Atmospheric Environment (v.56, #C)

Mechanism of carboxylic acid photooxidation in atmospheric aqueous phase: Formation, fate and reactivity by Tiffany Charbouillot; Sophie Gorini; Guillaume Voyard; Marius Parazols; Marcello Brigante; Laurent Deguillaume; Anne-Marie Delort; Gilles Mailhot (1-8).
In the first part of the work, we investigated the reactivity toward photogenerated hydroxyl radicals (OH) of seven monocarboxylic acids and six dicarboxylic acids found in natural cloud water. This leads to the proposition of a schematic degradation pathway linking glutaric acid (C5) to complete mineralization into CO2. We report a detailed mechanism on the succinic acid reactivity toward OH leading to the formation of malonic, glyoxylic and consequently oxalic acids and a comparison with reported pathways proposed by the CAPRAM (Chemical Aqueous Phase RAdical Mechanism) is discussed. We also investigated the photooxidation of formic acid under atmospherically relevant conditions leading to the possible formation of oxalic acid via radical mediated recombination.The second part focuses on the polychromatic irradiation (closed to solar irradiation) of a collected cloud aqueous phase showing that irradiation of cloud water leads to the formation of both formic and acetic acids. Carboxylic acid formation increases in the presence of photogenerated hydroxyl radicals from hydrogen peroxide, showing that photooxidation could play a key role in the formation of carboxylic acids under atmospherically relevant conditions.Display Omitted► We investigated the chemical photooxidantion of carboxylic acids under atmospherically relevant aqueous media. ► Hydroxyl radical reactivity with formic acid leads to the formation in small amounts of oxalic acid. ► Photochemistry of cloud water is responsible for the increase of carboxylic acids concentration in such medium.
Keywords: Atmosphere; Organic matter; Photochemistry; Phototransformation; Hydroxyl radical; Dimerization;

Many models of secondary organic aerosol (SOA) formation, adhering to gas-particle equilibrium partitioning theory, require known vapour pressures for low volatility products of volatile organic compound (VOC) oxidation. Since the majority of such products have yet to be isolated and analysed, few experimental determinations of pertinent vapour pressures have been achieved, and models are forced to rely on vapour pressure estimates, such as those available through the common, computer-based SPARC and MPBPWIN property calculators. Thus, the accuracy of the respective estimation methods must be measured and evaluated, in order to determine the consequences in the resulting models. However, published evaluations, and most models themselves, typically focus on moderate to high ambient temperatures, which may not be applicable year-round in colder regions, where the rate of VOC oxidation slows, while the vapour pressures of the products decrease, indicating an increased tendency to condense into the aerosol phase. In this paper, the accuracy of the SPARC and MPBPWIN methods is evaluated over a broad temperature range, from 248.15 to 298.15 K, in five degree intervals using a test set of 45 compounds. The results are reported in terms of mean average error (MAE) and mean bias error (MBE), and given for alcohol, carboxylic acid, aldehyde, and ketone compound classes at each temperature. Specific trends in MAE and MBE with regard to compound class and changing temperature are discussed. More generally, the evaluation indicates that SPARC, with MAE decreasing from 0.288 at 248.15 K to 0.165 at 298.15 K and MBE increasing from −0.180 at 248.15 K to a peak of −0.081 at 293.15 K, is more accurate at low to moderate temperatures than MPBPWIN, with MAE decreasing from 0.436 at 248.15 K to 0.272 at 298.15 K and MBE increasing from −0.328 at 248.15 K to −0.213 at 298.15 K. Decreasing accuracy at lower temperatures emphasizes a need for focused experimental and model efforts in this temperature range.► Vapour pressures are needed to estimate SOA formation at low temperatures. ► Vapour pressures are estimated for the temperature range 248.15 K to 298.15 K. ► SPARC and MPBPWIN are compared for performance at low temperatures. ► SPARC is more accurate at low to moderate temperatures than MPBPWIN. ► Poor model performance indicates need for more experiments at low temperatures.
Keywords: Secondary organic aerosol; Low temperature; Vapour pressure estimation; SPARC; MPBPWIN;

