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Atmospheric Environment (v.41, #11)

Editorial board (pp. i).

A land use regression for predicting fine particulate matter concentrations in the New York City region by Zev Ross; Michael Jerrett; Kazuhiko Ito; Barbara Tempalski; George D. Thurston (pp. 2255-2269).

We developed regression equations to predict fine particulate matter (PM_2.5) at air monitoring locations in the New York City region using data on nearby traffic and land use patterns. Three-year averages (1999–2001) of PM_2.5 at US Environmental Protection Agency (EPA) monitors in the 28 counties including and surrounding New York City were calculated using daily data from the EPA's Air Quality Subsystem. As the secondary contribution to PM_2.5 concentrations is lowest in the winter, we also calculated and modeled average winter 2000 PM_2.5 to conduct a preliminary evaluation of model sensitivity to source contribution. Candidate predictor variables included traffic, land use, census and emissions data from local, state and national sources and were tabulated for a series of circular buffer regions at varying distances around the monitors using a geographic information system. In total, more than 25 variables at 5 different buffer distances were considered for inclusion in the model. Before evaluating the variables we removed several samples from the modeling for validation. For comparison and validation purposes we computed both a model using data for the full 28-county region as well as a more urbanized 9-county region. We found that traffic within a buffer of 300 or 500m explains the greatest proportion of variance (37–44%) in all 3 models. Measures of urbanization, specifically population density, explain a significant amount of the residual variation (7–18%) after including a traffic variable. Finally, a measure of industrial land use further improves the 28-county and 9-county models based on the 3-yr annual averages, explaining an additional 4% and 11% of the variation, respectively, while vegetative land use improves the winter model explaining an additional 6%. The final models predicted well at validation locations. In total, the final land use regression models explain between 61% and 64% of the variation in PM_2.5.

Keywords: Land use regression; Particulate matter; New York; Traffic; Exposure

Measurements of GEM fluxes and atmospheric mercury concentrations (GEM, RGM and Hg^p) from an agricultural field amended with biosolids in Southern Ont., Canada (October 2004–November 2004) by Frank D. Cobbett; Bill J. Van Heyst (pp. 2270-2282).

Five weeks of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle bound mercury (Hg^p) concentrations as well as fluxes of GEM were measured at Maryhill, Ontario, Canada above a biosolids amended field. The study occurred during the autumn of 2004 (October–November) to capture the effects of cool weather conditions on the behaviour of mercury in the atmosphere. The initial concentration of total mercury (Hg) in the amended soil was relatively low (0.4μgg⁻¹±10%).A micrometeorological approach was used to infer the flux of GEM using a continuous two-level sampling system with inlets at 0.40 and 1.25m above the soil surface to measure the GEM concentration gradient. The required turbulent transfer coefficients were derived from meteorological parameters measured on site. The average GEM flux over the study was 0.1±0.2ngm⁻²h⁻¹(±one standard deviation). The highest averaged hourly GEM fluxes occurred when the averaged net radiation was highest, although the slight diurnal patterns observed were not statistically significant for the complete flux data series. GEM emission fluxes responded to various local events including the passage of a cold front when the flux increased to 2ngm⁻²h⁻¹ and during a biosolids application event at an adjacent field when depositional fluxes peaked at −3ngm⁻²h⁻¹. Three substantial rain events during the study kept the surface soil moisture near field capacity and only slightly increased the GEM flux. Average concentrations of RGM (2.3±3.0pgm⁻³), Hg^p (3.0±6.2pgm⁻³) and GEM (1.8±0.2ngm⁻³) remained relatively constant throughout the study except when specific local events resulted in elevated concentrations. The application of biosolids to an adjacent field produced large increases in Hg^p (25.8pgm⁻³) and RGM (21.7pgm⁻³) concentrations only when the wind aligned to impact the experimental equipment. Harvest events (corn) in adjacent fields also corresponded to higher concentrations of GEM and Hg^p but with no elevated peaks in RGM concentrations. Diurnal patterns were not statistically significant for RGM and Hg^p at Maryhill.

Keywords: Agriculture; Biosolid; Elemental mercury; Flux gradient; Micrometeorology; Particle bound mercury; Reactive gaseous mercury

Improving pollutant source characterization by better estimating wind direction with a genetic algorithm by Christopher T. Allen; George S. Young; Sue Ellen Haupt (pp. 2283-2289).

