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Atmospheric Environment (v.40, #33)

Editorial board (pp. i).

Photochemical pollution under sea breeze conditions, during summer, at the Portuguese West Coast by Margarita G. Evtyugina; Teresa Nunes; Casimiro Pio; Carla Sandra Costa (pp. 6277-6293).

Photochemical pollution was studied at three sampling places located on the Portuguese West Coast along the coast-to-continent breeze direction, during the summer period. A first basic campaign (June–July 2001) covered mainly the monitoring of trace gases, volatile organic compounds (VOCs) and the vertical profiles of O₃. During a second auxiliary campaign (July 2002), the vertical profiles of pollutants (O₃ and VOCs) at the west coast point were further assessed. The important role of marine breezes on the formation and transport of photochemical pollutants has been confirmed.Vertical profiles of O₃ revealed a depletion of ozone at altitudes lower than 100–300m during the night and the early morning and a good vertical mixture during the day in the sea breeze boundary layer. The analysis of vertical profiles of VOCs revealed that lower concentrations tended to exist at the top of the sea breeze layer. However some compounds, such as n-hexane, showed a higher concentration at higher levels. The concentration of O₃ in the diurnal boundary layer, resulting from photochemical reactions of both the anthropogenic and biogenic precursors, gradually increased with the sea breeze inland, ranging from around 30ppb at midday on the coast, to 70ppb in the inland rural zone. However, in all sampling places, the photochemical pollution episodes at 80–100ppb level took place under particular conditions of high photochemical activity and see breeze circulation. As revealed from analyses of propylene equivalent concentrations, the photochemical formation of O₃ in the inland rural zone is strongly affected by biogenic VOCs (isoprene and monoterpenes), whereas a major contribution to the photochemical pollution with ozone in the coastal zone issued from anthropogenic VOCs (alkenes and aromatics).

Keywords: Photochemical pollution; Air transport; Portuguese West Coast; Sea breeze

Nocturnal sink of NO _x via NO₃ and N₂O₅ in the outflow from a source area in Japan by Jun Matsumoto; Kousuke Imagawa; Hidekazu Imai; Naohiro Kosugi; Masumi Ideguchi; Shungo Kato; Yoshizumi Kajii (pp. 6294-6302).

To understand the nocturnal sink of NO _x in the outflow from the Asian source area, simultaneous observations of NO₃, N₂O₅, and related compounds were conducted utilizing an instrument based on laser-induced fluorescence at Izu-Oshima Island, Japan, during June 2004. Consequently, significant levels of NO₃ and N₂O₅ were successfully observed, particularly in the polluted air mass originating from Tokyo. This observation concurred with the equilibrium among NO₃, NO₂, and N₂O₅ gases. As a result of steady-state analysis, nocturnal NO _x losses were evaluated as 1.8 and 0.2ppbv night⁻¹ for polluted and maritime air, respectively. It was confirmed that the nocturnal NO _x sink during the observation was promoted by the NO₃ loss by VOC. DMS is significant for nocturnal loss of NO _x over the sea.

Keywords: Nitrate radical; Dinitrogen pentoxide; Laser-induced fluorescence; NO; _x; sink in the outflow; Nocturnal atmosphere

Variation of H₂S and COS emission fluxes from Calamagrostis angustifolia Wetlands in Sanjiang Plain, Northeast China by Xinhua Li; Jingshuang Liu; Jisong Yang (pp. 6303-6312).

Using the static chamber and Chromatograph method, H₂S and COS emission fluxes from the mash meadow Calamagrostis angustifolia and typical meadow C. angustifolia in Sanjiang Plain Northeast China were measured during growth season (5–9 month), the results showed that the seasonal and diurnal variations of H₂S and COS emission fluxes were obvious, the mean emission fluxes of H₂S and COS from the mash meadow C. angustifolia were 0.34 and −0.29μgSm⁻²h⁻¹, respectively, and from typical meadow C. angustifolia were 0.14 and −0.20μgSm⁻²h⁻¹, respectively, the mean emission fluxes of H₂S and COS from the mash meadow C. angustifolia were both higher than their from typical meadow C. angustifolia. The C. angustifolia wetlands both can emit H₂S to the atmosphere and absorb COS from the atmosphere in the growth season. The H₂S and COS emission fluxes were affected by the C. angustifolia growth, and the H₂S emission peak and COS absorbed peak were observed during the bloom growth time. There were negative correlations of H₂S and COS emission fluxes in C. angustifolia Wetlands.

