Atmospheric Environment (v.42, #10)

Size-differentiated source profiles for fugitive dust in the Chinese Loess Plateau by J.J. Cao; J.C. Chow; J.G. Watson; F. Wu; Y.M. Han; Z.D. Jin; Z.X. Shen; Z.S. An (2261-2275).
Size-differentiated fugitive dust chemical source profiles are determined for the Chinese Loess Plateau, a major source of Asian dust. Fifteen loess samples at five sites (Yulin, Yanchi, Huanxian, Luochuan, and Xi’an) were collected, dried, sieved, resuspended, and sampled through TSP, PM10, PM2.5, and PM1 inlets onto filters for analysis of 40 major and trace elements (Na to U), six ions (Cl, NO3 , SO4 2−, Na+, K+, and NH4 +), organic carbon (OC) and elemental carbon (EC), and carbonate carbon (CO3-C). The abundances of major species (>1%) include Al, Si, K, Ca, Fe, OC and CO3-C, in four size-differentiated source profiles. OC accounted for ∼90% of total carbon in four size fractions for most of the profiles. Enrichment factors indicated that the 18 elements (Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Y, Zr, Ba) found in the samples were dominated by crustal sources. Enrichment factors for Co, As, Se, Mo, Cd, In, Sb, and Tl are one to two orders of magnitude larger than crustal-derived elements, suggesting the influence of anthropogenic pollution sources. Compared with loess samples, V, Cr, Ni, Cu, Zn, Sb, SO4 2−, and NO3 are enriched in ambient PM2.5 aerosol samples, implying that Asian dust contains pollution components in downwind regions of the desert. The elemental ratios of Si, K, Ca, Ti, Mn, and Fe to Al in Asian dust source regions compared well with those found at downwind regions such as Korea, Japan, and the North Pacific. These ratios can be used as fingerprints to trace the transport path of Asian dust.
Keywords: Size differentiation; Source profiles; Loess; Asian dust; China;

Parameterization of secondary organic aerosol mass fractions from smog chamber data by Charles O. Stanier; Neil Donahue; Spyros N. Pandis (2276-2299).
A framework is presented and evaluated for the parameterization of smog chamber results for use in atmospheric chemical transport models (CTMs). The parameterization uses an absorptive partitioning model to describe formation of secondary organic aerosol (SOA). The key points of the framework are (1) the ability to fit results from several types of chamber experiments; (2) the use of a basis set of surrogate compounds characterized by fixed effective saturation concentrations instead of the more commonly used variable saturation concentrations; (3) calculation of uncertainties of the estimated SOA aerosol mass fractions (AMF) outside of the fitted experimental range; and (4) determination of the best effective enthalpy to reproduced observed temperature sensitivity. The features of this data analysis and fitting framework are demonstrated using simulated data, and actual measurements from α-pinene ozonolysis experiments. Representation of SOA formation using as many as 8 surrogate compounds with fixed effective saturation concentrations is shown to be feasible and has advantages over simpler parameterizations.
Keywords: Secondary organic aerosol; Modeling; Parameter estimation; α-pinene;

Removal of VOCs from indoor environment by ozonation over different porous materials by C.W. Kwong; Christopher Y.H. Chao; K.S. Hui; M.P. Wan (2300-2311).
Ozonation of toluene over NaX, NaY and MCM-41 adsorbents was studied targeting for indoor air purification. The combined use of ozone and the various micro- or meso-porous adsorbents aimed to take advantage of the strong oxidizing capability of ozone. At the same time the residual ozone would be minimized due to the enhanced catalytic reaction in the porous structure. To lower the residual ozone level is a crucial issue as ozone is itself an indoor pollutant. The Lewis acid sites in the adsorbents were believed to decompose ozone into atomic oxygen, and the subsequent reactions would then convert the adsorbed toluene into CO2 and H2O. In the dry conditions, the MCM-41 required the smallest amount of material to achieve the 90% reduction target, followed by NaY and NaX. In the more humid environment (50% RH), extra amounts of MCM-41 and NaX adsorbents were required to reach the target as compared with the dry conditions. Desorption experiments were also conducted to study the amounts of various major species held in the adsorbents during the catalytic process. A material balance analysis of the major species in both the effluents and the adsorbents showed that within our experimental conditions, about 20–40% of the removed toluene was carried out via catalytic ozonation while adsorption covered the rest. Trace amount of intermediate species such as aldehydes and organic acids were identified in the desorbed gas indicating that they were withheld by the adsorbents during the air purification process and those in the effluent were below detection levels.
Keywords: Ozone; VOC; Toluene; Zeolite; Adsorbent;

