Atmospheric Environment (v.41, #34)

Reviews on atmospheric selenium: Emissions, speciation and fate by Hanjie Wen; Jean Carignan (7151-7165).
The atmosphere is an important transient reservoir of selenium (Se). According to recent evaluations of the global Se budget, approximately 13,000–19,000 tons of Se is cycled through the troposphere annually. Most studies suggest that atmospheric deposition is an important source of Se contamination and it is therefore critical to evaluate the source emissions and fate of Se in the atmosphere. This paper presents a broad overview of current state of knowledge and understanding of major aspects of atmospheric Se and its natural and anthropogenic sources. The significant physical and chemical species encountered in the atmosphere are examined and special attention is paid to atmospheric speciation and its atmospheric pathways and processes. In addition, thermodynamic and kinetic data for atmospheric Se speciation are provided, which aid our understanding and the modelling of Se behaviour in the atmospheric environment. We also document how Se isotopes might be useful for tracing atmospheric sources and pathways. Important gaps in our current knowledge of Se in the atmospheric environment are identified, and suggestions for future research are offered.
Keywords: Atmospheric selenium; Source; Flux; Atmospheric pathway; Physical and chemical speciation;

Mineral dust is a sink for chlorine in the marine boundary layer by Ryan C. Sullivan; Sergio A. Guazzotti; David A. Sodeman; Youhua Tang; Gregory R. Carmichael; Kimberly A. Prather (7166-7179).
Dust particles affect the budgets of important traces gases by providing a surface on which heterogeneous reactions can occur. The uptake of soluble species on dust alters the physical, chemical, and optical properties and the overall ability of dust to act as cloud condensation and ice nuclei. It is commonly assumed that all measured chloride in particulate filter samples is associated with sea-salt particles and any chloride in dust occurs as the result of internal mixtures of sea-salt and dust particles, formed by cloud processing. Here we show high temporal resolution data demonstrating the direct uptake of chlorine by dust via heterogeneous reaction with HCl(g). This reaction added significant amounts of chlorine to the dust particles during a major dust storm, representing 4–9% of the individual dust particle mass. Up to 65±4% of the dust particles contained chlorine due to this heterogeneous reaction during the dust front. Ignoring this process leads to an overestimation of sea-salt concentrations from bulk measurements, and an underestimation of the degree of sea-salt aging. The uptake of chloride will change the pH and hygroscopic properties of the dust and thus can influence the budgets of other reactive gases. Including this heterogeneous process in atmospheric measurements and chemical transport models will improve our ability to predict the atmosphere's composition and radiation budget with greater accuracy.
Keywords: Mineral dust; Heterogeneous chemistry; Chemical transport model; sea-salt aerosol; Single-particle analysis;

Temporal variability of selected air toxics in the United States by Michael C. McCarthy; Hilary R. Hafner; Lyle R. Chinkin; Jessica G. Charrier (7180-7194).
Ambient measurements of hazardous air pollutants (HAPs, air toxics) collected in the United States from 1990 to 2005 were analyzed for diurnal, seasonal, and/or annual variability and trends. Visual and statistical analyses were used to identify and quantify temporal variations in air toxics at national and regional levels. Sufficient data were available to analyze diurnal variability for 14 air toxics, seasonal variability for 24 air toxics, and annual trends for 26 air toxics. Four diurnal variation patterns were identified and labeled invariant, nighttime peak, morning peak, and daytime peak. Three distinct seasonal patterns were identified and labeled invariant, cool, and warm. Multiple air toxics showed consistent decreasing trends over three trend periods, 1990–2005, 1995–2005, and 2000–2005. Trends appeared to be relatively consistent within chemically similar pollutant groups. Hydrocarbons such as benzene, 1,3-butadiene, styrene, xylene, and toluene decreased by approximately 5% or more per year at more than half of all monitoring sites. Concentrations of carbonyl compounds such as formaldehyde, acetaldehyde, and propionaldehyde were equally likely to have increased or decreased at monitoring sites. Chlorinated volatile organic compounds (VOCs) such as tetrachloroethylene, dichloromethane, and methyl chloroform decreased at more than half of all monitoring sites, but decreases among these species were much more variable than among the hydrocarbons. Lead particles decreased in concentration at most monitoring sites, but trends in other metals were not consistent over time.
Keywords: Air quality; Diurnal; Trends; Seasonal; Air toxics; Hazardous air pollutants;

