Simulation of stomatal conductance for Aleppo pine to estimate its ozone uptake

The data from a previous experiment carried out in open-top chambers to assess the effects of ozone (O3) exposure on growth and physiology of Aleppo pine (Pinus halepensis Mill.) were re-assessed to test the performance of the EMEP O3 stomatal conductance model used to estimate tree O3 uptake at a European scale. Aleppo pine seedlings were exposed during three consecutive years to three different O3 treatments: charcoal filtered air, non-filtered air and non-filtered air supplemented with 40 nl l(-1). The results of the model using the default parameterisation already published for Mediterranean conifers showed a poor performance when compared to measured data. Therefore, modifications of g(max), f(min), and new f(VPD), f(temp) and f(phen) functions were developed according to the observed data. This re-parameterisation resulted in a significant improvement of the performance of the model when compared to its original version.     

Interactive effects of CO2 and O3 on a ponderosa pine plant/litter/soil mesocosm.

To study individual and combined impacts of two important atmospheric trace gases, CO2 and O3, on C and N cycling in forest ecosystems; a multi-year experiment using a small-scale ponderosa pine (Pinus ponderosa Laws.) seedling/soil/litter system was initiated in April 1998. The experiment was conducted in outdoor, sun-lit chambers where aboveground and belowground ecological processes could be studied in detail. This paper describes the approach and methodology used, and presents preliminary data for the first two growing seasons. CO2 treatments were ambient and elevated (ambient + 280 ppm). O3 treatments were elevated (hourly averages to 159 ppb, cumulative exposure > 60 ppb O3, SUM 06 approximately 10.37 ppm h), and a low control level (nearly all hourly averages <40 ppb. SUM 06 approximately 0.07 ppm h). Significant (P < 0.05) individual and interactive effects occurred with elevated CO2 and elevated O3. Elevated CO2 increased needle-level net photosynthetic rates over both seasons. Following the first season, the highest photosynthetic rates were for trees which had previously received elevated O3 in addition to elevated CO2. Elevated CO2 increased seedling stem diameters, with the greatest increase at low O3. Elevated CO2 decreased current year needle % N in the summer. For 1-year-old needles measured in the fall there was a decrease in % N with elevated CO2 at low O3, but an increase in % N with elevated CO2 at elevated O3. Nitrogen fixation (measured by acetylene reduction) was low in ponderosa pine litter and there were no significant CO2 or O3 effects. Neither elevated CO2 nor elevated O3 affected standing root biomass or root length density. Elevated O3 decreased the % N in coarse-fine (1-2 mm diameter) but not in fine (< 1 mm diameter) roots. Both elevated CO2 and elevated O3 tended to increase the number of fungal colony forming units (CFUs) in the AC soil horizon, and elevated O3 tended to decrease bacterial CFUs in the C soil horizon. Thus, after two growing seasons we showed interactive effects of O3 and CO2 in combination, in addition to responses to CO2 or O3 alone for a ponderosa pine plant/litter/soil system.     

A new method to estimate air-quality levels using a synoptic-regression approach. Part II: Future O3 concentrations

Using the synoptic-regression based approach developed in Part I of this research, this study estimates future maximum 8 hourly mean O₃ levels (m8hO₃) using three future SRES (Special Report on Emission) scenarios for a rural background area situated in The Netherlands. The statistical downscaling tool was used to downscale the Atmospheric–Ocean Coupled General Circulation Model (AOGCM) ECHAM5-MPI/OM for the present-day 20 Century (20C) control run (1991–2000) and the future SRES scenarios A2, A1B and B1 for two periods (2051–2060 and 2091–2100). First, the statistical downscaling tool is evaluated in terms of downscaled m8hO₃ levels for the present-day climate, using a long record of observed m8hO₃ concentrations. It was found that a bias correction is needed and this bias correction is then further used to estimate future m8hO₃ concentrations. Under the various SRES scenarios, the overall mean m8hO₃ increases with 2.5–6.5 and 6.1–10.9 μg m^?3, for the 2051–2060 and 2091–2100 period respectively, which is about 20% of the present-day 10-year average. This effect is enhanced when considering the summer season only, with a range of increase between the different future scenarios of 5.4–12.5 μg m^?3 and 13.4–26 μg m^?3 (for 2051–2060 and 2091–2100 respectively) against a present-day summer average of 73.5 μg m^?3. An increase in maximum temperature and shortwave radiation, associated with a decrease in cloud cover under the various future scenarios are the main drivers of ozone increase. A comparison with August 2003 shows the physical plausibility of our results and reflects that the extreme summer of 2003 might show a close resemblance to future European summers in terms of m8hO₃ and meteorological characteristics.     

