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Atmospheric Environment (v.39, #7)

Editorial board (pp. i).

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

Haagen-Smit Prize 2004 (pp. 1181-1183).

Emission of volatile organic compounds from two silver birch ( Betula pendula Roth) clones grown under ambient and elevated CO₂ and different O₃ concentrations by Terhi Vuorinen; Anne-Marja Nerg; Elina Vapaavuori; Jarmo K. Holopainen (pp. 1185-1197).

We analysed the emission of volatile organic compounds (VOCs) from two clones (4 and 80) of silver birch ( Betula pendula Roth) trees exposed to doubled ambient CO₂ and O₃ singly and in combination, in open-top chambers. VOCs were collected in July and in August from detached twigs. The effect of twig detachment as such on emissions was separately studied, and it increased the emissions of green leaf volatiles. The emission in July from both clones was dominated by sesquiterpenes (SQTs) germacrene D, ( E,E)- α-farnesene, α-copaene and β-bourbonene, while in August, the emission was dominated by monoterpenes (MTs) ( E)- β-ocimene and ( Z)-ocimene. Elevated CO₂ concentration marginally decreased total MT emission in July, while in August the total MT emission was enhanced by elevated CO₂. O₃ or CO₂+O₃-exposure did not have any effect on total MT or total SQT emissions. In general clones 4 and 80 emitted total quantified VOCs (19 compounds) 12520 and 8590ngg⁻¹ fwh⁻¹ in July, and 4640 and 4990ngg⁻¹fwh⁻¹ in August, respectively. Clone 4 emitted more β-pinene+myrcene, ( Z)-ocimene and ( E)- β-ocimene in July than clone 80, which emitted more linalool in July, and hexanal in August than clone 4. Elevated CO₂ tended to decrease the emissions of nonanal and ( E)- β-ocimene in July, while O₃ and CO₂+O₃ had no effects on emissions. Our results indicate that elevated CO₂ and O₃ concentrations do not have considerable effect on silver birch emissions by increasing the carbon allocation to VOCs or by inducing the emission of novel compounds. Other factors, such as temperature, light and herbivores might conceal the effects of these atmospheric gases. High SQT proportion in emission profile suggests that B. pendula may have substantial role in biogenic aerosol formation in boreal forests.

Keywords: Green leaf volatiles; Induced defence; Monoterpene; Sesquiterpene; VOCs

Health impacts from power plant emissions in Mexico by Lopez M.T. L�pez; M. Zuk; V. Garibay; G. Tzintzun; R. Iniestra; Fernandez A. Fern�ndez (pp. 1199-1209).

Emissions from power plant pose a potentially large risk to human health and the environment. This pollution source is of particular concern in Mexico, where a large share of electricity is generated by the burning of high-sulfur fuel oil. In this paper, we estimate the health impacts due to air pollution from one of the Mexico's largest power plants, Tuxpan, located on the eastern coast. We calculate the annual average concentrations of primary and secondary (sulfates and nitrates) particulate matter, by modeling representative periods during the year 2001 using the CALPUFF–CALMET modeling system.We find that emissions from the power plant resulted in annual average concentrations of 0.12μgm⁻³ (min–max: 0.00–1.43) for primary PM_2.5, 0.64μgm⁻³ (0.01–2.84) for secondary PM_2.5 and 3.09μgm⁻³ (0.01–41.54) for SO₂ in the 120km×120km modeling domain. Such concentrations, while mostly affecting a relatively rural area, could result in significant public health and economic impacts for the local population. It is important to consider such damages when evaluating different electricity generation and control technologies.

Keywords: Health effects; Particulate matter; Power plants; Cluster analysis; Meteorological modeling

Meteorological pattern classification and application for forecasting air pollution episode potential in a mountain-valley area by N.T. Kim Oanh; P. Chutimon; W. Ekbordin; W. Supat (pp. 1211-1225).

