Atmospheric Environment (v.38, #33)
Editorial board (i).
List for forthcoming papers (I-II).
Constraining uncertainties about the sources and magnitude of polycyclic aromatic hydrocarbon (PAH) levels in ambient air: the state of Minnesota as a case study by Agnes B. Lobscheid; Thomas E. McKone (5501-5515).
Emissions data are often lacking or uncertain for many airborne contaminants. Polycyclic aromatic hydrocarbons (PAHs) emitted from combustion sources fall into this category. Currently available ambient-air emission inventories of PAHs either fail to account for population-based activities, such as residential wood combustion (RWC) and motor vehicle (MV) activity, and/or report “total PAH” or particulate organic matter emissions, instead of individual compound emissions. We assess the degree of overlap between predicted concentrations from estimated emissions with measured concentrations. Our analysis is based on probabilistic analysis of measured outdoor air concentrations with those predicted from mass-balance models. Based on available information, we estimate the relative magnitude of emissions from three major sources of PAHs to outdoor air: (1) on-road MVs, including light-duty gasoline vehicles and diesel-powered buses and medium and heavy-duty trucks; (2) RWC; and (3) power generation from external combustion boilers. We use the CalTOX regional multimedia mass-balance model to evaluate our emissions estimates in rural and urban regions of the state of Minnesota, USA. We compare model estimates of outdoor PAH airborne concentrations with those reported by the Minnesota Children's Pesticide Exposure Study (MNCPES). With these measured concentrations we probabilistically evaluate the reliability of our emissions estimates for specific PAHs. The median estimates of our predicted outdoor air concentrations agree within an order of magnitude of measured concentrations. For four representative PAHs, we obtain a reasonable degree of overlap between empirical and predicted distributions of outdoor air concentrations. Our combination of models, emissions estimates, and empirical concentration data estimate exposure in a manner that is more reliable than any of these tools alone. Thereby, we increase our confidence about our plausible ranges of emissions and predicted concentrations.
Keywords: Gasoline motor vehicles; Diesel fuel motor vehicles; External combustion boilers; Residential wood combustion; Emissions inventory;
Chemical characterization of outdoor PM2.5 and gas-phase compounds in Mira Loma, California by Aniket A. Sawant; Kwangsam Na; Xiaona Zhu; David R. Cocker (5517-5528).
Outdoor fine particulate matter (PM2.5) and gas-phase compounds were investigated in Mira Loma, a semi-rural community in southern California, between September 2001 and January 2002. Outdoor PM2.5 concentrations for the study duration averaged 41.8 μg m−3, with nitrate and organic carbon being the major contributors (∼26% each). Higher PM2.5 concentrations were observed during the first half of the study relative to the second half, corresponding with actinic flux calculations. Gas-phase ammonia concentrations were 6–7 times greater than nitric acid concentrations, while formaldehyde and acetaldehyde concentrations were consistent with Air Resources Board results. Use of a back trajectory model together with PM2.5 chemical composition data showed distinct differences in nitrate and trace element concentrations for back trajectories originating from Los Angeles and Orange counties versus those originating from Nevada. Source apportionment using a chemical mass balance model helped demonstrate that the total contribution of secondary aerosol (56%) was greater than the total primary vehicular exhaust contribution to PM2.5 by a factor of 5. These results highlight the importance of region-wide secondary sources to the local air quality in this semi-rural area.
Keywords: Source apportionment; HYSPLIT; Southern California; Aerosol; Carbonyls; Formaldehyde; Ammonia;
Effects of uncertainties in parameters of a Lagrangian particle model on mean ground-level concentrations under stable conditions by Kasemsan Manomaiphiboon; Armistead G. Russell (5529-5543).
