Atmospheric Environment (v.38, #7)

The objective of this study was to characterize the emissions of air pollutants from incense burning in a large environmental test chamber. Air pollutants emitted from ten types of commonly used incense manufactured in different regions were compared. The target pollutants included particulate matters (PM10, PM2.5), volatile organic compounds (VOCs), carbonyls, carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NO x ), methane (CH4) and non-methane hydrocarbon (NMHC). The particulate matters emitted from all the incense significantly exceeded the Recommended Indoor Air Quality Objectives for Office Buildings and Public Places in Hong Kong (HKIAQO). The CO peak levels of seven incense types greatly exceeded the HKIAQO standard. The formaldehyde concentrations of six types of incense were higher than the HKIAQO. The highest formaldehyde level exceeded the standard by 2 times. The results indicated that the concentrations of benzene, toluene, methyl chloride and methylene chloride significantly increased with the burning of all incense tested. In addition, the benzene concentrations of all tested incense were significantly higher than the HKIAQO standard. Although Incense 2 and 6 were claimed to be environmental friendly, the quantity of the pollutants emitted was not observed to be lower than the others. It was observed that when comparing the gas pollutant emission factors between two major incense categories (i.e. traditional and aromatic), the traditional incense (i.e. Incense 1−6) had relatively higher values than aromatic incense (i.e. Incense 7−9). Generally, it was found that the VOCs emitted sequence was aromatic incense>tradition incense>church incense (i.e. Incense 10). However, the carbonyl compounds emission sequence was traditional incense>aromatic incense>church incense. The results show that incense burning is one of the important indoor air pollution sources for PM, CO and VOCs.
Keywords: Burning of incense; Environmental Chamber; Emission rate; Emission factor; VOCs;

The origin of atmospheric particles in Paris: a view through carbon and lead isotopes by David Widory; Stéphane Roy; Yvon Le Moullec; Ghislaine Goupil; Alain Cocherie; Catherine Guerrot (953-961).
The origin of particulate matter in the urban atmosphere and the impact of its various sources are still subject to debate. This uncertainty cannot be alleviated by the sole use of ‘classic’ chemical parameters, creating a need for complementary indexes. We show that the use of coupled carbon and lead isotopes allows the identification of aerosol sources in the atmosphere of Paris, permitting a semi-quantification of their respective contributions. The two study sites, representative of background pollution and the influence of heavy road traffic, both show the domination of diesel exhaust fumes to the level of carbon in aerosols (either PM2.5 or PM10), while industry is the main vector for lead, with a contribution generally superior to 50%. Within the last 10 years, the origin of the inorganic phase shifted from road traffic towards industrial activities.
Keywords: PM2.5; PM10; Road traffic; Industry; Pre-industrial sediment;

Characterization of dicarboxylic acids in PM2.5 in Hong Kong by Xiaohong Yao; Ming Fang; Chak K. Chan; K.F. Ho; S.C. Lee (963-970).
Dicarboxylic acids in atmospheric aerosols have received much attention because of their potential roles in affecting the global climate. The composition and the sources of dicarboxylic acids in PM2.5 were studied at one remote and two urban sites in Hong Kong in the winter of 2000 and in the summer of 2001. Oxalate was the dominant dicarboxylic acid in all samples. The winter oxalate concentrations were high and spatially uniform, with an average value of 0.36 μg m−3, but the summer oxalate concentrations were low and had a large spatial variation. The influence of meteorological factors on the concentrations of dicarboxylic acids was also studied. The ratio of malonate to succinate was used to distinguish primary sources from secondary sources of these acids. This ratio at all three sites was close to that from direct vehicular exhaust in the winter, but it was close to that of secondary reactions in the summer. Hence, the acids were attributed to vehicular emissions in the winter and secondary sources in the summer. This hypothesis is also supported by a good correlation of oxalate with sulfate in the summer but a poor one in the winter. The correlations of oxalate with malonate, succinate, sulfate and K+ were also studied in terms of the routes of secondary formation of these dicarboxylic acids.
Keywords: Oxalic acid; Malonic acid; Succinic acid; PM2.5; Secondary water-soluble organic compounds;

