Atmospheric Environment (v.39, #3)

Atmospheric particulates with elevated trace metals may have a serious impact on human health. Biomonitoring using moss is a well-developed technique employed in many parts of the world to assess the concentrations of trace elements in the atmosphere and their potential sources. The suitability of the moss Hypnum plumaeforme as a new biomonitor of atmospheric trace element pollution in southern China was evaluated in the present study. The results showed that the moss had a good capacity to absorb and retain heavy metals such as Cd, Co, Cu, Cr, Pb, V and Zn. The northern part of the Nanling mountain range was found to have more trace elements than the southern range, possibly reflecting the long-range transport of pollutants from northern China. The elemental concentrations of the mosses in the northern range were found to be well correlated with elevations. The concentrations of heavy metals decreased as elevations increased, and became relatively constant above 1100 m a.s.l. The Pb isotopic compositions indicated that atmospheric inputs of Pb in mosses were mainly derived from anthropogenic sources, including vehicular emissions and Pb used in local industries.
Keywords: Moss (Hypnum plumaeforme); Biomonitor; Aerosol; Heavy metals; Pb isotopes; Pearl River Delta; South China;

The prediction of nitrogen dioxide (NO2) concentrations from simple and available data such as meteorological records accurately over time steps shorter than 1 yr would be of great benefit. Predictions of monthly, or more frequent, concentrations of NO2 would be especially valuable when calculating nitrogen deposition to vegetation, as concentrations of NO2 can fluctuate through the year. A model that predicts concentrations of NO2 (μg m−3) on a fortnightly time step at specific sites using mean fortnightly ambient air temperatures and a local annual concentration of NO2 from the nearest representative monitoring site has been developed. The model was tested at a variety of sites across the UK and showed a reasonable pattern of agreement with measured values (R 2 from 0.45 to 0.67) for the majority of sites. The model could be used to predict deposition of NO2-N from commonly recorded data sets, within the limits that have been tested.
Keywords: NO2 concentration; Predictive; Air temperature; Seasonal; Climate; Change;

Characterization of size-fractionated particulate mercury in Shanghai ambient air by Guangli L. Xiu; Qingxi Jin; Danian Zhang; Shuangyan Shi; Xuejuan Huang; Wenying Zhang; Liang Bao; Pengtao Gao; Bo Chen (419-427).
The size-fractionated particulate mercury in ambient air was collected at the top of a university campus building in Shanghai from March 2002 to September 2003. Wet digestion followed by cold vapor atom adsorption spectroscopy (CVAAS) was employed to analyze total particulate mercury concentration. Two-step extraction was performed to differentiate volatile particle-phase mercury (VPM), reactive particle-phase mercury (RPM) and inert particle-phase mercury (IPM). The average concentrations of mercury in PM1.6, PM8 and total suspended particle (TSP) were 0.058–0.252, 0.148–0.398 and 0.233–0.529 ng m−3, respectively. About 50%–60% of mercury in PM8 was in PM1.6, and about 60%–70% of mercury in TSP was in PM8. Particulate mercury was mainly concentrated on fine particles. The mercury fraction in fine particulate matters (<1.6 μm) was over 4 μg g−1 while 1–2 μg g−1 in TSP. Both were much higher than background values, suggesting that anthropogenic sources are the predominant emission contributors. Seasonal variation indicated that the mercury in TSP in spring was higher than that in summer; however, the mercury in fine particles (<1.6 μm) varied little. The fact that fine particulate mercury (<1.6 μm) was well correlated with sulfate and elemental carbon, but not with fluoride, chloride, nitrate and organic carbon, demonstrates that fine particulate mercury is closely associated with stationary sources and gas–particle transformation. Speciation analysis of mercury showed that VPM fraction decreased with the decrease of particle size, while IPM fraction increased and occupied over 50% in particle <1.6 μm. The detailed species in VPM, RPM and IPM were discussed. Coal burning was estimated to contribute approximately 80% of total atmospheric mercury.
Keywords: Particulate mercury; Size-fractionated particle; Speciation analysis; Shanghai;