This work evaluates the effects of uncertainties in five parameters or inputs of a source-receptor Lagrangian particle model on mean ground-level concentrations. The scope of work is short-range dispersion in the atmospheric boundary layer under weakly and moderately stable conditions over a smooth flat terrain within 3 km downwind from a continuous point source located near the ground. Model inputs include four meteorological parameters and the universal constant in the random component of the model. The meteorological parameters are friction velocity, mean surface turbulent heat flux magnitude (shortly, heat flux), surface roughness height (shortly, roughness height), and mean surface temperature (shortly, temperature). Model outputs of interest are mean ground-level concentrations at a number of receptors downwind from the source. The formal uncertainty analysis was performed for the atmospheric conditions corresponding to stability indices (defined as the ratio of mixing height to Monin-Obukhov length) of 1.2, 2.5, and 4.1. Input uncertainties were propagated through the model using Monte Carlo simulations with Latin hypercube sampling. Linear regression modeling was used to statistically partition an output uncertainty and determine the relative importance of an input to an output. It is shown that the concentration uncertainty increases with the level of meteorological uncertainty and that its magnitude varies with stability degree. Among the meteorological parameters, friction velocity is the most influential. Another important input is the universal constant whose contribution can dominate when the level of meteorological uncertainty becomes low. The overall contributions from roughness height and temperature are relatively small.
Keywords: Atmospheric turbulence; Dispersion; Latin hypercube sampling; Linear regression modeling; Meteorological parameters; Monte carlo simulations; Uncertainty;
Long-range sources of Toronto particulate matter (PM2.5) identified by Aerosol Laser Ablation Mass Spectrometry (LAMS) by Sandy Owega; Greg J. Evans; Robert E. Jervis; Mike Fila; Ryan D’Souza; Badi-Uz-Zaman Khan (5545-5553).
An aerosol laser ablation mass spectrometer (LAMS) was operated continuously in downtown Toronto for a period of 11 months. The mass spectra of individual particles were classified according to their chemical composition using neural net-based adaptive resonance theory (ART-2a). The types of particles thereby identified were used as the basis for classifying particles from a 10-day sampling period within the 11-month sampling study. The particles within a class were further segregated by size, and the number of particles analyzed per hour was calculated for each of the resulting composition and sized based classes. ART-2a was used to combine these classes into groups based on similarity in their temporal trends. Two unusual sources were thereby identified: forest fire particles and intercontinental dust. The forest fire particles primarily exhibited potassium and potassium sulphate, while the intercontinental dust exhibited crustal metals, like titanium, aluminum, and iron. Back trajectory analysis of the air masses that transported these particles to Toronto revealed their origins as Northern Canada and Africa. From the chemical composition and size of the particles, a forest fire episode in Western Canada was identified during the 11-month sampling study on 1 June 2002. Other episodes of particles originating from Africa were not observed. These findings demonstrated the use of temporal variations in single particle chemistry to identify sources.
Keywords: Neural networks; Forest fire and intercontinental particles; Back trajectory analysis; Chemical composition; Single particle analysis;
Modelling airborne concentration and deposition rate of maize pollen by Nathalie Jarosz; Benjamin Loubet; Laurent Huber (5555-5566).
The introduction of genetically modified (GM) crops has reinforced the need to quantify gene flow from crop to crop. This requires predictive tools which take into account meteorological conditions, canopy structure as well as pollen aerodynamic characteristics. A Lagrangian Stochastic (LS) model, called SMOP-2D (Stochastic Mechanistic model for Pollen dispersion and deposition in 2 Dimensions), is presented. It simulates wind dispersion of pollen by calculating individual pollen trajectories from their emission to their deposition. SMOP-2D was validated using two field experiments where airborne concentration and deposition rate of pollen were measured within and downwind from different sized maize (Zea mays) plots together with micrometeorological measurements. SMOP-2D correctly simulated the shapes of the concentration profiles but generally underestimated the deposition rates in the first 10 m downwind from the source. Potential explanations of this discrepancy are discussed. Incorrect parameterisation of turbulence in the transition from the crop to the surroundings is probably the most likely reason. This demonstrates that LS models for particle transfer need to be coupled with air-flow models under complex terrain conditions.