A new method to estimate air-quality levels using a synoptic-regression approach. Part I: Present-day O3 and PM10 analysis

In order to make projections for future air-quality levels, a robust methodology is needed that succeeds in reconstructing present-day air-quality levels. At present, climate projections for meteorological variables are available from Atmospheric-Ocean Coupled Global Climate Models (AOGCMs) but the temporal and spatial resolution is insufficient for air-quality assessment. Therefore, a variety of methods are tested in this paper in their ability to hindcast maximum 8 hourly levels of O₃ and daily mean PM₁₀ from observed meteorological data. The methods are based on a multiple linear regression technique combined with the automated Lamb weather classification. Moreover, we studied whether the above-mentioned multiple regression analysis still holds when driven by operational ECMWF (European Center for Medium-Range Weather Forecast) meteorological data. The main results show that a weather type classification prior to the regression analysis is superior to a simple linear regression approach. In contrast to PM₁₀ downscaling, seasonal characteristics should be taken into account during the downscaling of O₃ time series. Apart from a lower explained variance due to intrinsic limitations of the regression approach itself, a lower variability of the meteorological predictors (resolution effect) and model deficiencies, this synoptic-regression-based tool is generally able to reproduce the relevant statistical properties of the observed O₃ distributions important in terms of European air quality Directives and air quality mitigation strategies. For PM₁₀, the situation is different as the approach using only meteorology data was found to be insufficient to explain the observed PM₁₀ variability using the meteorological variables considered in this study.     

An evaluation of ozone exposure metrics for a seasonally drought-stressed ponderosa pine ecosystem

Ozone stress has become an increasingly significant factor in cases of forest decline reported throughout the world. Current metrics to estimate ozone exposure for forest trees are derived from atmospheric concentrations and assume that the forest is physiologically active at all times of the growing season. This may be inaccurate in regions with a Mediterranean climate, such as California and the Pacific Northwest, where peak physiological activity occurs early in the season to take advantage of high soil moisture and does not correspond to peak ozone concentrations. It may also misrepresent ecosystems experiencing non-average climate conditions such as drought years. We compared direct measurements of ozone flux into a ponderosa pine canopy with a suite of the most common ozone exposure metrics to determine which best correlated with actual ozone uptake by the forest. Of the metrics we assessed, SUM0 (the sum of all daytime ozone concentrations > 0) best corresponded to ozone uptake by ponderosa pine, however the correlation was only strong at times when the stomata were unconstrained by site moisture conditions. In the early growing season (May and June). SUM0 was an adequate metric for forest ozone exposure. Later in the season, when stomatal conductance was limited by drought. SUM0 overestimated ozone uptake. A better metric for seasonally drought-stressed forests would be one that incorporates forest physiological activity, either through mechanistic modeling, by weighting ozone concentrations by stomatal conductance, or by weighting concentrations by site moisture conditions.     

Isozyme markers associated with O(3) tolerance indicate shift in genetic structure of ponderosa and Jeffrey pine in Sequoia National Park, California

Effects of canopy ozone (O(3)) exposure and signatures of genetic structure using isozyme markers associated with O(3) tolerance were analyzed in approximately 20-, approximately 80-, and >200-yr-old ponderosa (Pinus ponderosa Dougl. ex Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) in Sequoia National Park, California. For both species, the number of alleles and genotypes per loci was higher in parental trees relative to saplings. In ponderosa pine, the heterozygosity value increased, and the fixation index indicated reduction of homozygosity with increasing tree age class. The opposite tendencies were observed for Jeffrey pine. Utilizing canopy attributes known to be responsive to O(3) exposure, ponderosa pine was more symptomatic than Jeffrey pine, and saplings were more symptomatic than old growth trees. We suggest that these trends are related to differing sensitivity of the two species to O(3) exposure, and to higher O(3) exposures and drought stress that younger trees may have experienced during germination and establishment.     

A statistical model to estimate long-term concentrations of pollutants associated with long-range transport

A simple statistical model is presented for estimating long-term concentrations of pollutants associated with long-range transport. Dispersion and removal of pollutants are described in terms of statistics of these physical processes. The model has been used to estimate wet deposition of sulfur over a grid covering Northeastern United States and Canada. Model estimates compare well with corresponding measurements of annual deposition. As an example of the applications of the model we have computed the relative contribution of U.S. and Canada to the sulfur deposition over the grid considered in the paper.     

