Atmospheric Environment (v.40, #8)

Field investigation into the diffusion of semi-volatile organic compounds into fresh and aged snow by B.M.J. Herbert; C.J. Halsall; K.C. Jones; R. Kallenborn (1385-1393).
Empirically derived field diffusivities were determined over a 24 h period for a selection of anthropogenic chlorinated chemicals in both fresh and aged snow at Tromsø, Norway. Diffusivities in fresh snow were 4.91×10−2, 4.79×10−1, 4.75×10−2 and 4.75×10−2  cm2  s−1 for PCB-6, HCB and α-/γ-HCH, respectively. These field diffusivities were compared to theoretical diffusivities (assuming no interaction between the chemical vapour and ice surfaces) and effective diffusivities (assuming sorption of the chemical vapour to the ice surface). Theoretical diffusivities were the highest values and were in good agreement with the empirical diffusivities derived from the field data. This suggests that the test chemicals used in this study have a low affinity for the snow/ice surfaces during diffusion into the snow. Differences in calculated diffusivities between these compounds can be largely accounted for by their physical–chemical properties, notably their snow interfacial-air partition coefficients (K ia snow). However, using calculated values of K ia snow to describe sorption to the snow surfaces greatly reduced the effective diffusivities of the chemicals relative to the empirical field diffusivities, and calls into question the accuracy of K ia snow and/or its suitability for describing snow/air interactions at the relatively mild temperatures encountered in this study. Comparison of diffusivities between fresh and aged snow revealed similar values (within the same order of magnitude) and may be due to similar porosities between the snow types, although this parameter was not measured. Mass transfer coefficients were determined using the empirical field diffusivities and depth of the snow-layer, allowing chemical fluxes from snow to air to be calculated through use of the Whitman two-film resistance model. Using derived fluxes the chemical half-lives (t 1/2) in fresh snow were calculated assuming that snow metamorphosis did not occur. The half-lives were in good agreement to half-lives measured in a separate field study for POPs, and serve to validate the empirical diffusivities measured in this study.
Keywords: Arctic; Polar; Organochlorine pesticides; Polychlorinated biphenyls; Persistent organic pollutants;

Carbon dioxide build-up within a suburban canopy layer in winter night by Ryo Moriwaki; Manabu Kanda; Harumi Nitta (1394-1407).
This study concerns the build-up of carbon dioxide, hereafter CO2, within a suburban canopy under nocturnal stably stratified conditions. The results were derived from wintertime field measurements of the vertical profiles of CO2, air temperature and turbulent exchange processes, in a residential area with a mean canopy height of 7.3 m in Tokyo, Japan. In the daytime, especially under very windy conditions, the CO2 concentration measured at a reference height of 29 m a.g.l. was almost the same as the background CO2 concentration (380 ppmv). In contrast, during night-time the CO2 concentration significantly increased under stably stratified conditions. We therefore examined the ensemble mean vertical profile of CO2 concentration using the bulk Richardson number (Rb) as a stability index. Under stably stratified conditions (Rb>5), the CO2 concentration above the canopy decreased with height such that the difference between within and above the canopy was as high as 40 ppmv. In contrast, the CO2 concentration within the canopy stayed at almost the same level, which indicates that the CO2 emitted from the houses accumulated within the canopy. Such behavior was not found in the H2O profile. We argue that these concentration profiles of CO2 and H2O are influenced by subsiding cold air from the rooftop, thus drawing the high CO2 levels from ventilation fans down towards the ground.
Keywords: Vertical profile; Carbon dioxide; Urban canopy layer; Urban roughness layer; Turbulent exchange; Cold-air pool;

Researchers or decision-makers frequently need information about atmospheric pollution patterns in urbanized areas. The preparation of this type of information is a complex task, due to the influence of several individual pollutants, with different units, on the global air pollution (e.g. nitrogen dioxide concentrations, ppm, and noise, dB). In this work, a new methodology based on the formulation of the Rasch model is proposed to obtain a measure of the atmospheric pollution. Two main results were obtained after applying this method: (1) A classification of all locations according to the pollution level, which was the value of the Rasch measure; (2) The influence on the environmental deterioration of each individual pollutant (particularly, in this work, NO2, NO, CO2, CO and noise). Finally, pollution at locations where no measurements were available was estimated with the optimum interpolation technique, kriging. Kriged estimates were subsequently used to map atmospheric pollution. To illustrate the application of this two-step method (Rasch model plus interpolation), which is useful to generate hazard assessment maps based on the spatial distribution of atmospheric pollution, an example is shown.
Keywords: Regionalized variable; Pollutant; Variogram; Kriging; GIS;