Atmospheric formation of 9,10-phenanthraquinone in the Los Angeles air basin by Arantza Eiguren-Fernandez; Antonio H. Miguel; Rong Lu; Kathie Purvis; Bill Grant; Paul Mayo; Emma Di Stefano; Arthur K. Cho; John Froines (2312-2319).
Quinones are highly reactive and toxic compounds, capable of increasing cellular oxidative stress by raising concentrations of intracellular hydrogen peroxide. It has been suggested that these compounds, although also directly emitted by vehicular exhaust, are mostly formed in the atmosphere by photochemical reactions of their parent polycyclic aromatic hydrocarbons (PAHs). However, because of the low concentrations and instability of some quinones, relatively little is known about their levels in ambient air samples. The tricyclic compound 9,10-phenanthraquinone (PQ), one of several quinones found in the particle-phase of ambient air, is a compound that can irreversibly inactivate key cellular proteins. In this study, we report concentration changes of PQ in atmospheric samples as the air moves across the Los Angeles basin by the prevailing wind trajectory. The trajectory is, for the most part, from the coastal areas to the Inland Empire in the eastern end of the Los Angeles basin; the samples were collected during the photoactive season of early summer. For this study, five sites along the predominant wind trajectory were selected and samples were collected as the air parcel passed over each site. Particle-phase PQ concentrations ranged from 100 to 2000 pg m−3. A significant increase in PQ concentration was observed as the air parcel moved inland from Long Beach (source area) to Riverside, the last sampling site in the wind trajectory and considered as the final receptor area. Our results suggest that ca. 90% of the PQ in the receptor site was photochemically formed during atmospheric transport.
Keywords: 9; Los Angeles basin; Transport; Photochemistry; PAH;

Chemical characteristics of precipitation in Okinawa Island, Japan by Hideaki Sakihama; Maki Ishiki; Akira Tokuyama (2320-2335).
This study examined the chemical composition and characteristics of precipitation collected from March 2003 to February 2005 in the central part of Okinawa Island, Japan. Chloride ions contributed most to the total ion equivalent concentration, and followed in order by Na+>Mg2+, SO4 2−>Ca2+>H+, NH4 +, K+>NO3 , HCO3 . Concentrations of Na+, K+, Ca2+, Mg2+, Cl, and sea salt SO4 2− (ss-SO4 2−) increased from summer to autumn and decreased from winter to spring. In contrast, concentrations of NH4 +, NO3 (except for July 2004), non-sea salt SO4 2− (nss-SO4 2−), and H+ were lower in summer and higher in winter. During periods with typhoons, concentrations of sea salt components, such as Na+ and Cl, increased while NO3 and nss-SO4 2− concentrations decreased. Wet deposition driven by typhoons accounted for about 77% of the total annual wet deposition. The pH values ranged from 3.89 to 7.61. Acid rain (pH<5.6) occurred in 72% of the collected samples, even though Okinawa Island is considered to be an unpolluted area. Principal component analysis indicated three main origins of the chemical components in precipitation: (1) sea salt generated from local surrounding ocean (Na+, K+, ss-Ca2+, Mg2+, Cl, and ss-SO4 2−), (2) soil generated from local land (nss-Ca2+ and D-SiO2), and (3) anthropogenic source of Asian Continent (NH4 +, NO3 , and nss-SO4 2−).
Keywords: Subtropical area; Chemical composition; Typhoon; Acid rain; Principal component analysis;

Air pollution modifies floral scent trails by Quinn S. McFrederick; James C. Kathilankal; Jose D. Fuentes (2336-2348).
Floral hydrocarbons provide essential signals to attract pollinators. As soon as they are emitted to the atmosphere, however, hydrocarbons are destroyed by chemical reactions involving pollutants such as ozone. It is therefore likely that increased air pollution interferes with pollinator attracting hydrocarbon signals. To test this hypothesis, a Lagrangian diffusion model was used to determine the position of air parcels away from hydrocarbon sources and to estimate the rate of chemical destruction of hydrocarbons as air parcels moved across the landscape. The hydrocarbon compounds linalool, β-myrcene, and β-ocimene were chosen because they are known to be common scents released from flowers. The suppressed ambient abundances of volatile organic compounds were determined in response to increased regional levels of ozone, hydroxyl, and nitrate radicals. The results indicate that the documented increases in air pollution concentrations, from pre-industrial to present times, can lead to reductions in volatile compound concentrations insects detect as they pollinate flowers. For highly reactive volatiles the maximum downwind distance from the source at which pollinators can detect the scents may have changed from kilometers during pre-industrial times to <200 m during the more polluted conditions of present times. The increased destruction of floral signals in polluted air masses may have important implications for both pollinators and signaling plants. When patches of flowers are further apart than the visual range of pollinators, such as in fragmented landscapes, the loss of scent signals may mean that pollinators spend more time searching for patches and less time foraging. This decrease in pollinator foraging efficiency will simultaneously decrease the pollinator's reproductive output and the amount of pollen flow in flowering plants.
Keywords: Hydrocarbons; Terpenes; Ozone; Hydroxyl radical; Pollinators; Pollution; Oxidants;