Journey-time exposure to particulate air pollution by John Gulliver; David J. Briggs (7195-7207).
Journey-time exposures to particulate air pollution were investigated in Leicester, UK, between January and March 2005. Samples of TSP, PM10, PM2.5, and PM1 were simultaneously collected using light scattering devices whilst journeys were made by walking an in-car. Over a period of two months, 33 pairs of walking and in-car measurements were collected along two circular routes. Average exposures while walking were seen to be higher than those found in-car for each of the particle fractions: average walking to in-car ratios were 1.2 (± 0.6), 1.5 (± 0.6), 1.3 (± 0.6), and 1.4 (± 0.6) μg m−3 for coarse (TSP–PM10), intermediate (PM10–PM2.5), fine (PM2.5–PM1), and very fine particles (PM1), respectively. Correlations between walking and in-car exposures were seen to be weak for coarse particles (r=0.10, p=0.58), moderate for the intermediate particles (r=0.49, p<0.01) but strong for fine (r=0.89, p<0.01) and very fine (r=0.90, P<0.01) particles. PM10 exposures while walking were on average 70% higher than a nearby roadside fixed-site monitor whilst in-car exposures were 25% higher than the same fixed-site monitor. Particles with an aerodynamic diameter of less than 2.5 μm were seen to be highly correlated between walking and in-car particle exposures and a rural fixed-site monitor about 30 km south of Leicester.
Keywords: Exposure; Personal monitoring; Particles; Transport; Microenvironment;

Spatial and seasonal variations of elemental composition in Mt. Everest (Qomolangma) snow/firn by Shichang Kang; Qianggong Zhang; Susan Kaspari; Dahe Qin; Zhiyuan Cong; Jiawen Ren; Paul A. Mayewski (7208-7218).
In May 2005, a total of 14 surface snow (0–10 cm) samples were collected along the climbing route from the advanced base camp to the summit (6500–8844 m a.s.l.) on the northern slope of Mt. Everest (Qomolangma). A 108 m firn/ice core was retrieved from the col of the East Rongbuk Glacier (28.03°N, 86.96°E, 6518 m a.s.l.) on the north eastern saddle of Mt. Everest in September 2002. Surface snow and the upper 3.5 m firn samples from the core were analyzed for major and trace elements by inductively coupled plasma mass spectroscopy (ICP-MS). Measurements show that crustal elements dominated both surface snow and the firn core, suggesting that Everest snow chemistry is mainly influenced by crustal aerosols from local rock or prevalent spring dust storms over southern/central Asia.There are no clear trends for element variations with elevation due to local crustal aerosol inputs or redistribution of surface snow by strong winds during the spring. Seasonal variability in snow/firn elements show that high elemental concentrations occur during the non-monsoon season and low values during the monsoon season. Ca, Cr, Cs, and Sr display the most distinct seasonal variations. Elemental concentrations (especially for heavy metals) at Mt. Everest are comparable with polar sites, generally lower than in suburban areas, and far lower than in large cities. This indicates that anthropogenic activities and heavy metal pollution have little effect on the Mt. Everest atmospheric environment. Everest firn core REE concentrations are the first reported in the region and seem to be comparable with those measured in modern and Last Glacial Maximum snow/ice samples from Greenland and Antarctica, and with precipitation samples from Japan and the East China Sea. This suggests that REE concentrations measured at Everest are representative of the background atmospheric environment.
Keywords: Snow/firn; Elements; Spatial and seasonal variations; Mt. Everest (Qomolangma);