The uptake of O3 by poplar leaves: the impact of a long-term exposure to low O3-concentrations

Poplar shoots were exposed for 3–4 weeks to filtered air, ambient (maximum values 50–60 nl ℓ^-1) or two times ambient O₃-concentrations under controlled environmental conditions in fumigation chambers. A sensitive (Populus nigra ‘Brandaris’) and a tolerant (P. euramericana ‘Robusta’) cultivar were used. At regular intervals the uptake of O₃, transpiration and CO₂ assimilation rate (P_n) of full-grown leaves were measured with leaf cuvettes. For unaffected leaves, the measured flux of O₃ into the leaves appeared to be larger than can be calculated using the stomatal conductance for O₃ (g_s,o) estimated from the transpiration rates of the same leaves. Resistance analysis revealed that the difference was partly a result of a reaction with the external leaf surface. However, when the O₃ flux into the leaf was corrected for this reaction, it was still larger than can be estimated using g_s,o. As a consequence, negative residual or internal resistances (r_i) for O₃ transport into the leaves were assessed. It is postulated that O₃ molecules moving into the leaf follow a shorter pathway than effluxing H₂O-molecules. P. ‘Brandaris’ leaves showed a reduction in P_n after 12 days of exposure to ambient O₃-concentrations, whereas for P. ‘Robusta’ a reduction in P_n was only observed at two times ambient concentrations. A simultaneous decline in the O₃-flux was found in both cases. The decline occurred before a decrease in g_s,o was observed suggesting that the O₃ flux into the affected leaves was first hindered by internal factors. The measured flux of the affected leaves became smaller than the flux estimated using g_s,o and, consequently, positive r_i-values were estimated. The change in r_i suggests that O₃ molecules not only penetrated deeper into the leaf, but also were accumulating at a prolonged exposure. Our results indicate that r_i may be a potentially important component of the overall resistance for O₃-uptake, which may have important consequences for estimating O₃ uptake from water vapour flux data.     

A statistical approach to the regional use of critical loads

The premise of this paper is that: (1) effects of spatial heterogeneity of watershed response to acid deposition must be considered when models are used to set abatement policies, and (2) the evaluation of critical chemical values is a better measure off the effects of abatement policies than the comparison of deposition values to critical loads. The authors used Monte Carlo methods to apply a site-specific version of the RAINS-Lake-Model to a regional data set from The Netherlands. Statistical methods were then used to identify the important parameters affecting the spatial and temporal response, i.e. a change in pH, of watersheds to acid deposition and a subset of sensitive and insensitive watersheds were derived. The results show that the failure to subset a region into sensitive and insensitive zones may result in an erroneous estimation of the effect of abatement policies based on critical loads alone.     

A theoretical estimate of O3 and H2O2 dry deposition over the northeast United States

Estimates of short-term, regional-scale spatial distributions of ozone (O₃) and hydrogen peroxide (H₂O₂) dry deposition over the northeast U.S. are presented. Dry deposition fluxes to surfaces are computed using a regional tropospheric chemistry model with deposition velocities which vary with local meteorology, land type, insolation, seasonal factors and surface wetness. A compilation of O₃ surface resistances is presented based on a survey of O₃ dry deposition measurements. The surface resistance for H₂O₂ is assumed to be small under most conditions, causing H₂O₂ to dry deposit at a rate which is frequently limited by surface-layer turbulence. Regional patterns of dry deposition velocities for these oxidants over the northeast U.S. are computed using landuse data and meteorological information predicted using a mesoscale meteorology model. Domain-averaged O₃ deposition velocities during a spring period reach a mid-day peak of 0.7–0.8 cm s⁻¹ and drop to 0.1–0.2 cm s⁻¹ at night. Domain-averaged H₂O₂ deposition velocities at a height of approximately 80 m are predicted to reach a mid-day peak of 1.6–2.0cm s⁻¹, and fall to 0.6–0.9 cm s⁻¹ at night. Time-averaged surface-layer H₂O₂ concentrations show a latitude dependence, with higher concentrations in the south. H₂O₂ concentrations are significantly reduced due to efficient wet removal and chemical destruction during the passage of a cyclonic frontal system. In contrast, O₃ concentrations are predicted to rise during the passage of a frontal system due to efficient vertical exchange of midtropospheric air into the boundary layer during convective conditions, followed by synoptic-scale subsidence occurring in the high pressure airmass following a cyclone. Maximum O₃ deposition during this 3-day springtime period occurs in polluted agricultural areas. In contrast, H₂O₂ dry deposition exhibits a latitude dependence with maximum 3-day accumulations occurring in the south. Domain-averaged mid-day deposition rates for O₃ and H₂O₂ were 45–50 μmol m⁻² h⁻¹ and 4–5 μmol m⁻² h⁻¹. At night, deposition rates were approximately 5–10 μmol m⁻² h⁻¹ and 1.5–2.5 μmol m⁻² h⁻¹ for O₃ and H₂O₂. These model results show that regional patterns of oxidant dry deposition are strongly influenced by oxidant concentrations, atmospheric stability, surface roughness and numerous other surface and meteorological factors. Each of these factors must be well-characterized before regional patterns of biological damage associated with oxidant dry deposition can be quantified.     