In homeland security applications, it is often necessary to characterize the source location and strength of a potentially harmful contaminant. Correct source characterization requires accurate meteorological data such as wind direction. Unfortunately, available meteorological data is often inaccurate or unrepresentative, having insufficient spatial and temporal resolution for precise modeling of pollutant dispersion. To address this issue, a method is presented that simultaneously determines the surface wind direction and the pollutant source characteristics. This method compares monitored receptor data to pollutant dispersion model output and uses a genetic algorithm (GA) to find the combination of source location, source strength, and surface wind direction that best matches the dispersion model output to the receptor data. A GA optimizes variables using principles from genetics and evolution.The approach is validated with an identical twin experiment using synthetic receptor data and a Gaussian plume equation as the dispersion model. Given sufficient receptor data, the GA is able to reproduce the wind direction, source location, and source strength. Additional runs incorporating white noise into the receptor data to simulate real-world variability demonstrate that the GA is still capable of computing the correct solution, as long as the magnitude of the noise does not exceed that of the receptor data.

Keywords: Source characterization; Dispersion model; Genetic algorithm; Wind data uncertainty; Data assimilation

Reference values for structure emissions measured on site in new residential buildings in Finland by Jarnstrom H. Järnström; K. Saarela; P. Kalliokoski; A.-L. Pasanen (pp. 2290-2302).

A 3-year research project was established in 1999 to create numerical reference data for material emissions during the time of construction and during the first year. Seven buildings, representing the present construction practice in Finland, were investigated. Material emissions were measured by using the field and laboratory cell (FLEC) during the time of construction, in the newly finished, and in the 6- and 12-month-old buildings. The emission rates for volatile organic compounds (VOCs), formaldehyde, and ammonia were determined.The highest total VOCs (TVOC) emissions were measured in the newly finished buildings from the ceiling structure and from some of the PVC floor coverings. These emissions were up to 1300–2000μgm⁻²h⁻¹. Individual VOCs with emission rates above 50μgm⁻²h⁻¹ included 2-(2-butoxyethoxy) ethanol and its acetate, C4–C16-substituted alkylbenzenes, and xylenes. The mean TVOC emission decreased at least to the Finnish M1-class level (200μgm⁻²h⁻¹) from all surfaces and in all the buildings in 6–12 months. The ammonia and formaldehyde emissions from the ceiling structure were 20–60μgm⁻²h⁻¹ in the newly finished buildings and the M1-levels (30/50μgm⁻²h⁻¹) were exceeded in some cases. These emissions even increased in some buildings during the follow-up period indicating the difference between emissions measured in the laboratory and on site from real structures. Reference values based on the means and 95th percentile are presented to be utilised in both quality control and while investigating indoor air quality problems which are suspected to be caused by a defect structure.

Keywords: Material emission; VOC; Ammonia; Formaldehyde; Reference value

Chemical segregation by heterogeneous emissions by L. Ludovic Auger; B. Bernard Legras (pp. 2303-2318).

Ozone pollution in the boundary layer results from photoactivated chemistry of primary pollutants released at the ground. As emissions are highly inhomogeneous in space and time and some chemical time-scales are of the order or larger than dynamical time-scales, it is admitted that turbulent transport and mixing is a key factor in ozone production. We study the interaction between chemistry and convective boundary layer turbulent with a large eddy simulation model coupled to CHIMERE, a detailed chemical model, over a10×10km domain. Our results show that when emissions are concentrated over a limited area, strong values of segregation between chemical species are obtained over the first two active hours during the morning, leading to significant impact in terms of pollutants concentration. After 3h, for each heterogeneous emission case considered, segregation drops to a few percents for most compounds pairs, due to the strong convective mixing of the boundary layer.

Keywords: Atmospheric chemistry; LES; Boundary layer; Segregation; Turbulence

An online coupled meteorological and air quality modeling study of the effect of complex terrain on the regional transport and transformation of air pollutants over the Western United States by Dongchul Kim; William R. Stockwell (pp. 2319-2334).