Source origin of trace elements in PM from regional background, urban and industrial sites of Spain by X. Querol; M. Viana; A. Alastuey; F. Amato; T. Moreno; S. Castillo; J. Pey; J. de la Rosa; A. Sánchez de la Campa; B. Artíñano; P. Salvador; S. García Dos Santos; R. Fernández-Patier; S. Moreno-Grau; L. Negral; M.C. Minguillón; E. Monfort; J.I. Gil; A. Inza; L.A. Ortega; J.M. Santamaría; J. Zabalza (7219-7231).
Despite their significant role in source apportionment analysis, studies dedicated to the identification of tracer elements of emission sources of atmospheric particulate matter based on air quality data are relatively scarce. The studies describing tracer elements of specific sources currently available in the literature mostly focus on emissions from traffic or large-scale combustion processes (e.g. power plants), but not on specific industrial processes. Furthermore, marker elements are not usually determined at receptor sites, but during emission. In our study, trace element concentrations in PM10 and PM2.5 were determined at 33 monitoring stations in Spain throughout the period 1995–2006. Industrial emissions from different forms of metallurgy (steel, stainless steel, copper, zinc), ceramic and petrochemical industries were evaluated. Results obtained at sites with no significant industrial development allowed us to define usual concentration ranges for a number of trace elements in rural and urban background environments. At industrial and traffic hotspots, average trace metal concentrations were highest, exceeding rural background levels by even one order of magnitude in the cases of Cr, Mn, Cu, Zn, As, Sn, W, V, Ni, Cs and Pb. Steel production emissions were linked to high levels of Cr, Mn, Ni, Zn, Mo, Cd, Se and Sn (and probably Pb). Copper metallurgy areas showed high levels of As, Bi, Ga and Cu. Zinc metallurgy was characterised by high levels of Zn and Cd. Glazed ceramic production areas were linked to high levels of Zn, As, Se, Zr, Cs, Tl, Li, Co and Pb. High levels of Ni and V (in association) were tracers of petrochemical plants and/or fuel-oil combustion. At one site under the influence of heavy vessel traffic these elements could be considered tracers (although not exclusively) of shipping emissions. Levels of Zn–Ba and Cu–Sb were relatively high in urban areas when compared with industrialised regions due to tyre and brake abrasion, respectively.
Keywords: Marker trace elements; Receptor modelling; Industrial emissions; 2004/107/CE; Shipping emissions;

Effects of biodiesel on emissions of regulated air pollutants and polycyclic aromatic hydrocarbons under engine durability testing by Hsi-Hsien Yang; Shu-Mei Chien; Mei-Yu Lo; John Chi-Wei Lan; Wen-Chang Lu; Yong-Yuan Ku (7232-7240).
An 80,000-km durability test was performed on two engines using diesel and biodiesel (methyl ester of waste cooking oil) as fuel in order to examine emissions resulting from the use of biodiesel. The test biodiesel (B20) was blended with 80% diesel and 20% methyl ester derived from waste cooking oil. Emissions of regulated air pollutants, including CO, HC, NO x , particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) were measured at 20,000-km intervals. The identical-model engines were installed on a standard dynamometer equipped with a dilution tunnel used to measure the pollutants. To simulate real-world driving conditions, emission measurements were made in accordance with the United States Environmental Protection Agency (USEPA) FTP transient cycle guidelines. At 0 km of the durability test, HC, CO and PM emission levels were lower for the B20 engine than those for diesel. After running for 20,000 km and longer, they were higher. However, the deterioration coefficients for these regulated air pollutants were not statistically higher than 1.0, implying that the emission factors do not increase significantly after 80,000 km of driving. Total (gaseous+particulate phase) PAH emission levels for both B20 and diesel decreased as the driving mileage accumulated. However, for the engine using B20 fuel, particulate PAH emissions increased as engine mileage increased. The average total PAH emission factors were 1097 and 1437 μg bhp h−1 for B20 and diesel, respectively. For B20, the benzo[a]pyrene equivalence emission factors were 0.77, 0.24, 0.20, 7.48, 5.43 and 14.1 μg bhp h−1 for 2-, 3-, 4-, 5-, 6-ringed and total PAHs. Results show that B20 use can reduce both PAH emission and its corresponding carcinogenic potency.
Keywords: Long-term driving; Biodiesel; Polycyclic aromatic hydrocarbons; Durability testing; Deterioration coefficient;

