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Atmospheric Environment (v.40, #35)

Editorial board (pp. i).

Personal sampler for monitoring of viable viruses; modelling of outdoor sampling conditions by A.I. Borodulin; B.M. Desyatkov; N.A. Lapteva; A.N. Sergeev; I.E. Agranovski (pp. 6687-6695).

A new personal bioaerosol sampler has recently been developed and verified to be very efficient for monitoring of viable airborne bacteria, fungi and viruses. The device is capable of providing high recovery rates even for microorganisms which are rather sensitive to physical and biological stresses. However, some mathematical procedure is required for realistic calculation of an actual concentration of viable bioaerosols in the air taking into account a rate of inactivation of targeted microorganisms, sampling parameters, and results of microbial analysis of collecting liquid from the sampler. In this paper, we develop such procedure along with the model of aerosol propagation for outdoor conditions. Combining these procedures allows one to determine the optimal sampling locations for the best possible coverage of the area to be monitored. A hypothetical episode concerned with terrorists’ attack during music concert in the central square of Novosibirsk, Russia was considered to evaluate possible coverage of the area by sampling equipment to detect bioaerosols at various locations within the square. It was found that, for chosen bioaerosol generation parameters and weather conditions, the new personal sampler would be capable to reliably detect pathogens at all locations occupied by crowd, even at distances of up to 600m from the source.

Keywords: Bioaerosol; Personal monitoring; Viable microorganisms; Collection efficiency; Air pollution modeling; Optimal sampling locations

Indoor secondary pollutants from cleaning product and air freshener use in the presence of ozone by Brett C. Singer; Beverly K. Coleman; Hugo Destaillats; Alfred T. Hodgson; Melissa M. Lunden; Charles J. Weschler; William W Nazaroff (pp. 6696-6710).

This study investigated the formation of secondary pollutants resulting from household product use in the presence of ozone. Experiments were conducted in a 50-m³ chamber simulating a residential room. The chamber was operated at conditions relevant to US residences in polluted areas during warm-weather seasons: an air exchange rate of 1.0h⁻¹ and an inlet ozone concentration of approximately 120ppb, when included. Three products were used in separate experiments. An orange oil-based degreaser and a pine oil-based general-purpose cleaner were used for surface cleaning applications. A plug-in scented-oil air freshener (AFR) was operated for several days. Cleaning products were applied realistically with quantities scaled to simulate residential use rates. Concentrations of organic gases and secondary organic aerosol from the terpene-containing consumer products were measured with and without ozone introduction. In the absence of reactive chemicals, the chamber ozone level was approximately 60ppb. Ozone was substantially consumed following cleaning product use, mainly by homogeneous reaction. For the AFR, ozone consumption was weaker and heterogeneous reaction with sorbed AFR-constituent VOCs was of similar magnitude to homogeneous reaction with continuously emitted constituents. Formaldehyde generation resulted from product use with ozone present, increasing indoor levels by the order of 10ppb. Cleaning product use in the presence of ozone generated substantial fine particle concentrations (more than 100μgm⁻³) in some experiments. Ozone consumption and elevated hydroxyl radical concentrations persisted for 10–12h following brief cleaning events, indicating that secondary pollutant production can persist for extended periods.

Keywords: Air quality; Formaldehyde; Indoor air chemistry; Secondary organic aerosol; Terpenes

A comparison of projections published in the 2000 United Kingdom air quality strategy with recent measurements and modelling assessments by John R. Stedman (pp. 6711-6717).

Air quality modelling assessments were carried out to inform the development of the UK Air Quality Strategy and in particular the setting the timescale for the achievement of objectives. These assessments were carried out in 1998 and the projections derived for 2005 and 2010 have been compared with air quality monitoring data for 2004 and 2005 and recent modelling assessments. Overall the predictions of air quality for 2005 are in reasonably good agreement with measurements and recent modelling assessments. This gives us confidence that the assessment methods used were suitable to inform the development of policy. Ambient benzene concentrations have declined more rapidly than expected and ambient NO₂ concentrations have not shown as steep a decline as expected, particularly at the roadside. The most challenging objectives to achieve are those for NO₂, PM₁₀ and ozone. The challenges presented by these pollutants are because of their trans-boundary nature and the importance of chemical processes.