Polybrominated diphenyl ethers in indoor air in Kuwait: Implications for human exposure by Bondi Gevao; Majed Al-Bahloul; Abdul Nabi Al-Ghadban; Lulwa Ali; Ali Al-Omair; Murad Helaleh; Khaled Al-Matrouk; Jamal Zafar (1419-1426).
Polyurethane foam plug passive samplers were used to concurrently measure air concentrations of polybrominated diphenyl ethers (PBDEs) in 70 indoor environments. PBDEs were detected in all homes and offices investigated with patterns similar to the distribution in the commercial penta technical formulation (Bromkal 70-5DE). The ubiquitous distribution of these compounds in indoor environments may be due to the volatilization of these chemicals from foam (e.g. mattresses, foam padded furniture), electronic equipments (e.g. TVs, printers, computers) and other consumer products to which they are added as flame retardants. Mean ΣPBDEs concentration in air was log-normally distributed and ranged from ∼2–385 pg m−3. Using an inhalation rate of 8 and 20 m3  day−1 for children and adults respectively, exposure via inhalation is estimated to be 173 and 399 pg day−1 for children and adults respectively. This study supports the growing body of evidence for the ubiquitous presence of these compounds in indoor air and the potential for continuous, low-level exposure both at work and home.
Keywords: Passive air sampling; PBDEs; Persistent organic pollutants; Indoor air;

Meteorological dependence of size-fractionated number concentrations of urban aerosol particles by Tareq Hussein; Ari Karppinen; Jaakko Kukkonen; Jari Härkönen; Pasi P. Aalto; Kaarle Hämeri; Veli-Matti Kerminen; Markku Kulmala (1427-1440).
We utilized a long-term data set of aerosol particle number size distributions (8–400 nm) in the urban background air of Helsinki during 1998–2000. We analyzed the number concentrations of both ultra-fine particles (UFP diameter <100 nm) and the fraction of fine particles (FP, diameter <2.5 μm) larger than 100 nm (accumulation mode), and we also investigated their dependencies on the relevant meteorological parameters. The meteorological parameters were obtained by a meteorological pre-processing model. Among the meteorological parameters considered in this study (wind speed and direction, temperature, atmospheric pressure, relative humidity, Monin–Obukhov length and mixing height), the ambient temperature and local wind conditions were found to be the most important factors that control the number concentrations of FP. We described the dependencies of FP number concentrations on meteorological variables by using an empirically based mathematical function that contains the ambient temperature, local wind speed and direction as independent variables. According to statistical analyses, the predicted number concentrations of accumulation mode particles follow this relationship more closely than those of UFP's. This is mainly due to the origin and type of aerosol particles in the accumulation mode size range, being mainly regional and long-range transported. The main limitations of the mathematical function presented in this study are during new particle formation events, precipitation and long-range pollution episodes of aerosol particles. This study provides an attempt to predict the particle number concentrations of FP by utilizing a simple model that connects the relationship between the aerosol particle number concentrations and the relevant meteorological parameters.
Keywords: Urban; Particulate matter; Ultra-fine particles; Submicron particles;