In this study, we developed an automated scheme to classify the synoptic meteorological conditions governing over the northern Thailand during the winter period (November–January) into six-synoptic patterns representing different development stages of the regional pressure system. The meteorological classification scheme is hybrid in nature combining the air mass and the flow pattern based approaches. The classification is done though the principal component analysis of data from six regional surface meteorological stations and one upper-air station at 01:00 Thailand Local Standard Time daily for 5-year winter periods, which is followed by a two-stage clustering technique. Examination of the SO₂ pollution levels in the complicated terrain of the Mae Moh valley in the northern Thailand, where a coal-fired power plant is located, shows that the scheme successfully identifies the patterns that are conducive to high pollutant and those that are conducive to low pollutant build up in the valley. Levels and spatial distributions of the daily highest 1-h SO₂ concentrations in the valley exhibited similar characteristics within each pattern, and distinct differences between the six-synoptic patterns. The scheme is recommended for the early warning of the episode potentials in the valley. The stepwise regression was performed to develop prediction models for the two most polluted synoptic patterns, which have high frequencies of exceeding the National Ambient Air Quality Standards. The regression equations haveR2 values above 60% and produce the daily highest 1-h SO₂ concentrations with average relative errors of around 33%.

Keywords: Automated meteorological classification; Synoptic climatological approach; Episode potential; Mountain-valley terrain; Thailand

The 23rd October 2002 dust storm in eastern Australia: characteristics and meteorological conditions by Grant McTainsh; Y.-c. Yiu-chung Chan; Hamish McGowan; John Leys; Kenn Tews (pp. 1227-1236).

The dust storm of 23 October 2002 covered most of eastern Australia and carried one of the largest recorded dust loads in Australia. In the 6 months leading up to the event, severe drought conditions in eastern Australia, plus above average maximum temperatures resulted in high potential evapo-transpiration rates, producing severe soil moisture deficits and reduced vegetation cover. Although increased wind speeds associated with a fast moving cold front were the meteorological driving force, these winds speeds were lower than those for the previously documented large dust storms. The dust storm was 2400km long, up to 400km across and 1.5–2.5km in height. The plume area was estimated at 840,860km² and the dust load at 0900h was 3.35–4.85 million tones (Mt). These dust load estimates are highly sensitive to assumptions, regarding visibility–dust concentration relationships, vertical dust concentration profiles and dust ceilings. The event is examined using meteorological records, remote sensing and air quality monitoring.

Keywords: Aeolian dust; Dust storm; Wind erosion; Australia

Physical characteristics of dust aerosol over Hunshan Dake sandland in Northern China by Tiantao Cheng; Daren Lu; Hongbin Chen; Yongfu Xu (pp. 1237-1243).

Physical characteristics of dust aerosol were determined for samples collected from Hunshan Dake sandland of China in spring 2001. Number concentration and size distributions of particles with0.5−3 on heavy dusty days and 31.4cm⁻³ on non-dusty days. The maximum of aerosol number concentration was 5776.2cm⁻³. The particles withDp<8.0μm accounted for over 90% of total aerosol number loading. With aerosol number concentration increasing the ratio of super-micron particles to total particles in per unit cubic volume gradually rose, but the ratio of sub-micron particles to total particles reduced. The particle size distributions of aerosols were characterized by bi-modal logarithm normal function in heavy and moderately dusty days, and mono-modal in windblown and non-dusty days.

Keywords: Dust aerosol; Aerosol number concentration; Particle size distributions

A lead isotope record of shanghai atmospheric lead emissions in total suspended particles during the period of phasing out of leaded gasoline by Jianmin Chen; Mingguang Tan; Yulan Li; Yuanmao Zhang; Wenwei Lu; Yongpeng Tong; Guilin Zhang; Yan Li (pp. 1245-1253).