Keywords: Atmospheric dispersion; Lagrangian model; Turbulence; Particles; Zea mays;
Application of the open path FTIR with COL1SB to measurements of ozone and VOCs in the urban area by Dae Woong Hong; Gwi Suk Heo; Jin Seok Han; Seog Yeon Cho (5567-5576).
The COnstrained L1-norm minimization with the Synthetic Background generation method (COL1SB) is newly developed open-path FTIR analysis software, designed to efficiently handle chemical interferences and to systematically generate background spectra. The performance of COL1SB was evaluated mainly against artificially generated field spectra. The present paper aims at application of COL1SB to ambient monitoring. In order to satisfy low detection limit requirements of ambient monitoring, COL1SB was further improved to accurately determine path averaged water vapor pressures, to dynamically select appropriate spectral bands, and to use site specific background spectra. The modified COL1SB was applied to measure ozone, ammonia, methane, carbon monoxide, and 26 VOC species in the park located at the urban area from 12:00 a.m., 25 May to 12:00 a.m., 26 May 2000. The open-path FTIR measurements for ozone, water vapor, alkane concentrations compared very well with those by sampling methods both in magnitudes and in diurnal variations. Furthermore, the detection rates of VOCs were considerably enhanced such that the detection rates based on the correlation coefficients appeared to be above 50% for 12 species out of 16 representative chemical species. Especially ethylene and isoprene, chemically reactive olefins, had high detection rates exceeding 80% despite of their low concentrations. These detection rates by COL1SB are 2–5 times higher than those derived by the conventional CLS method in the previous work (SPIE Conference on Environmental Monitoring and Remediation Technologies SPIE (1998) 3534, 140).
Keywords: Open-path Fourier transform infrared spectroscopy; VOCs; Water vapor pressure; Ambient monitoring; Site specific spectrum;
Henry's law constant measurements for phenol, o-, m-, and p-cresol as a function of temperature by Valérie Feigenbrugel; Stéphane Le Calvé; Philippe Mirabel; Florent Louis (5577-5588).
In this work, a dynamic system based on the water/air equilibrium at the interface within the length of a microporous tube was used to experimentally determine the Henry's law constants (HLC) of phenol and cresols. The measurements were conducted over the range 278–298 K in both deionized water and 35 g l - 1 solution of NaCl. At 293 K and in pure water, HLC were found to be equal to (in units of M atm - 1 ): phenol, HLC = ( 1005 ± 270 ) ; o-cresol, HLC = ( 690 ± 95 ) ; m-cresol, HLC = ( 1324 ± 172 ) ; p-cresol, HLC = ( 1742 ± 360 ) . The obtained data were used to derive the following Arrhenius expressions: HLC = ( 4.1 ± 0.6 ) × 10 - 9 exp ( ( 7684 ± 874 ) / T ) , HLC = ( 1.5 ± 0.1 ) × 10 - 10 exp ( ( 8544 ± 512 ) / T ) , HLC = ( 5.5 ± 0.4 ) × 10 - 11 exp ( ( 9028 ± 508 ) / T ) and HLC = ( 3.3 ± 0.4 ) × 10 - 11 exp ( ( 9258 ± 818 ) / T ) for phenol, o-cresol, m-cresol and p-cresol, respectively. All of the values for HLC in 35 g l - 1 salt solution were 10–30% lower than their respective values in deionized water, depending on the compound and the temperature.These data were then used to estimate the fractions of phenol or of cresols in atmospheric aqueous phase. In order to evaluate the impact of a cloud on the atmospheric chemistry of phenol and cresols, we compare also their atmospheric lifetimes under clear sky ( τ gas ) , and cloudy conditions ( τ multiphase ) . The calculated multiphase lifetimes (in units of days) are significantly lower than those in gas phase at a cumulus temperature of 283 K (in parentheses): phenol, 0.26 (0.45); o-cresol, 0.17 (0.24); m-cresol, 0.13 (0.22); p-cresol, 0.11 (0.23).