Epistemic assessment of radon level of offices in Hong Kong by L.T. Wong; K.W. Mui; K.Y. Law; P.S. Hui (1441-1451).
People spend most of their life working indoors. Human exposure to various air pollutants changed its importance in nature from outdoor to indoor. As some of the pollutant sources basically originate from the building envelope that could not be removed or is costly to mitigate, the remaining questions are: how the indoor air quality (IAQ) is monitored and how the information could be used for the environmental control system to achieve the best air quality delivery.Indoor radon level could be measured with a number of sampling approaches and used to determine the acceptance of an IAQ with respect to certain exposure limits. In determining the acceptable IAQ of a space, this study proposes that the measured indoor radon level must be accompanied with the confidence levels of the assessment. Radon levels in Hong Kong offices were studied by a cross-sectional measurement in 216 typical offices and a year-round longitudinal measurement in one office. The results showed that 96.5% (94.0–99.0% at 95% confidence interval) and 98.6% (97.0% to >99.9% at 95% confidence interval) of the sampled offices would satisfy action radon levels of 150 and 200 Bq m−3, respectively. The same results were then used to quantify the prior knowledge on radon level distributions of an office and the probable errors of the adopted sampling schemes. This study proposes an epistemic approach, with the prior knowledge and a sample test result, to assess the acceptance against an action radon level of an office in Hong Kong. With the certainty of the test results determined for judgmental purposes, it is possible to apply the method to an office for follow-up tests of acceptance.
Keywords: Radon; Measurement; Sampling; Offices;

Classification of PM10 distributions in Taiwan by Hsin-Chung Lu; Chung-Liang Chang; Jen-Chieh Hsieh (1452-1463).
Daily average PM10 concentrations of 71 stations in Taiwan in wintertime (October to March) and summertime periods (April to September) were fitted individually by a lognormal distribution for a 2 yr period (2001 to 2002). The distribution parameters (geometric mean and geometric standard deviation) in wintertime were used to determine the air-quality basins for PM10 by utilizing three clustering techniques, viz. of hierarchical clustering (Ward's method), non-hierarchical clustering (K-means) and two-level approach (self-organizing maps neural network, then K-means clustering). All three techniques suggested that 71 air-monitoring stations in Taiwan can be divided into five air-quality basins which are located in northern, central, eastern, southwestern and southern Taiwan, respectively. The sequence of PM10 pollution levels in the five basins is southern Taiwan>southwestern Taiwan>central Taiwan>northern Taiwan>eastern Taiwan. Geometric means and geometric standard deviations in each of the five air-quality basins were significantly different from each other for the two-level approach method by the Waller–Duncan k-ratio t-test ( k = 1 0 0 , P = 0.0 5 ), suggesting that the two-level approach method is best among the three clustering methods. The clustering results of five air-quality basins in Taiwan are useful to decide the corresponding control strategy at different air-quality basins.
Keywords: Self-organizing maps; Lognormal distribution; Hierarchical clustering; K-means; Air-quality basins;

This paper introduces a method to incorporate species-based variation of the emission of biogenic volatile organic compounds (BVOCs) into regional climate and weather models. We convert a species-based land-cover database for Texas into a database compatible with the community land model (CLM) and a database compatible with the Noah land-surface model (LSM). We link the LSM-compatible land-cover databases to the original species-based data set as a means to derive region-specific BVOC emission capacities for each plant functional type (in the CLM database) and for each land-cover type (in the Noah database).The spatial distribution of inherent BVOC flux (defined as the product of the BVOC emission capacity and the leaf biomass density) derived using the Texas-specific BVOC emission capacities is well correlated with the spatial distribution of inherent BVOC flux calculated using the original species data ( r = 0.8 9 ). The mean absolute error for the emission-capacity-derived inherent flux distribution is an order of magnitude lower than the statewide range of inherent fluxes.The ground-referenced land-cover databases derived here are likely more accurate than their satellite-derived counterparts; they can be used for a variety of regional model simulations in Texas. The inherent BVOC flux distributions derived using region-specific BVOC emission capacities are more consistent with observations than the BVOC flux distribution derived using the CLM3 standard BVOC emission capacities, which are top-down estimates based on the literature. When used in conjunction with detailed land-cover data sets, region-specific BVOC emission capacities produce reasonably accurate inherent BVOC fluxes.
Keywords: BVOC; Biogenic emissions; Regional climate models; Regional weather models; Emission capacity;

