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Atmospheric Environment (v.39, #2)

Editorial board (pp. i).

List for forthcoming papers (pp. i-ii).

A study of atmospheric ammonia by means of modeling analysis in the Kanto region of Japan by Tatsuya Sakurai; S.-i. Shin-ichi Fujita; Hiroshi Hayami; Noritaka Furuhashi (pp. 203-210).

To evaluate the primary factor for the seasonal variation and the level of atmospheric ammonia concentration in the local scale, the emission, transport, and deposition of atmospheric ammonia were analyzed in the Kanto region of Japan, which has an area of about 40,000km², by means of an atmospheric transport model. In the analysis of episodes of high concentration, the model reproduced an observed concentration of NH₃ and NH₄⁺ particles during a 5-day observation period in the summer of 2002. In the annual simulation, the calculated concentration showed reasonable agreement with the spatial distribution and seasonal variation of the annual observation in 2000. The NH₃ concentration strongly reflected the effect of local emission sources because of its short lifespan in the atmosphere. Moreover, it is found from the simulation results that atmospheric ammonia was transported over long distances when it existed as a particulate. The calculated deposition amount of NH₃ and NH₄⁺ particles was about the same as the emission amount of NH₃ throughout the year. Moreover, the model simulation showed that there was little contribution from sources outside the Kanto region. These findings suggest that the concentration and the deposition in the Kanto region mainly originated from the emission sources in itself.

Keywords: Ammonia; Ammonium; Deposition; Emission; Atmospheric transport modeling

The water-soluble organic component of size-segregated aerosol, cloud water and wet depositions from Jeju Island during ACE-Asia by S. Decesari; M.C. Facchini; S. Fuzzi; G.B. McFiggans; H. Coe; K.N. Bower (pp. 211-222).

Water-soluble organic compounds (WSOC) in size-segregated aerosol samples, cloud water and wet depositions collected at Jeju Island during the ACE-Asia experiment were characterized in terms of main functional groups and chemical classes by means of liquid chromatography coupled with total organic carbon (TOC) analysis, and by nuclear magnetic resonance (NMR) spectroscopy. The surface-active character of the WSOC was also deduced by measuring the surface tension (ST) of cloud water, wet depositions and aerosol water-extracts as a function of WSOC concentration. WSOC in the size-segregated aerosol samples at the Kosan coastal site show the occurrence of oxidized species, enriched in the accumulation mode, and a functional group composition characteristic of continental industrialized areas, with a small impact from biomass burning sources. The chemical classes identified and quantified by liquid chromatography accounted for 88% of the water-soluble organic carbon on average. The relatively high proportion of polycarboxylic acids (PA, 33–40% of total characterized WSOC) observed throughout the campaign indicates the persistence of WSOC from continental pollution sources in air masses which spent up to 5 days in the marine boundary layer (MBL) of the Yellow Sea. The analysis of cloud water and wet depositions collected at a mountain site in Jeju shows substantial differences in the organic composition between the cloud/rainwater solutes and the water-soluble fraction of the aerosol at the coastal site, with PA acids contributing to cloud water WSOC in far smaller proportions (6–11%) than in the fine MBL aerosols. It was proposed that such differences resulted from the entrainment of aerosol particles from the lifted layers into the stratiform clouds. Following this hypothesis, the saturated aliphatic compounds determined by NMR analysis in the rainwater samples, which are also responsible for the observed significant ST lowering, were scavenged above the boundary layer and had possibly been transported from the continent in the lifted layers. The hypothesized features of the vertical profiles in the inorganic and organic aerosol chemical composition are in agreement with the results of aircraft-based measurements performed during the same experiment.

Keywords: Water-soluble organic carbon; Atmospheric aerosols; Rainwater; NMR spectroscopy; Surface tension

A performance study of PEMS applied to the Hsinta power station of Taipower by T.W. Chien; H. Chu; W.C. Hsu; Y.Y. Tu; H.S. Tsai; K.Y. Chen (pp. 223-230).

