Check out our New Publishers' Select for Free Articles

Atmospheric Environment (v.39, #35)

Editorial board (pp. i).

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

A probabilistic modeling approach to assess human inhalation exposure risks to airborne aflatoxin B₁ (AFB₁) by C.-M. Chung-Min Liao; S.-C. Szu-Chieh Chen (pp. 6481-6490).

To assess how the human lung exposure to airborne aflatoxin B₁ (AFB₁) during on-farm activities including swine feeding, storage bin cleaning, corn harvest, and grain elevator loading/unloading, we present a probabilistic risk model, appraised with empirical data. The model integrates probabilistic exposure profiles from a compartmental lung model with the reconstructed dose–response relationships based on an empirical three-parameter Hill equation model, describing AFB₁ cytotoxicity for inhibition response in human bronchial epithelial cells, to quantitatively estimate the inhalation exposure risks. The risk assessment results implicate that exposure to airborne AFB₁ may pose no significance to corn harvest and grain elevator loading/unloading activities, yet a relatively high risk for swine feeding and storage bin cleaning. Applying a joint probability function method based on exceedence profiles, we estimate that a potential high risk for the bronchial region (inhibition=56.69% with 95% confidence interval (CI): 35.05–72.87%) and bronchiolar region (inhibition=44.93% with 95% CI: 21.61 – 66.78%) is alarming during swine feeding activity. We parameterized the proposed predictive model that should encourage a risk-management framework for discussion of carcinogenic risk in occupational settings where inhalation of AFB₁-contaminated dust occurs.

Keywords: Aflatoxins; Mycotoxins; Risk assessment; Lung; Probabilistic

Meteorologically adjusted trends of daily maximum ozone concentrations in Taipei, Taiwan by H.-C. Hsin-Chung Lu; T.-S. Tseng-Shuo Chang (pp. 6491-6501).

The meteorological conditions exert large impacts on ozone concentrations, and may mask the long-term trends in ozone concentrations resulting from precursor emissions. Estimation of long-term trends of ozone concentrations due to the changes in precursor emissions is important for corresponding control strategy. Multiple linear regression (method I), multilayer perceptron (MLP) neural network (method II) and Komogorov-Zurbenko (KZ) filter method plus MLP methodology (method III), are used to estimate the meteorologically adjusted long-term trends of daily maximum ozone concentrations by removing the masking effects of meteorological conditions in this study. The daily maximum ozone concentrations and relative meteorological variables were extracted from six air-monitoring stations in Taipei area from 1994 to 2001. The data collected during 1994–2000 period were used as modeling set and utilized to estimate the meteorologically adjusted trends, and the data of 2001 were used as the validation data. The meteorologically adjusted trends of ozone for these three methods were calculated and compared. The results show that both MLP and KZ filter +MLP models are more suitable than multiple linear regression for estimating the long-term trends of ozone in Taipei, Taiwan. The long-term linear trends of meteorologically adjusted ozone concentrations due to the precursor emissions show an increase trend at all stations, and the percent changes per year range from 1.0% to 2.25% during the modeling period in Taipei area.

Keywords: Meteorologically adjusted trend; Multiple linear regression; Multilayer perceptron neural network; Kolmogorov–Zurbenko filter

Measuring and simulating atmospheric concentration trends of polychlorinated biphenyls in the Northern Hemisphere by Hayley Hung; Sum Chi Lee; Frank Wania; Pierrette Blanchard; Ken Brice (pp. 6502-6512).