The concentrations of lead as well as the stable lead isotope ratios were measured in the total suspended particles (TSP), collected at three monitoring sites in Shanghai, China, since 1995 ranging the period of phasing out of leaded gasoline. During all these years, the variation of lead concentrations in TSP showed the feature of site- dependence. In the traditionally industrial area of YangPu district, the concentrations were sometimes extremely high and did not have temporal correlation. In the other residential areas, the concentrations dropped quite a lot, but were still highly above the average contents of other counterpart cities in the world. The analysis of stable lead isotope ratios showed that lead isotopic composition in YangPu district varied much and changed randomly with time, while in Huangpu and PuTuo districts, the value of²⁰⁷Pb/²⁰⁶Pb dropped significantly from 0.872�0.002 to 0.861�0.002. Combined with the data of lead contents and isotopic compositions of source-related samples, such as cements, coals, coal fly ashes, metallurgic dusts, oil combustion dusts, gasoline samples and soils, it was indicated that contribution from lead additives to airborne lead pollution in Shanghai was less than 30% in the time when leaded gasoline was used. However, stationary emission was always a dominant source in Shanghai, and the primary component of lead was believed to be contributed by the vast combustion of lead-containing coal emitted mainly by industrial activities all these years.

Keywords: Lead isotope ratio; ICP-MS; Gasoline; Coal combustion; Metallurgic dust

Validation of a 2D model using observed profiles ofSF6 with main focus on the tropics by Varun Sheel; Shyam Lal; Christoph Br�hl (pp. 1255-1261).

Sulfur hexafluoride(SF6) is a useful tracer to test the transport behavior of atmospheric models. There have been few measurements of the vertical distribution ofSF6 especially in the tropics, which have restricted the validation of vertical transport in two-dimensional (2D) global models. In an attempt to fill this void, we have used a 2D model in a transient mode to compare the calculated vertical distributions ofSF6 with observations. The gross feature of the simulated vertical profiles compares well with the observations particularly in the tropics. Comparisons with UARS/HALOECH4-data show that the sharp vertical gradient above the tropopause and the extremely weak gradient above 25km in the observations in India are due to the quasi biannual oscillation (QBO). The QBO is not taken into account in the model dynamics but in average between its west and east phase vertical profiles are represented well by the model. We also confirm that globalSF6 source emissions should be distributed on the model grid proportional to electrical power usage.

Keywords: Sulfur hexafluoride; 2D model; Vertical profile; Tropics

A lumping model for composition- and temperature-dependent partitioning of secondary organic aerosols by Fei Bian; Frank M. Bowman (pp. 1263-1274).

An improved lumping model is described for converting multiple semivolatile organic aerosol components into one or more lumped groups that can represent the organic aerosol mixture in atmospheric models. Lumping equations to calculate temperature- and composition-dependent absorption partitioning parameters are presented, together with lumping criteria for dividing components into groups based on component vapor pressure, chemical structure, and activity coefficient in water. Lumping performance of the model is evaluated using a base case mixture of organic aerosol components, random mixtures selected from a set of identified semivolatile organic compounds, and products from the α-pinene/ozone reaction. Modeling results show that aerosol composition has a strong influence on SOA partitioning and lumping accuracy. Comparisons of different lumping criteria suggest that lumping components by a combination of vapor pressure and water interactions or by vapor pressure alone will produce optimum results.

Keywords: Secondary organic aerosol; Partitioning; Lumping; Composition dependence; Modeling

A year of continuous measurements of three atmospheric mercury species (GEM, RGM and Hg_p) in southern Qu�bec, Canada by Laurier Poissant; Martin Pilote; Conrad Beauvais; Philippe Constant; Hong H. Zhang (pp. 1275-1287).