Pesticides analysed in rainwater in Alsace region (Eastern France): Comparison between urban and rural sites by Anne Scheyer; Stéphane Morville; Philippe Mirabel; Maurice Millet (7241-7252).
Current-used pesticides commonly applied in Alsace region (Eastern France) on diverse crops (maize, vineyard, vegetables, etc.) were analysed, together with Lindane, in rainwater between January 2002 and June 2003 simultaneously on two sites situated in a typical rural (Erstein, France) and urban area (Strasbourg, France).Rainwater samples were collected on a weekly basis by using two automatic wet only collectors associated with an open collector for the measurement of rainwater height.Pesticides were analysed by GC-MSMS and extracted from rainwater by SPME. Two runs were performed. The first one was performed by using a PDMS (100 μm) fibre for pesticides where direct injection into GC is possible (alachlor, atrazine, azinphos-ethyl, azinphos-methyl, captan, chlorfenvinphos, dichlorvos, diflufenican, α- and β-endosulfan, iprodione, lindane, metolachlor, mevinphos, parathion-methyl, phosalone, phosmet, tebuconazole, triadimefon and trifluralin). The second run was performed by using PDMS/DVB fibre and this run concerns pesticides where a preliminary derivatisation step with pentafluorobenzylbromide (PFBBr) is required for very low volatiles (bromoxynil,2,4-MCPA, MCPP and 2,4-D) or thermo labiles (chlorotoluron, diuron and isoproturon) pesticides.Results showed that the more concentrated pesticides detected were those used as herbicides in large quantities in Alsace region for maize crops (alachlor, metolachlor and atrazine). Maximum concentrations for these herbicides have been measured during intensive applications periods on maize crops following by rapid decrease immediately after use.For Alachlor, most important peaks have been observed between 21 and 28 April 2003 (3327 ng L−1 at Erstein and 5590 ng L−1 at Strasbourg). This is also the case for Metolachlor where most important peak was observed during the same week.Concentrations of pesticides measured out of application periods were very low for many pesticides and some others where never detected during this period. This is the case for diflufenican which was detected only during application. Two important peaks of concentrations were observed; a first one (101 ng L−1) in Erstein in November 2002 (4–11 November) and a second one (762 ng L−1) also in Erstein (28 April–15 May).The same behaviour can be seen for chlorfenvinphos and phosalone which have been detected, respectively, 2 and 4 times in Erstein and Strasbourg at high concentrations (28 April 2003–15 May 2003, 187 ng L−1 of phosalone and 157 ng L−1 of chlorfenvinphos in Erstein).MCPP, 2,4 MCPA and 2,4-D have been detected at high concentrations in rainwater but for the other pesticides very episodically and mainly during their use in agriculture. Maximal concentrations of MCPP and 2,4 MCPA have been measured in Erstein between 28 April and 15 May (904 and 746 ng L−1, respectively).Comparison between rural and urban sites showed that concentrations in rural areas are generally higher except for pesticides commonly applied in urban areas like Diuron.No seasonal phenomenon was observed for Diuron. This herbicide has been detected in practically all of the rainwater samples in Strasbourg (40/41) with a maximum of 1025 ng L−1 (16–23 September 2002) in 38 samples on 41 in Erstein with a maximum of 317 ng L−1 (15–23 October 2002). The total concentration of Diuron measured between 4 March 2002 and 20 July 2003 is of 4721 ng L−1 in Strasbourg and 5025 ng L−1 in Erstein. This result shows that wet deposition of Diuron in urban and rural sites was equivalent and can be explained by the “urban use” of this molecule together with its potential persistence.
Keywords: Pesticides; Rainwater; Urban and rural areas; Temporal and geographical variations of concentrations;