Modeling the ozone weekend effect in very complex terrains: a case study in the Northeastern Iberian Peninsula by Pedro Jiménez; René Parra; Santiago Gassó; José M. Baldasano (429-444).
Ambient ozone (O3) concentrations tend to be higher on weekends than on weekdays in urban areas, a phenomenon known as the weekend effect. Nevertheless, its downwind influence could be diverse. The MM5-CMAQ model has been used to assess the causes of weekday/weekend O3 differences in the north-eastern Iberian Peninsula during an episode of photochemical pollution covering the whole Western Mediterranean Basin (13–16 August 2000). Emissions were estimated with EMICAT2000 model. The key differences between weekday and weekend on-road vehicle emissions are in magnitude and timing. On-road traffic accounts for ∼57% of the anthropogenic NO x and VOC emissions in the modeling domain, and are principally located along the coast and mainly in the Barcelona Geographical Area. The drop of heavy-duty tracks traffic on weekends involves a 22% reduction of NO x emissions and just a slight change in VOC emissions. Changes in the timing of emissions are directly related to differences in weekday/weekend traffic profiles, being emissions shifted 1–2 h later on weekends. The response of both ambient and simulated O3 concentrations to day-of-week differences in emissions varies by location. The combination of VOC-sensitive regimes and NO x -titration in urban areas as Barcelona, in addition to the different magnitude and timing of emissions (decreasing NO x /VOC ratios on weekend mornings) causes the raise of O3 on weekends (+54%). In non-urban regimes, principally associated to NO x -sensitive chemistry, a lower concentration of O3 is observed in non-labor days (decreases of –10% in downwind areas). Rural locations, dominated by medium-long range transport, depict similar O3 concentrations. Both discrete and categorical model evaluations are shown in order to test the accuracy of the model for representing weekdays/weekends differences within the air basin. This work helps identifying the major causes of the weekend effect in the considered domain, as the changing in mass and time of precursors emissions, and may be a useful tool to reduce ambient O3 levels.
Keywords: Ozone; Weekend effect; Air quality modeling; Photochemistry; Very complex areas;

The convective boundary layer (CBL) is characterised by narrow vigorous thermals (updraft motions) surrounded by relatively large subsidence motions. In such a flow, reactants are normally segregated and their chemical transformations depend on the ability of atmospheric turbulence to mix them. This process is particularly important when the time-scale of the chemical transformation is similar to the turbulent characteristic time scale. For large atmospheric models, the segregation occurs at scales smaller than the grid length. As a result, instantaneous and homogeneous mixing of the reactants is normally assumed. This paper is aimed at the study of this assumption and to apply a parameterisation of an effective reaction rate accounting for the inefficient mixing due to convective turbulence in the CBL. We simulate a growing CBL with two models that use different physical assumptions. The first one, the so-called mixed-layer model, assumes an instantaneous and homogeneous mixing of the reactants in the boundary layer (BL). The second one, a three-dimensional large eddy simulation (LES) model, explicitly solves atmospheric turbulent motions and describes the heterogeneity of the mixing due to the turbulent characteristics of the CBL. By comparing their results in a simple case, i.e. a second-order chemical reaction, we show that the heterogeneous mixing due to convective turbulence has an important impact on the chemical transformations by slowing down the reaction rate. By introducing effective reaction rates through a parameterisation which accounts for this inefficient mixing, the mixed-layer model results improve significantly. We extend our study to a chemical mechanism that accounts for the ozone formation and depletion in the CBL. We show that the reaction rate can be slowed down or increased depending on whether the reactants are transported in opposite directions or not. We propose coefficients to be used to calculate the effective reaction rates in large-scale or mixed-layer models.
Keywords: Turbulent mixing of pollutants; Effective reaction rates; Convective boundary layer; Large-eddy simulation; Mixed-layer model;

