAHs ranged from 3 to 81 ng m^?3 and 0.1 to 6 ng m^?3 respectively, with higher concentrations during colder months. Ambient concentrations of Σalcohols and Σacids ranged from 21 to 184 ng m^?3 and 39 to 733 ng m^?3, respectively. Also, several components of secondary organic aerosol have been quantified, confirming the biogenic contribution to ambient aerosol. In addition, factor analysis was used to reveal origin of organic compounds associated to particulate matter. Eight factors were extracted accounting more than 83% of the variability in the original data. These factors were assigned to a typical high pollution episode by anthropogenic particles, crustal material, plant waxes, fossil fuel combustion, temperature, microbiological emissions, SOA and dispersion of pollutants by wind action. Finally, a cluster analysis was used to compare the organic composition between the four seasons.     

基于混合效应模型的京津冀地区PM2.5数值模拟

采用2017年京津冀地区中分辨率成像光谱仪提供的3km气溶胶光学厚度(AOD)和气象数据,分别在有无气象因子作为自变量的情况下对PM_(2.5)与AOD的关系进行解释。比较基于空间、时间及时空的78种混合效应模型的模拟效果,并利用十折交叉模型进行验证。经相关系数、拟合程度和模型误差对比,最终确定将气温、相对湿度、风速和气压4种气象因子作为影响因子的基于时空的混合效应模型效果最佳。利用该模型估算2017年京津冀地区的PM_(2.5)监测值,结果表明,PM_(2.5)监测值与模拟值的R~2为0.90(经十折交叉模型校正后为0.81),均方根误差、平均绝对误差分别为13.44、10.12μg/m~3,模型的拟合精度较高。同时研究表明,整体来说,京津冀地区呈现南高北低、平原地区东南高西北低、非平原地区高纬度区域相对低的空间格局。     

Characterization of n-alkanes in PM2.5 of the Taipei aerosol

Ambient concentrations of n-alkanes with carbon number ranging from 17 to 36 were determined for PM_2.5 samples collected in Taipei city during September 1997–February 1998. The measured concentrations of particulate n-alkanes were in the range of 69–702 ng m⁻³, considerably higher than the concentration levels observed in Los Angeles and Hong Kong. The concentration distributions of n-alkanes homologues obtained in this study exhibited peaks at C₁₉, C₂₄ or C₂₅. This suggests that fossil fuel utilization, such as vehicular exhaust and lubricant residues, was an important contributor to the Taipei aerosol. Source apportionment of PM_2.5 was conducted using carbon preference index (CPI, defined as the ratio of the total concentration of particulate n-alkanes with odd carbon number to that with even carbon number) and U : R ratio (the concentration ratio of unresolved components to resolved components obtained from chromatograms). The low CPI value (0.9–1.9) and high U : R ratio (2.6–6.4) for each sample further confirmed that fossil fuel utilization was the major source of n-alkanes in ambient PM_2.5 of Taipei city. Estimates from these results showed that 69–93% of the n-alkanes in PM_2.5 of the Taipei aerosol originated from vehicular exhaust. The higher concentration level of particulate n-alkanes in the Taipei aerosol was mainly a result of vehicular emissions.     

Correlation between PM concentrations and aerosol optical depth in eastern China

Using one year of Aerosol Optical Depth (AOD) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite and particular matter (PM) contents measured at eleven sites located mostly in the eastern China in 2007, the relationship between columnar AOD and hourly and daily average (DA) PM were established. The peak AOD observed from MODIS was generally consistent with the surface PM measurements in eastern China, where Zhengzhou had the maximum annual mean PM₁₀ of 182.1 μg m^?3, while Longfengshan had the minimum annual mean of 38.1 μg m^?3. Ground level observations indicated that PM concentration varies widely across different regions, which was mainly due to the difference in weather conditions and anthropogenic emissions. The coarse particles accounted for the main air pollution in Zhengzhou and Benxi whiles the fine particles, however, were the main constituents in other sites. Results showed that MODIS AOD (averaged over the box of 5 × 5 and 3 × 3 pixels) had a better positive correlation with the coincident hourly average (HA) PM concentration than with DA due to diurnal variation in PM mass measurements. After correcting AOD for relative humidity (RH), the correlation did not improve significantly, suggesting that the RH was not the main factor affecting the correlation of PM with AOD. The statistical regression analysis between MODIS AOD and PM mass suggested that the satellite-derived AOD is a useful tool for mapping PM distribution over large spatial domains.     