Predictive emission monitoring systems (PEMS) have been shown to be a promising technology for calculating the emissions from gas-fired stationary sources. One of the first demonstration PEMS in Taiwan was installed and operated successfully at the Hsinta power plant of the Taiwan Power Company (Taipower) in 2000. To improve the accuracy of this PEMS model, further studies were conducted at the same combined cycle gas turbine (CCGT) unit #1 of the Hsinta power plant.To optimize the NO _X PEMS model, several functions were progressively developed including a log model, a one-level linear model, a three-level linear model, a 15-variable linear model, and a 15-variable with start-up mode model. The latter gave the relative accuracies (RA) and correlation coefficients between PEMS and a continuous emission monitoring system (CEMS) in the range of 3.38–14.77% and 0.955–0.989, respectively, which fulfill the criteria of the USEPA draft on PEMS performance specifications.Similarly, this model demonstrated RAs for low, medium, high level, and a three-level average less than 20% which meet CEMS requirements set out by Taiwan EPA.

Keywords: PEMS; CEMS; RATA; NO; _X; Modeling

Nitrated phenols in the atmosphere: a review by Mark A.J. Harrison; Silvia Barra; Daniele Borghesi; Davide Vione; Cecilia Arsene; Romeo Iulian Olariu (pp. 231-248).

^{This paper reviews the data concerning the atmospheric occurrence of nitrophenols, both in the gas and in the condensed phase (rainwater, cloud, fog and snow). Data obtained from field campaigns are reported, together with a description of the analytical techniques employed for the identification and quantification of nitrophenols. Analysis is usually performed using techniques such as High Performance Liquid Chromatography (HPLC) or Gas Chromatography-Mass Spectrometry (GC-MS), with the sampling method largely determined according to the matrix under investigation. The sources of atmospheric nitrophenols include direct emissions resulting from combustion processes, hydrolysis of pesticides (e.g. parathion) and the secondary formation of nitrophenols in the atmosphere. Atmospheric nitration of phenol can take place both in the gas and liquid phases, but the relative importance of these processes is still under discussion. The gas-phase nitration involves reaction between phenol and}^OH+NO₂^{during the day or}NO₃⁺NO₂ during the night. Gas-phase nitration during the day yields only 2-nitrophenol (2-NP); while during the night it is thought that both 2-NP and 4-nitrophenol (4-NP) may be formed. Because of many gaps in the experimental evidence it is apparent that more research is required to indicate whether the 4-NP present in the environment can be accounted for by this nighttime process. Nitration in the condensed phase can be initiated by electrophilic nitration agents such as N₂O₅ and ClNO₂^{. Other liquid-phase processes can also take place, in the presence of}NO₃^{, nitrate and nitrite, in the dark and under irradiation. Condensed-phase processes have been shown to yield 2- and 4-NP in similar amounts. It is also important to consider the atmospheric sinks of nitrophenols. The rate constant for the reaction between 2-NP and}OH in the gas phase is rather low (9.0×10⁻¹³cm³molecule⁻¹s⁻¹^{), while incomplete data are available for the reaction with}NO₃^{. In addition, condensed-phase processes might also represent an important nitrophenol sink. Potential loss routes include the reaction with radicals such as}^{OH and}NO₃ in aqueous solution as well as the nitration to form the dinitrophenols.

Keywords: Nitrophenols; Nitroaromatic compounds; Nitration; Semivolatile organic compounds; Phytotoxicity

Gaseous methyl- and inorganic mercury in landfill gas from landfills in Florida, Minnesota, Delaware, and California by S.E. Lindberg; G. Southworth; E.M. Prestbo; D. Wallschl�ger; M.A. Bogle; J. Price (pp. 249-258).

Municipal waste landfills contain numerous sources of mercury which could be emitted to the atmosphere. Their generation of methane by anaerobic bacteria suggests that landfills may act as bioreactors for methylated mercury compounds. Since our previous study at a single Florida landfill, gaseous inorganic and methylated mercury species have now been identified and quantified in landfill gas at nine additional municipal landfills in several regions of the US. Total gaseous mercury occurs at concentrations in the μgm⁻³ range, while methylated compounds occur at concentrations in the ngm⁻³ range at all but one of the landfill sites. Dimethylmercury is the predominant methylated species, at concentrations up to 100ngm⁻³, while monomethyl mercury was generally lower. Limited measurements near sites where waste is exposed for processing (e.g. working face, transfer areas) suggest that dimethylmercury is released during these activities as well. Although increasing amounts of landfill gas generated in the US are flared (which should thermally decompose the organic mercury to inorganic mercury), unflared landfill gas is a potentially important anthropogenic source of methylated mercury emissions to the atmosphere.