Theoretical predictions of arsenic and selenium species under atmospheric conditions by MaryTheresa Monahan-Pendergast; Michelle Przybylek; Mark Lindblad; Jennifer Wilcox (2349-2357).
Thermochemical properties of arsenic and selenium species thought to be released into the atmosphere during the coal combustion were examined using ab initio methods. At various levels of theory, calculated geometries and vibrational frequencies of the species were compared with experimental data, where available. Through a comparison of equilibrium constants for a series of gaseous arsenic and selenium oxidation reactions involving OH and HO2, five thermodynamically favored reactions were found. In addition, it was determined that all favored reactions were more likely to go to completion under tropospheric, rather than stratospheric, conditions.
Keywords: Arsenic; Selenium; Ab initio; Coal combustion emissions; Atmospheric pollution;

An analysis of dust storms and blowing sand records at 681 stations in China during 1961–2000 and in Mongolia during 1980–2000 reveals that the dust source regions in central Asia and the Tibetan Plateau have monthly and interannual northward shifts from the Tibetan Plateau to Mongolia. The monthly shift is closely related to the location of the 200 hPa westerly jet and to the location and intensity of the 500 hPa westerly jet over central Asia and the Tibetan Plateau. The causes for interannual shifts vary by region. The westerly jet appears to drive the shift on the Tibetan Plateau; the intensity of the central Asian mid-latitude westerly, the Arctic oscillation (AO) and the East Asian winter monsoon may be the drivers in the Hexi Corridor region to the north of the Tibetan Plateau; and the AO and the location of the westerly jet in the Mongolian region. All these causes are closely related to the AO variations, which may provide a connection between climatic changes in East Asia and the North Atlantic, and the long-distance transport of dust. This connection could explain the shifts of dust source regions at interannual and millennial timescales and the roughly synchronous climate changes recorded in the Chinese loess and deep-sea sediments in the North Atlantic Ocean.
Keywords: Shift of dust source regions; Central Asia and Tibetan Plateau; Arctic oscillation; Westerly jet;

The effect of temperature and humidity on size segregated traffic exhaust particle emissions by Milan Jamriska; Lidia Morawska; Kerrie Mergersen (2369-2382).
The formation and behaviour of exhaust emissions is affected by environmental, traffic and meteorological conditions. The understanding of the governing processes and dependency between particles and other relevant parameters, as well as the magnitude of the impacts, is still limited and mostly based on a few laboratory studies. The focus of this work is the effect of temperature (TEMP) and relative humidity (RH) and their interaction on traffic emission particles in the size range of 15–850 nm. The relationship was assessed using a large data set collected over a period of six months at two road sites in Brisbane. A sequence of statistical analyses were designed and applied in order to quantify the relationships, comprising exploratory correlation analysis to identify pairwise linear associations, factor analysis to assess multivariate effects and nonparametric regression tree methods to more carefully explore interactions. The results show that total particle number concentration was dominated by traffic flow rate and wind speed and to a lesser degree by RH and TEMP. In general, an inverse relationship between TEMP and concentration and a direct relationship between RH and concentration was observed. While TEMP was a dominant parameter for particle concentrations in the size range 15–30 nm, its role diminished and RH emerged as a stronger influence as particle size increased. The observed increase for particle concentrations in the size range 50–150 nm could be associated with particle transfer from a smaller to larger size group due to coagulation and condensation induced growth, as well as an increase in primary (engine) emissions. The significant influence of RH on particles in 150–880 nm size range could be related to particle growth, changes in hygroscopic properties of traffic emissions and particles originating from sources other than traffic. Decreased combustion efficiency may also contribute to higher emissions of particles in this size range.
Keywords: Exhaust emissions; Particle nucleation; Airborne particles; Coagulation and condensation growth; Temperature; Humidity;