Keywords: Henry's law constant; Temperature; Salinity; Phenol; Cresols;
Erosion of limestone building surfaces caused by wind-driven rain: 1. Field measurements by Wei Tang; Cliff I. Davidson; Susan Finger; Kirk Vance (5589-5599).
Complex patterns of discoloration are often seen on the surfaces of stone buildings in urban areas. These patterns reflect interactions between atmospheric pollutants, the surface layers of stone, and wind-driven rain that can erode the surface. This first paper in a two-paper series presents field measurements of wind-driven rain on a tall limestone building. The volume of driving rain on the building wall was measured at 16 locations over a 21-month period, and meteorological data were recorded for the same period. Analysis of data from 94 rain events suggests that wind-driven rain is strongly affected by rainfall intensity, wind speed, wind direction and measurement location. The five locations with driving rain volumes < 4 l over this period are characterized by heavily soiled walls, while the two locations with driving rain volumes > 8 l are characterized by white, eroded walls. The remaining nine locations have driving rain volumes in the range 4– 8 l and varying amounts of soiling, with no clear relationship between these two variables. It is hypothesized that variation in raindrop momentum, which was not measured, is partially responsible for surface erosion and thus removal of soiling in this last category.
Keywords: Soiling; Deterioration; Driving rain; Wet deposition; Cathedral; Buildings; Limestone;
Erosion of limestone building surfaces caused by wind-driven rain: 2. Numerical modeling by Wei Tang; Cliff I. Davidson (5601-5609).
Wind-driven rain and its effect on surface stone deterioration have been studied at the Cathedral of Learning, a tall limestone building on the University of Pittsburgh campus. In this second paper of the series, a numerical method based on computational fluid dynamics techniques is used to predict wind-driven rain on the Cathedral. Three steps are involved: computing the airflow field around the building, determining raindrop trajectories, and estimating total rain impingement based on meteorological data. Results are expressed in terms of the Catch Ratio, the flux of rain on the building walls divided by the flux of rain on the ground. The method is applied to 94 rain events during the measurement period. Results show good agreement with field data, indicating that the method can provide reasonable predictions of wind-driven rain.
Keywords: Soiling; CFD; Driving rain; Raindrop trajectories; Airflow field;
Low 15N/14N ratios for nitrate in snow in the High Arctic (79°N) by Tim H.E. Heaton; Peter Wynn; Andy M. Tye (5611-5621).
We report on the 15N/14N and 18O/16O ratio analysis of nitrate in accumulated winter snowpack and fresh spring snow collected near Ny Å lesund, Svalbard (79°N), in the early summers of 2001–2003. The presence of contaminant organic matter in the silver nitrate prepared for analysis must be carefully monitored to assess its effects on δ 15 N , and particularly δ 18 O results. δ 15 N values ranged - 18 ‰ to - 7 ‰ (versus air N 2 ) and δ 18 O values +60 to + 85 ‰ (versus VSMOW). The δ 18 O values are in the reported range for atmospheric nitrate in other parts of the globe, and will tend to reflect the relationship between NO y oxygen and H 2 O + O 2 in the troposphere immediately prior to nitrate deposition. δ 15 N values, however, are lower than those for atmospheric nitrate over most parts of the globe, but show similarities to 15N/14N ratios reported for atmospheric nitrate in the Antarctic. We discuss mechanisms for producing 15N-depleted nitrate in the troposphere, or the possibility that it reflects NO y nitrogen derived from the stratosphere.
Keywords: Nitrogen isotopes; Oxygen isotopes; Stratosphere; Troposphere; Polar;
Acidic loadings in South Korean ecosystems by long-range transport and local emissions by Jae-Myun Shim; Soon-Ung Park (5623-5636).