Keywords: Dimethylmercury; Emissions; Waste; Analytical methods

Development of an individual exposure model for application to the Southern California children's health study by Jun Wu; Fred Lurmann; Arthur Winer; Rong Lu; Richard Turco; Tami Funk (pp. 259-273).

The Southern California Children's Health Study (CHS) investigated the relationship between air pollution and children's chronic respiratory health outcomes. Ambient air pollutant measurements from a single CHS monitoring station in each community were used as surrogates for personal exposures of all children in that community. To improve exposure estimates for the CHS children, we developed an Individual Exposure Model (IEM) to retrospectively estimate the long-term average exposure of the individual CHS children to CO, NO₂, PM₁₀, PM_2.5, and elemental carbon (EC) of ambient origin. In the IEM, pollutant concentrations due to both local mobile source emissions (LMSE) and meteorologically transported pollutants were taken into account by combining a line source model (CALINE4) with a regional air quality model (SMOG). To avoid double counting, local mobile sources were removed from SMOG and added back by CALINE4. Limited information from the CHS survey was used to group each child into a specific time-activity category, for which corresponding Consolidated Human Activity Database (CHAD) time-activity profiles were sampled. We found local traffic significantly increased within-community variability of exposure to vehicle-related pollutants. PM-associated exposures were influenced more by meteorologically transported pollutants and local non-mobile source emissions than by LMSE. The overall within-community variability of personal exposures was highest for NO₂ (±20–40%), followed by EC (±17–27%), PM₁₀ (±15–25%), PM_2.5 (±15–20%), and CO (±9–14%). Between-community exposure differences were affected by community location, traffic density, and locations of residences and schools in each community. Proper siting of air monitoring stations relative to emission sources is important to capture community mean exposures.

Keywords: Exposure model; Vehicle-related pollutants; Meteorologically transported pollutants; Local pollutant emissions; Time-activity patterns

Atmospheric transport of lindane ( γ-hexachlorocyclohexane) from the Canadian prairies—a possible source for the Canadian Great Lakes, Arctic and Rocky mountains by Don T. Waite; Fraser G. Hunter (Retired); Brian J. Wiens (pp. 275-282).

Lindane ( γ-hexachlorocyclohexane) is used as an insecticide in many countries. Concentrations of lindane have been found in air, water, soil, snow and tissue samples throughout the world, including the Great Lakes, and concerns have been raised for its potential effects on human and ecosystem health. In Canada, lindane was, until 2003, principally used as a treatment on canola seed, a crop grown mostly on the Canadian prairies. Approximately 455.3 and 510.4t of lindane were applied in May of 1997 and 1998 respectively. An estimated 12–30% of this lindane volatilised within the first 6 weeks after planting, resulting in an atmospheric loading of from 66.4 to 188.8t. Five-day forward air trajectories (movement) were calculated from three locations on the Canadian prairies, for the 6-week period following sowing of canola seed, to estimate if such movements might contribute to the seasonal increases of γ-HCH in five Canadian target locations. These target locations were: Point Petrie on Lake Ontario (eastern Great Lakes region); the Front Range of the Rocky Mountains of southern Canada; the low Canadian Arctic between latitudes 60^o and 70^oN; the central Arctic between latitudes 70^o and 80^oN; and, Eureka in the high Arctic, north of latitude 80^oN. The percent of air mass trajectories moving from the prairies to these target areas was: Point Petrie 20%; Rocky Mountains 27%; low Arctic 30%; high Arctic 6%; Eureka 0%. It is possible, then, that volatilisation of γ-HCH from Canadian prairie canola crops contributed to the atmospheric loading in these remote regions.

Keywords: Atmospheric transport; Lindane; γ; -HCH; Forward trajectories

Inhalation of motor vehicle emissions: effects of urban population and land area by Julian D. Marshall; Thomas E. McKone; Elizabeth Deakin; William W. Nazaroff (pp. 283-295).