Keywords: Sanjiang Plain; Calamagrostis angustifolia; wetlands; Hydrogen sulfide; Carbonyl sulfide

Seasonal and diurnal variations of carbonyl compounds in Beijing ambient air by Xiaobing Pang; Yujing Mu (pp. 6313-6320).

The levels of carbonyl compounds in Beijing ambient air were measured from November 2004 to October 2005. Formaldehyde, acetaldehyde and acetone were found to be the most abundant carbonyls. The concentrations of formaldehyde, acetaldehyde and acetone increased to 19.51±6.34, 17.18±4.57, 22.14±5.98μgm⁻³, respectively, in summer from 5.14±2.56, 8.68±3.48, 9.18±3.27μgm⁻³ in winter. Carbonyls showed excellent correlations with ozone in summer and significant correlations with CO in winter, which indicated that the sources of carbonyls were dominated by photo-oxidation of VOCs in summer and vehicular exhaust in winter. The photolysis rates of lower carbonyls calculated based on local zenith angle were one magnitude greater in summer than in winter. The distribution frequencies of carbonyls were analyzed from a database including 350 samples. The concentrations of the highest frequency were 9.0–19.0, 5.0–15.0 and 13.0–23.0μgm⁻³ for formaldehyde, acetaldehyde and acetone, respectively.

Keywords: Carbonyl compounds; Photo-oxidation; Vehicular exhaust; Ozone

Mercury in fog on the Bay of Fundy (Canada) by Charles D. Ritchie; William Richards; Paul A. Arp (pp. 6321-6328).

Mercury concentrations in fog water, collected during the summer of 2003, were found to vary along a geospatial gradient from Grand Manan (an island at the mouth of the Bay of Fundy, with Hg levels 42–435ngl⁻¹), the main coastline of New Brunswick at Point Lepreau (2–33ngl⁻¹), to an inland location in Fredericton, Canada (3.5ngl⁻¹). Hg concentrations were higher during days when air masses were stationary and fog conditions were extended over several days. High concentrations on Grand Manan were most likely due to continued atmospheric deposition of Hg into fog banks of long duration, high air turbulence along the steep 100m cliffs, and decreasing droplet size with increasing air temperature during the course of the day. We found that fog Hg deposition was about 0.4–7.5% of wet Hg deposition along the coastal area, whereas on Grand Manan Island, fog Hg deposition from was 31–74% of wet Hg deposition.

Keywords: Fog; Mercury; Geospatial gradient; Atmospheric; Pollution; Grand Manan; Bay of Fundy; Air mass trajectories

Air/surface exchange of nitric oxide between two typical vegetable lands and the atmosphere in the Yangtze Delta, China by Shuangxi Fang; Yujing Mu (pp. 6329-6337).

Few researches had been carried out so far to study Air/surface exchange of nitric oxide between vegetable lands and the atmosphere. In this study, NO fluxes from two kinds of widely cultivated vegetable fields in the Yangtze Delta, China were measured with static chamber method. The average NO fluxes were 11.5 and 34.2ngNm⁻²s⁻¹ for cabbage (CA) and potato (PO) fields, respectively. The volatile NON from the applied fertilizer approximately amounted to 0.6% and 3.6% for CA and PO fields, respectively. The total amount of NO emitted from the vegetable lands in this area during the investigated period was roughly estimated to be 9.1GgN, which accounted for about 6.5% of the total emissions from uplands in China. These results indicated that the vegetable fields acted as an important source of atmospheric NO in this area.