Measurements of trace gases in the tropical tropopause layer by T.P. Marcy; P.J. Popp; R.S. Gao; D.W. Fahey; E.A. Ray; E.C. Richard; T.L. Thompson; E.L. Atlas; M. Loewenstein; S.C. Wofsy; S. Park; E.M. Weinstock; W.H. Swartz; M.J. Mahoney (7253-7261).
A unique dataset of airborne in situ observations of HCl, O3, HNO3, H2O, CO, CO2 and CH3Cl has been made in and near the tropical tropopause layer (TTL). A total of 16 profiles across the tropopause were obtained at latitudes between 10°N and 3°S from the NASA WB-57F high-altitude aircraft flying from Costa Rica. Few in situ measurements of these gases, particularly HCl and HNO3, have been reported for the TTL. The general features of the trace gas vertical profiles are consistent with the concept of the TTL as distinct from the lower troposphere and lower stratosphere. A combination of the tracer profiles and correlations with O3 is used to show that a measurable amount of stratospheric air is mixed into this region. The HCl measurements offer an important constraint on stratospheric mixing into the TTL because once the contribution from halocarbon decomposition is quantified, the remaining HCl (>60% in this study) must have a stratospheric source. Stratospheric HCl in the TTL brings with it a proportional amount of stratospheric O3. Quantifying the sources of O3 in the TTL is important because O3 is particularly effective as a greenhouse gas in the tropopause region.
Keywords: Tropical; Tropopause; Stratosphere; Hydrochloric acid; Ozone;

Pollution events over the East Mediterranean: Synergistic use of GOME, ground-based and sonde observations and models by A. Ladstätter-Weißenmayer; M. Kanakidou; J. Meyer-Arnek; E.V. Dermitzaki; A. Richter; M. Vrekoussis; F. Wittrock; J.P. Burrows (7262-7273).
The behaviour of ozone (O3) and two important precursors, nitrogen dioxide (NO2) and formaldehyde (HCHO), over the East Mediterranean in spring from 1996 to 2002 is studied in order to characterise the buildup of tropospheric O3. The vertical distribution of O3 observed over Crete during the Photochemical Activity and Solar Ultraviolet Radiation (PAUR II) campaign in May 1999 has been used for validation of satellite-derived data. Retrievals of O3 columns from measurements of backscattered radiation by Global Ozone Monitoring Experiment (GOME) are compared with Total Ozone Mapping Spectrometer (TOMS), balloon, Systeme d’Analyse par Observation Zenithale (SAOZ) and LIDAR observations. The total O3 vertical columns vary between 270 and 402 DU and correlate well with changes in air circulation patterns. The total observed variability in tropospheric O3 is about 25 DU. Chemical box model calculations associate the GOME-observed NO2 and HCHO tropospheric columns with a potential of daily photochemical enhancement in the tropospheric O3 columns of about 0.8–1 DU over Crete and estimate the daily potential of regional photochemical buildup within upwind polluted air masses at about 2–8 DU. A Langrangian analysis attributes at most 10–20 DU of tropospheric O3 to stratosphere–troposphere exchange (STE). The remainder is attributed to long-range transport of O3 from industrial regions in Central Europe. From 1996 to 2002, in May no significant inter-annual variation in the tropospheric NO2 and HCHO columns over Crete has been observed by GOME suggesting no detectable increase in regionally produced tropospheric O3.
Keywords: Pollution; East Mediterranean; GOME; Ground-based measurements; Sonde observations; Model output;