Keywords: Air quality targets; Future predictions; Policy models; Comparison with measurements

Chemical apportionment of shortwave direct aerosol radiative forcing at the Gosan super-site, Korea during ACE-Asia by Jiyoung Kim; S.-C. Soon-Chang Yoon; S.-W. Sang-Woo Kim; Fred Brechtel; Anne Jefferson; Ellsworth G. Dutton; Keith N. Bower; Steven Cliff; James J. Schauer (pp. 6718-6729).

Shortwave direct aerosol radiative forcing (DARF) at the surface as well as aerosol optical depth (AOD) were estimated and chemically apportioned on the basis of ground-based aerosol and radiation measurements at the Gosan super-site in Korea during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) in April 2001. An aerosol optical model and a radiative transfer model (RTM) were employed to calculate the aerosol extinction coefficient and radiative flux at the surface, respectively. The calculated scattering and absorption coefficients for D_p<10μm aerosols agreed well with measured scattering and absorption coefficients with root mean square errors (RMSEs) of 23.6 and 3.0Mm⁻¹, respectively. The modeled direct and diffuse irradiances at the surface were also in good agreement with the measured direct and diffuse irradiances. In this study we found that the 17-day mean aerosol radiative forcing of −38.3Wm⁻² at the surface is attributable to mineral dust (45.7%), water-soluble components (sum of sulfate, nitrate, ammonium, and water-soluble organic carbon (WSOC)) (26.8%), and elemental carbon (EC) (26.4%). However, sea salt does not play a major role. For the cases of Asian dust and smoke episodic events on 26 April 2001, a diurnal averaged forcing of −36.2Wm⁻² was contributed by mineral dust (−18.8Wm⁻²), EC (−6.7Wm⁻²), and water-soluble components (−10.7Wm⁻²). The results of this study suggest that water-soluble and EC components as well as a mineral dust component are responsible for a large portion of the aerosol radiative forcing at the surface in the continental outflow region of East Asia.

Keywords: Surface aerosol radiative forcing; Extinction; Closure study; Chemical apportionment; Aerosol; ACE-Asia

Long-term variation of Asian dust and related climate factors by Yukari Hara; Itsushi Uno; Zifa Wang (pp. 6730-6740).

The relationship between long-term variation of Asian dust and climate indices was studied using a regional scale dust-transport model. Simulation results were examined using visibility-based observations by Chinese and Japanese Meteorological Agencies. Those results showed that the model reasonably captured interannual variations of Asian dust during 1972–2004. The long-term trend of dust days in the Gobi desert region showed a remarkable declining trend from the early 1980s–1997; the increasing trend of recent years (2000–02) was more conspicuous in Japan. Analyses of time variation of meteorological parameters in the Gobi region showed that the decreasing trend of dust days in this region is explained by the decreased frequency of strong winds. Additionally, anomaly analyses for dust and meteorological parameters in the Gobi region indicated that invasion of polar cold air played an important role in increasing dust phenomena. To clarify climate factors that affect dust emission and transport, regional climate indices that are appropriate for the scale of Asian dust storms were newly introduced. Correlation analyses between climate indices and simulated dust emissions showed that the dominant climate indices, which are closely correlated with dust emissions, were different in March and April. In March, the climate indices related to divergence of cold air from the polar region to mid-latitudes displayed a strong correlation with dust emissions, but during April, the climate index related to the south-north pressure gradient over the Gobi region exhibited a strong correlation with dust emission. Analyses of correlation between simulated surface dust concentrations and the Southern Oscillation Index (SOI) suggest that the El Niño/Southern Oscillation (ENSO) affects the dust transport path. Analyses of average dust transport flux at 130°E clarified variation of the transport path between La Niña years and El Niño years.

Keywords: Dust; Interannual variation; Dust transport model; Climate index

Concentrations of H₂O₂ and HNO₃ and O₃–VOC–NO _x sensitivity in ambient air in southern Taiwan by Y.P. Peng; K.S. Chen; C.H. Lai; P.J. Lu; J.H. Kao (pp. 6741-6751).