Exceedances of sulfur and nitrogen critical loads in South Korean ecosystems caused by long-range transport and local emissions of sulfur and nitrogen have been estimated using the maximum critical load of sulfur and the critical load of nutrient nitrogen. The long-term-averaged deposition of sulfur and nitrogen is estimated with a simplified chemical model and the K-mean clustering technique. The three consecutive days of gridded daily mean National Center for Environmental Protection (NCEP) reanalyzed 850 hPa geopotential height fields with and without precipitation on the last day over South Korea are used for clustering of synoptic patterns for the period of 1994–1998. Two emission conditions are simulated for each cluster to estimate long-term averaged depositions of sulfur and nitrogen by long-range transport and local emissions over South Korea. One condition takes all emissions within the simulated domain into account as a base case and the other condition excludes all South Korean emissions but includes all of the other emissions, as a control case. The results of the present study indicate that the contribution of long-range transport to the annual total deposition over South Korea is found to be about 40% ( 530 eq ha - 1 yr - 1 ) for sulfur and 49% ( 650 eq ha - 1 yr - 1 ) for nitrogen, of which 55% for sulfur and 58% for nitrogen are contributed by wet deposition. This suggests the importance of wet deposition through the transformed acidic precursors for long-range transport to South Korea's total deposition of sulfur and nitrogen. The estimated exceedance for South Korean ecosystems indicates that the current estimate of total sulfur deposition affects about 42% of the South Korean ecosystems adversely, of which 14% is attributed to South Korean source only and the rest 28% is attributed to long-range transport together with South Korean source. Long-range transport of sulfur itself does not exceed the maximum critical load of sulfur. On the other hand, the current estimate of total nitrogen deposition is found to affect all South Korean ecosystems adversely. About 65% and 15% of the Korean ecosystems are, respectively, found to be affected adversely by South Korean nitrogen emissions and by long-range transport, suggesting that the reduction of nitrogen deposition from both South Korean sources and long-range transport is a prerequisite to ensure South Korean ecosystem sustainability.
Keywords: Critical load; Exceedance; Long-range transport contribution; South Korean ecosystem; Sulfur and nitrogen deposition modeling;
Aerosol chemistry of emissions from three contrasting volcanoes in Italy by T.A. Mather; C. Oppenheimer; A.G. Allen; A.J.S. McGonigle (5637-5649).
Volcanoes constitute an important source of aerosol. Here we report the size-resolved compositions of major water-soluble ions in particles collected in near-source emissions from three contrasting volcanoes (Solfatara, Vulcano and Stromboli, in Italy). Concentrations of soluble SO4 2−, Cl−, F−, NO3 −, H+, K+, Na+, NH4 +, Ca2+ and Mg2+ were determined in 11 particle size bins from 0.069 to >25.5 μm in diameter. Soluble ions were most concentrated in the emissions from Solfatara and Stromboli. At Solfatara the major ions were NH4 + and Cl−, tightly correlated in ∼0.8–1.5 μm diameter particles, strongly suggesting speciation as NH4Cl. At Stromboli enhanced levels of SO4 2−, H+, Na+, K+ and NH4 + were present in ∼0.5–1.5 μm diameter particles. Near-source soluble sulphate was observed in the plumes from Stromboli and Vulcano, with that from Stromboli in much higher concentration (0.94–2.14 compared with 0.07–0.13 μmol m−3). Comparing SO4 2− measurements from Vulcano to those from other volcanic systems suggests that near-source sulphate aerosol emissions scale with SO2 and contribute ∼0.03–0.05 Tg yr−1 of sulphur to the atmosphere. Simple calculations suggest that all the particles containing these soluble ions will act as cloud condensation nuclei at typical atmospheric supersaturations.
Keywords: Sulfate; Size distribution; Primary particles; Solfatara; Vulcano; Stromboli;
Diurnal variability of size-differentiated inorganic aerosols and their gas-phase precursors during January and February of 2003 near downtown Mexico City by Mireya Moya; Michel Grutter; Armando Báez (5651-5661).