Particle emissions from diesel engine cars depend firstly on exhaust aftertreatment systems but the use of the vehicle becomes also crucial. In urban areas, this use depends on: transport demand, route choices, traffic density, street conditions, weather, driver behaviour and topographical characteristics of the roads. Nowadays, most diesel vehicles in urban areas across Europe are equipped with exhaust aftertreatment systems aiming to reduce the total mass of emitted particles. In comparison to earlier aftertreatment systems, the implementation of modern procedures is causing a reduction in the size of the emitted particles up to a nanometric range. The main goal of this work is the characterization of particle size and number distribution in the submicrometric range from a modern diesel vehicle emission in real traffic conditions in the city of Madrid with the purpose of assessing the actual weight of the different city parameters influencing the particle emission. In order to accomplish this objective, up to 12 on board emission measurement experiments have been performed with a Euro IV Diesel passenger car driving along a single urban circuit in Madrid City. To cover the main external factors, stretch, traffic conditions and driving directions have been considered as independent variables for this study. Assuming a proper car operating conditions, the results show that street characteristics, vehicle density and topographic features are the main factors conditioning the particle emission. Extrapolating our results, a diesel standard passenger car circulating across a city like Madrid can emit more nanoparticles per kilometre (up to 114% more in this study) at peak hour than at off peak hour. Moreover, the driving direction can also influence dramatically the emission of nanoparticles per second. This difference in the emission rate depends on the street but in our study it can be higher than 110% depending on the driving direction.► The subject was a diesel engine running in real traffic in Madrid. ► Particle number per kilometre is closely related with the vehicle speed profile. ► Particle number concentration depends significantly on topography and street type. ► Nanoparticle size and number distribution depends on hourly traffic intensity. ► Vehicle low speed and idle periods cause an increase in accumulation particle mode.
Keywords: Nanoparticle emissions; Particle size distribution; Diesel exhaust; On board measurement; Madrid; Urban traffic;

Anthropogenic 129I concentration and 129I/127I ratio in rainwater from Seville (Spain) in the period 2005–2008 as affected by airborne releases from Sellafield and La Hague facilities by J.M. Gómez-Guzmán; S.M. Enamorado-Báez; A.R. Pinto-Gómez; J.M. Abril-Hernández; J.M. López-Gutiérrez; M. García-León (26-32).
129I is a very long-lived radionuclide (T 1/2  = 15.7 × 106 years) that is present in the environment both because of natural and anthropogenic sources. In this work 129I concentration and 129I/129I ratio have been determined in rainwater samples collected at Seville (south-western Spain) during the period 2005–2008. Typical 129I concentration range from (0.26–8.86)×108 atoms/L, while 129I deposition are normally in the order of 107–108 atoms/m2d. Variability in the isotopic ratio 129I/129I indicates a range of (0.17–8.71) × 10−8. Temporal evolution of the 129I deposition seem to be related with the history of the 129I gaseous releases from the European reprocessing facilities at Sellafield and La Hague. The results obtained in this work are lower than the reported in previous works for the same location during the period 1996–1999, probably due to the reduction of the total gaseous 129I releases emitted by Sellafield and La Hague. The study of the dependence of the 129I deposition with some atmospheric parameters suggests that deposition seems to be more important in wet than in dry periods and that also depends in the wind direction, being more important for winds with north to south component. The agreement between the 129I concentration and the 129I/129I ratio suggest that the gaseous 129I emitted by the reprocessing plants has enough time to equilibrate with the 127I present in the atmosphere before arriving to southern Spain, probably due to the distance between Seville and these reprocessing plants.► 129I and 129I/127I were determined in rainwater from Seville during 2005–2008. ► The results are lower than previous ones for the same location during 1996–1999. ► 129I deposition is more important in wet periods and depends on the wind direction. ► Southern Spain was affected by airborne 129I releases from Sellafield and La Hague.
Keywords: AMS; ICP-MS; 129I; 127I; Rainwater; Reprocessing plants;