Investigation and estimation of emission sources of 54 volatile organic compounds in ambient air in Tokyo by Jun-ya Hoshi; Saeko Amano; Yuko Sasaki; Takashi Korenaga (2383-2393).
Atmospheric concentrations of 52 hydrocarbons and two aldehydes at roadside and urban sites in Tokyo metropolitan area, Japan were analyzed using GC/MS and HPLC. Monthly sampling was conducted during April 2003–March 2005. Annual average concentrations of individual volatile organic compounds (VOCs) at the roadside site were 1.7–1.9 times higher than at the urban site, suggesting that vehicle exhausts strongly affect VOC concentrations. Since high temperatures and under the stagnant meteorological conditions might increase VOC concentrations in air, the levels of alkanes, alkenes, and aromatic hydrocarbons rose in summer and autumn in 2003 and 2004. The VOCs concentrations against benzene (VOCs/Bz) suggest classifying three groups of VOCs: those mainly from mobile emission sources, those mainly from stationary sources, and those comprising unstable compounds such as aldehydes and 1,3-butadiene. The VOC/Bz technique was applied to registered VOC data from the Pollutant Release and Transfer Register (PRTR). Results show that these VOCs in ambient air in Tokyo reflect the PRTR estimated release amounts. The VOC/Bz technique based on environmental monitoring data is useful to estimate non-registered VOCs such as butane and isopentane. Results show the possibility of estimating emission sources using VOC/Bz ratios from environmental monitoring data, even when sufficient information on the emission sources are not available.
Keywords: VOCs against benzene (VOCs/Bz); Pollutant Release and Transfer Register (PRTR); Stationary source; Mobile source;

A source-area model for estimating population exposure to air pollutants at the scale of a neighborhood is developed. The model explicitly accounts for the first-order influence of atmospheric dispersion of emissions on surface concentrations. The model is used to produce concentration surfaces at high spatial and temporal resolution, and is calibrated using measurements from a fixed monitoring network and evaluated against measurements from two intensive measurement campaigns. The source area model is compared against a fixed buffer model that ignores meteorological dispersion. The source area model captures the influence of wind speed, wind direction and stability on the dispersion and advection of emissions, and thereby achieves modest improvement of performance over the fixed buffer model. The model is useful for the determination of personal exposures and health effects to local emissions.
Keywords: Exposure; Source area; Atmospheric dispersion;

Distribution and origin of carbonaceous aerosol over a rural high-mountain lake area, Northern China and its transport significance by Y.M. Han; Z.W. Han; J.J. Cao; J.C. Chow; J.G. Watson; Z.S. An; S.X. Liu; R.J. Zhang (2405-2414).
PM2.5 and TSP samples were collected at Lake Daihai, a rural high-mountain area in China, in four seasons during 2005–2007. Organic carbon (OC), elemental carbon (EC), char-EC, and soot-EC were analyzed using the thermal/optical reflectance (TOR) method with different temperature plateaus and oxidation atmospheres. TC, OC, EC, and char-EC concentrations of TSP and PM2.5 showed seasonal variations with the highest concentrations in winter and the lowest in summer, while soot-EC reveals a little different variation, with the highest concentration in spring, indicating different source contributions from other parameters. OC/EC correlations were weaker at Daihai than those from urban areas. Although little differences existed in TSP and PM2.5, average OC/EC ratios varied seasonally and ranged from ∼9.0 in winter to ∼5.0 in spring. Char-/soot-EC ratios showed similar pattern, with the highest average ratios (>3.0) in winter, consistent with the contributions from residential biomass burning and coal combustion. Back trajectories related the highest carbon concentrations with the southeasterly air masses and the lowest carbon levels with northward flows.
Keywords: Black carbon; Char; Soot; Char-/soot-EC ratios; Thermal/optical reflectance (TOR) method;

Estimation of the Lagrangian Kolmogorov constant from Eulerian measurements for distinct Reynolds number with application to pollution dispersion model by Gervásio Annes Degrazia; Guilherme Sausen Welter; Adrián Roberto Wittwer; Jonas da Costa Carvalho; Débora Regina Roberti; Otávio Costa Acevedo; Osvaldo L.L. Moraes; Haroldo F. de Campos Velho (2415-2423).
An expression that allows the determination of the Lagrangian Kolmogorov structure function constant C 0 from the knowledge of the constant C S associated to the second order Eulerian velocity structure function and the γ numerical coefficient relating the Eulerian spectra constant to the Lagrangian one, is suggested. Experimental data from both wind tunnel and atmospheric boundary layer observation were used to determine C S. The study agrees with the universal nature of the Eulerian C S constant for fully developed turbulence. The analysis leads to an estimate of C 0≅5.09±0.93, in agreement with previous studies. This estimated value has been employed in a Lagrangian stochastic dispersion model to simulate the observed concentration obtained from classical diffusion experiments.
Keywords: Lagrangian and Eulerian statistics; Structure functions; Kolmogorov constant; Fully developed turbulence; Lagrangian dispersion model;