Urban population density may influence transportation demand, e.g., as expressed through average daily vehicle-kilometers traveled in private motor vehicles per capita. In turn, changes in transportation demand influence total passenger vehicle emissions to which populations are exposed. Population density can also influence the fraction of total emissions that are inhaled by the exposed urban population. Equations are presented that describe these relationships for an idealized representation of an urban area. Using analytic solutions to these equations, we investigate the effect of three changes in urban population and urban land area (infill, sprawl, and constant-density growth) on per capita inhalation intake of primary pollutants from passenger vehicles. For the system considered, the magnitude of these effects depends on density–emissions elasticity(εe), a normalized derivative relating change in population density to change in vehicle emissions. For example, based on the idealized representation of the emissions-to-intake relationship presented herein, if urban population increases, then per capita intake is less with infill development than with constant-density growth ifεe is <−0.5, while forεe >−0.5, the reverse is true.

Keywords: Population density; Infill; Sprawl; Land-use planning; Transportation planning; Smart growth

Seasonal cycle and composition of background fine particles along the west coast of the US by Dan Jaffe; Shihoko Tamura; Joyce Harris (pp. 297-306).

We used aerosol data from 4 sites along the west coast of the U.S. to evaluate the role of transport, seasonal pattern, chemical composition and possible trends in the marine background aerosol for the Pacific Northwest. For the Crater Lake samples, the data have been segregated using 10 day back isentropic trajectories to evaluate the role of transport. Our analysis of the segregated data indicates that the trajectories can successfully separate “locally influenced�? from “marine background�? aerosol, but are not able to identify a significant difference in the mean concentrations during marine vs Asian transport pathways.The background marine aerosol has an annual mean and median concentrations of 2.0 and 1.5 μgm⁻³, respectively, for particles less than 2.5μm diameter. There is a seasonal pattern in all components of the aerosol mass, with a summer maximum and winter minimum. This pattern is most likely due to the strong seasonal pattern in precipitation, which peaks in winter, combined with enhanced sources in summer. The Crater Lake marine aerosol composition is dominated by organics (∼40% by mass), with smaller contributions from sulfates, mineral dust and elemental carbon. Analysis of the background marine aerosol found no apparent trend since 1988. This is in contrast to results reported by Prospero et al. (J. Geophys. Res. 108 (2003) 4019) for nss-SO₄²⁻ samples from Midway Island in the North Pacific. Comparison of the mean concentrations for each site shows that the Midway samples are significantly more influenced by Asian industrial sources of sulfur, compared to Crater Lake, which implies a substantial loss of nss-SO₄²⁻ from Asian sources that occurs during transit across the Pacific to Crater Lake due to precipitation scavenging.

Keywords: Aerosols; Asian pollutants; Long-range transport

Long-term PAH accumulation after bud break in Quercus ilex L. leaves in a polluted environment by Anna Alfani; Flavia De Nicola; Giulia Maisto; Maria Vittoria Prati (pp. 307-314).

The dynamics of polycyclic aromatic hydrocarbon (PAH) concentrations in the leaves of Quercus ilex L. for 16 months after bud break (May 2001–September 2002) were studied at a polluted site in the urban area of Naples by comparison to the dynamics at a control site in the Vesuvius National Park. Twenty-seven PAHs were extracted by sonication and quantified by GC-MS. Total PAH concentrations in the leaves sampled at the urban site showed a considerable increase from bud break, with the highest values during the winter (about 3-fold greater than the initial value) and a subsequent decrease, unlike the control site. The control site exhibited PAH concentrations one order of magnitude lower than the urban site. At the urban site, the medium molecular weight PAHs, amounting to 72% of the total, appear responsible for the temporal trend, while the low and high molecular weight PAHs (respectively, 10% and 18%) exhibited only narrow variations over time. At the control site, the low, medium and high molecular weight PAHs contributed similarly to the total concentrations (32%, 31% and 37%, respectively); the low molecular weight PAHs showed the widest temporal variations. Carcinogenic PAHs showed a dynamic at the urban site comparable to that shown by the total PAHs. At the control site dibenzo( a, h)anthracene exhibited concentrations higher than at the urban site.

Keywords: Polycyclic aromatic hydrocarbons; Air contamination; PAH leaf accumulation; PAH dynamics; Carcinogenic PAHs

Reactive nitrogen oxides in the southeast United States national parks: source identification, origin, and process budget by Daniel Quansong Tong; Daiwen Kang; Viney P. Aneja; John D. Ray (pp. 315-327).