Effect of global climatic change on carbonation progress of concrete by In-Seok Yoon; Oğuzhan Çopuroğlu; Ki-Bong Park (7274-7285).
In the recent years, global warming has dramatically increased the atmospheric carbon-dioxide (CO2) concentration and temperature. As a consequence of this, carbonation has become one of the most critical durability issues for concrete structures in urban environment.In this study, the climate scenario IS92a recommended by Intergovernmental Panel on Climate Change (IPCC) is used for evaluating the effect of CO2 concentration on carbonation of concrete. A modified mathematical equation, based on Fick's 1st law of diffusion, is used to evaluate CO2 diffusion coefficient of concrete. The required cover depth of concrete is estimated by using the applicative methods of reliability and stochastic concepts to take microclimatic conditions into consideration.The tolerance of cover depth should be considered in order to prevent carbonation-induced corrosion. From the relationship between the weight loss of reinforcement and corrosion current density for a given time, the tolerance of cover depth to prevent carbonation-induced corrosion is suggested. It was observed that corrosion occurs when the distance between carbonation front and reinforcement bar surface (the uncarbonated depth) is <5 mm.
Keywords: Carbonation of concrete; CO2 diffusion coefficient; Global warming phenomena; Microclimatic condition; Tolerance of cover depth;

A gas/aerosol air pollutants study over the urban area of Rome using a comprehensive chemical transport model by Claudio Gariazzo; Camillo Silibello; Sandro Finardi; Paola Radice; Antonio Piersanti; Giuseppe Calori; Angelo Cecinato; Cinzia Perrino; Fabio Nussio; Marco Cagnoli; Armando Pelliccioni; Gian Paolo Gobbi; Patrizia Di Filippo (7286-7303).
The aim of this study was to identify areas of potential relevant exposure to pollutants within Rome's urban core. To meet this goal, intensive field campaigns were conducted and simulations were performed, using the flexible air quality regional model (FARM), to study winter and summer pollution episodes. The simulations were performed using a complete emission inventory that included traffic flow model results of the Roman street network to better describe, with respect to the available diffuse national emission inventory, the hourly variation of traffic emissions in the city. The meteorological reconstruction was performed by means of both prognostic and diagnostic models by using experimental data collected during the field campaigns. To evaluate the capability of the FARM model to capture the main features of the selected episodes, a comparison of modelled results against observed air quality data for different pollutants was performed at urban and rural sites. FARM performed well in predicting ozone (O3) and nitrogen dioxide (NO2) concentrations, showing a good reproduction of both daily peaks and their diurnal variations. The model also showed a good capability to reproduce the magnitude of volatile alkane, aromatic and carbonyl compound concentrations. PM10 model results revealed the tendency to under-predict the observed values. PM composition model results were compared with observed data, evidencing good results for elemental carbon (EC), nitrate (NO3 ) and ammonium (NH4 +), underestimation for sulphate (SO4 2−) and poor performance for organic matter (OM). The soil components of PM were found to be significantly under-predicted by the model, especially during Saharan dust episodes. Overall, the study results show large areas of high O3 and PM10 concentrations where levels of pollutants should be carefully monitored and population exposure evaluated.
Keywords: Data assimilation; Population exposure; Ozone; VOC; PM10;

A large eddy simulation (LES) model that accounts for chemical reactions between oxides of nitrogen and ozone has been used to investigate the effect of local shading within an idealised street canyon on pollutant concentrations. It has shown that local shading can have a substantial impact on kerbside concentrations (>6 ppb difference for some situations presented) and that this may need to be taken into account to set up numerical model runs as well as sampling sites. A sensitivity study has been performed to investigate the effect of various governing parameters. A strong influence was found for the actual reduction of the photolytic rate constant within the shaded areas. A near linear relationship appeared between the reduction and the effect on pollutant concentrations. The chemical regime above and within the street canyon (determined by background concentrations aloft and emission rates at the ground) was also shown to be of high importance. The geometrical layout of the shading within the canyon and the wind speed in the canyon was shown to affect the spatial distribution of the shading effect rather than its overall magnitude.
Keywords: Large eddy simulation; Street canyon modelling; Nitrogen dioxide; Ozone; Shading effect; Photolysis rate;