Air change rate and concentration of formaldehyde in residential indoor air by Nicolas L. Gilbert; Mireille Guay; Denis Gauvin; Russell N. Dietz; Cecilia C. Chan; Benoît Lévesque (2424-2428).
The purpose of this study was to investigate the relationship between air change rates and indoor concentrations of formaldehyde. Concentrations of formaldehyde and air change rates were measured in 96 homes in Québec City, Canada, in winter 2005. House characteristics such as heating systems or recent renovations were also documented. Formaldehyde concentrations were regressed to air change rates among the entire sample and among some sub-samples of homes, and predictive intervals were computed. The air change rate ensuring a formaldehyde concentration below Health Canada's guideline value of 50 μg m−3 in 95% of homes was 0.26 h−1 based on the entire sample, 0.34 h−1 in homes with recent off-gassing sources of formaldehyde, and 0.37 h−1 in homes heated mainly by electrical baseboard heaters. These results indicate that ventilation effectively decreases formaldehyde concentrations, but some categories of homes such as those with new off-gassing sources and homes heated by electrical baseboard heaters may require a higher air change rate to keep their formaldehyde levels within Health Canada's guidelines.
Keywords: Indoor air quality; Formaldehyde; Air change rate; Ventilation;

Development of a method for time-resolved measurement of airborne acrolein by Jason S. Herrington; Junfeng Jim Zhang (2429-2436).
Over the past several years there has been an ever-increasing demand for method(s) that can reliably and simply measure environmental concentrations of airborne acrolein. There are several methods that appear to reliably measure acrolein. However, these methods are either extremely complex, requiring specialized equipment and therefore are not practical for personal sampling, or have relatively low-sampling rates, requiring relatively long (i.e., >24 h) sampling durations. This manuscript reports the development and evaluation of a method that can provide time-resolved measurements of airborne acrolein at typical environmental levels and can be used for personal measurement. The method utilizes a dansylhydrazine (DNSH)-coated silica-based-bonded C18 sorbent to collect acrolein using an air sampling pump. Results indicated that the method was suitable for short-term (i.e., 30 min) and long-term (i.e., 24 h) sampling durations at sampling rates from 50 to 250 mL min−1. Results also indicated that relative humidity from 30% to 90%, temperature from 20 to 40 °C, and the presence of ozone up to 250 ppb did not affect the performance of the method. The method had a limit of detection of 0.24 μg m−3 for a 30 min sampling duration at 250 mL min−1. This method sensitivity is comparable to those of the other more complex acrolein measurement methods.
Keywords: Acrolein; Carbonyls; DNSH; Air toxics; Air sampling;

Nitrous oxide flux to the atmosphere from two coastal tundra wetlands in eastern Antarctica by Renbin Zhu; Yashu Liu; Jing Ma; Hua Xu; Liguang Sun (2437-2447).
Only few estimates of nitrous oxide (N2O) emissions are available from Antarctic tundra ecosystems. During the summer of 2005/2006, for the first time field measurements of N2O emissions were conducted by a static chamber technique in two coastal marshes (Wolong Marsh and Tuanjie Marsh) of eastern Antarctica. In Wolong Marsh, the N2O fluxes ranged from −20.6 to 85.6 μg N2O-N m−2  h−1, −5.3 to 50.8 μg N2O-N m−2  h−1 and 6.4 to 27.1 μg N2O-N m−2  h−1 at the wet, mesic and dry sites, respectively. In Tuanjie Marsh, the fluxes ranged from −5.9 to 12.6 μg N2O-N m−2  h−1, −3.6 to 12.1 μg N2O-N m−2  h−1 and 12.8 to 59.8 μg N2O-N m−2  h−1 at the ponds, shallow fens and dry tundra sites, respectively. The seasonal pattern of N2O fluxes followed the warming of the sediment/soil, indicating that the variation of ground temperatures had an important effect on N2O emissions. The freezing–thawing cycle seemed to increase the N2O emissions from the wetlands, and water table was the major parameter for spatial variations of controlling N2O fluxes. There was a consistent diurnal pattern in the N2O emission rates from two wetlands and a good correlation with ground temperatures. The sparse data in this study hint at the potential importance of coastal tundra wetlands in the total local atmospheric N2O load in eastern Antarctica.
Keywords: Nitrous oxide flux; Wetland; Antarctica; Peat; Spatial variation; Temporal variation;