An intensive field campaign was conducted from 1 January to 31 December 2003 in St. Anicet (Québec, Canada) using a set of Automatic Atmospheric Mercury Speciation Analyzers (Tekran 2537A with 1130 and 1135 units) for the measurements of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (Hg_p). This study is one of the first attempts to present the most extensive data sets of a year of continuous measurements of atmospheric mercury species. Average concentrations of GEM, RGM and Hg_p in 2003 were 1.65±0.42ngm⁻³, 3±11 and 26±54pgm⁻³ (mean±SD), respectively. On an average, the atmospheric mercury apportioned as follows: GEM (98.4%)>Hg_p (1.4%)>RGM (0.2%). Regional atmospheric mercury sources contributed to the Southern Québec atmospheric mercury contamination. The results showed large seasonality of GEM, RGM and Hg_p (GEM: 0.37–10.4ngm⁻³; RGM: 0–386pgm⁻³ and Hg_p: 0–1528pgm⁻³). As a whole, mercury speciation concentrations are larger in wintertime than in summertime. RGM and Hg_p concentrations showed the sharpest seasonal variations. Hourly variations were observed for the mercury species. Maximum RGM and Hg_p concentrations were measured normally during mid-day with a Gaussian shape whereas GEM showed a bimodal shape with minimum values early in the morning. The backward trajectory model showed that atmospheric mercury speciation might be transported from local or regional sources. Also, it was observed that atmospheric mercury transformation times converting GEM to Hg_p were short (∼4h). However, atmospheric kinetics involving O₃ and OH radicals do not support such fast oxidation processes with normal concentrations.

Keywords: Atmospheric mercury speciation; GEM; RGM; Hg; _p; Oxidation; Lifetime

A mechanism for bimodal emission of gaseous mercury from aquatic macrophytes by Steve E. Lindberg; Weijin Dong; Jeff Chanton; Robert G. Qualls; Tilden Meyers (pp. 1289-1301).

We performed intensive sampling campaigns of Hg⁰ fluxes over emergent macrophytes in the Florida Everglades to find a surrogate for Hg fluxes from water and vegetation to identify the mechanisms of emission. We measured daytime lacunal and sediment gas concentrations of Hg⁰, which suggested that the lacunal space acts as temporary storage for Hg⁰ and CH₄. The absence of detectable Hg⁰ fluxes measured over uprooted (floating) plants and sediment incubation experiments suggest that the Hg⁰ emitted from emergent macrophytes such as Typha and Cladium originates in the sediment. HgII in the rhizosphere is reduced to Hg⁰ in these sediments by various processes, and is then transported by the plants to the atmosphere by two separate processes. At night, Hg⁰ and CH₄ formed in the sediment accumulate in the lacunal space after crossing the root-sediment barrier. At sunrise, a form of pressurized through-flow purges the lacunal space of Typha into the atmosphere forming an early morning emission pulse for both gases, and coincidental peaks of CH₄ and Hg⁰ suggest that the same lacunal gas transport mechanism is involved. Later in the day while the release of methane continues to deplete the lacunal pool, the Hg⁰ flux increases again to form a second peak in the afternoon when the CH₄ emission has decreased. This peak parallels that of transpiration, and is presumably due to xylem transport of Hg⁰ from continued production of Hg⁰ in the rhizosphere, perhaps in response to release of root exudates. A mass balance for this ∼1500ha wetland suggested that the total transpiration of Hg⁰ is ∼1kgyr⁻¹, or ∼20 times the amount evaded from the water surface.

Keywords: Everglades; Methane; Typha domingensis; Cladium jamaicense; Fluxes

Evaluation of isoprene degradation in the detailed tropospheric chemical mechanism, MCM v3, using environmental chamber data by P.G. Pinho; C.A. Pio; M.E. Jenkin (pp. 1303-1322).

The isoprene degradation mechanism included in version 3 of the Master Chemical Mechanism (MCM v3) has been evaluated and refined, using the Statewide Air Pollution Research Center (SAPRC) environmental chamber datasets on the photo-oxidation of isoprene and its degradation products, methacrolein (MACR) and methylvinyl ketone (MVK). Prior to this, the MCM v3 butane degradation chemistry was also evaluated using chamber data on the photo-oxidation of butane, and its degradation products, methylethyl ketone (MEK), acetaldehyde (CH₃CHO) and formaldehyde (HCHO), in conjunction with an initial evaluation of the chamber-dependent auxiliary mechanisms for the series of relevant chambers. The MCM v3 mechanisms for both isoprene and butane generally performed well and were found to provide an acceptable reaction framework for describing the NO _x-photo-oxidation experiments on the above systems, although a number of parameter modifications and refinements were identified which resulted in an improved performance. All these relate to the magnitude of sources of free radicals from organic chemical process, such as carbonyl photolysis rates and the yields of radicals from the reactions of O₃ with unsaturated oxygenates, and specific recommendations are made for refinements. In addition to this, it was necessary to include a representation of the reactions of O(³P) with isoprene, MACR and MVK (which were not previously treated in MCM v3), and conclusions are drawn concerning the required extent of free radical formation from these reactions. Throughout the study, the performance of MCM v3 was also compared with that of the SAPRC-99 mechanism, which was developed and optimized in conjunction with the chamber datasets.