Accurate estimations of the emissions of primary pollutants are crucial for the modeling of photo-oxidants’ concentrations. For a majority of chemistry-transport models (CTMs), these emissions are taken into account near the surface only. They are expressed as surface fluxes and represent surface activities such as traffic, industries or biogenic processes. However, in the vicinity of large cities, commercial aircraft emissions represent a nonnegligible source, located both at the surface and at altitude, including landing and take-off of aircraft within the boundary layer. This is the case of Paris where one national airport (Le Bourget) and two international airports (Roissy-Charles-de-Gaulle and Orly) are located less than 30  km away from the city center. This study presents the first-model analysis of the impact of aircraft emissions on photo-oxidant concentrations over the Paris area. Using a three-dimensional aircraft emission inventory, we compare ozone surface concentrations obtained with and without these emissions by running the CTM CHIMERE during the second Intensive Observation Period of the ESQUIF project. The simulated differences enable us to estimate the impact of aircraft traffic emissions on ozone surface concentrations in and around the city. The results showed that the maximum impact, which consists in a fast ozone titration by NO near the airports within the surface layer, occurs during the night. In remote areas and at altitude, adding new emissions enhanced photo-chemistry during the afternoon. In order to estimate the impact of the uncertainty of our inventory, aircraft emitted masses of volatile organic compounds (VOCs) and NO x are perturbed. The results showed that NO x air traffic emissions have a more important impact than VOC emissions, particularly during the night and near the sources. Nevertheless, these variations of air traffic emissions do not change previous conclusions.
Keywords: Urban air pollution; Three-dimensional modeling; Regional chemistry-transport model; Ozone sensitivity; Emission inventory;

A systematic temporal analysis of surface ozone observations in four sites representative of the main types of habitats: coast, mountain, inland and urban in the North Western Mediterranean basin is presented here for the period between 1994 and 2001. Concentrations were relatively high, especially in the coastal site where the European human and plant protection thresholds were surpassed an average of 54 and 297 days per year, respectively. We observed a 22% decrease in the ozone concentrations along the past decade in the coastal site, a 14% increase in the mountain site, and no significant change in the inland and urban sites. The annual cycle of ozone in the coastal site (maximum concentrations in spring) was typical of areas with higher influences of background ozone, whereas in the other sites, the broad spring–summer maximum indicated dominance of local photochemical production. The site differences were also evident in their diurnal cycles, which were very evident in all sites except in the coastal one. There was thus significant variability among the monitoring sites, due to both the influence of local and background sources and the complex orographic and meteorological conditions of this region.
Keywords: Annual pattern; Daily pattern; Mediterranean region; Regional photochemical pollution; Tropospheric ozone;

Precipitation scavenging can effectively remove particulates from the atmosphere. Interest in the phenomena waxed in the 1980s, but models developed at that time remain limited by the lack of both detailed, time-resolved wet deposition pattern measurements for model confirmation and real-time rain data for model execution. Recently, new rain products have become available that can revolutionize real-time use of precipitation scavenging models on the regional scale. We have utilized a 4-km, hourly resolution precipitation data set from the Arkansas Red-Basin River Forecast Center. A standard below-cloud aerosol scavenging model has been modified to incorporate the potentially larger scavenging in heavy rain events. This paper demonstrates the model on a sample rainfall data set. The simulations demonstrate the concentrating effect of rainfall, especially heavy rain, on deposition patterns. Wet deposition played an important role in the simulated fate and transport, removing as much as 70% of the released aerosol.
Keywords: Wet deposition; Aerosol; Modeling; Particle; Washout;