Nitrate reductase activity as an indicator of ponderosa pine response to atmospheric nitrogen deposition in the San Bernardino Mountains

Determinations of nitrate reductase (NR) activity in ponderosa pine (Pinus ponderosa Dougl. ex. Laws.) needles were performed during summer 1994 in two areas (consisting of six different sites) with different nitrogen (N) deposition levels in the San Bernardino Mountains, southern California. Nitrate reductase activity was used as an integrative indicator of atmospheric nitrogen deposition to pine trees (direct uptake of N species from the atmosphere and N transported from the soil). Deposition of nitrate (NO3-) to pine branches was measured in order to determine dry atmospheric inputs of the oxidized N species to tree foliage. High NR activity was detected in all of the experimental sites. Activity of the enzyme was significantly higher at the locations characterized by higher NO3- deposition to branches--slight positive correlation between branch deposited NO3- and NR activity was found. However, high variability of NR in time and between the experimental sites discredit the NR assay as a reliable indicator of N deposition for ponderosa pine in the field conditions. This could be caused by substantial interference from other abiotic and biotic factors with tropospheric ozone as probably the most important one.     

A statistical approach applied to trace metal data from biomonitoring studies

This work underlines the importance of the statistical procedures necessary for the significant assessment of analytical data of heavy metals derived from marine organisms (biomonitors) collected at five stations in Ustica at the Southern Tyrrhenian Sea. The statistical method described indicates that, where the differences among the averages of Pb, Cu and Zn concentrations in the molluscs of the sites analysed tested with ANOVA are significant, it is necessary to conduct multiple comparison tests in order to determine which average is significantly different from the other. Using the method described, it is possible to indicate which site or sites is/are more contaminated in comparison with the other sites. This way it is possible to make a preliminary evaluation of the basal levels of trace metals present in the reference marine ecosystem under study.     

A statistical assessment of saturation and mobile sampling strategies to estimate long-term average concentrations across urban areas

The objectives of this study were: (1) to quantify the errors associated with saturation air quality monitoring in estimating the long-term (i.e., annual and 5 yr) mean at a given site from four 2-week measurements, once per season; and (2) to develop a sampling strategy to guide the deployment of mobile air quality facilities for characterizing intraurban gradients of air pollutants, that is, to determine how often a given location should be visited to obtain relatively accurate estimates of the mean air pollutant concentrations. Computer simulations were conducted by randomly sampling ambient monitoring data collected in six Canadian cities at a variety of settings (e.g., population-based sites, near-roadway sites). The 5-yr (1998-2002) dataset consisted of hourly measurements of nitric oxide (NO), nitrogen dioxide (NO2), oxides of nitrogen (NOx), sulfur dioxide (SO2), coarse particulate matter (PM10), fine particulate matter (PM2.5), and CO. The strategy of randomly selecting one 2-week measurement per season to determine the annual or long-term average concentration yields estimates within 30% of the true value 95% of the time for NO2, PM10 and NOx. Larger errors, up to 50%, are expected for NO, SO2, PM2.5, and CO. Combining concentrations from 85 random 1-hr visits per season provides annual and 5-yr average estimates within 30% of the true value with good confidence. Overall, the magnitude of error in the estimates was strongly correlated with the variability of the pollutant. A better estimation can be expected for pollutants known to be less temporally variable and/or over geographic areas where concentrations are less variable. By using multiple sites located in different settings, the relationships determined for estimation error versus number of measurement periods used to determine long-term average are expected to realistically portray the true distribution. Thus, the results should be a good indication of the potential errors one could expect in a variety of different cities, particularly in more northern latitudes.     