One of the most prominent of characteristics of the western United States that affects its meteorology is the complexity of its mountainous terrain. The meteorological Mesoscale Model, version 5 with Chemistry (MM5-Chem), an online-coupled atmospheric chemistry model, was used to investigate the effect of this terrain on a high air pollution event in the free troposphere. The simulations were evaluated by comparisons with data from the North American Regional Reanalysis (NARR). Complex terrain was shown to have an important influence on the vertical transport of air pollutants on the regional scale; emissions from ground level were vertically mixed as high as 5km above sea surface level for the wintertime conditions simulated. The simulations showed that the vertical transport of emissions from the Earth's surface could have a more significant effect on mid and upper level chemical concentrations than chemical production. The vertical transport was caused predominately by terrain forced flow over the mountains’ ridge-line and the terrain forced flow was affected by the mountain peak height and the complexity of the terrain downwind.

Keywords: Meteorology; Air pollution; Vertical transport; Regional transport; Complex terrain; Online coupled models

On the errors associated with the use of hourly data in wind-driven rain calculations on building facades by Bert Blocken; Jan Carmeliet (pp. 2335-2343).

Wind-driven rain (WDR) is the one of the main moisture sources for building facades. It is an important factor in the dry and wet deposition of pollutants, facade surface soiling and facade erosion. WDR calculations require data records of wind speed, wind direction and horizontal rainfall intensity as input. Most meteorological datasets contain at best arithmetically averaged hourly wind and rain data. Their use is common practice in WDR calculations. As an example, existing WDR standards request at best hourly data. This paper however demonstrates that the use of such data can yield (very) large errors in the calculated WDR amounts and intensities. The reason is that arithmetic averaging on an hourly basis generally causes an important loss of information about the co-occurrence of wind and rain. An improved data averaging technique for wind and rain data is proposed that respects this co-occurrence by applying appropriate weighting factors in the averaging procedure. The performance of this technique is evaluated by WDR calculations on buildings in three cities with different climates. While arithmetically averaged hourly data yield large underestimation errors (Eindhoven, The Netherlands: 11%, Bloomington, USA: 45%, Grahamstown, South Africa: 31%), the improved averaging technique provides very good results (errors: 0%, 4%, 3%, respectively). In conclusion, WDR calculations should not be performed with arithmetically averaged hourly data. Instead, either high-resolution data (e.g. 10-min data) or hourly data that have been obtained with the proposed weighted averaging technique should be used.

Keywords: Driving rain; Building; Error; Time resolution; Climatic data; Data averaging

Control of volatile organic compounds indoors—Development of an integrated mass-transfer-based model and its application by Feng Li; Jianlei Niu (pp. 2344-2354).

Building envelopes are usually comprised of several different layers of building materials, which may alternatively act as VOC sources or sinks depending on their emission and sorption potentials and the indoor environmental conditions as well. In this research, a whole room IAQ model consisting of multi-phase emission/sorption model for wall materials and room volume mass balance model catering for practical ventilation schemes was developed. The interactions of VOC and building materials composing different building components can be modeled based on fundamental mass transfer theories. The effects of various construction materials and ventilation strategies on the emission characteristics were investigated. Results show that measures like pre-occupancy flush-out, lead-time ventilation, etc. have substantial impacts on indoor VOC concentration and the model can successfully handle different building scenarios. Although more rigorous validation, in particular more experimental verification, is needed, the proposed model has proven to be valuable in handling different building scenarios. It is useful in analyzing the levels of contaminant buildup that would occur during no ventilation period for intermittent ventilation situations and in determining the amount of outdoor air and the lead-time period required to flush out the contaminants prior to occupancy. It is likely to be a simple routine tool for building owners, designers and operators to attain acceptable indoor VOC concentration level.

Keywords: Indoor air quality; Building material; Emission; Sorption; Diffusion; Ventilation

Modelling the atmospheric transport and deposition of sulphur and nitrogen over the United Kingdom and assessment of the influence of SO₂ emissions from international shipping by A.J. Dore; M. Vieno; Y.S. Tang; U. Dragosits; A. Dosio; K.J. Weston; M.A. Sutton (pp. 2355-2367).