The gaseous concentrations of hydrogen peroxide (H₂O₂) and nitric acid (HNO₃) were measured at two sites in Kaohsiung City and two sites in Pingtung County, on three days in autumn, winter and spring during 2002–2003. The mean H₂O₂ concentrations were 1.76–1.79ppbv at Nan-Chie and Hsiung-Kong in Kaohsiung City and 1.40–1.76ppbv at Pingtung and Chao-Chou in Pingtung County. Meanwhile, the mean concentrations of HNO₃ were 6.11–7.79ppbv in Kaohsiung City and 3.78–4.92ppbv in Pingtung County. The hourly data were then used to evaluate VOC and NO _x sensitivity of ozone (O₃) formation. The threshold values of either H₂O₂/HNO₃=0.3–0.6 or O₃/HNO₃=12–16 indicate that VOC-sensitive chemistry were dominant at Nan-Chie, Hsiung-Kong, and Pingtung in all three seasons; while VOC-sensitive chemistry was dominant at Chao-Chou only in winter, but NO _x-sensitive chemistry was dominant in spring. The VOC-sensitive and NO _x-sensitive regimes determined using the indicator ratios agree well with those obtained from the SPM (smog production model) using threshold value E (extent of reaction)=0.6–0.8.

Keywords: Hydrogen peroxide; Nitric acid; Ozone; Volatile organic compounds; Photochemical indicators; Smog production model

Ammonia emissions from outdoor concrete yards used by livestock—quantification and mitigation by T.H. Misselbrook; J. Webb; S.L. Gilhespy (pp. 6752-6763).

Outdoor concrete yards are commonly found on UK livestock farms, and, to a lesser extent, elsewhere in Europe, and represent a potentially significant source of ammonia (NH₃) emissions to the atmosphere. This study provided further measurements from a larger sample than previously made, to improve the robustness of the estimate of total NH₃ emission for inclusion in the UK NH₃ emission inventory. In addition, an assessment was made of a number of potential mitigation strategies. Measurements were made using the equilibrium concentration technique, employing small dynamic chambers and passive diffusion samplers, from 20 yards used by livestock on commercial farms. Mean emission rates (±standard error) were 0.31±0.07, 0.23±0.12, 0.19±0.05 and 0.18±0.09g NH₃–Nm⁻²h⁻¹ (0.70±0.21, 0.53±0.34, 0.76±0.22 and 0.18±0.14g NH₃–Nanimal⁻¹h⁻¹) for dairy cow-collecting yards, dairy cow-feeding yards, beef-feeding yards and sheep-feeding/handling areas, respectively, with mean respective livestock densities of 0.3, 0.5, 0.2 and 1.1animalsperm². There was a significant effect of season, with lower emission rates in the winter. There was a significant, albeit poor, positive linear relationship between emission rate and ambient air temperature ( r²=0.22) and between emission rate and total ammoniacal N content on the yard surface ( r²=0.14), but not with ambient wind speed. Pooling data from the present study with that from previous studies gave mean emission factors of 0.47±0.09, 0.98±0.39 and 0.13±0.09g NH₃–Nanimal⁻¹h⁻¹ for yards used by dairy cattle, beef cattle and sheep, respectively. Inclusion of these values, together with survey data on yard use, gave a total annual UK emission of approximately 25ktNH₃ (95% confidence interval of 12–40ktNH₃), representing almost 10% of total NH₃ emission from UK agriculture. In controlled studies, pressure washing and the use of a urease inhibitor in addition to yard scraping were found to be effective means of reducing emissions compared with yard scraping alone. Reduction of yard area per animal was also an effective strategy to reduce total emissions.

Keywords: Ammonia emission; Outdoor yards; Livestock; Mitigation; Emission factor

Improved GC/MS methods for measuring hourly PAH and nitro-PAH concentrations in urban particulate matter by Bernard S. Crimmins; Joel E. Baker (pp. 6764-6779).

This study presents two methods for the quantification of nitro-substituted and parent polycyclic aromatic hydrocarbons (NPAH and PAH, respectively), respectively, utilizing large volume injection gas chromatography/mass spectrometry (GC/MS). Both methods (PAH and NPAH, respectively) employed a programmed temperature vaporization injector (PTV) in solvent vent mode, optimized using standard solutions. For the PAH method, the precision of the PTV was comparable to hot splitless injection for exhibiting a percent relative standard deviation (%RSD) consistently below 8% for 100pg injections. Compound %RSDs for the NPAH method were consistently below 5% using the PTV. Microgram quantities (30–500μg) of particulate matter Standard Reference Materials (SRM 1649 and 1650, National Institutes of Standards and Technology) were analyzed to simulate PAH and NPAH quantification on small aerosol mass loadings. The method detection limits from this study suggest PAHs and NPAHs can be easily quantified using low-volume samplers (>5Lpm) on hourly timescales. In addition, this technique enabled the quantification of 12-h NPAH size distributions in the Baltimore, MD, atmosphere.