A modeling method is developed for use in predicting the stability of multiple liquid phases in atmospheric particulate matter (PM). The method utilizes a pseudo-diffusion process that simulates the multicomponent inter-phasic movement of constituents between adjacent PM phases. It can be used as a stand-alone application, and can also be incorporated in overall gas/particle (G/P) partitioning models of aerosol PM formation. Previously studied (Environ. Sci. Technol. 35 (2001) 1806) relative-humidity (RH)-dependent PM compositions resulting from the ozone oxidation of five different volatile organic compounds (VOCs) were verified as being stable as single phases. A number of additional cases were considered in which RH-dependent secondary PM compositions were amended with a mix of low-polarity (LP) organic compounds. It was determined that, depending on the mass fraction of added LP-mix, the PM can be more stable as a two-phase system. Phase separation into two phases can occur even in the absence of water in the PM. Assuming a single liquid PM phase when two are actually present will generally lead to an underprediction of TPM. For the cases considered here, the calculated errors in predicted TPM levels were found to range from −3.9% to −21.8%; conditions can be envisioned that would lead to even larger errors.
Keywords: Organic particulate matter; Water–organic particulate matter; Secondary organic aerosols; Phase stability; Low-polarity organic compounds; Multicomponent interdiffusion;

Photolysis is an important loss process of carbonyl, peroxy, and nitrate species in the atmosphere. In general, photolysis rate coefficients depend on the intensity of radiation, wavelength, temperature, and the specific molecule reacting. One key source of differences in rate coefficients between different molecules is the absorption cross-section, σ, which is specific to the reactive molecule under consideration. In order to calculate rate coefficients for photolytic processes, a value of σ must be specified or estimated. To this end, a group additivity approach was developed that can be used to estimate the values of σ of species that photolyze primarily in the 290–370  nm wavelength region. We demonstrate that this approach can be used to predict accurately unknown values of σ of species for which experimental data are not available.
Keywords: Absorption cross-section; Photolysis; Troposphere; Group additivity; Rate coefficient;

Dissolution of azaarenes from urban aerosols by Hung-Yu Chen; Martin R. Preston (1023-1028).
Laboratory studies show the potential for significant dissolution processes of highly toxic azaarenes from the urban aerosols. Over a pH range from 6 to 8>90% of the azaarene compounds in the aerosol dissolve within an hour. At realistic urban rainwater pH values it follows that most of the azaarenes will be rapidly removed from the particulate phase resulting in depositional fluxes dominated by wet deposition. It is suggested that the results of this study also have implications for human health because contaminated aerosol particles inhaled into the lungs will be exposed to fluids at pH<8 and will therefore rapidly release azaarenes in locally high concentrations.
Keywords: Azaarenes; Dissolution; Urban aerosols; Semi-volatile organic compounds; Nitrogen species;