Keywords: VOC oxidation; Butane; Formaldehyde; Acetaldehyde; Methylethyl ketone; Isoprene; Methacrolein; Methylvinyl ketone; Tropospheric chemistry; Degradation mechanisms; Environmental chamber data; Ozone modelling

Source apportionment based on an atmospheric dispersion model and multiple linear regression analysis by Akihiro Fushimi; Hiroto Kawashima; Hideo Kajihara (pp. 1323-1334).

Understanding the contribution of each emission source of air pollutants to ambient concentrations is important to establish effective measures for risk reduction. We have developed a source apportionment method based on an atmospheric dispersion model and multiple linear regression analysis (MLR) in conjunction with ambient concentrations simultaneously measured at points in a grid network. We used a Gaussian plume dispersion model developed by the US Environmental Protection Agency called the Industrial Source Complex model (ISC) in the method. Our method does not require emission amounts or source profiles. The method was applied to the case of benzene in the vicinity of the Keiyo Central Coastal Industrial Complex (KCCIC), one of the biggest industrial complexes in Japan. Benzene concentrations were simultaneously measured from December 2001 to July 2002 at sites in a grid network established in the KCCIC and the surrounding residential area. The method was used to estimate benzene emissions from the factories in the KCCIC and from automobiles along a section of a road, and then the annual average contribution of the KCCIC to the ambient concentrations was estimated based on the estimated emissions. The estimated contributions of the KCCIC were 65% inside the complex, 49% at 0.5-km sites, 35% at 1.5-km sites, 20% at 3.3-km sites, and 9% at a 5.6-km site. The estimated concentrations agreed well with the measured values. The estimated emissions from the factories and the road were slightly larger than those reported in the first Pollutant Release and Transfer Register (PRTR). These results support the reliability of our method. This method can be applied to other chemicals or regions to achieve reasonable source apportionments.

Keywords: Benzene; Air pollutants; Industrial complex; Industrial source complex model (ISC); Receptor model

Modelling of diesel exhaust aerosol during laboratory sampling by Elias Vouitsis; Leonidas Ntziachristos; Zissis Samaras (pp. 1335-1345).

A modelling approach which applies fundamental mechanisms of aerosol formation and dynamics to simulate the effect of sampling conditions on exhaust particle distributions is presented. The model examines the evolution of exhaust aerosol immediately after its mixing with dilution air, which is assumed to occur adiabatically and instantaneously. Particle number and mass balances are expressed separately for two aerosol modes: the nucleation mode (mean diameter <30nm) and the accumulation mode (>30nm). The number and mass balances include homogeneous nucleation, condensation on existing particles, intra- and inter-mode coagulation and diffusional losses to the walls. The model takes into account the sulphuric acid–water system and a heavy (C₁₆) hydrocarbon in diesel exhaust. First, it is shown that the number concentration of the nucleation mode can be described if a barrierless nucleation is assumed for the sulphuric acid. At a second step, it is computationally demonstrated that the measured volume concentration in the nucleation mode can only be reached, if hydrocarbon condensation occurs on the sulphuric acid–water nuclei. Finally, it is shown that the nucleation mode is significantly suppressed by the presence of soot mode, due to the high surface area of the latter, which consumes volatile species. The model may be used to estimate the effect of sampling conditions on exhaust particle size distributions, with emphasis on the nucleation mode profiles.