Temporal trend analysis of polychlorinated biphenyls (PCB) air concentration data measured in the Canadian Arctic and around the Great Lakes in the 1990s has shown that individual PCB congeners decline at different rates in air. The atmospheric decline rate of the same congener also varied from site to site. To determine whether these site-specific variations in atmospheric trends of PCB concentrations are controlled by changes in primary emissions or various removal processes in the environment (transfer to deep sea, freshwater sediment burial, reaction with OH radicals, degradation in media other than air), the measured trends are compared to those simulated by a zonally averaged global fate and transport model using historical emission estimates and realistic and hypothetical environmental scenarios. The modelled decline rates of a specific congener in both the North Polar and the North Temperate zones are similar and mimic closely those of the historical emission estimates fed into the model, suggesting that the rate of decline of PCB air concentrations during the 1990s was mostly driven by declines in primary emission. This implies that measured air concentration data reflect primary PCB emissions as long as these continue. Under the assumption that primary emission completely ceased after 2001, the model predicted that the terrestrial surface media would eventually become the only major global PCB reservoir, and the rate of concentration decline in air then depends solely on that in soil. Also, primary emissions and volatilization from soil, respectively, are the primary input to the atmosphere before and after primary emissions stopped. The model further illustrates that even during periods when primary emissions still dominate PCB air concentrations temperature-driven cycles of air/surface exchange may be observed. Large scale re-distribution of PCBs by the grass-hopper effect can thus also occur while primary emissions are still dominant.

Keywords: Atmospheric half-lives; Globo-POP; PCB emission; Environmental removal processes; Long-term air monitoring of POPs

Air mass characterization and source region analysis for the Gosan super-site, Korea, during the ACE-Asia 2001 field campaign by Jiyoung Kim; S.-C. Soon-Chang Yoon; Anne Jefferson; Wlodek Zahorowski; C.-H. Chang-Hee Kang (pp. 6513-6523).

This paper presents results of air mass characterization and the associated microphysical and optical properties of Asian aerosols, using the cluster analysis technique for classifying air mass back-trajectories arrived at Gosan on the Jeju Island, Korea during the ACE-Asia campaign. Five distinct clusters of trajectories were taken to explain each transport regime. The temporal variation of the transported air masses could be well explained by the consecutive and stepwise change of air masses between statistically classified clusters. The cluster-mean trajectory exhibited its close relationship with the synoptic-scale circulation pattern. In addition, it was shown that the composite of mean sea-level pressure field is useful for explaining favorable meteorological conditions for long-range transport of dust and anthropogenic pollution in East Asia. The highest light scattering and absorption coefficients for sub-10- and submicron aerosols as well as highest concentrations of²²²Rn and condensation nuclei are associated with the air mass types accompanying dusts and pollutants. The cluster-mean single scattering albedo (SSA) for sub-10- and submicron aerosols ranged 0.88–0.90 and 0.81–0.86, respectively. This value of SSA indicates the large contribution of submicron aerosol for the light absorption in East Asia. The concentration of²²²Rn and aerosol microphysical and optical properties for marine air mass suggests that the marine air masses are somewhat influenced by continental outflows. The minor differences in aerosol microphysical and optical properties among continental clusters with similar routes and different transport speed implies that the effect of transport speed may not be significant if the transport routes are similar.

Keywords: Air mass; Cluster analysis; Trajectory; Aerosol; ACE-Asia

Evaluation of an integrated modelling system containing a multi-layer perceptron model and the numerical weather prediction model HIRLAM for the forecasting of urban airborne pollutant concentrations by Harri Niska; Rantamaki Minna Rantam�ki; Teri Hiltunen; Ari Karppinen; Jaakko Kukkonen; Juhani Ruuskanen; Mikko Kolehmainen (pp. 6524-6536).

In this paper, a multi-layer perceptron (MLP) model and the Finnish variant of the numerical weather prediction model HIRLAM (High Resolution Limited Area Model) were integrated and evaluated for the forecasting in time of urban pollutant concentrations. The forecasts of the combination of the MLP and HIRLAM models are compared with the corresponding forecasts of the MLP models that utilise meteorologically pre-processed input data. A novel input selection method based on the use of a multi-objective genetic algorithm (MOGA) is applied in conjunction with the sensitivity analysis to reduce the excessively large number of potential meteorological input variables; its use improves the performance of the MLP model. The computed air quality forecasts contain the sequential hourly time series of the concentrations of nitrogen dioxide (NO₂) and fine particulate matter (PM_2.5) from May 2000 to April 2003; the corresponding concentrations have also been measured at two urban air quality stations in Helsinki. The results obtained with the MLP models that use HIRLAM forecasts show fairly good overall agreement for both pollutants. The model performance is substantially better, when the HIRLAM forecasts are used, compared with those obtained both using either HIRLAM analysis data or meteorological pre-processor, for both pollutants. The performance of the currently widely used statistical forecasting methods (such as those based on neural networks) could therefore be significantly improved by using the forecasts of NWP models, instead of the conventionally utilised directly measured or meteorological pre-processed input data. However, the performance of all operational models considered is relatively worse in the course of air pollution episodes.