Identification and quantification of volatile organic compounds from a dairy by Jenny Filipy; Brian Rumburg; George Mount; Hal Westberg; Brian Lamb (1480-1494).
Volatile organic compounds (VOCs) that contribute to odor and air quality problems have been identified from the Washington State University Knott Dairy Farm using gas chromatography–mass spectroscopy (GC–MS). Eighty-two VOCs were identified at a lactating cow open stall and 73 were detected from a slurry wastewater lagoon. These compounds included alcohols, aldehydes, ketones, esters, ethers, aromatic hydrocarbons, halogenated hydrocarbons, terpenes, other hydrocarbons, amines, other nitrogen containing compounds, and sulfur-containing compounds. The concentration of VOCs directly associated with cattle waste increased with ambient air temperature, with the highest concentrations present during the summer months. Concentrations of most detected compounds were below published odor detection thresholds. Emission rates of ethanol (1026±513 μg cow−1  s−1) and dimethyl sulfide (DMS) (13.8±10.3 μg cow−1  s−1) were measured from the lactating stall area using an atmospheric tracer method and concentrations were plotted using data over a 2-year period. Emission rates of acetone (3.03±0.85 ng cow−1  s−1), 2-butanone (145±35 ng cow−1  s−1), methyl isobutyl ketone (3.46±1.11 ng cow−1  s−1), 2-methyl-3-pentanone (25.1±8.0 ng cow−1  s−1), DMS (2.19±0.92 ng cow−1  s−1), and dimethyl disulfide (DMDS) (16.1±3.9 ng cow−1  s−1) were measured from the slurry waste lagoon using a laboratory emission chamber.
Keywords: Cattle; Livestock; Manure; Odors; Emissions;

Climatology of aerosol optical properties in northern China by Tiantao Cheng; Hua Wang; Yongfu Xu; Hongyu Li; Liqing Tian (1495-1509).
The climatology of aerosol optical properties in northern China were examined from the ground-based sun and sky radiance measurements at six sites during 2001–2005. Cases of high aerosol optical thickness (AOT) mostly attributed to the occurrence of dust events in spring and the impacts of pollutant particles in summer. The Alfa parameter decreased with AOT even zero or negative in appearance of dust events. The relationship between Alfa and AOT at sites of downwind regions was characterized by one integrated exponent during summer and autumn and by two integrated exponents during spring and winter. But for the sites near dust source regions, only one integrated exponent was enough in any season. This is a possible way to identify and estimate the effects of different sources on aerosol loading and particle size. The aerosol volume size distributions had three modes, one accumulation mode with radius 0.07–0.15 μm and two coarse modes with radii 1.3–1.7 and 3.8–5.0 μm. As AOT larger than 0.5, a pseudo mode appeared between the accumulation mode and two coarse modes with radius 0.3–0.5 μm at sites of dust source regions. The average effective radii during winter and spring were commonly larger than that of summer and autumn. Real parts of the refractive index at 440–1020 nm varied with AOT in range of 1.40–1.54 at sites of dust source regions and in range of 1.45–1.55 at sites of downwind regions. Imaginary parts of the refractive index appeared low sensitivity to wavelengths from 440 to 1020 nm. The averages of imaginary parts during winter and spring were 0.0015–0.0018 for 440–1020 nm at DH and IM sites, and 0.009–0.014 during winter and spring and 0.011–0.058 during summer and autumn at other sites.
Keywords: Aerosols; Optical properties; Dust event; Northern China;

Monte Carlo solution of wet removal of aerosols by precipitation by Haibo Zhao; Chuguang Zheng (1510-1525).
The time evolution of aerosol size distribution (ASD) during precipitation describes quantitatively aerosols wet scavenging process. Scavenging coefficient, which takes account of the three most important wet removal mechanisms: Brownian diffusion, interception and inertial impaction, is used to parameterize wet scavenging process. A new multi-Monte Carlo method (MMC) is promoted to solve general dynamic equation for wet removal of aerosols. Two special cases in which analytical solutions exist are adopted to validate computation precision of MMC method. Furthermore, the influence of precipitation type on aerosols wet scavenging process is investigated by numerical simulation of the method. The results show that for lognormal raindrop size distribution and lognormal ASD (1) the increase of rainfall intensity (from light precipitation to moderate precipitation and then to heavy precipitation) can help scavenge aerosols with any size; (2) any precipitation type scavenges large aerosols (>2 μm) more effectively than small aerosols (<0.01 μm) and intermediate aerosols (>0.01 μm and <2 μm) (in that order); (3) the three precipitation types have a weak effect of wet scavenging on intermediate aerosols.
Keywords: Scavenging coefficient; Collision efficiency; Brownian diffusion; Interception; Inertial impaction;