Characterization of the elemental and polycyclic aromatic hydrocarbons (PAHs) compositions of urban air was undertaken at three major sites in Brisbane, Australia. 17 elements and 16 US EPA priority PAHs were quantified at the sites. The most commonly detected elements in the TSP and PM2.5 fractions were Al, Cd, Co, Cr, Cu, Fe, Mn, Mo, Si, Sn, Sr and Zn. Compared to the two other sites, PM2.5 was found to contain higher concentrations of Zr, Mo, V, Al, Mn and Sr at the Queensland University of Technology (QUT) site. In contrast, the Woolloongabba sampling site, which was highly influenced by the vehicular emission and local industrial activities, has higher concentrations of Co, Sn, Cu, Zn and Mg while ANZ site has significantly lower concentration levels of most elements than the other sites; possibly due to the shielding effect of the nearby bush and forest. NAP, PHE, ANT, FLT, PYR and CRY were the most widespread PAHs found in all sites. But only QUT and Woolloongabba bus platform sites had detectable levels of the most carcinogenic US EPA PAH, BAP. The multi-criteria decision making procedures, Preference Ranking Organisation Method for Enrichment Evaluation (PROMETHEE) and Geometrical Analysis for Interactive Aid (GAIA) were used to rank the air samples and to identify the sources of the pollutants. Thus Woolloongabba bus platform was ranked as the most polluted site on the basis of the elemental and PAH compositions of its air samples while Woolloongabba bus platform and QUT sites were ranked as the worst polluted sites in terms of PAHs and PM2.5 elemental contents, respectively.
Keywords: Urban air pollution; Polycyclic aromatic hydrocarbons; Elements; Multivariate data analyses;

n-Alkanes and polycyclic aromatic hydrocarbons (PAHs) were identified in particle-sized aerosols of the urban and rural atmospheres of Guangzhou, China. Most of the organic compounds were mainly associated with fine particles with aerodynamic diameters less than 1.5 μm in the urban and rural atmospheres. In the urban aerosol close to the road, about 57% of n-alkanes and 62% of PAHs were found in the particle fraction with diameters of <0.49 μm. Size distributions of particulate mass and low molecular weight organic compounds exhibited bimodal patterns, while high molecular weight organic compounds exhibited unimodal distribution. Mass mean diameter (MMD) of total n-alkanes calculated over the whole size range was 0.43 μm in urban and 0.83 μm in rural. A similar trend was observed for PAHs. MMD for total PAHs in the urban and rural aerosol was 0.40 and 0.69 μm, respectively.
Keywords: Size distribution; PAHs; n-alkanes; Particle; China;

Naphthalene distributions and human exposure in Southern California by Rong Lu; Jun Wu; Richard P. Turco; Arthur M. Winer; Roger Atkinson; Janet Arey; Suzanne E. Paulson; Fred W. Lurmann; Antonio H. Miguel; Arantzazu Eiguren-Fernandez (489-507).
The regional distribution of, and human exposure to, naphthalene are investigated for Southern California. A comprehensive approach is taken in which advanced models are linked for the first time to quantify population exposure to the emissions of naphthalene throughout Southern California. Naphthalene is the simplest and most abundant of the polycyclic aromatic hydrocarbons found in polluted urban environments, and has been detected in both outdoor and indoor air samples. Exposure to high concentrations of naphthalene may have adverse health effects, possibly causing cancer in humans. Among the significant emission sources are volatilization from naphthalene-containing products, petroleum refining, and combustion of fossil fuels and wood. Gasoline and diesel engine exhaust, with related vaporization from fuels, are found to contribute roughly half of the daily total naphthalene burden in Southern California. As part of this study, the emission inventory for naphthalene has been verified against new field measurements of the naphthalene-to-benzene ratio in a busy traffic tunnel in Los Angeles, supporting the modeling work carried out here.The Surface Meteorology and Ozone Generation (SMOG) airshed model is used to compute the spatial and temporal distributions of naphthalene and its photooxidation products in Southern California. The present simulations reveal a high degree of spatial variability in the concentrations of naphthalene-related species, with large diurnal and seasonal variations as well. Peak naphthalene concentrations are estimated to occur in the early morning hours in the winter season. The naphthalene concentration estimates obtained from the SMOG model are employed in the Regional Human Exposure (REHEX) model to calculate population exposure statistics. Results show average hourly naphthalene exposures in Southern California under summer and winter conditions of 270 and 430 ng m−3, respectively. Exposure to significantly higher concentrations may occur for individuals close to local sources, or in naphthalene “hotspots” revealed by simulations and observations. Such levels of naphthalene exposure may be used to gauge the potential health impacts of long-term naphthalene exposure. Results are also given for the distributions of 1,4-naphthoquinone, a naphthalene reaction product that may have significant health effects.
Keywords: Air pollution; Los Angeles; Polycyclic aromatic hydrocarbon (PAH); Naphthalene and 1; 4-naphthoquinone; Health effects and exposures; Modeling air quality;