We present in this study both measurement-based and modeling analyses for elucidation of source attribution, influence areas, and process budget of reactive nitrogen oxides at two rural southeast United States sites (Great Smoky Mountains national park (GRSM) and Mammoth Cave national park (MACA)). Availability of nitrogen oxides is considered as the limiting factor to ozone production in these areas and the relative source contribution of reactive nitrogen oxides from point or mobile sources is important in understanding why these areas have high ozone. Using two independent observation-based techniques, multiple linear regression analysis and emission inventory analysis, we demonstrate that point sources contribute a minimum of 23% of total NO _y at GRSM and 27% at MACA. The influence areas for these two sites, or origins of nitrogen oxides, are investigated using trajectory-cluster analysis. The result shows that air masses from the West and Southwest sweep over GRSM most frequently, while pollutants transported from the eastern half (i.e., East, Northeast, and Southeast) have limited influence (<10% out of all air masses) on air quality at GRSM. The processes responsible for formation and removal of reactive nitrogen oxides are investigated using a comprehensive 3-D air quality model (Multiscale Air Quality SImulation Platform (MAQSIP)). The NO _y contribution associated with chemical transformations to NO _z and O₃, based on process budget analysis, is as follows: 32% and 84% for NO _z, and 26% and 80% for O₃ at GRSM and MACA, respectively. The similarity between NO _z and O₃ process budgets suggests a close association between nitrogen oxides and effective O₃ production at these rural locations.

Keywords: Nitrogen oxides; Ozone; Atmospheric chemistry; Budget analysis

Sulfur dioxide dry deposition on the loess surface–surface reaction concept for measuring dry deposition flux by Masahiro Utiyama; Tsutomu Fukuyama; Kazuhiko Sakamoto; Hidekazu Ishihara; Atsuyuki Sorimachi; Takeshi Tanonaka; Xuhui Dong; Hao Quan; Wei Wang; Dagang Tang (pp. 329-335).

As an effort to obtain more extensive data on sulfur dioxide dry deposition in northern China, experiments were carried out in Beijing by trying a new approach to the deposition flux determination. In this approach we determined the flux by a traditional concentration gradient method in the cases where the wind velocity profile conformed to the logarithmic law. In the cases outside the efficacy of the logarithmic law, in which considerable difficulty had been experienced in the traditional method, we resorted to a new concept of regarding the deposition as a reaction between sulfur dioxide and the ground surface. We introduced a mathematical model for the surface reaction, and, determining the reaction parameters on the basis of the logarithmic wind profile data, used the model to evaluate the flux in the non-logarithmic law cases. This method should enable us to obtain the dry deposition data for much more situations, including those which are difficult to be dealt with by the traditional method.

Keywords: Dry deposition; Deposition velocity; Sulfur dioxide; Surface reaction; Loess surface

An evidential example of airborne bacteria in a crowded, underground public concourse in Tokyo by Kaoruko Seino; Takehito Takano; Keiko Nakamura; Masafumi Watanabe (pp. 337-341).

We examined airborne bacteria in an underground concourse in Tokyo and investigated conditions that influenced bacterial counts. Airborne bacteria were collected by using an impactor sampler. Colonies on plate count agar (PCA) and Columbia colistin–nalidixic acid agar with 5% sheep blood (CNA agar) were enumerated. The range, geometric mean, and 95% CI of the bacterial counts (CFU m⁻³) on PCA and CNA agar were 150–1380, 456, 382–550 and 50–990, 237, 182–309, respectively. Bacterial counts on PCA significantly correlated with number of the pedestrians ( r=0.89), relative humidity ( r=0.70) and airborne dust (PM5.0) ( r=0.73). Results of a multiple regression indicated independent positive association between the number of pedestrians and bacterial counts on PCA ( p<0.01) after excluding the influence of relative humidity and airborne dust. Similar results were obtained with the statistical analysis for the counts of bacteria on CNA agar. Gram-positive cocci were dominant on PCA and CNA agar. Staphylococcus epidermidis and Micrococcus spp. were dominant among the 11 genera and 19 species identified in the present study. Considering the pattern of identified species and the significant independent association between number of pedestrians and bacterial counts, airborne bacteria in a crowded underground concourse were mostly originated from the pedestrians who were walking in the underground concourse. This study gave an evidential example of bacterial conditions in the air of an underground crowded public space in Tokyo.