Keywords: NO; Flux; Surface-exchange

Spatial variation of CO concentrations within an office building and outdoor influences by James T. Milner; Helen M. ApSimon; Ben Croxford (pp. 6338-6348).

This paper presents the results of a monitoring study to assess the spatial variation of CO concentrations within the Westminster City Council building, an office building close to two busy roads in Central London. In general, CO concentrations and correlations with outdoor CO were found to decrease both horizontally and vertically throughout the building away from the busy roads, while the time delay between outdoor and indoor peaks generally increased. This indicates that, within a building, the protection afforded by the building shell to outdoor pollution may be increased away from busy roads. Additionally, the local meteorological conditions were observed to influence significantly the CO concentrations. In particular, south-easterly winds resulted in the highest indoor and outdoor levels, although the highest I/O ratios were for north-westerly winds.

Keywords: Indoor CO; I/O ratio; Office building; Urban; Meteorological conditions

Assessment of vehicular and non-vehicular contributions to hydrocarbons using exclusive vehicular indicators by C.-C. Chih-Chung Chang; J.-L. Jia-Lin Wang; S.-C. Shaw-Chen Liu; S.-C. Shih-Chun Candice Lung (pp. 6349-6361).

This study investigates suitable non-methane hydrocarbon (NMHC) species to be used as motor vehicle indicators, and examines their possible applications and limitations. Suitable indicators are employed to assess vehicular and non-vehicular contributions of individual NMHCs in a given environment. The concept involves using concentration ratios of individual NMHCs to the indicators characteristic of vehicular emissions to reveal the excess concentration contributed by non-vehicular sources.By comparing the correlation between NMHCs and methyl tert-butyl ether (MTBE), a proven good motor vehicle indicator, in metropolitan Kaohsiung, Taiwan known for its heavy traffic and variety of heavy industries, it was found that 2,2-dimethylbutane (22DMC4A), 3-methylpentane (3MC5A), methylcyclopentane (McC5A), 2-methylhexane (2MC6A) and 3-methylhexane (3MC6A) revealed good concentration correlation with MTBE. The result implies these species in Kaohsiung have the same source as MTBE originated primarily from motor vehicle sources consisting of tailpipe exhaust and gasoline evaporation. 22DMC4A, 3MC5A, McC5A, 2MC6A and 3MC6A are common components in nearly all gasoline evaporation and tailpipe exhaust world-wide, and more exclusive to motor vehicle emissions. Moreover, they can be easily analyzed by the popular gas chromatography/flame ionization detection (GC/FID) and, thus can be the potential indicators to be applied generally in many regions of the world.Possible chemical and physical removals affecting the NMHCs/indicator ratios in the atmosphere are discussed. The ethylbenzene/ m,p-xylene ratios could be used as an effective indicator of photochemical removal degree to test and sift out the data affected by excessive photochemical reaction to enhance the accuracy of NMHC source apportionment.

Keywords: NMHC; Motor vehicle emissions; MTBE; Chemical mass balance

INDAIR: A probabilistic model of indoor air pollution in UK homes by C. Dimitroulopoulou; M.R. Ashmore; M.T.R. Hill; M.A. Byrne; R. Kinnersley (pp. 6362-6379).

A probabilistic model (INDAIR) has been developed to predict air pollutant concentrations in home microenvironments in the UK. The model has been parameterised using probability functions for four pollutants simultaneously (NO₂, CO, PM₁₀ and PM_2.5), under three emission scenarios (no source, cooking, smoking). Model predictions are broadly consistent with data on indoor concentrations in UK homes. Modelled mean concentrations were most sensitive to variation in outdoor concentrations, air exchange rate and deposition velocity in no-source scenarios, while modelled peak concentrations in source rooms were most sensitive to variation in emission rate and room size. Under model assumptions, smoking and cooking made a significant contribution to annual mean indoor concentrations of PM₁₀ and PM_2.5, gas cooking made a significant contribution to annual mean indoor NO₂ concentrations, while annual mean CO concentrations were dominated by infiltration of outdoor air. The modelled frequency distributions of 24h mean values showed 95 percentile concentrations that were typically twice the mean concentrations in no-source scenarios, and 3–4 times the mean concentration during emission peaks. The higher exposure of residents in homes at the upper ends of the frequency distributions may be associated with adverse health outcomes, and probabilistic modelling approaches can contribute to identification of the characteristics of homes with high indoor concentrations.