Keywords: Polycyclic aromatic hydrocarbons; Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs); Programmed temperature vaporization (PTV); Large volume injection; Aerosol; Organic

Element partitioning and potential mobility within surface dusts on buildings in a polluted urban environment, Budapest by J.J. McAlister; B.J. Smith; Torok A. Török (pp. 6780-6790).

A voluminous literature exists on the analysis of water-soluble ions extracted from gypsum crusts and patinas formed on building surfaces. However, less data is available on the intermediate dust layer and the important role its complex matrix and constituents play in crust/patina formation. To address this issue, surface dust samples were collected from two buildings in the city of Budapest. Substrate properties, different pollution levels and environmental variations were considered by collecting samples from a city centre granite building exposed to intense traffic conditions and from an oolitic limestone church situated in a pedestrian area outside and high above the main pollution zone. Selective extraction examines both water-soluble ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, NO₃⁻, SO₄²⁻) and selected elements (Fe, Mn, Zn, Cu, Cr, Pb, Ni) from the water-soluble, exchangeable/carbonate, amorphous Mn, amorphous Fe/Mn, crystalline Fe/Mn, organic and residual phases, their mobility and potential to catalyse heterogeneous surface reactions. Salt weathering processes are highlighted by high concentrations of water-soluble Ca²⁺, Na⁺, Cl⁻ and SO₄²⁻ at both sites. Manganese, Zn and Cu and to a lesser extent Pb and Ni, are very mobile in the city centre dust, where 30%, 54%, 38%, 11% and 11% of their totals are bound by the water-soluble phase, respectively. Church dust shows a sharp contrast for Mn, Zn, Cu and Pb with only 3%, 1%, 12% and 3% of their totals being bound by the water-soluble phase, respectively. This may be due to (a) different environmental conditions at the church e.g. lower humidity (b) continuous replenishment of salts under intensive city centre traffic conditions (c) enrichment in oxidisable organic carbon by a factor of 4.5 and a tenfold increase in acidity in the city centre dust.

Keywords: Dust; Stone; Crust/patina formation; Selective extraction; Element mobility

Variations in atmospheric PM trace metal content in Spanish towns: Illustrating the chemical complexity of the inorganic urban aerosol cocktail by Teresa Moreno; Xavier Querol; A. Andrés Alastuey; Mar Viana; Pedro Salvador; Sanchez de la Campa Ana Sánchez de la Campa; B. Artinano Begoña Artiñano; J. Jesús de la Rosa; Wes Gibbons (pp. 6791-6803).

The majority of the Spanish urban population breathe air containing inhalable ambient airborne particles at average concentrations of 30–46μgm⁻³ (PM₁₀) and 20–30μgm⁻³ (PM_2.5). Even though the average weight of inhaled urban aerosol is commonly similar, however, there can be large chemical differences between the ambient dusts from different towns, including the more bioreactive elements such as some metals. In this context, we compare the source-apportioned trace metal content of airborne PM₁₀ and PM_2.5 collected daily over a 1-year period from six population centres in Spain: Barcelona, Alcobendas, Llodio, Huelva, Tarragona and Las Palmas de Gran Canaria. Total average trace metal (ΣTM) PM₁₀ and PM_2.5 contents vary by up to a factor of around 3, reaching a maximum of ΣTM₁₀ 811ngm⁻³ and ΣTM_2.5 503ngm⁻³ at Llodio, an industrial but humid site with the lowest PM₁₀ mass levels but high contamination by Zn, Pb, Mn, Sn, Ni and Cr. In contrast, pollution at Huelva, although another industrially influenced site, instead emphasises Cu and As, whereas Barcelona, where traffic emissions and resuspension contribute to some of the highest average PM₁₀ levels in Spain, has unusually raised levels of Ti, V and Ba. Such variations in both daily and annual average PM bulk chemistry, particularly in potentially toxic trace metals concentrated in the finer aerosols (such as Cd, As, Pb, Hg and Ni), predict that PM health effects on resident populations from different towns are unlikely to be the same.

Keywords: Trace metals; PM; ₁₀; Source apportionment; Spain

Treatment of clouds and the associated response of atmospheric sulfur in the Community Multiscale Air Quality (CMAQ) modeling system by Stephen F. Mueller; Elizabeth M. Bailey; Toree M. Cook; Qi Mao (pp. 6804-6820).