Keywords: Multi-layer perceptron; Numerical weather prediction; Genetic algorithms; Air quality forecasting; Model input selection

Extratropical case study of stratosphere–troposphere exchange using multivariate analyses from mozaic aircraft data by F. Fran�ois Borchi; Emmanouil Oikonomou; Alain Marenco (pp. 6537-6549).

A multivariate analysis methodology, applied to ozone, water vapour and potential temperature data collected from MOZAIC aircraft allowed to identify and to quantify three types of air masses directly linked to stratosphere-troposphere exchanges (STE). These air masses occurred in February 1997 over the North Atlantic during the development of a Rossby wave, which is manifested in the form of four different structures, namely trough, ridge, streamer and cut-off low (COL). Here a study is conducted on 20 isobaric (i.e. at 230hPa) flights crossing all these upper-level structures. It is shown that the first type of air mass corresponds to a mixed zone between the stratosphere and the troposphere when the tropopause is poorly defined and when there exist medium values and weak gradients of ozone, potential temperature and humidity. The second type of air mass reveals an irreversible transport from the troposphere to the stratosphere for all these structures leading to a “wet�? stratosphere with high values of water vapour. The third type of air mass corresponds to the classical stratosphere with high values of ozone and low values of water vapour. The comparison with the model results of Kowol-Santen et al. (2000) shows that these first two air masses are directly linked to either diabatic processes or turbulent diffusion depending on the orientation and the type of the structure. The western side of the trough (with no mixing zone on the eastern side) and the ridge are dominated by clear air turbulence (CAT). On the other hand, the decay of the COL seems to be the result of strong convection on its northern and eastern flanks. Concerning the decay of the streamer, it is found to be due to both diabatic and turbulent processes. The above results suggest that the existence of a mixing zone during STE seems to be a more realistic concept instead of that where the tropopause is considered as a surface.

Keywords: MOZAIC; Stratosphere–troposphere exchange; Trough and ridge; Cut-off low; Streamer; Multivariate analyses

Temperature trends in twentieth century at Pune, India by Alaka Gadgil; Amit Dhorde (pp. 6550-6556).

Climatic change is one of the most important issues of present times. Unlike the greenhouse gases, which have a predominantly warming effect, atmospheric aerosols could either warm or cool the atmosphere depending upon the size, distribution and optical properties. Of all the climatic elements, temperature plays a major role in detecting climatic change brought about by urbanization and industrialization. This paper, therefore, attempts to study temporal variation in temperature over Pune city, India, during the period 1901–2000. The long-term change in temperature has been evaluated by Mann–Kendall rank statistics and linear trend. The analysis reveals significant decrease in mean annual and mean maximum temperature. This decrease in temperature is more pronounced during the winter season, which can be ascribed to a significant increase in the amount of suspended particulate matter (SPM) in the ambient air during the last decade. On the contrary, monsoon season shows warming. This warming can be attributed to a significant increase in the low cloud amount.

Keywords: Urbanization; Mann–Kendall rank statistics; Cooling trend; Aerosols; SPM

Kinetic study of the reactions of NO₂ with polycyclic aromatic hydrocarbons adsorbed on silica particles by Emilie Perraudin; H. H�l�ne Budzinski; Eric Villenave (pp. 6557-6567).

This experimental work deals with the kinetic study of the reactions of nitrogen dioxide (NO₂) radical with tri- to hexa-aromatic hydrocarbons adsorbed on silica particles. Measurements were performed using a flow-tube, at 295K, in the absence of light. Polycyclic aromatic hydrocarbons (PAHs) were extracted from particles by focused microwave extraction and analyses were performed using gas chromatography coupled to mass spectrometry (GC/MS). Rate constants varied from 1.4×10⁻³ to 4×10⁻⁸s⁻¹, depending on the structure of the PAH, for NO₂ concentration of 1.5×10¹²moleculescm⁻³. Benzo[ a]pyrene was the most reactive, with a lifetime regarding NO₂ of a few minutes in polluted air conditions. The comparison of these results with those previously reported for carbonaceous particles leads to the conclusion that gas/solid interface reactivity of PAHs depends on the nature of the particle.