Accurate and high-resolution boundary conditions and flow fields in the first-class cabin of an MD-82 commercial airliner by Wei Liu; Jizhou Wen; Jiangyue Chao; Weiyou Yin; Chen Shen; Dayi Lai; Chao-Hsin Lin; Junjie Liu; Hejiang Sun; Qingyan Chen (33-44).
Flow fields in commercial airliner cabins are crucial for creating a thermally comfortable and healthy cabin environment. Flow fields depend on the thermo-fluid boundary conditions at the diffusers, in addition to the cabin geometry and furnishing. To study the flow fields in cabins, this paper describes a procedure to obtain the cabin geometry, boundary conditions at the diffusers, and flow fields. This investigation used a laser tracking system and reverse engineering to generate a digital model of an MD-82 aircraft cabin. Even though the measuring error by the system was very small, approximations and assumptions were needed to reduce the workload and data size. The geometric model can also be easily used to calculate the space volume. A combination of hot-sphere anemometers (HSA) and ultrasonic anemometers (UA) were applied to obtain the velocity magnitude, velocity direction, and turbulence intensity at the diffusers. The measured results indicate that the flow boundary conditions in a real cabin were rather complex and the velocity magnitude, velocity direction, and turbulence intensity varied significantly from one slot opening to another. UAs were also applied to measure the three-dimensional air velocity at 20 Hz, which could also be used to determine the turbulence intensity. Due to the instability of the flow, it should at least be measured for 4 min to obtain accurate averaged velocity and turbulence information. It was found that the flow fields were of low speed and high turbulence intensity. This study provides high quality data for validating Computational Fluid Dynamics (CFD) models, including cabin geometry, boundary conditions of diffusers, and high-resolution flow field in the first-class cabin of a functional MD-82 commercial airliner.► High quality data for validating Computational Fluid Dynamics (CFD) models. ► High quality cabin geometry was obtained by reverse engineering. ► UAs can be used to accurately measure the distributions of 3D air velocity. ► The flow boundary conditions in a real cabin were rather complex. ► The measurement found significant longitudinal flow in the cabin.
Keywords: Airliner cabin; Cabin geometry; Flow field; Experiment; Diffuser;

Interactions of fire emissions and urban pollution over California: Ozone formation and air quality simulations by H.B. Singh; C. Cai; A. Kaduwela; A. Weinheimer; A. Wisthaler (45-51).
An instrumented DC-8 aircraft was employed to perform airborne observations in rural and urban environs of California during the summer 2008 NASA ARCTAS-CARB campaign. The fortuitous occurrence of large wildfire episodes in Northern California allowed for studies of fire emissions, their composition, and their interactions with rural and urban air. Relative to CO, emissions of HCN were shown to vary non-linearly with fire characteristics while those of CH3CN were nearly unchanged, making the latter a superior quantitative tracer of biomass combustion. Although some fire plumes over California contained little NOx and virtually no O3 enhancement, others contained ample VOCs and sufficient NOx, largely from urban influences, to result in significant ozone formation. The highest observed O3 mixing ratios (170 ppb) were also in fire-influenced urban air masses. Attempts to simulate these interactions using CMAQ, a high-resolution state of the art air quality model, were only minimally successful and indicated several shortcomings in simulating fire emission influences on urban smog formation. A variety of secondary oxidation products (e.g. O3, PAN, HCHO) were substantially underestimated in fire-influenced air masses. Available data involving fire plumes and anthropogenic pollution interactions are presently quite sparse and additional observational and mechanistic studies are needed.► Forest fire plumes produce significant ozone when mixed with urban pollution. ► Models are unable to simulate interactions of fire emissions with urban smog. ► Available data on fire emissions and smog interactions are sparse. ► Fire emissions may be poorly characterized and underestimated.
Keywords: Ozone; Wildfires; Urban pollution; Nitrogen oxides; PAN; Formaldehyde; Aerosol;

Emissions of HC, CO, NO x , CO2, and SO2 from civil aviation in China in 2010 by Weiyi Fan; Yifei Sun; Tianle Zhu; Yi Wen (52-57).
Civil aviation in China has developed rapidly in recent years, and the effects of civil aviation emissions on the atmospheric environment should not be neglected. The establishment of emission inventories of atmospheric pollutants from civil aviation contributes to related policy formation and pollution control. According to the 2010’s China flight schedules, aircraft/engine combination information and revised emission indices from the International Civil Aviation Organization emission data bank based on meteorological data, the fuel consumption and HC, CO, NO x , CO2, SO2 emissions from domestic flights of civil aviation in China (excluding Taiwan Province) in 2010 are estimated in this paper. The results show that fuel consumption in 2010 on domestic flights in China is 12.12 million tons (metric tons), HC, CO, NO x , CO2 and SO2 emissions are 4600 tons, 39,700 tons, 154,100 tons, 38.21 million tons and 9700 tons, respectively. The fuel consumption and pollutant emissions of China Southern Airline are responsible for the largest national proportion of each, accounting for 27% and 25–28%, respectively.► We estimated the fuel consumption on China civil aviation domestic flights in 2010. ► We established emission inventories of HC, CO, NO x , CO2 and SO2. ► The B737-800s account for the largest fuel consumption and pollutant emissions. ► China Southern Airline owns the largest fuel consumption and pollutant emissions. ► High-combustion-efficiency engines lead to less pollutant emissions.
Keywords: Emission inventory; Fuel consumption; CO; NO x ; SO2;