Source apportionment of PM2.5 in Beijing by positive matrix factorization by Yu Song; Yuanhang Zhang; Shaodong Xie; Limin Zeng; Mei Zheng; Lynn G. Salmon; Min Shao; Sjaak Slanina (1526-1537).
Air pollution associated with atmospheric fine particulate matter (PM2.5, i.e., particles with an aerodynamic diameter of 2.5 μm or less) is a serious problem in Beijing, China. To provide a better understanding of the sources contributing to PM2.5, 24-h samples were collected at 6-day intervals in January, April, July, and October in 2000 at five locations in the Beijing metropolitan area. Both backward trajectory and elemental analyses identified two dust storm events; the distinctly low value of Ca:Si (<0.2) and high Al:Ca (>1.7) in Beijing PM2.5 appear indicative of contributions from dust storms. Positive matrix factorization (PMF) was used to apportion sources of PM2.5, and eight sources were identified: biomass burning (11%), secondary sulfates (17%), secondary nitrates (14%), coal combustion (19%), industry (6%), motor vehicles (6%), road dust (9%), and yellow dust. The lower organic carbon (OC), elemental carbon (EC), SO4 2−, and Ca values of yellow dust enable it to be distinguished from road dust. The PMF method resolved 82% of PM2.5 mass concentrations and showed excellent agreement with a previous calculation using organic tracers in a chemical mass balance (CMB) model. The present study is the first reported comparison between a PMF source apportionment model and a molecular marker-based CMB in Beijing.
Keywords: China; Fine particle; Dust storm; Source profiles; Backward trajectories;

Precipitation chemistry at four sites along a longitudinal line in western Japan is discussed in terms of meteorological parameters. Wet-only samples were collected at Oki, Matsue, Kurahashi and Ashizuri along the line from north to south during April 1994–March 1999. The volume-weighted mean concentrations of nss-SO4 2− showed a 12% decline and NO3 showed a 29% decline from north to south. For NH4 + and nss-Ca2+, stronger negative concentration gradients were found from north to south, and the opposite gradient held true for H+. The fractional acidity, [H+]/([nss-SO4 2−]+[NO3 ]), was lower at Oki and Matsue than at Kurahashi and Ashizuri. Monthly concentrations of these five ions showed a marked seasonal variation with a winter maximum and a summer minimum. In order to explore the relation between high concentration episodes of nss-SO4 2− and NO3 , and air mass transport, back-trajectory analysis was applied to daily precipitation at the Oki and Ashizuri sites, the northernmost and southernmost of the four sites, respectively. For Oki, air masses for most of the episodic concentrations of the two ions were from the coastal areas of the Yellow Sea, the Bo Hay, and South Korea in winter. For Ashizuri, episodic air masses came from a wide region of the Asian Continent in the cold season, whereas no characteristic patterns were noted for warm-season trajectories. Sulfur emissions from a volcano located to the southwest of the Ashizuri site are also responsible for acidic nss-SO4 2− episodes.
Keywords: Acidic precipitation; Back trajectory; Nss-sulfate; Nitrate; East Asia;

Measurements of the aerosol hygroscopic growth factor, f(RH), and the physical and optical properties of aerosols were made at Gosan, Korea during the aerosol characterization experiment (ACE)-Asia 2001 field campaign (April 2001). The optical and hygroscopic properties of aerosols were characterized in terms of the air mass transport pathways. During the Asian dust period, σ sp and σ ap were remarkably elevated with mean and standard deviation of 238.6±55.3 Mm−1 and 24.2±10.9 Mm−1, respectively. The mean f(RH) for the pollution aerosols from Chinese sectors (2.75±0.38) in this study was much higher than that for the anthropogenic aerosols in Europe during ACE-2 (1.46±0.10) as well as that of the urban/industrial aerosols of the US east coast during TARFOX (1.81±0.37–2.30±0.24). The mean f(RH) during the smoke period (1.60±0.20) was comparable to that during INDOEX (1.58±0.21), and higher than that for SCAR-B in Brazil (1.16). We found a negative correlation ( r = 0.81 ) between f(RH) and OC concentration. This negative correlation suggests that organic aerosols have a strong influence on the smoke aerosol hygroscopicity.
Keywords: Hygroscopic growth; Dust; Pollution; Organic carbon; Smoke; ACE-Asia;