Keywords: PAHs; Mineral particles; Silica; Reactivity; Kinetics; NO; ₂

An extremely low visibility event over the Guangzhou region: A case study by Dui Wu; Xuexi Tie; Chengcai Li; Zhuming Ying; Alexis Kai-Hon Lau; Jian Huang; Xuejiao Deng; Xueyan Bi (pp. 6568-6577).

Over the Guangzhou region, also called the Pearl River Delta (PRD) of Southern China, there are often high aerosol concentrations. The satellite (MODIS) data show that the aerosol optical depth is often higher than 0.6 in this area, which is known as Asian Brown Cloud region. In some extreme events, these high aerosol levels have caused very low visibilities. In this paper, we will show that on 2 November 2003, the daily average visibility is less than 2km (the instantaneous value is less than 200m), and the aerosol optical depth is greater than 1.2. We analyze the cause of this particular event. The analysis indicates that this event is related to the hurricane of “Melor 0319�?. The hurricane is located at the northwest Philippines on 2 November 2003, and the Guangzhou region is outside the hurricane. The hurricane produces a strong descent motion in the lower troposphere, a weak surface wind speed, and a relatively low planetary boundary layer (PBL) in the Guangzhou region. As a result, the strong subsidence causes descending air motions to force the aerosol particles into a very shallow layer, and the weak horizontal wind acts to keep the aerosol particles inside the source region, producing very high aerosol concentrations and extremely low visibility in the Guangzhou region on 2 November 2003. This case analysis will be useful to better understand the causes of the poor air quality over Guangzhou, which is a first step for ultimately improving it in the future. For example, one can reduce emissions when synoptic conditions are expected to cause recurrences of the phenomenon discussed in the paper.

Keywords: Aerosol; Asian Brown Cloud (ABC); Visibility; Guangzhou

Chemical composition of surface films on glass windows and implications for atmospheric chemistry by Buuan Lam; Miriam L. Diamond; Andre Andr� J. Simpson; Paul A. Makar; Jennifer Truong; Nadia A. Hernandez-Martinez (pp. 6578-6586).

Atmospherically derived surface films that cover impervious surfaces in cities, have areas comparable to that of atmospheric particulate matter (PM). The films compete with PM for sorption of volatile and semi-volatile organic compounds and alter the functionality of urban surfaces. The determination of surface-film composition is therefore vital to understanding their role in mediating chemical fate and transport within cities. Here, we show the composition of urban surface films collected from windows in downtown Toronto (Ontario, Canada) to be comprised of ∼94% inorganic compounds of which 8% are sulfate, 7% nitrate and 18% metals. Approximately 5% of the urban film mass is organic carbon, with ∼35% of the organic carbon mass corresponding to carbohydrates, ∼35% aliphatics, ∼20% aromatics and ∼10% carbonyls. The composition of surface films differs significantly from that of PM, suggesting differential accumulation, depositional degradation, and/or processes within films differing from those affecting PM. A rigid polymeric component comprising a small fraction of the organic carbon was also found, which may suggest direct deposition from environmental sources, or possible secondary in situ reactions within the film. Here, we suggest a potential mechanism for the oxidation of surface films to form organic polymers via radical initiation processes. Thus, the composition of surface films has important implications for chemical fate of contaminants within cities and presents a significant aspect of contaminant uptake that has not been considered in many air-quality models.

Keywords: Surface-air exchange; Impervious surfaces; Urban air chemistry; NMR; Atmospheric deposition

Study of the profile of polycyclic aromatic hydrocarbons in atmospheric particles (PM₁₀) using multivariate methods by Juliana Braga Dallarosa; Elba Calesso Teixeira; Mar�al Pires; Jandyra Fachel (pp. 6587-6596).