An air quality modeling system—“Models-3/CMAQ�?—is studied to determine the relationship between simulated cloud cover and atmospheric sulfur. Sulfur dioxide oxidation to sulfate occurs in the atmosphere through gas-phase reactions and reactions in clouds. The latter heterogeneous reactions can be rapid compared to gas-phase chemistry and a model must correctly simulate cloud cover to avoid serious bias. An evaluation of CMAQ revealed serious problems with diagnosed cloud cover and a bias in simulated sulfate production that was consistent with cloud biases. CMAQ modifications were tested to determine the sensitivity of the sulfur balance to cloud modeling assumptions. The model's vertical layer structure, limits on subgrid-scale cloud base and top heights, and the ability to simulate subgrid-scale convective cloud formation were found to be important. After applying model changes, atmospheric sulfur simulations were less biased and sulfur dioxide and sulfate were in better balance.

Keywords: Sulfur dioxide; Sulfate; Heterogeneous chemistry; Clouds; Modeling

Aromatic hydrocarbons emissions in diesel and biodiesel exhaust by S.M. Correa Sérgio Machado Corrêa; Graciela Arbilla (pp. 6821-6826).

Regulated emissions of biodiesel blends are reasonably well documented in several works, non-regulated emissions, on the contrary, lack research. In this work, mono- and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively) emission tests were performed with a heavy-duty diesel engine, fueled with pure diesel (D) and biodiesel blends (v/v) of 2% (B2), 5% (B5) and 20% (B20%). The main objective of this study is to investigate the effect of the biodiesel addition on the emission profile of MAHs and PAHs. The tests were conducted using a six cylinder heavy-duty engine, typical of the Brazilian fleet of urban buses, in a steady-state condition under 1500rpm. The PAHs were sampled with Teflon filters and XAD-2 cartridges and were identified by gaseous chromatograph coupled to a mass spectrometer (GC/MS) and quantified by flame ionization detection (GC/FID). The MAHs were sampled with active charcoal cartridges and analyzed by GC/FID. Both MAHs and PAHs filters and cartridges were extracted with dichloromethane in an ultrasonic bath. Ten PAHs and eight MAHs were identified and the average reduction of MAHs was 4.2% (B5), 8.2% (B5), and 21.1% (B20). The average reduction for PAHs was 2.7% (B2), 6.3% (B5), and 17.2% (B20). However, some PAHs and MAHs emissions increased because of/due to the biodiesel blends like phenanthrene, ethyl benzene, and trimethyl benzenes.

Keywords: Polycyclic aromatic hydrocarbons; Mono-aromatic hydrocarbons; Vehicular emissions; Biodiesel; Diesel

Integrated and sequential bulk and wet-only samplings of atmospheric precipitation in Londrina, South Brazil (1998–2002) by A.F. Aléscio F. Pelicho; Leila D. Martins; Sonia N. Nomi; Maria Cristina Solci (pp. 6827-6835).

The present study investigated the chemical composition of bulk and wet atmospheric precipitation samples in Londrina city, in south Brazil. The samples were collected from April 1998 to November 2002. A total of 350 rainwater samples were collected on an event basis, integrated for 24h, and analyzed for pH, conductivity, Na⁺, K⁺,NH4+,Cl-,NO3-, andSO42-. The concentration variability of rainwater was evaluated through sequential analysis of fractionated rainwater samples during three rainfall events. The comparison of bulk and wet-only sample results revealed that there are differences between collectors as to ionic composition and conductivity. Acid rain was characterized in 34% (bulk collector) and 35% (wet-only collector) of the samples. The correlation (>0.5) ofNH4+withCl-,NO3- andSO42- suggests thatNH4+ is the neutralizing constituent. Below cloud scavenging processes were observed due to the decline in the concentrations of all chemical species analyzed in the fractions along event. The total wet deposition rate of NH⁺,NO3- andSO42- were, respectively, 18.3, 17.1 and 13.4meqm⁻²yr⁻¹. The composition of the rainwater collected appeared to be controlled by the following potential sources: crustal, agricultural activity (animal/fertilizer), and biomass and fossil fuel combustion. The precipitation chemistry in Londrina seems to be controlled by man-made emissions of S and N gases.