Comparisons between FLUENT and ADMS for atmospheric dispersion modelling by Andrew Riddle; David Carruthers; Alan Sharpe; Christine McHugh; Jennifer Stocker (1029-1038).
The dispersion of gases in complex situations such as the case of buildings in close proximity is a difficult problem, but important for the safety of people living and working in such areas. Computational fluid dynamics (CFD) provides a method to build and run models that can simulate gas dispersion in such geometrically complex situations; however, the accuracy of the results needs to be assessed. As a first step in such an assessment, this study considers the simulation of the dynamics of the basic atmospheric boundary layer using the FLUENT CFD code and the prediction of gas dispersion from a single stack. The CFD results are compared with the predictions from the Atmospheric Dispersion Modelling System (ADMS), a well tested and validated quasi-Gaussian model.When FLUENT was set up to simulate the neutrally stable atmospheric boundary layer, the mean velocity profiles were well predicted and were maintained with downwind distance. The algebraic Reynolds stress turbulence model provided the best predictions for the turbulence kinetic energy (TKE) and dissipation. The dissipation rate was maintained throughout the length of the model domain and, on average, the TKE levels were within 80% of the expected values up to a height of 100 m, but at the ground reduced to 50% of the inlet values. Predictions of TKE using the simpler kε model turbulence was much poorer. Spread of the gas plume were predicted using an advection-diffusion (AD) method, a Lagrangian particle tracking (LP) method and a large eddy simulation (LES) method. The LP method gave the best results; the horizontal and vertical plume spreads were similar to those predicted by ADMS and ground level and plume centre line concentrations were close to ADMS values. However, some differences were observed with the ground level concentrations rising more rapidly with distance than for ADMS, but reaching similar peak values while the plume centreline concentrations dropped more rapidly than in ADMS. For the AD method the horizontal cross-wind plume spread was significantly lower than expected resulting in higher ground level concentrations than predicted by ADMS, an effect that was attributed to the isotropic formulation of the AD equation in FLUENT. The LES results were intermediate between the AD and LP predictions.Overall, the CFD simulations with the LP method were satisfactory; however, they could not be considered as an appropriate alternative to a model such as ADMS for normal atmospheric dispersion studies because of the much larger run times and the greater complexity of setting up model runs. CFD is more appropriate for applications that involve complex geometry that could not be simulated using ADMS; however, further studies are required to assess the ability of CFD to calculate dispersion in such situations, for instance, around groups of buildings and under a range of atmospheric stability conditions, rather than just the neutral stability considered in this paper.
Keywords: Atmosphere; Dispersion; Turbulence; Atmospheric stability; CFD; Lagrangian particle tracking;

Sources of optically active aerosol particles over the Amazon forest by Pascal Guyon; Bim Graham; Gregory C Roberts; Olga L Mayol-Bracero; Willy Maenhaut; Paulo Artaxo; Meinrat O Andreae (1039-1051).
Size-fractionated ambient aerosol samples were collected at a pasture site and a primary rainforest site in the Brazilian Amazon Basin during two field campaigns (April–May and September–October 1999), as part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The samples were analyzed for up to 19 trace elements by particle-induced X-ray emission analysis (PIXE), for equivalent black carbon (BCe) by a light reflectance technique and for mass concentration by gravimetric analysis. Additionally, we made continuous measurements of absorption and light scattering by aerosol particles. The vertical chemical composition gradients at the forest site have been discussed in a companion article (Journal of Geophysical Research-Atmospheres 108 (D18), 4591 (doi:4510.1029/2003JD003465)). In this article, we present the results of a source identification and quantitative apportionment study of the wet and dry season aerosols, including an apportionment of the measured scattering and absorption properties of the total aerosol in terms of the identified aerosol sources. Source apportionments (obtained from absolute principal component analysis) revealed that the wet and dry season aerosols contained the same three main components, but in different (absolute and relative) amounts: the wet season aerosol consisted mainly of a natural biogenic component, whereas pyrogenic aerosols dominated the dry season aerosol mass. The third component identified was soil dust, which was often internally mixed with the biomass-burning aerosol. All three components contributed significantly to light extinction during both seasons. At the pasture site, up to 47% of the light absorption was attributed to biogenic particles during the wet season, and up to 35% at the tower site during the wet-to-dry transition period. The results from the present study suggest that, in addition to pyrogenic particles, biogenic and soil dust aerosols must be taken into account when modeling the physical and optical properties of aerosols in forested regions such the Amazon Basin.
Keywords: Natural background aerosols; Biomass burning; Black carbon; Aerosol scattering; Aerosol absorption; Amazonia;