Keywords: Indoor air quality; Modelling; Carbon monoxide; Nitrogen dioxide; Particulate matter; PM; ₁₀; PM; _2.5

A preliminary assessment of major air pollutants in the city of Suzhou, China by Francesca Costabile; Giuliano Bertoni; Franco Desantis; Fenjuan Wang; Hong Weimin; Liu Fenglei; Ivo Allegrini (pp. 6380-6395).

Nitrogen oxides (NO₂ and NO _x), sulphur dioxide (SO₂), and benzene, toluene, xylene (BTX) in ambient air were preliminarily assessed, by diffusive sampling technique, in 2003 through three measurement campaigns at 100 locations in the Chinese city of Suzhou. Statistical analysis of space series so-generated was performed to infer source contributions and frequency distributions (FD). It was found that nitrogen oxides, benzene and xylene were mostly emitted from motor vehicles; in contrast, industrial sources were a major contributor to sulfur and toluene pollution. Normal FD (NFD) described significantly SO₂ in summer and NO₂ and NO _x in autumn (95% confidence interval); on the contrary, BTX presented a most peculiar FD rather different to the NFD. Lognormal distribution was often unacceptable. Predominant factors influencing FDs and its normality were found to be associated to those elements conditioning air pollutant diffusion: meteorology (wind speed and direction), relevant emission sources (especially for toluene), emission seasonality (mainly for SO₂ and NO _x), and photochemistry (mainly for NO₂ and xylene).

Keywords: Urban air pollution; Frequency distribution; Normality test; BTX; China

Characteristics of air exchange in a street canyon with ground heating by Xiaomin Xie; C.-H. Chun-Ho Liu; Dennis Y.C. Leung; Michael K.H. Leung (pp. 6396-6409).

This paper investigates the effects of solar radiation (in the form of ground-level heating) on the air exchange rate (AER) of an idealized street canyon using computational fluid dynamic (CFD) technique. A two-dimensional numerical model based on Reynolds-averaged Navier–Stokes equations equipped with the standard, Renormalization Group (RNG), and realizable k− ε turbulence models was developed using the commercial CFD code FLUENT. The newly developed numerical model was validated by published wind tunnel results with buoyancy force. It was found that different k− ε turbulence models yielded comparable simulation results. The sensitivity tests based on a street canyon of unity aspect ratio showed that the existence of buoyancy force markedly affected its airflow structure and AER, particularly under calm wind condition. The AER induced by vertical velocity fluctuationAERw″ is larger than that induced by mean vertical velocity AER _w. Their difference decreased with increasing the dimensionless parameter Gr/ Re². The functional relationship between total AER and Gr/ Re² could be expressed in the form of a second-order polynomial.

Keywords: Computational fluid dynamic (CFD) modeling; Ground-level heating; k; −; ε; turbulence models; Air exchange rate (AER)

Prediction of activity coefficients in liquid aerosol particles containing organic compounds, dissolved inorganic salts, and water—Part 1: Organic compounds and water by consideration of short- and long-range effects using X-UNIFAC.1 by Garnet B. Erdakos; William E. Asher; John H. Seinfeld; James F. Pankow (pp. 6410-6421).