电解法去除重污染河水中的磷

近年来,河流污染严重,严重影响了社会的发展,治理河水污染成为目前急需解决的问题。研究了石墨-铁板电极电解法对城市内河中重污染水体中磷去除的可行性;分析了静置时间、电解时长、初始磷浓度、电压、pH及极板间距对电解法除磷效果的影响,确定了电解法处理重污染水体的最佳运行参数,比较了电解法处理实际河水和模拟河水的TP去除效果。结果表明,重污染河流水体中的磷在较短时间内可以得到去除,在静置时间为3 h,电压为10 V,极板间距为1.5cm,pH保持在中性或弱酸性,电解时长在10~15 min时,TP去除率达到90%以上。同时,在最佳运行条件下,电解法处理实际河水效果较好。     

Comparisons of coarse-mode aerosol nitrate and ammonium at two polluted coastal sites

Direct atmospheric fixed-nitrogen deposition can contribute to eutrophication in coastal and estuarine waters and can be enhanced by heterogeneous reactions between gaseous atmospheric nitrogen species and aerosol sea salt, which increase deposition rates. Size-segregated aerosol samples were collected from two coastal sites: Weybourne, England and Mace Head, Ireland. Major-ion aerosol concentrations were determined and temporal patterns were interpreted with the use of air-mass back trajectories. Low levels of terrestrially derived material were seen during periods of clean, onshore flow, with respective concentration ranges for nitrate and ammonium of 0.47–220 and below detection limit to 340 nmol m⁻³. Corresponding levels of marine derived material during these periods were high, with sodium concentrations ranging from 39 to 1400 nmol m⁻³. Highest levels of terrestrially derived material were seen during polluted, offshore flow, where the air had passed recently over strong source regions of the UK and northern Europe, with concentration ranges of nitrate and ammonium of 5.6–790 and 9.7–1000 nmol m⁻³, respectively. During polluted flow ∼40–60% of the nitrate was found in the coarse mode (>1 μm diameter) and under clean marine conditions almost 100% conversion was seen. In addition, our data suggests strong evidence for dissolution/coagulation processes that also shift nitrate to the coarse mode. Furthermore, such processes are thought also to give rise to the size-shifting of aerosol ammonium, since significant coarse-mode fractions of this species (∼19–45%) were seen at both sites. A comparison of the relative importance of nitrate and ammonium in the overall dry deposition of inorganic fixed-nitrogen at each site indicates that at Weybourne the mass-weighted dry deposition velocity of the latter is around double that seen at Mace Head with its resultant contribution to the overall inorganic nitrogen dry flux exceeding that of nitrate.     

Production of sulfate in rain and raindrops in polluted atmospheres

A physico-chemical model for the accumulation of sulfur species in raindrops is developed in which account is taken of the mass transfer of SO₂, O₃, NH₃ and CO₂ into ideal raindrops containing the catalyst Fe(III). The sulfur accumulation was calculated for the droplets as a function off all distance. The model predicts the formation of sulfate due to the oxidation of dissolved SO₂ by O₃ and catalytic ions in the presence of NH₃ and CO₂. The initial pH of a drop was taken as 5.56. The final value depended on drop size, fall distance, and ambient concentrations, but in all cases was between 4.2 and 6.6. Sulfate values also depended on the same conditions and ranged from 2 to 2000 μmol 1⁻¹ for individual drops. For a precipitation rate of 10 mm h⁻¹ and a fall distance of 2000 m, the raindrop pH varied from 4.5 to 6.5 and the average sulfate concentration from 3 to 87 μmol 1⁻¹ depending on ambient pollutant concentrations. These results conform to the experimentally measured values of the rain pH (3–9) and sulfate concentration (20–150 μmol 1⁻¹), and corresponding air SO₂ concentration (1–10 ppb) as reported in the literature.     

Spatial differences in outdoor PM10 mass and aerosol composition in Mexico City

Twenty-five MiniVol samplers were operated throughout the Mexico City metropolitan region from February 22 through March 22, 1997, to evaluate the variability of PM10 concentrations and composition. The highest PM10 concentrations were found in neighborhoods with unpaved or dirty roads, and elements related to crustal material were the main cause of differences from nearby (<200 m) monitors that were not adjacent to the roadbed. SO4(2-) concentrations were homogeneous across the city. SO4(2-) measured at the city boundaries was about two-thirds of the concentrations measured within the urbanized area, indicating that most SO4(2-) is of regional origin. Elemental carbon (EC) and organic carbon (OC) concentrations were highly variable, with higher concentrations in areas that had high diesel traffic and older vehicles. Spatial correlations among PM10 concentrations were high, even though absolute concentrations were variable, indicating a common effect of meteorology on the concentration or dispersion of local emissions.     