Multiple batch extraction test to estimate contaminant release parameters using a Bayesian approach

Industrial activities produce vast amounts of weakly contaminated materials which are commonly reused as filling materials on natural ground. There is a strong demand to define guidelines for the application of these materials, to estimate the leaching potential of contaminants from the materials, and to assess the potential hazard for groundwater pollution. We present a multiple batch experiment, where measurements of liquid-phase concentrations at varying liquid/solid ratios are used to estimate the total mass of contaminant that can be extracted from a contaminated material with a mild extractant like water. Furthermore, the experiment yields estimates of the isotherm describing the partitioning of the contaminant between the solid and liquid phases, and a concentration that might be expected under soil hydraulic conditions representative for the field situation. Model parameters are estimated from liquid-phase concentrations within a Bayesian framework by applying the Shuffled Complex Evolution Metropolis Algorithm (SCEM-UA), an efficient Markov Chain Monte Carlo sampler. A sensitivity analysis and inversions of synthetically generated data corrupted with noise show the general suitability of the proposed method. An uncertainty analysis for model parameters and model predictions shows the expected accuracy of the estimates. An application to concentration measurements obtained from a multiple batch extraction test illustrates the applicability of the approach for a real situation.     

Contaminant transport in a municipal drinking water supply: a steady-state approach to estimate rate and uncertainty

Contaminant transport is generally considered to be a key factor when assessing and classifying the environmental risk of polluted areas. In the study presented here, a steady-state approach was applied to obtain estimates of the transit time and concentration of the pesticide metabolite BAM (2,6-dichlorobenzoamide) at a site where it is contaminating a municipal drinking water supply. A Monte Carlo simulation technique was used to quantify the uncertainty of the results and to evaluate the sensitivity of the used parameters. The adopted approach yielded an estimated median transit time of 10 y for the BAM transport from the polluted site to the water supply. Soil organic carbon content in the unsaturated zone and the hydraulic conductivity in the saturated zone explained 44% and 23% of the uncertainty in the transit time estimate, respectively. The sensitivity analysis showed that the dilution factor due to regional groundwater flow and the soil organic carbon content at the polluted site explained 53% and 31% of the uncertainty of concentration estimates, respectively. In conclusion, the adopted steady-state approach can be used to obtain reliable first estimates of transit time and concentration, but to improve concentration predictions of degrading contaminants, a dynamic model is probably required.     

Seasonal variation of gas exchange and pigmentation in branches of three grafted clones of mature ponderosa pine exposed to ozone and acid rain

Gas exchange and pigmentation responses of mature ponderosa pine (Pinus ponderosa Laws.) branches to ozone and acid rain exposure were investigated using three grafted clones growing in a managed seed orchard. Exposure of one-year-old foliage to twice ambient ozone (2 x AMB) resulted in significant decreases in net photosynthesis (Pn), stomatal conductance (gsw) and pigmentation relative to charcoal-filtered (CF) and ambient (AMB) ozone treatments. Ozone effects on gas exchange and pigmentation were most pronounced during late-season and differed significantly among clones. Environmental parameters (e.g. light, vapor pressure deficit, and temperature) accounted for more variation in Pn than did cumulative ozone exposure. Minimal differences in gsw and Pn among ozone treatments occurred during seasonal periods of high temperature and evaporative demand. Negative effects of 2 x AMB ozone on gsw and pigmentation were greatest for the clones having highest and lowest phenotypic vigor under ambient conditions; the clone of moderate phenotypic vigor under ambient conditions was least sensitive to ozone. Application of simulated acid rain of pH 3.0, pH 5.1 or no rain (NR) had little impact on gas exchange or pigmentation.     

Screening loblolly pine seedling responses to SO2 and O3: analysis of families differing in resistance to fusiform rust disease