The semi-empirical group contribution method (GCM) of Kikic et al. [Chem. Eng. Sci. 46 (1991) 2775–2780] for estimating activity coefficient ( ζ) values of neutral organic compounds and water in solutions composed of organic compounds, dissolved inorganic salts, and water is adapted for application to atmospheric particulate matter (PM). It is assumed that ζ values are determined by a combination of short- and long-range interactions. The ζ expression involves conventional UNIFAC terms and a Debye–Hückel term, with the former computed using group–group interaction parameters. Organic–organic interaction parameters are assigned the values from the UNIFAC-LLE model of Magnussen et al. [Ind. Eng. Chem. Process Design Develop. 20 (1981) 331–339]. Forty interaction parameters (ion–solvent group and anion–cation) were obtained from Kikic et al. [Chem. Eng. Sci. 46 (1991) 2775–2780], Achard et al. [Fluid Phase Equilibria 98 (1994) 71–89], and Ming and Russell [Am. Inst. Chem. Eng. J. 48 (2002) 1331–1348]. Twenty additional interaction parameters (ion–solvent group) are estimated based on 879 UNIQUAC-fitted ζ values for organic compounds and water. The fitted ζ values are based on liquid–liquid equilibrium (LLE) data for a range of ternary and quaternary organic/inorganic salt/water mixtures at 293–308K. The UNIQUAC fits are analogous to those described by Fredenslund et al. [Vapor–Liquid Equilibria Using UNIFAC: A Group-Contribution Method, Elsevier Scientific Publishing, New York, 1977]. The LLE mixture compositions range from primarily organic solutions to primarily aqueous solutions with maximum ionic strengths of ∼5molkg⁻¹. The groups characteristic of organic compounds found in atmospheric PM considered here include: CH₃–, –CH₂–,-CH|-,-C||-, –OH, –CH₂CO–, and –COOH. These are: single bonded carbon with three, two, one, and zero hydrogens, respectively, hydroxyl, –CH₂-carbonyl, and carboxyl, respectively. The inorganic salts represented in the mixture data include NaCl, NaNO₃, Na₂SO₄, (NH₄)₂SO₄, and CaCl₂ so that the cations and anions considered include Na⁺, NH₄⁺, and Ca²⁺, and Cl⁻,NO3-, andSO42-, respectively. The method predicts the UNIQUAC-fitted ζ values for all datasets with an average error of ∼20%. In an application of the method, ζ values are predicted in an aerosol PM phase containing four oxidation products (from α-pinene/O₃) and water, without and with 1 and 2molkg⁻¹ dissolved (NH₄)₂SO₄. The presence of the dissolved salt can cause significant increases in the ζ values of the oxidation products considered, reflecting a potential “salting-out�? effect for (NH₄)₂SO₄ on the oxidation products considered. Results indicate an important role played by dissolved salts in affecting the thermodynamic properties of atmospheric organic PM and the utility of X-UNIFAC.1 as a tool for evaluating those effects.

Keywords: Activity coefficients; Particulate matter; Organic compounds; Inorganic salts; UNIFAC

Prediction of activity coefficients in liquid aerosol particles containing organic compounds, dissolved inorganic salts, and water—Part 2: Consideration of phase separation effects by an X-UNIFAC model by Elsa I. Chang; James F. Pankow (pp. 6422-6436).

A thermodynamic model is presented for predicting the formation of particulate matter (PM) within an aerosol that contains organic compounds, inorganic salts, and water. Neutral components are allowed to partition from the gas phase to the PM, with the latter potentially composed of both a primarily aqueous ( α) liquid phase and a primarily organic ( β) liquid phase. Partitioning is allowed to occur without any artificial restraints: when both α and β PM phases are present, ionic constituents are allowed to partition to both. X-UNIFAC.2, an extended UNIFAC method based on Yan et al. (1999. Prediction of vapor–liquid equilibria in mixed-solvent electrolyte systems using the group contribution concept. Fluid Phase Equilibria 162, 97–113), was developed for activity coefficient estimation. X-UNIFAC.2 utilizes the standard UNIFAC terms, a Debye–Hückel term, and a virial equation term that represents the middle-range (MR) contribution to activity coefficient effects. A large number (234) of MR parameters are already available from Yan et al. (1999). Six additional MR parameters were optimized here to enable X-UNIFAC.2 to account for interactions between the carboxylic acid group and Na⁺, Cl⁻, and Ca²⁺. Predictions of PM formation were made for a hypothetical sabinene/O₃ system with varying amounts of NaCl in the PM. Predictions were also made for the chamber experiments with α-pinene/O₃ (and CaCl₂ seed) carried out by Cocker et al. (2001. The effect of water on gas-particle partitioning of secondary organic aerosol. Part I. α-pinene/ozone system. Atmospheric Environment 35, 6049–6072); good agreement between the predicted and chamber-measured PM mass concentrations was achieved.