The scope of the present study is to identify and quantify the main sources of polycyclic aromatic hydrocarbons (PAHs) in the Candiota region, Rio Grande do Sul, Brazil. Four sampling sites at a distance of 50km from the emission source were selected: Aceguá, Aeroporto, 8 de Agosto and Pedras Altas. Samples were collected from February 2001 to October 2001, using an HV PM₁₀ sampler for high volumes during a continuous period of 24h every 15 days. The filters containing the particulate matter were extracted with dichloromethane in soxhlet and later analyzed by gas chromatography/mass spectrometry (GC/MS). The average concentrations of PAHs varied from 0.051 to 1.791ngm⁻³. The analysis of their distribution amongst the main emission sources was done through the diagnosis of concentration ratios of PAHs, as well as using statistical methods like factor analysis. The statistical analysis separated the 13 compounds studied in 3 Factors, grouping under Factor 1 emissions from the combustion of coal and wood, under Factor 2 vehicular emissions from the combustion of diesel oil and gasoline and under Factor 3 emissions from unburned diesel oil and gasoline.

Keywords: Polycyclic aromatic hydrocarbons; Air quality; Atmospheric particulate; Coal combustion

Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—2. Dialdehydes, methylglyoxal, and diketones by Kelley C. Barsanti; James F. Pankow (pp. 6597-6607).

Predicting the formation of organic particulate matter (OPM) in the atmosphere by absorptive gas/particle partitioning requires a knowledge of the identities, atmospheric levels, and physical properties of all condensable species. Data from field and chamber experiments have shown that a portion of atmospheric OPM samples are comprised of products generated during oxidation of volatile organic compounds. It has been suggested that some of these initially formed oxidation products also contribute to the formation of atmospheric OPM via molecular-weight (MW) building “accretion reactions�?. The role of such reactions as well as a general theoretical approach for evaluating their thermodynamic relevance in regard to atmospheric OPM formation, have been discussed in prior work. This work utilizes that approach in considerations of accretion reactions of glyoxal, two other dialdehydes, methylglyoxal, and two diketones. The methods used to predict free energy of formation (ΔGf°) values (and hence equilibrium constant (K) values) indicate that: (1) for 1,4-butanedial, 2,3-butanedione, and 2,5-hexanedione, the accretion reactions considered are not favorable; (2) for C₆ and higher dialdehydes, reaction by aldol condensation may contribute to atmospheric OPM formation under certain circumstances, if kinetically favorable; and (3) for glyoxal, diol and subsequent oligomer formation, and for methylglyoxal, aldol condensation, are thermodynamically favorable, and may contribute significantly to OPM in the atmosphere, if kinetically favorable.

Keywords: Secondary organic aerosol (SOA); Organic aerosol formation; Organic particulate matter (OPM); Oligomers; Aldol condensation

Study of scavenging of submicron-sized aerosol particles by thunderstorm rain events by D.M. Chate (pp. 6608-6619).

Observed scavenging coefficients for 0.013–0.75μm particles are between 1.08×10⁻⁵ and 7.58×10⁻⁴s⁻¹. Based on observed results a correlation between scavenging coefficient and rain intensity is obtained to study below thundercloud scavenging of atmospheric aerosols during thunderstorm rain events. When the rain intensity increases from 5.24 to 45.54mmh⁻¹, the corresponding scavenging coefficient increases from 0.5×10⁻⁵ to 4×10⁻⁵s⁻¹ for thunderstorm rain episodes. The overall scavenging coefficients for 0.02 – 10μm particles at different rainfall rates are estimated from contributions of Brownian diffusion, directional interception, inertial impaction, thermophoresis, diffusiophoresis and electrical forces during thunderstorms. The evolutions of PSD are predicted at different time intervals with theoretical scavenging rates. Comparison of observed evolutions of PSD during thunderstorm rain events with predicted evolutions of PSD shows an order of discrepancy between the observed and model results. Possible causes for discrepancy are discussed in terms of uncertainties in observed data and shortcomings in theoretical approach. The present results are useful for recommendations for the type of experimental setup essential for the field study of precipitation scavenging and improvements in theoretical approach close to atmospheric conditions during thunderstorm rain events.

Keywords: Wet scavenging; Electrical scavenging mechanism; Diffusiophoresis; Thermophoresis; Directional interception

Estimation of the radiative forcing by key aerosol types in worldwide locations using a column model and AERONET data by S.-C. Soon-Chang Yoon; J.-G. Jae-Gwang Won; Ali H. Omar; S.-W. Sang-Woo Kim; B.-J. Byung-Ju Sohn (pp. 6620-6630).