Aerosol climatology and discrimination of different types over Athens, Greece, based on MODIS data by D.G. Kaskaoutis; P. Kosmopoulos; H.D. Kambezidis; P.T. Nastos (7315-7329).
A long-term (2000–2005) monitoring of aerosol data from the moderate resolution imaging spectroradiometer (MODIS) is analyzed focusing on the Greater Athens Area (GAA) in the Eastern Mediterranean region. The MODIS aerosol optical depth standard product (AOD at 550 nm) and its respective ratio attributed to fine-mode (FM) particles are employed to evaluate the seasonal variability of the aerosol properties over Athens. The climatological trend of both parameters in the period 2000–2005 is nearly absent, while remarkable year-to-year variability can be observed. The seasonal analysis reveals a significant AOD variability over Athens, with minimum values in winter ( AOD 550 ∼ 0.2 ) , and maximum in summer ( AOD 550 ∼ 0.45 ) . Regarding the FM fraction, maximum values are present in spring and minimum in summer, thus revealing the dominance of FM and coarse-mode particles, respectively. For the whole data set, a method is implemented to distinguish the main aerosol types (urban/industrial (hereafter UI), clean maritime (hereafter CM type) and desert dust (hereafter DD) over Athens, based on both AOD and FM values. Because of the mixing processes in the atmosphere the majority of the cases (46.6%) belong to a mixed (hereafter MT) aerosol type. The UI aerosols are more frequent in spring (41.2%) and less in winter (9.1%), while the coarse particles, probably DD, more frequent in summer (35.8%) and less in winter (3.5%). In contrast, the clean atmospheric conditions are more frequent in winter (23.9%), when the mixing processes are also well established (63.5%). For each aerosol type, the mean AOD 550 and FM values are also computed. Their seasonal variability exhibits a clear summer maximum for UI, CM and MT aerosols, while the DD exhibits maximum in spring. As regards the FM values of the different aerosol types they exhibit a rather constant variation with small fluctuations from season to season.
Keywords: Aerosol optical depth; Fine-mode fraction; MODIS; Aerosol types; Athens; Greece;

Using the relative technique, rate coefficients have been measured for the gas phase reactions of hydroxyl radicals with four fluoroacetates, methyl trifluoroacetate (CF3COOCH3), ethyl trifluoroacetate (CF3COOCH2CH3), methyl difluoroacetate (CF2HCOOCH3) and 2,2,2-trifluoroethyl trifluoroacetate (CF3COOCH2CF3). Experiments were carried out at 296±2 K and atmospheric pressure (∼750 Torr) using nitrogen or synthetic air as bath gases. The following rate coefficients were derived for the reaction of OH radicals (in units of cm3  mol−1  s−1) with CF3COOCH3, k=(4.97±1.04)×10−14, CF3COOCH2CH3, k=(2.64±0.59)×10−13, CF2HCOOCH3, k=(1.48±0.34)×10−13 and CF3COOCH2CF3, (1.05±0.23)×10−13. The rate constants obtained are compared with previous literature data of other volatile organic compounds to establish reactivity trends. Atmospheric implications are discussed in terms of lifetimes and fates of the fluoroacetates in the troposphere.
Keywords: Fluoroacetates; Hydroxyl radicals; Rate constants; Tropospheric chemistry;