Keywords: Activity coefficients; Particulate matter (PM); Organic; Inorganic; Inorganic salts; Phase separation

Prediction of activity coefficients in liquid aerosol particles containing organic compounds, dissolved inorganic salts, and water—Part 3: Organic compounds, water, and ionic constituents by consideration of short-, mid-, and long-range effects using X-UNIFAC.3 by Garnet B. Erdakos; Elsa I. Chang; James F. Pankow; John H. Seinfeld (pp. 6437-6452).

X-UNIFAC.3, a group contribution method for estimating activity coefficients of neutral and ionic components in liquid mixtures of organic compounds, inorganic salts, and water, is presented here. It is an extended UNIFAC method, in that traditional UNIFAC terms for short-range energetic interaction effects are extended to include ions as mixture components, and are combined with a Debye–Hückel long-range effect term and a second virial coefficient-type mid-range effect term. The method is formulated for application in modeling the formation of liquid aerosol particles consisting of general organic+inorganic salt+water solutions in which phase separation is likely to occur. Existing extended UNIFAC activity coefficient estimation methods can be problematic in modeling phase separation, since they require independent reference state corrections that may introduce significant errors. In X-UNIFAC.3, this problem is avoided by selecting appropriate reference states for all solution components, and imposing additional constraints on method parameters, when necessary, by inclusion of reference state correction terms within the activity coefficient expressions. Interaction parameters in the X-UNIFAC.3 equations are optimized for 12 different chemical groups (CH₃–, –CH₂–,-C|H-,-C||-, −OH, −COOH, H₂O, NH₄⁺, Na⁺, Cl⁻,NO3-, andSO42-) using available data for systems containing multi-functional oxygenated organic compounds and/or inorganic salts that are relevant to atmospheric aerosol applications. Estimations of water activities and mean ionic activity coefficients using X-UNIFAC.3 are compared with those of other extended UNIFAC methods. To demonstrate the use of X-UNIFAC.3 in predicting phase separation, the method is also applied to the butanoic acid+NaCl+water system, for which experimental liquid–liquid equilibrium data is available. The method performs well for aqueous salt solutions with salt concentrations within 30molkg⁻¹ and for organic+inorganic salt+water solutions with salt concentrations less than or equal to 10molkg⁻¹. Suggestions are proposed for improving the predictive capabilities of the method in future work.

Keywords: Activity coefficients; Aerosol particulate matter; Organic compounds; Inorganic salts; Unifac

Atmospheric aerosols during the 2003 heat wave in southeastern Spain I: Spectral optical depth by H. Lyamani; F.J. Olmo; Alcantara A. Alcántara; L. Alados-Arboledas (pp. 6453-6464).