Size-differentiated atmospheric aerosol particles along with gas-phase precursors were measured at a site near downtown Mexico City (MER site) during January and February 2003 to provide information regarding the diurnal variability and partitioning of semi-volatile inorganic compounds between the gas phase and different-size particles. The aerosols were sampled with cascade impactors (MOUDI's) in the following periods: 1st (06:00–09:00 h, LST), 2nd (09:00–12:00 h, LST), 3rd (12:00–15:00 h, LST) and 4th (15:00–18:00 h, LST). The gas-phase measurements were continuously recorded with an open-path FTIR spectrometer. Overall, inorganic aerosol size/composition measurements observed a bimodal distribution: one mode was present in the accumulation size range (0.18–0.32 μm, aerodynamic diameter) and the other in the coarse mode (over 1 μm, aerodynamic diameter). During the morning sampling periods, the highest concentrations occurred mainly over the accumulation mode while during the afternoon sampling periods, concentration peaks were observed over both accumulation and coarse modes. More than half of the ammonium was found in the accumulation mode. The rest of the ions (sodium, chloride, sulfate, nitrate, calcium and potassium) were prominent in both modes. The significant presence of sodium and crustals (calcium and potassium) are explained in terms of the potential influence of the dry salt-lake of Texcoco and resuspended dust/soil, respectively. Based on the analysis of the time-resolved PM and gas-phase composition, the significant presence of gas-phase ammonia (>35 ppb) during the morning sampling periods was of importance in neutralizing the aerosol particles.
Keywords: Atmospheric aerosols; Gas-phase precursors; Aerosol partitioning; Mexico City;
Emission estimates and trends (1990–2000) for megacity Delhi and implications by B.R. Gurjar; J.A. van Aardenne; J. Lelieveld; M. Mohan (5663-5681).
A comprehensive emission inventory for megacity Delhi, India, for the period 1990–2000 has been developed in support of air quality, atmospheric chemistry and climate studies. It appears that SO2 and total suspended particles (TSP) are largely emitted by thermal power plants (∼68% and ∼80%, respectively), while the transport sector contributes most to NO x , CO and non-methane volatile organic compound (NMVOC) emissions (>80%). Further, while CO2 has been largely emitted by power plants in the past (about 60% in 1990, and 48% in 2000), the contribution by the transport sector is increasing (27% in 1990 and 39% in 2000). NH3 and N2O are largely emitted from agriculture (∼70% and ∼50%, respectively), and solid waste disposal is the main source of CH4 (∼80%). In the past TSP abatement to improve air quality has largely focused on traffic emissions; however, our results suggest that it would be most efficient to also reduce TSP emissions by power plants. We also assessed the potential large-scale transport of the Delhi emissions based on 10-day forward trajectory calculations. The relatively strong growth of NO x emissions indicates that photochemical O3 formation in the regional environment may be increasing substantially, in particular in the dry season. During the summer, on the other hand, convective mixing of air pollutants may reduce regional but increase large-scale, i.e. hemispheric effects.
Keywords: Urban air pollution; Emission inventory; Atmospheric chemistry; Trajectory analysis; Regional-global impact;
Northeast United States and Southeast Canada natural mercury emissions estimated with a surface emission model by Jesse O. Bash; David R. Miller; Thomas H. Meyer; Patricia A. Bresnahan (5683-5692).
Most mercury emission inventories only include anthropogenic emissions and neglect the large contribution of the natural mercury cycle due to difficulty in spatially estimating natural emissions and uncertainties in the natural emissions process. The Mercury (Hg) Surface Interface Model (HgSIM) has been developed to estimate the natural emissions of mercury, for inclusion in a more complete mercury emissions inventory. The model used a 3422 cell, 36 km on each side, gridded domain and 1 h time steps. The emissions over land are modeled as a function of the land cover, evapotranspiration, and temperature. The emissions over water are modeled as a function of the concentration gradient, the mixing of the air and water, and the temperature.The spatially distributed model is shown to account for the extreme spatial variability across the Northeast (NE) US and Southeast (SE) Canada. Estimates of natural mercury flux from uncontaminated surfaces are presented for a 2 week period in July. The total natural emissions for the domain, 4,434,912 km2, was 2101.5 kg over the 2 week simulation. The highest total natural emissions were 820 ng m−2 from the Atlantic Ocean in the SE part of the domain and the lowest total natural emissions were 74 ng m−2 in the urban areas with little vegetation. The flux estimates from vegetation canopies, averaged over the 14 days, ranged from 0.0 ng m−2 h−1 during the night time hours when transpiration ceased to 4.46 ng m−2 h−1 during the afternoon in a mixed deciduous–coniferous forest. The range of the air-water flux was between 0.5 and 2.73 ng m−2 h−1 over the model domain with the higher emission rates corresponding to windier and warmer areas. The soil emissions ranged from near 0 to 2.3 ng m−2 h−1 with the higher rates corresponding to warmer agricultural regions.