Keywords: Urban health; Gram-positive bacteria; Particulate matter; Subsurface space; Field air sampling

Ambient particles at an urban, semi-urban and rural site in Central Europe: hygroscopic properties by G.A. G.A. Ferron; E. Karg; B. Busch; J. Heyder (pp. 343-352).

Measurements on hygroscopic properties of sub-micrometer atmospheric particles have been carried out using a tandem differential mobility analyser (TDMA). It measures the growth of initially dry monodisperse particles with sizes of50,100,150 and 250nm at a relative humidity (RH) of 0.85. Measurements have been carried out at an urban, semi-urban and rural location in Bavaria (Germany) each during 1 week in winter, summer and fall. Two fractions of particles are found, hygroscopic and non-hygroscopic particles with mean growth factors of 1.37 and 1.03, respectively. Growth factors are nearly independent of location and season, but increased significantly with initial particle size from 1.31 to 1.47 for 50 and 250nm particles, respectively. The mean number concentration of non-hygroscopic particles is strongly dependent on location and increases by a factor of 2.4 for the semi-urban site and by a factor of 9 for the urban site, compared to the rural location. The corresponding differences for hygroscopic particles are less than a factor of three, respectively. Individual measurements strongly differ in number concentration from each other. Assuming that the hygroscopic material is ammonium sulphate, the non-hygroscopic particles and the hygroscopic particles contain about 3% and 54% ammonium sulphate, respectively. For the hygroscopic particles the mean increase of ammonium sulphate was 38–74% for 50 and 250nm particles, respectively.

Keywords: Atmospheric particles; Hygroscopic particles; TDMA; Growth factor; Hygroscopic mass fraction

Source proximity reflected in spatial and temporal variability in particle and vapor phase Hg concentrations in Detroit, MI by Amy E. Gildemeister; Joseph Graney; Gerald J. Keeler (pp. 353-358).

Vapor-phase Hg, particulate Hg, and total suspended particulate matter were collected from 1 April 1996–31 October 1996 at two sites located in industrial areas of northeast and southwest Detroit, at a suburban residential site 2km west of Detroit, and at a rural site 60km west of Detroit as part of a larger study designed to assess the Hg cycling within the urban area. Near-source short-range transport can cause large differences in pollutant concentration and deposition within a small geographic area. Hg deposition and the resulting impact on the local environment is a result not only of the ambient concentrations present, but of the chemical form and physical properties of the pollutant. All site-to-site differences in vapor phase Hg concentration were statistically significant ( p<0.05) with mean concentrations ranging from 1.6–2.8ngm⁻³. The mean particulate Hg concentrations ranged from 12.0–54.0pgm⁻³ with concentrations at the less industrialized sites significantly lower than those at the industrialized sites ( p<0.05). Hg associated with coarse particles (diameter⩾2.5μm) had a median daily contribution of 37% to the total (range 4–68%) in south–west Detroit vs. a median daily contribution of 20% at the rural sampling site (range 6–37%).

Keywords: Urban; Local transport; Atmospheric transport; Hg; Particle phase Hg; Great Lakes; Detroit

Dust composition and mixing state inferred from airborne composition measurements during ACE-Asia C130 Flight #6 by C.H. Song; K. Maxwell-Meier; R.J. Weber; V. Kapustin; A. Clarke (pp. 359-369).

In this study ∼3.5min average bulk aerosol composition data recorded from aircraft during ACE-ASIA C130 Flight #6 are used to investigate the extent of fine particle (D_{p 50} < 1.3μm) mixing among various inorganic aerosol particle constituents. Dust-laden air masses that had mixed with urban air pollutants over the Beijing and Tianjin region were subsequently recorded in the marine boundary layer over the Yellow Sea during the ACE-ASIA mission. An analysis of correlations and molar ratios between cations and anions suggest that dust particles are largely composed of CaCO₃ (i.e., the dust particles are fresh), and that NH₄⁺ and K⁺ are likely associated with SO₄²⁻ and NO₃⁻. The results point to an external mixture of mineral dust and urban pollutant particles. Aerosol simulations carried out assuming various degrees of internal mixing (by Ca²⁺ mass) between dust and urban particles indicate the observed 2NH₄⁺–SO₄²⁻ association exists only when most of the fine-mode dust particles exist externally to SO₄²⁻. In this case, the degree of external mixing (by Ca²⁺ mass) is estimated to be larger than 70%.