During the first half of August 2003 the Iberian Peninsula (IP) and a great part of Western Europe suffered a severe heat wave. This event was associated with a very robust and persistent high-pressure system over Western Europe that blocked the flow of rain-bearing low-pressure systems at 700 and 500mb. Using sun-photometric data obtained during August 2003 we evidenced an exceptionally high turbidity event over Granada (37.16°N, 3.60°W, 680m a.s.l.) in southeastern Spain from 1 to 15 August. Under heat wave conditions we found δ_a(440nm) in the range 0.12–0.70 with an average value of 0.35±0.10 whereas in the second half of the month δ_a(440nm) ranged between 0.04 and 0.30 with an average value of 0.15±0.06, with similar changes for other wavelengths. This long lasting turbidity event was also observed at other AERONET stations in the IP, El Arenosillo (37.11°N, 6.71°W, 17m a.s.l.) and Évora (38.57°N, 7.91°W, 293m a.s.l.), suggesting that this pronounced change in the atmospheric turbidity was not due to local causes. At a regional level the atmospheric aerosol is influenced by the synoptic situation and thus the special characteristics associated to the heat wave development can have strongly affected the regional atmospheric aerosol properties. The Ångström exponent, α, presented a rather large range of values, evidencing the high variety of aerosol particles that affected the area. Thus, during the heat wave α varied between 0.3 and 1.7 with an average value of 1.2±0.3 whereas after the heat wave it varied between 0.4 and 1.4 with an average value of 0.9±0.3. Considering the relationship between the Ångström exponent and the aerosol size distribution, it is evident that there was an increase in the contribution of fine particles during the heat wave period related to the typical summer conditions. This increase appears to be produced mainly by intense forest fires in southern Europe and by European-Mediterranean air masses influence. Trajectories ending at Granada (on 1–15 August) show that in all cases air masses overpass active forest fires in southern Europe, and that our study area was predominantly influenced by European-Mediterranean air masses. Also, in some cases air masses arrived from Africa. The occurrence of additional Saharan dust events after the heat wave highlighted changes in the features of these aerosol particles when combined with an important load of urban industrial particles and biomass burning aerosols. During dust events occurred in the heat wave period the average values of δ_a(440nm) and α ranged from 0.32 to 0.41 and from 0.8 to 1.0, respectively, while during those occurred after the heat wave event δ_a(440nm) and α ranged from 0.13 to 0.19 and from 0.4 to 0.5, respectively.

Keywords: Aerosol properties; Heat wave; Ångström exponent; Dust

Atmospheric aerosols during the 2003 heat wave in southeastern Spain II: Microphysical columnar properties and radiative forcing by H. Lyamani; F.J. Olmo; Alcantara A. Alcántara; L. Alados-Arboledas (pp. 6465-6476).

The columnar properties of atmospheric aerosol (size distributions, single scattering albedo and asymmetry parameter) are investigated based on sun/sky photometer measurements obtained during August 2003 at Granada (37.18°N, 3.58°W, 680m a.s.l.), southeastern Spain. Also, we compute and analyze the average aerosol radiative forcing under two different atmospheric situations that occurred during the heat wave event that affected Western Europe during first half of August 2003: intrusions of desert dust and episodes of European–Mediterranean (EUR–MED) air masses influence, both combined with the impact of the intense biomass burning due to the multiple forest fires that affected southern Europe during this period. Interpretation of the results obtained in these analyses has been done using key synoptic aspects evidenced in a previous paper. The results showed that during the heat wave episode and under the different air masses influence the fine particle concentration was more important than that obtained after this event. In the situation of EUR–MED influence the single scattering albedo decreased sharply with wavelength from 0.91±0.02 at 440nm to 0.83±0.04 at 1020nm. These values are similar to those obtained by other authors for urban-industrial particles and biomass burning aerosols. The single scattering albedo reported during the dust events (0.87±0.02 at 670nm) was lower than that obtained using AERONET data characterizing pure desert dust, and did not show the spectral variation indicated in the literature, indicating the possible combination of dust, urban-industrial particles and biomass burning aerosols. Estimates of the local direct aerosol radiative forcing in the 400–700nm wavelength range were obtained both at ground level and at the top of atmosphere (TOA). The daily radiative forcing efficiencies at the surface ranged between −78.2 and −73.4Wm⁻² whereas they were between −19.4 and −14.5Wm⁻² at TOA. Aerosol radiative forcing efficiencies at the surface and TOA were slightly larger for EUR–MED case than for desert dust episode. Nevertheless, the daily atmospheric radiative forcing efficiencies obtained in the both cases were similar, about 59Wm⁻², indicating that during desert dust episode dust was mixed with considerable amounts of absorbing aerosols.

Keywords: Aerosol properties; Radiative forcing; Saharan dust and forest fires

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Atmospheric Environment (v.40, #33)