A laboratory-scale study was set up to investigate ammonia (NH3), nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) emissions during storage of untreated pig and cattle slurry and the fractions (solid and liquid) obtained by mechanical separation. The solid and liquid fractions were obtained from the same untreated slurry by means of a lab-scale mechanical separator.The manures were stored for a period of 30 days in open vessels (1500 cm3 capacity) in two temperature-controlled rooms, which were kept at 5±0.5 and 25±0.2 °C. Gaseous emissions were determined using a dynamic chamber method and infrared photoacoustic detection (IPD).Over the storage period, gaseous emissions from pig manures were significantly (P<0.05) higher than those from cattle manures. N2O fluxes of up to 232 mg m−2  h−1 were measured, but from pig solid fraction only. Between 40.8% (from pig liquid fraction stored at 25 °C) and 3.60% (from untreated cattle slurry stored at 25 °C) of the initial nitrogen content of the manures was lost as NH3. Over the 30-day-storage period, the predominant emission of carbon was in the CO2 form. Total C-CH4 losses, expressed as a percent of the carbon initially present in the volatile solids (C-VS), ranged from 0.60% to 12.8% for pig manures and from 0.23% to 1.56% for cattle manures. The mechanical separation of cattle slurry increased by up to 30% the emissions of CO2 equivalents to the atmosphere, during the storage of the separated fractions, when compared with the slurries. Results indicated that NH3, N2O, CO2 and CH4 emissions were affected by the interaction between a number of variables, including storage temperature, chemical characteristics and type of manure. Results also indicated that mechanical separation does not reduce emissions, but has the potential to increase the emissions of CO2 equivalents to the atmosphere during the storage of the separated fractions.
Keywords: Ammonia; Greenhouse gas emissions; Manure storage; Slurry separation;

Dust samples collected from the surface of glaciers and in dust traps on the remote West Coast of New Zealand's South Island can reliably be identified as being of both Australian and New Zealand origin. Most are, however, found to be enriched in Cu, Zn, Cd, Sb, Sn, Pb, Ni and Cr, when compared with their source-area sediments. The degree of metal enrichment in the dust samples is proportionally related to the percentage of Australian dust implying that the pollutants were transported with dust from eastern Australia. Pollution enrichment factors for these metals in dusts were calculated with a high degree of certainty, because the specific source regions of the dust could be identified. Rates of trace metal pollution transport were then calculated using a record of Australian dust transport over New Zealand. Results show that significant concentrations of trace metal pollutants are transported to New Zealand at levels that are between 1.5 and 100 times background conditions. Results also show that Sb, Pb and Cr are highly particle reactive and their transport in this region is almost exclusively associated with dust scavenging (up-take of pollutants by dust). By comparison, Cu, Zn, Cd, Sn and Ni may also be transported independently of dust. While the rates of pollution metal transport reported here are lower than in more industrialised regions of the globe, the majority of these metals are being deposited in a region internationally recognised for its environmental and conservation values.
Keywords: Dust; Trace metal pollution; New Zealand; Australia; Atmospheric scavenging; Lake Eyre Basin;

Polyurethane foam disk passive air samplers (PAS) were deployed in a steel complex, and in residential and semi-rural areas of a city in Southern Korea between January and April 2006. Dioxin-like polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) were monitored to investigate the influence of the steel complex on the residential and semi-rural areas. The average levels of ∑12PCB (26.2; 6.1–61.8 pg m−3) and ∑9PBDE (25.2; 9.0–61.6 pg m−3) in the steel complex were higher than those of neighboring areas, indicating that the steel complex is a major source of both chemical groups. No significant difference in the congener patterns for the different areas suggests that the study area is commonly affected by the same sources. Elevated air concentrations at the eastern sites of the city and relatively low concentrations at the residential area close to the steel complex were observed. According to air dispersion modeling, the major wind direction plays a key role in determining this spatial distribution of PCBs and PBDEs. Consequently, the levels of these chemicals at the residential area might not be strongly influenced by the emissions from the steel complex. This study suggests that the combination of passive air sampling and air dispersion modeling is a useful tool for assessing source–receptor relationships of persistent organic pollutants (POPs) on a local scale.
Keywords: Dioxin-like PCBs; PBDEs; Passive air sampler; Steel complex;

The flow across a street canyon of variable width—Part 2: by Serge Simoëns; James M. Wallace (2489-2503).
As described in Part 1 [Simoëns et al., 2007. The flow across a street canyon of variable width—Part 1: kinematic description. Atmospheric Environment 41, 9002–9017] measurements have been made of the velocity field around and within the canyon formed by two obstacles placed on the wall of a turbulent boundary layer. Here in Part 2 measurements of the scalar dispersion of smoke released from a two-dimensional slot in the wall perpendicular to the mean flow and located parallel to and midway between these two square obstacles are presented. The Reynolds number of the boundary layer at the slot location without the obstacles in place was R θ ≈ 980 . Statistical properties of the concentration field and the scalar fluxes in the streamwise plane are reported here for canyon openings that have been chosen based on characteristics of the kinematic description. These opening widths, expressed as multiples of the obstacle height, are 1h, 4h and 8h.The mean concentration field revealed that the much of the scalar is trapped on the leeward side of the upstream obstacle before some of it escapes the canyon and is entrained on the roof of the upstream obstacle. It then is spread downstream by the turbulence in the wake of this obstacle. Surprisingly, the root mean square (rms) concentration field reveals that high concentration fluctuations exist in a zone where velocity field turbulence is very low. Measured streamwise scalar fluxes were found to be negative above the obstacles, whereas they are mainly positive between the obstacles. The measured wall normal scalar fluxes have an inverse behavior. Within the canyon, the scalar fluxes are greatest in the region between the large primary vortex, evident in the kinematic field, and the secondary vortex located in the corner of the leeward side of the upstream obstacle. In the flow above the obstacle roofs the wake of the upstream obstacle seems to dominate the scalar transport. Between the obstacles in and above the canyon, the existence of intermittent and intense events appear to prevent the modelling of these fluxes with a simple mean concentration gradient model.
Keywords: Concentration; Dispersion; Street canyon; Boundary layer; PIV; Obstacles;