A statistical Lagrangian atmospheric transport model was used to generate annual maps of deposition of sulphur and oxidised and reduced nitrogen for the UK at a 5×5km² resolution. The model was run using emissions for the year 2002. The model was compared with measurements of gas concentrations (SO₂, NO _x, HNO₃ and NH₃) and of wet deposition and aerosol concentrations of SO₄²⁻, NO₃⁻ and NH₄⁺ from national monitoring networks. Good correlation was obtained, demonstrating that the model is capable of accurately estimating the mass balance and spatial distribution of sulphur and nitrogen compounds in the atmosphere. A future emissions scenario for the year 2020 was used to test the influence of shipping emissions on sulphur deposition in the UK. The results show that, if shipping emissions are assumed to increase at a rate of 2.5% per year, their relative contribution to sulphur deposition is expected to increase from 9% to 28% between 2002 and 2020. The model was compared to both a European scale and a global scale chemical transport model and found to give broad agreement with the magnitude and location of sulphur deposition associated with shipping emissions. Enforcement of the MARPOL convention to reduce the sulphur content in marine fuel to 1% was estimated to result in a 6% reduction in total sulphur deposition to the UK for the year 2020. The percentage area of sensitive habitats with exceedance of critical loads for acidity in the UK was predicted to decrease by 1% with the implementation of the MARPOL convention.

Keywords: Atmospheric transport model; Acidification; Shipping; Sulphur; Nitrogen; Ammonia

Size distribution and sources of trace metals and n-alkanes in the Athens urban aerosol during summer by A.A. Karanasiou; I.E. Sitaras; P.A. Siskos; K. Eleftheriadis (pp. 2368-2381).

Size-resolved, 24-h aerosol samples were collected from June–July 2001 by means of an Andersen high-volume cascade impactor. Sampling was conducted in a central avenue (Patission) characterised by heavy traffic, 21m above street level, in the Athens city centre. Samples were analysed by atomic absorption spectrometry and gas chromatography to determine the size distribution of nine metallic elements (Cd, Pb, V, Ni, Mn, Cr, Cu, Fe, Al) and n-alkanes (with carbon numbers in the range 18–35). The aerosol mass median diameter (MMD) was calculated by means of probit analysis on the cumulative mass concentration size distribution for each metals and n-alkane. The total n-alkane mass concentration (TNA) in total suspended particles (TSP) ranged from 72 to 1506ngm⁻³ while the total metal concentration ranged from 5.6 to 28.6μgm⁻³. The results showed that metals such as Cd, V and Ni are characterised by a MMD <1μm, while the MMD for Pb and Mn are ∼1μm. Such metals are generally considered to have anthropogenic emission sources. Other metals such as Al, Fe, Cu and Cr were found to have MMD=2–6μm, which generally originate from soil dust or mechanical abrasion processes. The Carbon number profile of n-alkane compounds showed a strong anthropogenic source with only a minor biogenic influence. The concentration of most n-alkanes was characterised by high variability during the sampling period, in contrast to the concentration of most trace metals. Most n-alkanes had a unimodal size distribution with MMD=1–2μm similar to those of some trace metals (Pb, Mn), which originate mostly from vehicle emissions. This is a strong indication that these species have a common source. Finally, gas–particle partitioning of n-alkanes was also examined for different particle sizes by means of the relationship between the partition constant K_p and saturation vapour pressure ( p_L⁰) as proposed by current sorption models.

Keywords: Mass median aerodynamic diameter; Trace metals; n; -alkanes; Size distribution; Motor vehicle emissions; Coarse/fine aerosol

Nitrogen isotopes: Tracers of origin and processes affecting PM₁₀ in the atmosphere of Paris by David Widory (pp. 2382-2390).

Nitrogen in atmospheric particles in an urban environment is the result of complex primary and secondary processes, which renders identifying its origin somewhat complicated. Using the example of PM₁₀ in the atmosphere of Paris (France), it is shown that the use of stable nitrogen-isotope compositions ( δ¹⁵N) alleviates this difficulty and provides clear information on the sources of primary and possibly of secondary nitrogen. Characterization of emissions of the different types of emitters in the city (road traffic, waste incinerators and heating sources) shows that these are clearly discriminated by specific isotope signatures. δ¹⁵N is particularly useful in showing that a substantial portion of the nitrogen is the result of secondary reactions, reactions that are different in summer and winter, as are the corresponding pollution sources. While it is unclear, among point sources, what the winter source of primary nitrogen is, road traffic appear to be the source of primary nitrogen in summer. Identification of the sources of the secondary nitrogen strongly depends on the nitrogen isotope fractionations ( Δ¹⁵N) associated to atmospheric conversion of NO _x to nitrate, but hypothesises presented here hint at the possible corresponding pollution sources.

Keywords: Air pollution; δ; ¹⁵; N; Post-combustion process

Greenhouse gas emissions from swine barns of various production stages in suburban Beijing, China by H. Dong; Z. Zhu; B. Shang; G. Kang; H. Zhu; H. Xin (pp. 2391-2399).