Ozone deposition to the sea surface: chemical enhancement and wind speed dependence by Wonil Chang; Brian G. Heikes; Meehye Lee (1053-1059).
Deposition of ozone to the sea surface is controlled by complex physical and chemical processes. There is a large variability in the observed deposition velocity of ozone v d needed to be better characterized. In addition, the existing formulations for estimating (v d) cannot explain a significant ozone loss, particularly, at low wind speed. By amalgamating previous works, a more general formula was developed to account for v d dependence on wind speed and chemical enhancement. The result shows that v d can be elevated from 0.016 to 0.078  cm s −1 by about a factor of 5 as wind speed increases from 0 to 20  m s −1 , indicating the importance of wind-induced turbulent gas-transfer. To estimate molecular gas-transfer, represented by the surface reactivity of ozone, reaction rates of species known to react with ozone in seawater were investigated. Iodide was found to be capable of describing the substantial chemical destruction of ozone at low wind speed. Due to a wide range of distribution in the surface oceans (20–400  nM ), iodide appears to be a candidate elucidating the variability of v d. This study suggests that the physical and chemical processes are coupled and both play significant roles in determining ozone deposition to the sea surface.
Keywords: Ozone; Deposition dry; Chemical enhancement; Air–sea exchange; Gas-transfer;

Aerosol mass size distributions of water-soluble organic carbon (WSOC) were studied at a coastal site in Hong Kong. Eleven sets of 72-h samples were collected using an eight-stage impactor sampler over three seasons in 2000–2001. Regardless of air mass origins being mainly marine or continental, WSOC exhibited bimodal size distributions with a dominant fine mode and a minor coarse mode in the size range of >0.43 μm. The two modes had a mass mean aerodynamic diameter (MMAD) of 0.7±0.1 and 4.0±0.3 μm, respectively. The fine WSOC accounted for the major proportion of the total WSOC, ranging from two-thirds to four-fifths. The WSOC mixtures were resolved into 3–5 peaks under controlled progressive heating and combustion conditions. A positive matrix factorization analysis deconvoluted the WSOC mixtures into three component groups of different thermal behaviors. The three groups of WSOC species were postulated to be low, medium, and high molecular weight (MW) polar compounds on the basis of their thermal evolution features. On average, they accounted for 21%, 39%, and 40% of fine WSOC (<2.1 μm) mass, respectively. Coarse WSOC (>2.1 μm) was largely made of the low MW polar compound group. The low MW group had a bimodal distribution with a dominant coarse mode, likely associated with sea salt aerosols. The medium and the high MW groups had a single mode distribution in the droplet mode, both with an average MMAD of 0.7±0.1 μm. Their droplet mode presence indicated that they were associated with cloud-processed particles. There is evidence to suggest that the high MW group was likely secondary in origin, formed during cloud processing.
Keywords: Water-soluble organic compounds; Formation mechanisms; Cloud processing; Positive matrix factorization; Hong Kong;

The Ultraviolet B (UV-B, 280–315 nm) and total (300–3000 nm) irradiances in a suburban site in Córdoba city (31.44°S; 64.19°W) were measured and calculated between November 1998 and December 2002. Measurements were carried out with a pyranometer YES UVB-1 (UV-B) and a pyranometer YES TSP-700 (total) while UV-B calculations were performed by using the radiative transfer model TUV 4.1 (Tropospheric Ultraviolet Visible). The evolution and characteristics of total ozone column values over Córdoba during the last 12 years was analyzed. The stratospheric ozone depletion over Antarctica during the springtime does not affect the UV-B measurements. The agreement between UV-B measurements and calculations for clear sky days at solar noon is better than 10% for zenith angles <70°. A simple model to calculate total radiation was obtained by fitting the experimental values under clear sky conditions. The agreement is better than 5% for zenith angles <70°. The small interannual variability in the total radiation, allows us to use a set of parameters for one year to calculate the annual cycle for any other year. Daily, seasonal, and interannual variations of UV-B and total radiation were characterized for this period. The effect of the total ozone column variability on UV-B annual cycle was analyzed by using the UV-B values in a fixed solar zenith angle interval (55–60°). The role of clouds on the UV-B and total annual cycle is also examined.
Keywords: Aerosols; Clouds; Ozone; Radiative model; UV-B and total radiation;