Keywords: Dust mixing state; Ion association; Aerosol thermodynamic modeling; ACE-ASIA campaign

Relating plume spread to meteorology in urban areas by Akula Venkatram; Vlad Isakov; David Pankratz; Jing Yuan (pp. 371-380).

This paper examines relationships between dispersion and meteorology measured in a field study conducted in Barrio Logan, a suburb of San Diego, during 5 days of the period 21 August 2001–31 August 2001. The mean building height in Barrio Logan is about 4m. The tracer, SF₆, was released at a height of 5m from a shipyard on the shoreline, and the concentrations of the tracer were sampled on 4 arcs at 200, 500, 1000, and 2000m from the source during ten hours of the day starting at 10am. The meteorological conditions that governed dispersion were measured using sonic anemometers and a SODAR with a range of 200m in the vertical.It turned out that ground-level concentrations at the receptors used in this study were governed by the meteorological variables in the urban boundary layer above the urban roughness sublayer (RSL). In this region between 15 and 150m above ground-level, the horizontal and vertical turbulent intensities were relatively uniform. This uniformity in turbulent intensities allowed the formulation of simple expressions for horizontal and vertical plume spreads that could be used in a Gaussian dispersion model. These expressions are similar to those proposed by Briggs (ERL, ARL USAEC Report ATDL-106, U.S. Atomic Energy Commission Oak Ridge, Tennessee, 1975) and Hanna et al. (Atmos. Environ. 37 (2003) 5069) to model dispersion in St. Louis and Salt Lake City, respectively. However, the application of these dispersion curves requires information on the meteorology of the boundary layer. It might be possible to use measurements above the average building height (4m in our case) to infer these boundary layer properties.The dispersion model based on boundary layer meteorological information explained about 63% of the variance of the maximum observed concentrations on each sampling arc, and 60% of these concentrations was within a factor of two of the corresponding model estimates. It was necessary to account for initial plume spread caused by building effects to explain concentrations on the 200 and 500m arcs.

Keywords: Dispersion; Urban areas; Field experiment; Tracer study; Dispersion model; Data analysis; Barrio logan; Urban dispersion; Plume spread; Turbulent intensity

Wet and dry season ecosystem level fluxes of isoprene and monoterpenes from a southeast Asian secondary forest and rubber tree plantation by Brad Baker; J.-H. Jian-Hui Bai; Curtis Johnson; Z.-T. Zhong-Tao Cai; Q.-J. Qing-Jun Li; Y.-F. Yong-Feng Wang; Alex Guenther; Jim Greenberg; Lee Klinger; Chris Geron; Rei Rasmussen (pp. 381-390).

Canopy scale fluxes of isoprene and monoterpenes were investigated in both wet and dry seasons above a rubber tree ( Hevea brasiliensis)/secondary tropical forest in the Yunnan province of southwestern China. Drought conditions were unusually high during the dry season experiment. The eddy covariance measurement technique was used to measure isoprene fluxes, while monoterpene fluxes were modeled based on leaf level emission measurements. Maximum observed isoprene fluxes occurred during the wet season and daytime average fluxes were about 1mg Cm⁻²h⁻¹. Dry season fluxes were much lower with a daytime average of 0.15mg Cm⁻²h⁻¹. Wet season isoprene fluxes compare quite well with isoprene fluxes observed from other tropical forests. Monoterpene fluxes came, almost entirely, from Hevea brasiliensis, which is a light-dependent monoterpene emitter. Modeled wet season total monoterpene fluxes were about 2mg Cm⁻²h⁻¹ (average for the daytime), and in the dry season were undetectable. Extreme drought conditions, and the drought deciduous nature of Hevea brasiliensis may be the cause of the low dry season fluxes.

Keywords: Isoprene; Monoterpenes; Biogenic volatile organic compounds; Eddy covariance; Hevea brasiliensis

New Directions: Megacities and global change by B.R. Gurjar; J. Lelieveld (pp. 391-393).

Erratum to “Heterogeneous chemistry of individual mineral dust particles from different dust source regions: the importance of particle mineralogy�? by B.J. Krueger; V.H. Grassian; J.P. Cowin; A. Laskin (pp. 395-395).

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Atmospheric Environment (v.39, #2)