The aerosol direct radiative forcing (ADRF) is calculated using aerosol robotic network (AERONET) data, and based on aerosol categorization results, the global ADRF is estimated. The CRM-2.1.2, a stand-alone version of the radiative transfer model implemented in NCAR's community climate model, CCM-3.6, is used for the evaluation. A method of determining the aerosol optical parameters is proposed for the ADRF calculation using AERONET data. Linear regression in the log–log plane makes it possible to represent the wavelength-dependent optical properties in the model using AERONET measurements.The local ADRF is estimated at Gosan, Jeju in Korea in Spring from 2001 to 2003, and the ground-based radiation measurements during the ACE-Asia IOP are used to validate the calculation. Using 3 years of AERONET data, the mean forcing efficiency at 500nm at Gosan in Spring season is evaluated as −80.5±13.2Wm⁻² at the surface and −29.9±4.9Wm⁻² at the top of atmosphere (TOA).The seasonal variations of the ADRF at eight AERONET sites are calculated from AERONET climatology data. The ADRF calculation at the TOA is compared with the CERES/Terra measurement, and the comparison verifies that the methodology used in this study is suitable for the global ADRF evaluation. Finally, the ADRF values in 14 regions are evaluated. Large ADRF values in Asia and Sahara regions suggest the relative importance of the aerosols on the energy budget in these regions.

Keywords: Aerosol direct radiative forcing (ADRF); CRM-2.1.2; AERONET; Wavelength-dependent optical properties; ACE-Asia

Development of a local real world driving cycle for motorcycles for emission factor measurements by J.-H. Jiun-Horng Tsai; H.-L. Hung-Lung Chiang; Y.-C. Yi-Chun Hsu; B.-J. Bo-Jun Peng; R.-F. Rong-Fang Hung (pp. 6631-6641).

The development of driving cycles is important for the success of a mobile source management program. A comparison between a localized driving cycle (Kaohsiung Driving Cycle, KHM), European (Economic Commission of Europe Driving Cycle, ECE), USA, Japanese and Hong Kong cycles was investigated in this study. The CO, THC, NO _x and CO₂ emission factors of the entire KHM and ECE cycles as well as the speed–time relationship between these two cycles were also compared in this study. Results indicated that the KHM and ECE as well as worldwide harmonized motorcycle emissions certification/test procedure (WMTC) cycles were completely different in driving characteristic parameters, emission factors and fuel consumption. For example, the time percentages of acceleration and deceleration of ECE cycle are much less than those values in Kaohsiung city. In contrast, the duration of cruising mode (8.6%) in the Kaohsiung area driving cycle is lower than those of ECE (32.3%), WMTC (27–53%) Japanese 10–15 mode (21.2%) and Hong Kong (9.4%). Results further indicated the emission factor ratios of the KHM and ECE driving cycles of 2stroke new/in-use motorcycles for CO, THC, NO _x and CO₂ were 2.5/1.5, 1.5/1.3, 2.0/1.4 and 1.0/1.0, respectively. In addition, the emission factors in the KHM cycle for 4-stoke cycles are higher than those of the ECE. For fuel consumption, the KHM cycle was 10% higher than ECE cycle for the same engine type. Consequently, the KHM pattern developed in the present study for the Kaohsiung metropolitan area should be used to truly represent the traffic pattern, emission factor and fuel consumption.

Keywords: Driving cycle; Dynamometer testing; Emission factor; Fuel consumption

Comparative study of glass tube and mist chamber sampling techniques for the analysis of gaseous carbonyl compounds by S. Francois St�phanie Fran�ois; V. V�ronique Perraud; Maryline Pflieger; Anne Monod; Henri Wortham (pp. 6642-6653).