Regional characteristics of three kinds of dust storm events in China by Shigong Wang; Jinyan Wang; Zijiang Zhou; Kezheng Shang (509-520).
The regional characteristics of dust storm events including dust storm, blowing dust and floating dust in China have been studied by using the data from 701 meteorological observation stations during 1954–2000. The results are as follows: in China, there are two main areas (the South Xinjiang Region and the Hexi Region) where dust storm events happen the most frequently. The spatial distributions of the three types of dust storm events are different. Dust storms mainly occur in the arid and semiarid areas in Northern China. Blowing dust and floating dust not only occur in those areas, but also in neighboring areas. Compared with dust storm and blowing dust, the floating dust very seldom occurs in high-latitude areas. The frequencies of dust storm events decreased generally during 1954–2000. However, they have gradually increased since 1998. The interannual variations of dust storm events showed some characters including two cycles of 3–4 and 11–12 years. The annual changes of the dust storm events were characterized by a strong unimodal distribution with spring maximum. The daily variation of the dust storm occurrence was remarkable, most of dust storms happened in the afternoon, especially between 18:01–21:00 LST. The areas of dust storms could be divided into seven sub-regions. The most frequent areas of dust storms and floating dust were in the South Xinjiang Region, but that of blowing dust was in the Hexi Region. Their maximum interannual variance also happened in both areas. Dust storm events generally occurred most frequently in April in most parts of China, but it happened a little earlier in the Qinghai-Xizang Region and a little later in the Xinjiang Region. The months in which dust storm events occurred more frequently were relatively concentrated in the Northeastern Region and Hetao Region, but were relatively dispersed in the Xinjiang Region.
Keywords: Dust storm events; Regional characteristic; Spatial distribution; Temporal distribution;

The EMEP precipitation chemistry network was used in combination with the Reanalysis NCEP/NCAR archive to analyze the influence of climatic-scale variations in atmospheric circulation on summertime wet sulfate deposition over central Europe from 1984 to 1999. Correlation of deposition with hemispheric and global circulation patterns indicates a significant role (49% of the variance) for the North Hemispheric Pacific Transition (PT) teleconnection in the wet deposition of sulfate over central Europe in August. The seasonal correlation of air temperature at shallow tropospheric layers reveals significantly cooler air masses over central Europe, Alaska and the southwestern US coast and warmer air over Greenland, the Barents and Kara Sea and the South Atlantic and Indian Ocean. The geopotential height (GPH) anomalies for sulfate-rich deposition years exhibit a pattern consistent with the seasonal correlation. A weakening of both belts of Sub-Polar lows and Antarctic Polar Highs is also observed. In the Northern Hemisphere, a distinct dipole in GPH is observed, with a positive anomaly over Iceland and the Norwegian Sea and a negative anomaly over Russia and Scandinavia. Composite plots of the most loaded/unloaded days of sulfate deposition yielded a prominent signal of the associated mean atmospheric field patterns. The composite sea-level pressure (SLP) for the 20 highest deposition days shows an average intensification of 1 hPa and a northeastward migration of the Azores Subtropical High, leading to a significant anomaly in the negative meridional wind component at the 925-hPa level. This flow presumably enables the transport and oxidation of SO2 emitted from major upwind pollution sources toward central Europe. The observed downward trend in sulfate deposition suggests that the study period was characterized by predominantly warm zonal circulation. More frequent zonal flows in the future, together with further reductions in sulfur dioxide emissions are likely to lead to lower sulfate deposition.
Keywords: Sulfate wet deposition; Europe; EMEP; Atmospheric circulation patterns;

Approximately, hourly C2–C7 hydrocarbon concentrations from gas chromatographic measurements are reported for an urban background site in Birmingham, UK, from summer 1999 and winter 1999–2000. Comparison with another measurement site suggests that the observed behaviour is typical of the urban background in the whole conurbation. The lack of any correlation between seasonal variation and OH rate coefficient shows that hydrocarbon concentrations are dominated by local sources. Chemical mass balance techniques have been applied and indicate the main sources are vehicle emissions (exhaust and fugitive) and natural gas leakage. Winter concentrations of isoprene correlate well with butadiene concentrations suggesting an automotive related source. This correlation disappears during the summer when isoprene displays a high correlation with radiation. During a period of the summer campaign ethane and propane concentrations displayed a regular diurnal behaviour, which has been utilized to estimate the ratios of the day/night boundary layer height and natural gas emission rates for the West Midlands conurbation.
Keywords: Emissions; Isoprene; Ethane; Urban; Boundary layer;