Gaseous emissions from animal feeding operations may be influenced by production stage, genetics, dietary type and nutritional plan, housing type, manure handling schemes, and climatic conditions. This study was conducted to quantify annual emission rates (ERs) of greenhouse gases (GHGs)—methane (CH₄), carbon dioxide (CO₂) and nitrous oxide (N₂O) from naturally ventilated swine gestation (GE), farrowing (FA), nursery (NU) and growing-finishing (GF) barns under typical operational conditions in suburban Beijing, China. Variables relative to the GHG ERs were measured every two months for a one-year period, with each measurement episode lasting 72h. Air exchange rate of the naturally ventilated barns was estimated using CO₂ balance method. The annual mean daily GHG ERs (mean± SD), expressed ingd-1AU-1(AU=animal unit=500 live body weight), for the GE, FA, NU, and GF barns were, respectively,5920±440,7490±110,29670±1090 and16730±1060 for CO₂;9.6±1.9,9.6±3.6,58.4±21.8 and32.1±11.7 for CH₄; and0.75±0.56,0.54±0.15,1.29±0.37 and0.86±0.75 for N₂O. The GHG ER values from the current study paralleled those reported in the literature in some cases but differed considerably in other cases. This outcome of similarity and disparity confirms the need to exercise caution when applying literature data to estimation of GHG emissions under various production systems. Results of this study are expected to contribute to the global GHG inventory.

Keywords: Methane; Nitrous oxide; Carbon dioxide; CO; ₂; balance; Natural ventilation

Atmospheric bulk deposition of dioxin and furans to Danish background areas by M.F. Hovmand; Vikelsoe J. Vikelsøe; H.V. Andersen (pp. 2400-2411).

Polychlorinated dibenzo- p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were measured in bulk deposition at three Danish rural forest sites with a mutual maximum distance of 450km. At one of the forest sites concentrations in the ambient atmosphere were sampled from a 12m high tower. Sampling was carried out within a period of 3 years with sampling intervals of 1–2 months. Mean bulk deposition fluxes were 1ngm⁻²yr⁻¹ I-TEQ and deviated less than 30% between the sites. Yearly average PCDD/F concentrations in the atmosphere were 24fgm⁻³ I-TEQ with maximum values in the winter period. During winter months atmospheric concentrations of PCDD/F and oxidized sulphur compounds showed a positive correlation, furthermore seasonal bulk deposition showed correlation between PCDD/F and sulphate.

Keywords: PCDDs; PCDFs; Wet deposition; Air concentration; Oxidized sulphur compounds

Photooxidation of methylhydroperoxide and ethylhydroperoxide in the aqueous phase under simulated cloud droplet conditions by A. Monod; E. Chevallier; R. Durand Jolibois; J.F. Doussin; B. Picquet-Varrault; P. Carlier (pp. 2412-2426).

The photooxidation of methylhydroperoxide (MHP) and ethylhydroperoxide (EHP) was studied in the aqueous phase under simulated cloud droplet conditions. The kinetics and the reaction products of direct photolysis and OH-oxidation were studied for both compounds. The photolysis frequencies obtained were J_MHP=4.5 (±1.0)×10⁻⁵s⁻¹ and J_EHP=3.8 (±1.0)×10⁻⁵s⁻¹ for MHP and EHP respectively at 6°C. The rate constants of OH-oxidation of MHP at 6°C were 6.3 (±2.6)×10⁸M⁻¹s⁻¹ and 5.8 (±1.9)×10⁸M⁻¹s⁻¹ relative to ethanol and 2-propanol respectively, and the rate constant of OH-oxidation of EHP was 2.1 (±0.6)×10⁹M⁻¹s⁻¹ relative to 2-propanol at 6°C. The reaction products obtained were not only the corresponding aldehydes, but also the corresponding acids, and hydroxyhydroperoxides as primary reaction products. The yields for these products were sensitive to the pH value. The carbon balance was higher than 85% for all experiments, showing that most reaction products were detected. A chemical mechanism was proposed for each reaction, and the atmospheric implications were discussed.

Keywords: ^Photolysis; OH-oxidation; Organic hydroperoxide; Kinetics; Criegee biradical

Sulfur dioxide measurements in the lower, middle and upper troposphere: Deployment of an aircraft-based chemical ionization mass spectrometer with permanent in-flight calibration by M. Speidel; R. Nau; F. Arnold; H. Schlager; A. Stohl (pp. 2427-2437).