Chemical fingerprint and source apportionment of PM 2.5 in highly polluted events of southern Taiwan

To investigate the spatial distribution and diurnal variation of the chemical composition of PM2.5 pollution in an industrial city of southern Taiwan, 12-h PM2.5 was diurnally continuously collected simultaneously at the Kaoping Air Quality Zone (KAQZ) during one highly PM2.5-polluted episode. Water-soluble ions, metallic elements, carbonaceous contents, dicarboxylic acids, and anhydrosugars were analyzed to characterize the chemical fingerprint of PM2.5. Backward trajectory simulation and chemical mass balance (CMB) receptor modeling were applied to identify the potential sources of PM2.5 and their contributions. It showed that Chaozhou (rural area) accompanying the highest SORs and NORs suffered from the most severe PM2.5 pollution during the episode. Sulfate (SO42−) was probably formed by the atmospheric chemical reaction in the daytime, while NO3− processed at nighttime at the KAQZ. A homogeneous formation of NO3− occurred at Chaozhou. The concentrations of Zn, Pb, Fe, Cu, V, and Al, mainly emitted from anthropogenic sources, increased significantly at the KAQZ. The highest OC, SOC/OC, and DA/OCs at Daliao (industrial area) were attributed to the transformation of primary VOCs to secondary OC via photo-oxidation during the episode. Oxalic acid was mainly produced through photochemical reactions since a high correlation between oxalic acid and Ca2+ was observed at Nanzi (urban area) and Daliao during the episode. During the episode, PM2.5 mostly originated from local primary or secondary aerosol than long-range overseas transport. The dominant source was anthropogenic emissions, accounting for 67.1% and 70.4% of PM2.5 at Nanzi and Daliao, respectively. At Chaozhou, the contribution of anthropogenic emissions was the lowest (42.4%), but secondary aerosols had the highest contribution of 38.3% of PM2.5 among the three areas during the episode.     

Separate chemical characterizations of fog water,aerosol, and gas before,during, and after fog events near an industrialized area in Japan

Fog water, aerosol, and gas were separately collected at Mt. Rokko (altitude 931 m) in Kobe, Japan, using a new sampling method at a mountainous site near a highly industrialized area. The fog water was collected by an active string-fog collector and the aerosol and gas by using the filter pack method. Using plural filter packs and controlling or switching the airflow before, during, and after a fog event made it possible to collect the fog water, aerosol, and gas separately. Nitrate species such as NO₃⁻(p) and HNO₃(g) were effectively scavenged by fog water, while sulfur species such as SO₄²⁻(p) and SO₂(g) could not be easily and effectively scavenged because of the poor solubility of SO₂(g). This difficulty was experimentally examined through an in situ investigation. Ion species (especially Na⁺(p) and Ca²⁺(p)) which form coarse particles were easily and effectively scavenged by fog water. On the other hand, the difficulty of scavenging Mg²⁺(p) could not be explained by particle size.     

底泥修复对城市污染河道水体污染修复的影响研究

为开发城市黑臭河道的有效治理方法,利用人工模拟河道就河道底泥对上覆水体的二次污染、底泥污染生物修复对其氮磷营养盐释放及河道水体污染生物修复的影响进行了研究,并对实验结果进行了工程现场应证。研究结果表明：河道污染底泥生物修复状况对上覆水体水质产生大的影响,在底泥不加修复时,底泥污染物释放使水体COD、TP、NH₃-N浓度分别达到30～35 mg/L、0.4～0.5 mg/L和3.0 mg/L,底泥修复后分别为15～20 mg/L、0.1 mg/L和2.5 mg/L;底泥G值（y）与底泥氮、磷污染物释放量（x）呈负相关关系,关系式分别为：y=0.5124x-0.1394（R₂=0.9222）,y=0.17772x-0.4781（R₂=0.8701）;结合底泥的生物修复,采用曝气增氧投加生物制剂措施对水体进行生物修复时COD、NH₃-N和PO^3-₄的去除率分别提高13.6%、25.0%和15.7%;对古廖涌的现场治理工程表明,在未对河道底泥进行生物修复的情况下,经过氧化塘预处理河道水体增氧-水体原位强化生物修复等措施的治理,河道中、下游水体又逐渐恢复黑臭,在对河道底泥进行修复后,河道污染水体水质得到显著的改善和提高。     

水源中NH+4-N对生物预处理污染原水除NH+4-N效果影响研究

采用弹性填料微孔曝气生物预处理方法净化受污染的某饮用水源,探讨了水源水环境中NH4+-N变化对生物预处理除NH4+-N作用效果的影响。结果表明,水源水环境中的NH4+-N对生物预处理工艺除NH4+-N有一定的影响作用。     

SRT影响MBR污泥体系去除污染物动力学研究

利用Eckenfelder公式得出了MBR系统中不同污泥停留时间底物降解速率和氨氮的去除速率,结果表明在对数增长阶段和减数增长阶段,SRT为17 d时,对有机底物的降解速率和氨氮的去除速率都高于SRT为8、27、37和42 d的污泥系统对两者的去除,说明SRT对MBR污泥系统的活性有较大影响,确定排泥时间应综合考虑污泥活性、污泥产量和膜通量等因素.