Sampling of particles (PM10) was conducted during a one-year period at two rural sites in Central Chile, Quillota and Linares. The samples were analyzed for elemental composition. The data sets have undergone source–receptor analyses in order to estimate the sources and their abundance's in the PM10 size fraction, by using the factor analytical method positive matrix factorization (PMF). The analysis showed that PM10 was dominated by soil resuspension at both sites during the summer months, while during winter traffic dominated the particle mass at Quillota and local wood burning dominated the particle mass at Linares. Two copper smelters impacted the Quillota station, and contributed to 10% and 16% of PM10 as an average during summer and winter, respectively. One smelter impacted Linares by 8% and 19% of PM10 in the summer and winter, respectively.For arsenic the two smelters accounted for 87% of the monitored arsenic levels at Quillota and at Linares one smelter contributed with 72% of the measured mass. In comparison with PMF, the use of a dispersion model tended to overestimate the smelter contribution to arsenic levels at both sites.The robustness of the PMF model was tested by using randomly reduced data sets, where 85%, 70%, 50% and 33% of the samples were included. In this way the ability of the model to reconstruct the sources initially found by the original data set could be tested. On average for all sources the relative standard deviation increased from 7% to 25% for the variables identifying the sources, when decreasing the data set from 85% to 33% of the samples, indicating that the solution initially found was very stable to begin with. But it was also noted that sources due to industrial or combustion processes were more sensitive for the size of the data set, compared to the natural sources as local soil and sea spray sources.
Keywords: Source–receptor modelling; PMF; Elemental source profile; Smelter emission; Particles;

Air quality in many of the cities in India is gradually deteriorated due to various activities. One of such activities is open burning of garden biomasses in cities. This study was aimed to estimate the emissions from various types of garden biomasses namely grass, leaves, twigs and mixtures of these three in a controlled SIFT chamber. Although the particulate emission (1.51 g kg−1) was lowest from grass, the particle size distribution indicates that the emission contains 10% of fine particulates (<2.5 μm) and significant quantity (70%) of respirable fraction (<10 μm). On the other hand leaves, though generating 32.3 g kg−1 particulate matter contained major portion in non-respirable range (around 40%). CO2 emission from leaves (1064.6 g kg−1) and twigs (897.3 g kg−1) are significantly lower than the emission from mixture (1423 g kg−1) of equal proportion of these two. Similar trend is followed in case of carbon monoxide and nitrogen oxides emissions. However, hydrocarbon emission followed a reverse trend of emitting high emission load (11.4 g kg−1) in the mixture of leaves and twigs than their individual type 2.4 g kg−1 (leaves) and 0.2 g kg−1 (twigs). The toxicity indices for all categories were very low (0.06–0.12). However, out of the five categories grass was found to have lowest toxicity index (0.06) and followed by mixtures (1:1:1) having 0.07. The particulate matter emission load computed for the cities of India shows that the leaves contribute 97 tons day−1 and 4.5 tons day−1 contribution from grass. Among gaseous pollutants CO2 emission was highest, as the computed values were 3212 tons day−1 from leaves and 92 tons day−1 from grass.
Keywords: Garden biomass; Combustion gases; Particulate matter emission;

An analytic formula is derived expressing the tropospheric O3 production rate, P(O3), as a power law function of radical production rate, NO x concentration, and VOC–OH reactivity. Power law exponents depend on a single parameter, L N / Q , which is the fraction of free radicals removed by reactions with NO x . The formula reproduces the functional form of P(O3) obtained from photochemical box model calculations. Ozone production rates are shown to have a smooth transition between previously derived low and high NO x limits. Potential applications of this formula include analysis of day to day and place to place variations in P(O3), with P(O3) either obtained from measurements collected during field campaigns or produced as output from chemical-transport models.
Keywords: Ozone production rate; Tropospheric photochemistry; Ozone sensitivity; Low and high NO x ; Ozone precursors;