Open pollinated families of loblolly pine differing in resistance to fusiform rust disease were screened in laboratory studies for responses to gaseous air pollutants. Twenty families were given acute exposures (2 fumigations for 4 h each) to SO(2) (0.4-1.0 ppm), O(3) (0.25 ppm), SO(2) (0.4-1.0 ppm) + O(3) (0.25 ppm) and control. Analyses of variance were performed to evaluate the treatment effects of these air pollutants on percent foliar injury, and to determine whether the families responded differentially to the air pollution treatments. Treatment effects were significant, with the combination treatment of SO(2) + O(3) producing a higher percentage of foliar injury than the controls; however, injury levels were very low and may not be of biological significance. Subsequently, twelve families were grown in two soil types for exposure to chronic levels of SO(2) (0.06 ppm), O(3) (0.07 ppm), SO(2) (0.06 ppm) + O(3) (0.07 ppm) and control. The families were then ranked for decreased primary shoot growth, shoot dry weight, root dry weight, total plant dry weight and root/shoot ratio after exposure to air pollution treatments. Air pollution treatments as a main effect were significant for only one of five growth parameters measured, that of primary shoot growth. The main effect of family, and the interaction of family and air pollution treatments, were significant for most growth parameters measured. In general, O(3) alone and in combination with SO(2) reduced growth more than SO(2) alone. Fumigation with O(3) reduced growth of two families in comparison with control groups, whereas SO(2) alone produced decreased growth in one family and stimulated growth in three families. Treatment with O(3) alone produced higher root/shoot ratios than fumigation with charcoal-filtered air in two families. Overall, families which were fast growers under control conditions maintained their ranking after exposure to air pollution. Families producing less growth in charcoal-filtered air also produced less growth under various air pollution regimes. Results indicated that these families exhibited a high degree of resistance to air pollution injury. Growth responses of seedlings may not reflect family differences in long-term productivity. No relationship was apparent between fusiform rust resistance and growth reductions due to air pollutants.     

Detoxification and repair process of ozone injury: from O3 uptake to gene expression adjustment

Plants react to O₃ threat by setting up a variety of defensive strategies involving the co-ordinated modulation of stress perception, signalling and metabolic responses. Although stomata largely controls O₃ uptake, differences in O₃ tolerance cannot always be ascribed to changes in stomatal conductance but cell protective and repair processes should be taken into account. O₃-driven ROS production in the apoplast induces a secondary, active, self-propagating generation of ROS, whose levels must be finely tuned, by many enzymatic and non-enzymatic antioxidant systems, to induce gene activation without determining uncontrolled cell death. Additional signalling molecules, as ethylene, jasmonic and salicylic acid are also crucial to determine the spreading and the containment of leaf lesions. The main recent results obtained on O₃ sensing, signal transduction, ROS formation and detoxification mechanisms are here discussed.     

Multivariate statistical and GIS-based approach to identify heavy metal sources in soils

The knowledge of the regional variability, the background values and the anthropic vs. natural origin for potentially harmful elements in soils is of critical importance to assess human impact and to fix guide values and quality standards. The present study was undertaken as a preliminary survey on soil contamination on a regional scale in Piemonte (NW Italy). The aims of the study were: (1) to determine average regional concentrations of some heavy metals (Cr, Co, Ni, Cu, Zn, Pb); (2) to find out their large-scale variability; (3) to define their natural or artificial origin; and (4) to identify possible non-point sources of contamination. Multivariate statistic approaches (Principal Component Analysis and Cluster Analysis) were adopted for data treatment, allowing the identification of three main factors controlling the heavy metal variability in cultivated soils. Geostatistics were used to construct regional distribution maps, to be compared with the geographical, geologic and land use regional database using GIS software. This approach, evidencing spatial relationships, proved very useful to the confirmation and refinement of geochemical interpretations of the statistical output. Cr, Co and Ni were associated with and controlled by parent rocks, whereas Cu together with Zn, and Pb alone were controlled by anthropic activities. The study indicates that background values and realistic mandatory guidelines are impossible to fix without an extensive data collection and without a correct geochemical interpretation of the data.     

Characterization of PM(2.5) collected during broadcast and slash-pile prescribed burns of predominately ponderosa pine forests in northern Arizona

Prescribed burning, in combination with mechanical thinning, is a successful method for reducing heavy fuel loads from forest floors and thereby lowering the risk of catastrophic wildfire. However, an undesirable consequence of managed fire is the production of fine particulate matter or PM(2.5) (particles ≤2.5 μm in aerodynamic diameter). Wood-smoke particulate data from 21 prescribed burns are described, including results from broadcast and slash-pile burns. All PM(2.5) samples were collected in situ on day 1 (ignition) or day 2. Samples were analyzed for mass, polycyclic aromatic hydrocarbons (PAHs), inorganic elements, organic carbon (OC), and elemental carbon (EC). Results were characteristic of low intensity, smoldering fires. PM(2.5) concentrations varied from 523 to 8357 μg m(-3) and were higher on day 1. PAH weight percents (19 PAHs) were higher in slash-pile burns (0.21 ± 0.08% OC) than broadcast burns (0.07 ± 0.03% OC). The major elements were K, Cl, S, and Si. OC and EC values averaged 66 ± 7 and 2.8 ± 1.4% PM(2.5), respectively, for all burns studied, in good agreement with literature values for smoldering fires.