Keywords: Particle; Particulate matter; Nucleation; Condensation; Coagulation

Reliability of a BTEX radial diffusive sampler for thermal desorption: field measurements by P. Bruno; M. Caputi; M. Caselli; G. de Gennaro; M. de Rienzo (pp. 1347-1355).

Radiello^�, a radial symmetry diffusive sampler, has been evaluated for its potential for ambient air quality monitoring, in particular for benzene, toluene, ethyl benzene, p-xylene, m-xylene, o-xylene (BTEX) measurements. BTEX were first sampled onto adsorbing cartridges before analyses were performed by thermal desorption and GC-MS. Tests were carried out to determine blank values and any storage effects. The results of an investigation into repeatability of the Radiello^� sampler and the influence of sampling time under field conditions are reported. Inter-comparison with automatic instruments is also illustrated.

Keywords: BTEX (benzene, toluene, ethyl benzene,; p; -xylene,; m; -xylene,; o; -xylene); Radial symmetry diffusive sampler; Thermal desorption; Atmospheric pollution

Relative contribution of chemical composition to acidification of sea fog (stratus) over the northern North Pacific and its marginal seas by Motoki Sasakawa; Mitsuo Uematsu (pp. 1357-1362).

We collected sea fog (stratus), cloud forming a continuous horizontal gray sheet, over the northern North Pacific and its marginal seas (Sea of Japan, Sea of Okhotsk, and Bering Sea) in late spring through summer from 1998 to 2001. Non-sea-salt component occupies maximum 54% of ion in fog water, and hence sea fog waters are usually acidified over a wide region of the seas which is far from the anthropogenic emission sources on land. Both nss-SO₄²⁻ and H⁺ mainly contribute to the non-sea-salt fraction. The ratios of MSA/Na⁺ in rain waters range from 0.00051 to 0.0046. In contrast, the regional mean ratios in fog water range from 0.0042 to 0.16. Sea fog scavenges MSA aerosol produced from the oxidation of DMS more effectively than rain. We characterize the typical chemical composition of sea fog, and find that each region has specific character in the relationship between acidifying potential (AP=[nss-SO₄²⁻]+[NO₃⁻]) and neutralizing potential (NP=[NH₄⁺]+[nss-Ca²⁺]), which relationship leads to the illumination for the acidification process.

Keywords: Low cloud droplet; Ionic concentration; Northern North Pacific; Sea of Okhotsk; MSA

Intake fraction of nonreactive vehicle emissions in US urban areas by Julian D. Marshall; S.-K. Soon-Kay Teoh; William W. Nazaroff (pp. 1363-1371).

Intake fraction, which is the fraction of emissions that are inhaled by people, quantifies the “exposure efficiency�? of an emission source. We use three methods to estimate intake fractions for vehicle emissions in US urban areas. First, we use a one-compartment steady-state mass-balance model, incorporating meteorological and demographic data. Second, we use an empirical emissions-to-concentration relationship for vehicle carbon monoxide developed for 15 US urban areas. Third, we analyze model results for benzene and diesel particulate matter from the US Environmental Protection Agency's National-scale Air Toxics Assessment (NATA). The population-weighted mean intraurban intake fraction for nonreactive gaseous vehicle emissions in US urban areas is estimated to be in the range 7–21 per million, with a best estimate of 14 per million. The intake fraction for diesel particles is 4 per million, based on NATA results. An intake fraction of 4 per million means that 4mg of pollution are inhaled per kg emitted. Intake fraction values for urban vehicle emissions are usually higher in winter than in summer because of seasonal variability in the atmospheric mixing height. The results presented in this work can be used in health risk assessments, cost–benefit analyses, and other investigations that require a summary of the emission-to-intake relationship.

Keywords: Automobiles; Benzene; Box model; Carbon monoxide; Diesel particulate matter; Exposure; National-scale Air Toxics Assessment; One-compartment model

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Atmospheric Environment (v.39, #7)