Keywords: Acid rain; Bulk deposition; Rainwater chemistry; South America; Wet deposition

Adjoint inverse modeling of CO emissions over Eastern Asia using four-dimensional variational data assimilation by Keiya Yumimoto; Itsushi Uno (pp. 6836-6845).

We developed a four-dimensional variational (4DVAR) data assimilation system for a regional chemical transport model (CTM). In this study, we applied it to inverse modeling of CO emissions in the eastern Asia during April 2001 and demonstrated the feasibility of our assimilation system. Three ground-based observations were used for data assimilation. Assimilated results showed better agreement with observations; they reduced the RMS difference by 16–27%. Observations obtained on board the R/V Ronald H. Brown were used for independent validation of the assimilated results. The CO emissions over industrialized east central China between Shanghai and Beijing were increased markedly by the assimilation. The results show that the annual anthropogenic (fossil and biofuel combustion) CO emissions over China are 147Tg. Sensitivity analyses using the adjoint model indicate that the high CO concentration measured on 17 April at Rishiri, Japan (which the assimilation was unable to reproduce) originated in Russia or had traveled from outside the Asian region (e.g. Europe).

Keywords: Adjoint model; Data assimilation; Asian emissions; Carbon monoxide

Oxodicarboxylic acids in atmospheric aerosol particles by Rompp Andreas Römpp; Richard Winterhalter; Geert K. Moortgat (pp. 6846-6862).

Fine mode aerosol was collected on quartz fiber filters at several sites across Europe. These samples were analyzed for carboxylic acids by liquid chromatography coupled to a hybrid (quadrupole and time-of-flight) mass spectrometer (LC/MS/MS-TOF). A series of oxodicarboxylic acids (C₇–C₁₁) was detected. Oxodicarboxylic acids are linear dicarboxylic acids with an additional carbonyl group. Previous measurements of these acids are scarce and their sources are largely unknown. Several structural isomers (different positions of the carbonyl group within the molecule) could be identified and differentiated by the combination of laboratory experiments and high mass accuracy measurements. The homologs with 9–11 carbon atoms were identified for the first time in atmospheric aerosol particles. The concentrations of oxodicarboxylic acids in ambient aerosol samples frequently exceeded those of the corresponding unsubstituted dicarboxylic acids. Oxodicarboxylic acids have been shown to be products of the reaction of dicarboxylic acids with OH radicals in chamber experiments and a reaction mechanism is proposed. Good correlation of oxodicarboxylic acid and hydroxyl radical concentrations was found at two measurement sites (Finland and Crete) of different geographic location and meteorological conditions. The ratios of individual isomers from the field samples are comparable to those of the laboratory experiments. The results of this study imply that the reaction of OH radicals and dicarboxylic acids is an important pathway for the production of oxodicarboxylic acids in the atmosphere. Oxodicarboxylic acids seem to be important intermediates in atmospheric oxidation processes of organic compounds.

Keywords: Oxodicarboxylic acids; Linear dicarboxylic acid; OH-radical; Aerosol ageing

Acid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction products by Rebecca M. Garland; Matthew J. Elrod; Kristi Kincaid; Melinda R. Beaver; Jose L. Jimenez; Margaret A. Tolbert (pp. 6863-6878).

While it is well established that organics compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe the uptake of gas-phase hexanal into ammonium sulfate and sulfuric acid aerosols. While both deliquesced and dry non-acidic ammonium sulfate aerosols showed no organic uptake, the acidic aerosols took up substantial amounts of organic material when exposed to hexanal vapor. Further, we used¹H-NMR, Fourier transform infrared (FTIR) spectroscopy and GC–MS to identify the products of the acid-catalyzed reaction of hexanal in acidic aerosols. Both aldol condensation and hemiacetal products were identified, with the dominant reaction products dependent upon the initial acid concentration of the aerosol. The aldol condensation product was formed only at initial concentrations of 75–96wt% sulfuric acid in water. The hemiacetal was produced at all sulfuric acid concentrations studied, 30–96wt% sulfuric acid in water. Aerosols up to 88.4wt% organic/11.1wt% H₂SO₄/0.5wt% water were produced via these two dimerization reaction pathways. The UV-VIS spectrum of the isolated aldol condensation product, 2-butyl 2-octenal, extends into the visible region, suggesting these reactions may impact aerosol optical properties as well as aerosol composition. In contrast to previous suggestions, no polymerization of hexanal or its products was observed at any sulfuric acid concentration studied, from 30 to 96wt% in water.