Polycyclic aromatic hydrocarbons in Costa Rican air and soil: A tropical/temperate comparison by Gillian L. Daly; Ying D. Lei; Luisa E. Castillo; Derek C.G. Muir; Frank Wania (7339-7350).
Surface soil and passive air samples from a network of 23 sampling sites across Costa Rica were analyzed for polycyclic aromatic hydrocarbons (PAHs), allowing for an evaluation of absolute levels, spatial distribution patterns, air/soil concentration (A/S) ratios and relative composition. Annual mean concentrations of four-ring PAHs in air were low (median of approximately 40 pg m−3), except in Costa Rica's densely populated central valley (approximately 650 pg m−3). PAH concentrations in soil were also low (median of 5 ng g−1 dry weight) and comparable to those reported for other tropical regions. These low soil concentrations result in A/S ratios of four-ring PAHs in Costa Rica that are higher than the equilibrium air–soil partitioning coefficients and also higher than A/S ratios reported for temperate locations. A series of model calculations of increasing complexity were used to seek an explanation for variable A/S ratios of PAHs under tropical and temperate conditions. Temperature-driven changes in air–soil partitioning and differences in PAH degradability under temperate and tropical conditions are insufficient to explain the higher soil concentrations and lower A/S ratios in temperate regions. However, these can be explained by atmospheric deposition of PAHs during historical periods of much higher emissions and air concentrations and by persistence of PAHs in soils on the order of decades. Low PAH concentrations in tropical soils were found to be consistent with constant or increasing emissions, and in particular, do not require that degradation rates in soil are much faster than in temperate areas. In comparison to temperate soils, soils from Costa Rica and other tropical regions have a higher relative abundance of the lighter PAHs. This likely reflects a higher source contribution from biomass burning in the tropics, as well as the preferential loss of lighter PAHs from temperate soils that experienced high PAH deposition in the past.
Keywords: Polycyclic aromatic hydrocarbons; Soil; Air; Costa Rica; Tropical environment; Mountain; Air–soil distribution;

Chemical composition of the fine and coarse fraction of aerosols in the northeastern Mediterranean by Mustafa Koçak; Nikos Mihalopoulos; Nilgün Kubilay (7351-7368).
Two-stage aerosol samples (PM10–2.5 and PM2.5) were collected at a coastal rural site located in the northeastern Mediterranean, between April 2001 and 2002. A total of 562 aerosol samples were analyzed for trace elements (Fe, Ti, Mn, Ca, V, Ni, Zn, Cr) and water-soluble ions (Na+, NH4 +, K+, Mg2+, Ca2+, Cl, Br, NO3 , SO4 2−, C2O4 2− and MS:methane sulfonate). PM10, crustal elements, sea salt aerosols and NO3 were mainly associated with the coarse mode whereas non-sea salt (nss)SO4 2−, C2O4 2−; MS, NH4 +, Cr and Ni were found predominantly in the fine fraction. Concentrations of aerosol species exhibited orders of magnitude change from day to day and the aerosol chemical composition is heavily affected by dust events under the influence of airflow from North Africa. During the sampling period, 11 specific mineral dust events of duration varying from 1 day to a week have been identified and their influence on the chemical composition of aerosols has been studied in detail. Ionic balance analysis performed in the coarse and fine aerosol fractions indicated anion and cation deficiency due to CO3 2− and H+, respectively. A relationship between nssSO4 2− and NH4 + denoted that sulfate particles were partially neutralized (70%) by ammonium. Excess-K/BC presented two distinct ratios for winter and summer, indicating two different sources: fossil fuel burning in winter and biomass burning in summer.
Keywords: Chemical composition; Fine and coarse mode; Dust; Northeastern Mediterranean; Sources;

Comment on ‘Long-term atmospheric measurements of C1–C5 alkyl nitrates in the Pearl River Delta region of southeast China’ by Simpson et al. by A.T. Archibald; M.A.H. Khan; L.A. Watson; K.C. Clemitshaw; S.R. Utembe; M.E. Jenkin; D.E. Shallcross (7369-7370).

Reply to “Comment on ‘Long-term atmospheric measurements of C1–C5 alkyl nitrates in the Pearl River Delta region of southeast China’” by Isobel J. Simpson; Frank Flocke; Elliot Atlas; F. Sherwood Rowland; Simone Meinardi; Tao Wang; Hai Guo; Y.H. Kwok; Donald R. Blake (7371-7372).

New Directions: Enhancing the natural sulfur cycle to slow global warming by Oliver W. Wingenter; Scott M. Elliot; Donald R. Blake (7373-7375).