In this work, glass tube and mist chamber sampling techniques using 2,4-dinitrophenylhydrazine as derivative agent for the analysis of gaseous carbonyl compounds are compared. Trapping efficiencies of formaldehyde, acetaldehyde, propionaldehyde, acetone, acrolein, glyoxal, crotonaldehyde, benzaldehyde, butyraldehyde and valeraldehyde are experimentally determined using a gas-phase generator. In addition to generalise our results to all atmospheric gaseous compounds and derivative agents, theoretical trapping efficiencies and enrichment factors are expressed taking into account mechanisms involved in the two kinds of traps. Theoretical and experimental results show that, as expected, the trapping efficiencies of the glass tube depend mainly on solubility of compounds. The results provide new information and better understanding of phenomena occurring in the mist chamber and the ability of this sampler to concentrate the samples. Hence, the mist chamber is the more convenient sampling method when the trapping is associated to a fast derivatisation of the compounds and the glass tube technique must be used to trap atmospheric compounds without simultaneous derivatisation.

Keywords: Glass tube; Mist chamber; Simulation; Trapping efficiencies; Enrichment factors

Emissions of polycyclic aromatic hydrocarbons from combustion of agricultural and sylvicultural debris by Francisco J. Conde; Juan H. Ayala; Ana M. Afonso; Gonzalez Venerando Gonz�lez (pp. 6654-6663).

In this work, 28 parent and substituted-polycyclic aromatic hydrocarbons (PAHs) have been quantified in 76 smoke samples produced by burning pine wood, pine needles, prickly pear and almond skin using two different kinds of combustion devices. The results show a great variability in the total concentrations of the PAHs, while their proportions in the different samples are practically independent of the type of biomass that is burned. Just a few PAHs with low molecular weight—naphthalene, 1- and 2-methylnaphthalene, acenaphthylene and phenanthrene—are the most common in the different smoke samples, representing between 61% and 72% of the total. The high correlation coefficients between naphthalene and the total concentrations of PAHs, or between naphthalene and the concentrations of PAHs grouped by number of rings, demonstrate that all combustion processes studied are equally affected by the variables that regulate those processes. The results underscore the important role that naphthalene plays in the formation of higher molecular weight PAHs by pyrosynthesis and show that the naphthalene concentration can be used as an indicator of the total hydrocarbons content in the smoke.

Keywords: Pine wood; Pine needles; Prickly pear; Almond skin; Polycyclic aromatic hydrocarbons

Nitric acid measurements in connection with corrosion studies by Martin Ferm; Franco De Santis; Costas Varotsos (pp. 6664-6672).

Atmospheric nitric acid does not only contribute to acidification and eutrophication but causes also deterioration of many materials. Material belonging to our cultural heritage is irreplaceable and its lifetime can depend on the corrosion rate. Nowadays, only very few long-term measurements of nitric acid concentration in Europe and elsewhere have been published so far. Due to the fact that atmospheric corrosion is a long-term effect, the relevant research does not necessarily require monitoring of nitric acid on a daily basis. Moreover, power supply is often not available at sites where it is of interest to study the corrosion rate of objects belonging to our cultural heritage. Besides, such measurements must not disturb the impression of the objects. In this context, the diffusive sampling technique provides average concentrations over long-term periods at a low cost. In addition, the samplers used are noiseless, comparatively small in size, and thus, their ambient exposure can be made inconspicuously and with discretion. The present paper is focussed on an intensive corrosion study, which was performed at 11 rural and 23 urban sites in Europe and one rural site in Canada during 2002/2003. For the above-mentioned reasons, the diffusive sampler's technique was employed for the nitric acid monitoring, where the diffusive samplers were first tested against the denuder technique and bi-monthly measurements of nitric acid were thus obtained. The bi-monthly concentrations varied from 0.05 to 4.3μgm⁻³ and the annual averages from 0.16 to 2.0μgm⁻³. The observations collected, depicted a summertime maximum and a wintertime minimum in the nitric acid concentrations, except at the northern rural sites, where a maximum in the winter was observed. Furthermore, the observed nitric acid concentrations in Southern Europe were higher than in Northern Europe. In a few places, close to the sites of urban measurements, rural measurements of nitric acid were also performed. The obtained nitric acid concentrations were higher in the cities, especially during the period of maximum concentrations.

Keywords: HNO; ₃; Diffusive sampling; Urban; Rural; Europe

Micromixing modelling of mean and fluctuating scalar fields in the convective boundary layer by Ashok K. Luhar; Brian L. Sawford (pp. 6673-6685).