Keywords: Troposphere; Organic aerosols; Acid-catalyzed reactions; Product identification

Emission of CO₂, CH₄ and N₂O from freshwater marsh during freeze–thaw period in Northeast of China by Changchun Song; Yuesi Wang; Yiyong Wang; Zhichun Zhao (pp. 6879-6885).

The freeze–thaw period, 7–8 months in Sanjiang Plain, influences the greenhouse gases fluxes greatly. The static chamber technique aided by gas chromatogram was used for investigating characteristics of emission of CO₂, CH₄ and N₂O from freshwater marsh wetlands located in the Sanjiang Plain. The results showed that there were obvious CH₄ and CO₂ emissions in winter and the CH₄ emission made a relatively large contribution to the total CH₄ flux in the different type freshwater marshes during winter in Sanjiang Plain. And there were significant CH₄ and CO₂ emission peak values during thawing time. The CH₄ and CO₂ emissions from freshwater marsh seasonal flooded were larger than that from freshwater marsh continuously flooded during thawing time. On the contrary, the CH₄ and CO₂ emissions from freshwater marsh continuously flooded were larger than that from freshwater marsh seasonal flooded in winter. During thawing, there was exponential relationship between CO₂ fluxes and the soil temperature (5cm) ( R²=0.912, P<0.001). Meanwhile, ecosystem respiration was obviously correlated with the CH₄ fluxes ( R²=0.751, P<0.001). We found that the freshwater marshs were N₂O sink in winter and gradually became N₂O source, with increasing temperature during thaw. The characters of the greenhouse gases emission, during freeze–thaw in the Sanjiang Plain, responded to the microbial activity in winter and the effects of thawing on soil carbon mineralization, nitrification and denitrification.

Keywords: CH; ₄; CO; ₂; Freeze–thaw; N; ₂; O; Northeast of China

Chemical composition of rainwater in a tropical urban area of northern India by Abdul Hameed M. Jawad Al Obaidy; Himanshu Joshi (pp. 6886-6891).

Rainwater samples during the monsoon of 2001 and 2002 were collected from Roorkee urban area, a medium sized “town group�? situated on the right bank of Solani River, a tributary of the Ganga River, near the Himalayan foothills and analyzed for EC, pH, TSS, TDS and major ions. The median value of pH was 7.05, well above 5.6, which is the reference pH. The ratios of SO₄²⁻+NO₃⁻ and Ca²⁺+Mg²⁺ (TA/TC) have been considered for acidity. In this study, ratio of TA/TC is quite below 1.0, indicating alkaline nature of rainwater. The concentration of ions in rain water have been observed to follow the pattern Ca²⁺>HCO₃⁻>Cl⁻>NO₃⁻>Na⁺>Mg²⁺>SO₄²⁻>K⁺. In order to estimate the marine and non-marine contribution, sea salt fraction has been calculated taking Na⁺ as reference. All ionic ratios have been found to be higher than the recommended sea water ratios in all three types of land use, viz. residential, commercial and industrial, suggesting a significant contribution of non-marine origin for these components. A comparison with the data of the other Indian sites validates the inverse relation of Cl⁻ and Na⁺ with distance from the sea and highlights higher Ca²⁺ concentration and lower SO₄²⁻ concentration.

Keywords: Rainwater; Ion balance; Sea salt fraction; Alkalinity

An iterative solution of flux–profile relationships in the surface layer for regional model applications by Mariusz Pagowski (pp. 6892-6897).

Due to the implicit character of flux–profile relationships in the atmospheric surface layer, in mesoscale modeling it is common practice to calculate fluxes of momentum, heat, and moisture with approximate formulas. The study presented here shows that a Newton–Raphson iterative procedure to calculate surface fluxes using broadly accepted formulations for universal stability functions is always convergent when an interval for the solution is properly specified. Independent of surface type(z0,zH/z0), iterations converge to a solution for Obukhov stability parameterζ with an accuracy of1×10-3 within three iterations for the unstable stratification, and within four iterations for the stable stratification. Thus, this investigation suggests that a proper iterative procedure to obtain surface fluxes is not only always convergent but is also computationally efficient and remains a practical alternative to approximate explicit methods.

Keywords: Similarity theory; Iterative solution; Regional modeling

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Atmospheric Environment (v.40, #35)