A practical uncertainty budget for ambient mercury vapour measurement by Richard J.C. Brown; Andrew S. Brown; Rachel E. Yardley; Warren T. Corns; Peter B. Stockwell (2504-2517).
Measurements of mercury in ambient air are assuming greater importance, because of increasing health concerns and European legislation. In order to have confidence in measured values and to assess compliance with target values, measurements must be made with validated methodologies which have traceable uncertainty statements associated with them. This paper presents a practical uncertainty budget for the measurement of vapour-phase mercury in ambient air, sampling onto a gold-coated silica adsorption tube and measuring with atomic fluorescence spectrometry. Moreover, this budget may be generalised for other related measurement methods for mercury vapour and other ambient air pollutants. All significant sources of uncertainty are discussed and estimated. Expanded relative uncertainties at the 95% confidence interval of approximately 17% are estimated for exemplar measurements made by the National Physical Laboratory (NPL) as part of the UK Heavy Metals Monitoring Network.
Keywords: Mercury vapour; Ambient air; Uncertainty budget; Chemical metrology; Atomic fluorescence spectroscopy;

Past acid deposition studies in North America have demonstrated that SO2 and NO x emissions from Canada and the United States are transported across the Canada–United States border and deposited in the other country. In this study, we use an observation-based mass balance approach to estimate the percentage contribution of eastern US (EUS) emissions to wet deposition in eastern Canada (EC) during two 5-year periods: 1990–1994 and 1996–2000. The estimates are made using a set of mass balance equations derived from 5-year-average integrated emissions in EC and the EUS (taken from emission inventories) and 5-year-average wet deposition values integrated over the same areas (based on wet deposition measurements). In deriving the mass balance equations, it was found that EC emitted, on average, 8–9% of eastern North American SO2 emissions but received 28–29% of eastern North American non-sea-salt-SO4 2− wet deposition, even though the integration area of EC was approximately half that of the EUS. Similar figures were found for NO x emissions and nitrate wet deposition. This emission-versus-deposition imbalance is assumed to be due to the transboundary transport of EUS emissions into EC, which is factored into the mass balance equations. The results of the mass balance calculations indicate that SO2 and NO x emission sources in the EUS are responsible for between 56% and 83% of the non-sea-salt-SO4 2− and NO3 wet deposition in EC. This range is consistent with previously published, model-based, mass balance studies in this region and provides an independent, observation-based confirmation of the model results.
Keywords: Wet deposition; Acid rain; Transboundary transport; Mass balance; Source–receptor; Acidifying emissions;

Atmospheric H2O2 measurement and modeling campaign during summer 2004 in Zagreb, Croatia by Karin Acker; Nenad Kezele; Leo Klasinc; Detlev Möller; Gordana Pehnec; Glenda Šorgo; Wolfgang Wieprecht; Silva Žužul (2530-2542).
Hydrogen peroxide (H2O2) in the gas phase and a number of other atmospheric components and variables (O3, CO, SO2, NO, NO2, benzene, toluene, ethylbenzene and xylene (BTEX)) were simultaneously measured during a field study performed in Zagreb, Croatia, from May until July 2004 (for selected variables until October 2004). Meteorological data from the nearby stations were provided by the Geophysical Institute and by Meteorological and Hydrological Service of Croatia. The collected data adjusted to hourly averages were used for modeling diurnal concentration behavior and development over a couple of days using Master Mechanism model developed by S. Madronich (NCAR, Boulder, CO). The H2O2 mixing ratios were found to vary between <0.05 and 6.2 ppb and also exhibited a strong diurnal pattern very similar to that of ozone, with concentration maxima in the afternoon, between 15:00 and 16:00 h, CET. Linear regression analysis showed that, during daytime, H2O2 positively correlated with ozone (r=0.4) and solar radiation (r=0.52), but showed only very weak negative correlations with NO2, CO and BTEX. Our H2O2 data are the first such reported data for the region and their modeling, along with ozone data, gives a valuable insight into the interplay of pollutants that affect their concentrations.
Keywords: Air; Hydrogen peroxide; Master Mechanism model; Oxidants; Ozone;