Measurements of atmospheric SO₂ have been made at altitudes between ground level and 12km in the lower, middle and upper troposphere. The measurements were carried out within the framework of the ITOP (Intercontinental Transport of Ozone and Precursors) campaign in summer 2004 above Europe and the Eastern Atlantic. They were made using a novel very sensitive and fast-response aircraft-based ion trap CIMS instrument (ITCIMS; CIMS=chemical ionization mass spectrometry), which was continuously calibrated using isotopically labelled SO₂. During a total of eight flights of the research aircraft FALCON (DLR) air masses of different origin and different degree of pollution, indicated by measured elevated atmospheric SO₂ mole fractions, were intercepted. Often elevated concentrations of SO₂, which stemmed from North America were observed over Europe and the eastern Atlantic.

Keywords: Sulfur dioxide; Chemical ionization mass spectrometry; Isotopic calibration

Data assimilation in the atmospheric dispersion model for nuclear accident assessments by D.Q. Zheng; J.K.C. Leung; B.Y. Lee; H.Y. Lam (pp. 2438-2446).

Uncertainty factors in atmospheric dispersion models may influence the reliability of model prediction. The ability of a model in assimilating measurement data will be helpful to improve model prediction. In this paper, data assimilation based on ensemble Kalman filter (EnKF) is introduced to a Monte Carlo atmospheric dispersion model (MCADM) designed for assessment of consequences after an accident release of radionuclides. Twin experiment has been performed in which simulated ground-level dose rates have been assimilated. Uncertainties in the source term and turbulence intensity of wind field are considered, respectively. Methodologies and preliminary results of the application are described. It is shown that it is possible to reduce the discrepancy between the model forecast and the true situation by data assimilation. About 80% of error caused by the uncertainty in the source term is reduced, and the value for that caused by uncertainty in the turbulence intensity is about 50%.

Keywords: Data assimilation; Dispersion model; Ensemble Kalman filter; Nuclear accident

Seasonal soil and leaf CO₂ exchange rates in a Mediterranean holm oak forest and their responses to drought conditions by Dolores Asensio; Penuelas Josep Peñuelas; R. Romà Ogaya; Llusia Joan Llusià (pp. 2447-2455).

We measured the soil and leaf CO₂ exchange in Quercus ilex and Phillyrea latifolia seasonally throughout the year in a representative site of the Mediterranean region, a natural holm oak forest growing in the Prades Mountains in southeastern Catalonia. In the wet seasons (spring and autumn), we experimentally decreased soil moisture by 30%, by excluding rainfall and water runoff in 12 plots, 1×10m, and left 12 further plots as controls. Our aim was to predict the response of these gas exchanges to the drought forecasted for the next decades for this region by GCM and ecophysiological models.Annual average soil CO₂ exchange rate was 2.27±0.27μmolCO₂m⁻²s⁻¹. Annual average leaf CO₂ exchange rates were 8±1 and 5±1μmolm⁻²s⁻¹ in Q. ilex and P. latifolia, respectively. Soil respiration rates in control treatments followed a seasonal pattern similar to photosynthetic activity. They reached maximum values in spring and autumn (2.5–3.8μmolm⁻²s⁻¹ soil CO₂ emission rates and 7–15μmolm⁻²s⁻¹ net photosynthetic rates) and minimum values (almost 0 for both variables) in summer, showing that soil moisture was the most important factor driving the soil microbial activity and the photosynthetic activity of plants. In autumn, drought treatment strongly decreased net photosynthesis rates and stomatal conductance of Q. ilex by 44% and 53%, respectively. Soil respiration was also reduced by 43% under drought treatment in the wet seasons. In summer there were larger soil CO₂ emissions in drought plots than in control plots, probably driven by autotrophic (roots) metabolism. The results indicate that leaf and soil CO₂ exchange may be strongly reduced (by ca. 44%) by the predicted decreases of soil water availability in the next decades. Long-term studies are needed to confirm these predictions or to find out possible acclimation of those processes.

Keywords: Soil CO; ₂; exchange; Foliar net photosynthetic rates; Mediterranean holm oak forest; Climate change; Drought; Roots; Microorganisms

Seasonal soil VOC exchange rates in a Mediterranean holm oak forest and their responses to drought conditions by Dolores Asensio; Penuelas Josep Peñuelas; Roma Romà Ogaya; Llusia Joan Llusià (pp. 2456-2466).