Keywords: Spatial variability; Semivariogram; Surface flux; Transpiration;
Baseline air mass selection at Cape Point, South Africa: application of 222Rn and other filter criteria to CO2 by E.-G. Brunke; C. Labuschagne; B. Parker; H.E. Scheel; S. Whittlestone (5693-5702).
Concentrations of 222Rn (March 1999–August 2002) from a recently installed analyser at the station Cape Point (34°S, 18°E), South Africa, were analysed statistically. The combination of 222Rn with information on wind direction and carbon monoxide (CO) permitted a classification of air masses into continental, marine, and mixtures of both. The ability to select trace gas data representing purely maritime conditions is shown through application to carbon dioxide (CO2) data. 222Rn levels at Cape Point ranged from near zero to above 5000 mBq m−3. Monthly percentiles show practically no seasonal dependence for values up to the 25th percentile (P25), corresponding to 222Rn <100 mBq m−3, which is considered typical for marine air. In contrast, 222Rn percentiles exceeding P50 reveal an austral winter maximum, related to a higher incidence of continental air at that time of the year. The wind sector pattern for 222Rn concentrations largely coincides with that observed for CO, but covers a wider sector to the east, reflecting continental source areas. Air masses with 222Rn levels between 100 and 250 mBq m−3 were found to be still affected by terrestrial sources. Our routinely used percentile-based statistical filter applied to CO2 accepted <75% of the data compared to the radon criterion for maritime air (222Rn <100 mBq m−3), which only yielded 18%, but is more stringent in excluding terrestrial influences. CO2 data filtered by using a combination of various selection parameters agreed well with data obtained for 222Rn <100 mBq m−3, confirming that this 222Rn threshold is a suitable criterion for purely maritime data. Nonetheless, for CO2 the statistical filter, which does not depend on other species and has better data coverage, still retains its applicability for routine trace gas filtering with respect to baseline concentrations.
Keywords: Background concentration; Air mass classification; 222Rn (radon); Data filtering; CO2;
The Washington aerial spray drift study: assessment of off-target organophosphorus insecticide atmospheric movement by plant surface volatilization by Jaya Ramaprasad; Ming-Yi Tsai; Kai Elgethun; Vincent R. Hebert; Allan Felsot; Michael G. Yost; Richard A. Fenske (5703-5713).
Post-application pesticide emissions from wetted leaf surfaces and soil may present a significant pathway of exposure to humans in nearby residential communities. In this study, high volume air sampling was performed to measure airborne concentrations of the pesticide methamidophos in a residential community in close proximity to aerial spraying. Sampling occurred before, during and 24 h post-application. To evaluate whether predictive models could reliably estimate residential exposure to methamidophos, an emission factor was used for estimating fluxes of volatilized material over the sprayed area for a 1-day post-application period. These flux estimates were then incorporated into a fugitive dust gaussian dispersion model (FDM) for assessing distribution of mass around the sprayed area. The predictive model output was compared with the field air sampler measurements. In our comparison, 1-day flux estimates from the model were found to be associated to observed field measurement data, with an r 2=0.63 the day of the spray and r 2=0.67 the day after the spray. The volatilization model however appears to underestimate surface emission flux immediately after the spray and overestimate the emission the next day.
Keywords: Pesticide; Methamidophos; Volatilization; Drift;
New Directions: Ozone-initiated reaction products indoors may be more harmful than ozone itself by Charles J. Weschler (5715-5716).