Trends of NO-, NO2-, and NH3-emissions from gasoline-fueled Euro-3- to Euro-4-passenger cars by Norbert V. Heeb; Christian J. Saxer; Anna-Maria Forss; Stefan Brühlmann (2543-2554).
Vehicular emissions of reactive nitrogen compounds (RNCs) such as nitric oxide (NO), nitrogen dioxide (NO2), and ammonia (NH3) have a substantial impact on urban air quality. NO and NO2 support the photochemical formation of ozone, and NH3 is involved in the atmospheric formation of secondary aerosols. Vehicular NO is mainly formed during combustion, whereas NO2 and NH3 are both secondary pollutants of the catalytic converter systems. Herein we report on tail-pipe RNC emissions of gasoline-fueled Euro-3- and Euro-4-passenger cars at transient driving from 0 to 150 km h−1. Two sets of 10 in-use vehicles with comparable engine size and mileage were studied with time-resolved chemical ionization-mass spectrometry (CI-MS). Each vehicle was tested in 7 different driving cycles including the legislative European (EDC) and the US FTP-75 driving cycles. Mean emission factors (EFs) for different traffic situations are reported and effects of cold start, velocity, acceleration, and deceleration are discussed. Furthermore, critical operating conditions supporting the de novo formation of NH3 have been identified. In the EDC, mean NO- and NH3-EFs of 57±26 and 16±12 mg km−1 were obtained for Euro-3-vehicles; those of the Euro-4-technology were lower by about 25% and 33% at the levels of 43±46 and 10±7 mg km−1, respectively. NO2 emissions of the investigated three-way catalyst (TWC) vehicles accounted for <1% of the detected RNCs, whereas NH3 was found to be the dominant RNC for most vehicle conditions. Molar NH3 proportions varied from about 0.4–0.8, as soon as catalyst light-off occurred. NO was found in large excess only during the cold-start period. Catalyst light-off is indicated by a fast transition from NO- to NH3-rich exhaust. Velocity and acceleration had pronounced effects on the RNC emission characteristics. Mean velocity-dependent EFs for NO and NH3 varied by about one order of magnitude from 10 to 74 and 15 to 161 mg km−1 for Euro-3-vehicles and from 12 to 44 and 7 to 144 mg km−1 for the Euro-4 fleet. We conclude that the investigated Euro-3- and Euro-4-vehicles are mainly operated under slightly reducing conditions, where the NH3 emissions dominate over those of the NO. Under these conditions, both vehicle fleets on an average fulfilled the valid Euro-3 and Euro-4 limits for nitrogen oxides (NO x ) of 150 and 80 mg km−1, respectively (as NO2 equivalents).
Keywords: Vehicle emissions; Catalytic reduction of nitrogen oxides; Reactive nitrogen compounds (RNCs); Secondary pollutants of three-way catalysts; Time-resolved exhaust analysis; Chemical ionization-mass spectrometry (CI-MS);

Assessment of uncertainty of benzene measurements by Radiello diffusive sampler by Hervé Plaisance; Thierry Leonardis; Michel Gerboles (2555-2568).
The uncertainty of benzene measurements obtained by the analysis of thermally desorbable Radiello diffusive samplers was evaluated according to the recent standard EN 14662-4 [EN 14662-4, 2005. Ambient air quality. Standard method for measurement of benzene concentrations. Part 4: diffusive sampling followed by thermal desorption and gas chromatography]. Considering the results of laboratory experiments, all the sources of uncertainty regarding the diffusive sampler method characteristics were accessed for the sampling times of 7 and 14 days. The major part of the uncertainty budget (>79%) was explained by the variation of the sampling rate due to the environmental factors (temperature and concentration level). For weekly sampling, the diffusive sampler method satisfies the data quality objectives of the European Directive to supply the indicative measurements as well as the reference measurement, since the expanded uncertainty is found <25%. Using a model-predicted sampling rate which depends on the concentration and temperature, the expanded uncertainty is significantly decreased. The Radiello sampler was found to give correct results for a weekly sampling in a limited range of benzene concentrations between 0 and 10 μg m−3, which is generally observed in environmental air monitoring. This narrow validation domain limits the application fields of the Radiello sampler exposed for 7 days to indoor air, personal exposure and ambient atmospheric monitoring excluding workplaces. For 2-week sampling, the expanded uncertainty of measurements exceeds 30%. However, this diffusive sampler can still be used to carry out an objective evaluation of benzene (minimum quality objective for the accuracy of 100%). Therefore, the performance of this diffusive sampler method appears to be suitable for the benzene monitoring in ambiant air.
Keywords: Diffusive sampler; Benzene; Passive sampling; Quality assurance; Uncertainty; Environmental exposure;