Available information on soil volatile organic compound (VOC) exchange, emissions and uptake, is very scarce. We here describe the amounts and seasonality of soil VOC exchange during a year in a natural Mediterranean holm oak forest growing in Southern Catalonia. We investigated changes in soil VOC dynamics in drought conditions by decreasing the soil moisture to 30% of ambient conditions by artificially excluding rainfall and water runoff, and predicted the response of VOC exchange to the drought forecasted in the Mediterranean region for the next decades by GCM and ecophysiological models.The annual average of the total (detected) soil VOC and total monoterpene exchange rates were 3.2±3.2 and −0.4±0.3μgm⁻²h⁻¹, respectively, in control plots. These values represent 0.003% of the total C emitted by soil at the study site as CO₂ whereas the annual mean of soil monoterpene exchange represents 0.0004% of total C. Total soil VOC exchange rates in control plots showed seasonal variations following changes in soil moisture and phenology. Maximum values were found in spring (17±8μgm⁻²h⁻¹). Although there was no significant global effect of drought treatment on the total soil VOC exchange rates, annual average of total VOC exchange rates in drought plots resulted in an uptake rate (−0.5±1.8μgm⁻²h⁻¹) instead of positive net emission rates. Larger soil VOC and monoterpene exchanges were measured in drought plots than in control plots in summer, which might be mostly attributable to autotrophic (roots) metabolism.The results show that the diversity and magnitude of monoterpene and VOC soil emissions are low compared with plant emissions, that they are driven by soil moisture, that they represent a very small part of the soil-released carbon and that they may be strongly reduced or even reversed into net uptakes by the predicted decreases of soil water availability in the next decades. In all cases, it seems that VOC fluxes in soil might have greater impact on soil ecology than on atmospheric chemistry.

Keywords: Soil VOC exchange; Soil CO; ₂; flux; Mediterranean holm oak forest; Climate change; Monoterpenes; Drought

Airborne particle PM_2.5/PM₁₀ mass distribution and particle-bound PAH concentrations near a medical waste incinerator by I.F. I-Fang Mao; C.N. Chien-Nan Chen; Y.C. Yi-Chang Lin; M.L. Mei-Lien Chen (pp. 2467-2475).

This study attempts to determine the influence of air quality in a residential area near a medical waste incineration plant. Ambient air concentrations of polycyclic aromatic hydrocarbons (PAHs), PM₁₀ and PM_2.5 (PM—particulate matter) were determined by collecting air samples in areas both upwind and downwind of the plant. The differences in air pollutant levels between the study area and a reference area 11km away from the plant were evaluated.Dichotomous samplers were used for sampling PM_2.5 and PM₁₀ from ambient air. Two hundred and twenty samples were obtained from the study area, and 100 samples were taken from a reference area. Samples were weighed by an electronic microbalance and concentrations of PM_2.5 and PM₁₀ were determined. A HPLC equipped with a fluorescence detector was employed to analyze the concentrations of 15 PAHs compounds adsorbed into PM_2.5 and PM₁₀.The experimental results indicated that the average concentrations of PM_2.5 and PM₁₀ were 30.34±17.95 and 36.81±20.45μgm⁻³, respectively, in the study area, while the average ratio of PM_2.5/PM₁₀ was 0.82±0.01. The concentrations of PM_2.5 and PM₁₀ of the study area located downwind of the incinerator were significantly higher than the study area upwind of the incinerator ( P<0.05).The concentration of PAHs in PM_2.5 in the study area was 2.2 times higher than in the reference area ( P<0.05). Furthermore, the benzo( a)pyrene concentrations in PM_2.5 and PM₁₀ were 0.11±0.05ngm⁻³ and 0.12±0.06ngm⁻³ in the study area, respectively. The benzo( a)pyrene concentrations of PM_2.5 and PM₁₀ in the study area were 7 and 5.3 times higher than in the reference area ( P<0.05), respectively.The study indicated that the air quality of PM_2.5, PM₁₀ and PAHs had significant contamination by air pollutants emitted from a medical waste incineration factory, representing a public health problem for nearby residences, despite the factory being equipped with a modern air pollution control system.

Keywords: PM; _2.5; PM; ₁₀; Polycyclic aromatic hydrocarbons; Medical waste incinerator

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Atmospheric Environment (v.41, #11)