Coupling the concepts of the Lagrangian marked-particle approach and the interaction-by-exchange-with-the-conditional-mean (IECM) micromixing approach, a Lagrangian micromixing model is developed to calculate the mean and fluctuating scalar fields generated by scalar fluxes emitted into the convective boundary layer (CBL) from continuous area sources located at the top and bottom of the CBL. A continuous area source is simulated as a superposition of a series of instantaneous area sources. The scalar fields due to the continuous area sources are represented as the sum of top-down and bottom-up components with their cross-correlations included, and mixed-layer similarity is used for normalising the scalar quantities. The mixing time scale is parameterised as a linear function of time. The model-derived profile functions of top-down and bottom-up terms can be used to derive scalar concentration moments for any value of the ratio of the entrainment flux to the surface flux, including cases where a scalar material is extracted from the boundary layer (i.e. sinks). Model results on the concentration gradients; top-down and bottom-up profile functions; and scalar (temperature and humidity) variances, skewness and kurtosis are discussed; and compared with large-eddy simulation results and field and laboratory data where available. The comparison shows good performance by the Lagrangian micromixing model, considering the fact that the model used minimal flow information (i.e. the variance and third moment of the vertical turbulent velocity, and the turbulent kinetic energy dissipation rate) in the form of parameterised profiles.

Keywords: Top-down diffusion; Bottom-up diffusion; Continuous area sources; Lagrangian stochastic modelling; IECM model; Concentration moments; Flux-gradient relationship; Turbulent diffusion

The use of trajectory cluster analysis to examine the long-range transport of secondary inorganic aerosol in the UK by Salah S. Abdalmogith; Roy M. Harrison (pp. 6686-6695).

The influence of synoptic-scale atmospheric transport patterns on observed levels of sulphate, nitrate and PM₁₀ at Belfast (urban) and Harwell (rural) has been examined. Three-day 6-hourly back trajectories for January 2002 to December 2003, arriving at the two sampling locations at 1200 GMT and 900hPa were calculated. A K-means clustering algorithm is used to group these trajectories into 10 clusters depending on their direction and speed. Non-parametric statistics were used to test for significant differences in mean aerosol concentration across clusters. Significant inter-cluster differences were observed with highest nitrate and sulphate levels associated with south-easterly and easterly trajectory clusters at Belfast and Harwell respectively, and highest chloride concentrations associated with fast moving maritime trajectory categories at both sites. Easterly trajectory clusters show lower sulphate/nitrate ratios compared to other clusters, especially for air travelling from the near continent. Nitrate shows greater episodicity than sulphate with implications for achievement of the daily PM₁₀ limit value of 50μgm⁻³. Our trajectory analysis suggests that control of NO _x emissions from the UK and adjacent continental European countries has a major role to play in achieving compliance with the current PM₁₀ limit value.

Keywords: Back trajectory; Clustering; Sulphate; Nitrate; Chloride

Emissions of fine particles, NO _x, and CO from on-road vehicles in Finland by Tarja Yli-Tuomi; P. P�ivi Aarnio; Liisa Pirjola; Makela Timo M�kel�; Risto Hillamo; Matti Jantunen (pp. 6696-6706).

Real-time particle number size distributions and NO, NO₂, NO _x, CO, and CO₂ concentrations were measured with a mobile laboratory van in October 2003 on the streets and highways of the Helsinki metropolitan area, Finland. A bimodal particle size distribution was observed with about 85% of the particles being smaller than 29nm. Real-time fuel-based emission factors for size-resolved particle numbers, CO, and NO _x were determined. Wide distributions of emission factors were obtained for all pollutants. In addition, PM_2.5 samples were collected and the elemental compositions were analysed. Relative to fixed site urban PM_2.5, street air PM_2.5 concentrations of Cu, BC, Fe, and Zn were elevated. Weather and road conditions influenced PM concentrations more than the differences between the city and highway traffic environments.

Keywords: Traffic; Particles; Carbon monoxide; Nitrogen oxides; Emission factors

Sections

Personal tools

Atmospheric Environment (v.39, #35)

Sections

Personal tools

Local resources

Atmospheric Environment (v.39, #35)