Uptake kinetics of three epoxides into sulfuric acid solution by Tianhe Wang; Ze Liu; Weigang Wang; Maofa Ge (58-64).
This work presents a study of the uptake of isoprene epoxide, butadiene epoxide (BMO) and butadiene diepoxide (BDO) into sulfuric acid solutions which helps to understand the reactivity of epoxides existing in the atmosphere toward acidic aerosols. The uptake of these three compounds into 0−30 wt % H2SO4 solutions were measured using a rotated wetted-wall reactor (RWW) coupled to a single-photon ionization time of flight mass spectrometer (SPI-TOFMS). The epoxides were found to be very easily taken up by H2SO4 solutions even in dilute concentrations of pH levels. Isoprene epoxide was found to partition reversibly into solution at pH = 4, whereas irreversible uptake was observed when pH ≤ 3. We reported the reactive uptake coefficients from 1.87 × 10−5 to 2.67 × 10−3 for pH = 3−20 wt % H2SO4 solutions. A chemical reaction for isoprene epoxide was responsible for the reactive uptake. By means of mass spectrometry, gas chromatography and FTIR spectroscopy, a gas product was identified to be 2-methyl-3-butenal. The uptake behavior of butadiene epoxide was similar with that of isoprene epoxide, while butadiene diepoxide partitioned irreversibly over the whole acidity range of 0–30 wt %, and the reactive uptake coefficients increased slightly (0.849 × 10−4–1.36 × 10−4) from pure water to pH = 1. The reactivity that displayed close dependence on the hydrolysis rates of the three epoxides was analyzed and compared according to their molecular structural differences. The atmospheric lifetimes were calculated and atmospheric implication was discussed based on the corresponding reactive uptake coefficients.► The uptake of three epoxides on H2SO4 was studied. ► The reactive uptake coefficients increase with increasing acidity. ► Isoprene monoxide transformed to 2-methyl-3-butenal on H2SO4. ► The chemical mechanism of isoprene monoxide was proposed. ► This process may play an important role in SOA formation in upper troposphere.
Keywords: Epoxides; Sulfuric acid; Reactive uptake coefficients;

Assessment of indoor PM2.5 in different residential environments by Mohamed F. Yassin; Bothaina E.Y. AlThaqeb; Eman A.E. Al-Mutiri (65-68).
The indoor air quality (IAQ) as assessed by PM2.5 (particulate matter with an aerodynamic diameter of less than 2.5 μm) was measured at indoor settings in various residential houses which were located in different local environments across Kuwait. The indoor house settings included kitchen, living room, and bedrooms. Samples were collected from houses over 24 h. PM2.5 was estimated using a Dust-Trak personal sampler. Results were analyzed and compared with the US Environmental Protection Agencies (EPA) and World Health Organization (WHO) standards and guidelines. The results demonstrated that kitchens have the highest PM2.5 concentration probably due to cooking activities; the bedroom has the lowest PM2.5 concentration. The study shows that Kuwait indoor residential pollution is among the worst in comparison with other countries.► Measured PM2.5 at different locations in house at various residential environments. ► The kitchen has the highest PM2.5 concentration due to cooking activities. ► The bedroom has the lowest PM2.5 concentration. ► The PM2.5 concentration in the residential living room in Kuwait is higher than EPA.
Keywords: Indoor air quality; Personal sampler; PM2.5 concentration; Residential environments;

Understanding haze pollution over the southern Hebei area of China using the CMAQ model by Litao Wang; Jing Xu; Jing Yang; Xiujuan Zhao; Wei Wei; Dandan Cheng; Xuemei Pan; Jie Su (69-79).
Haze has been one of the major air pollution problems in Chinese cities, and the southern Hebei area has attracted particular attention because of its high frequency of haze weather and the rapid deterioration in visibility in recent years. This study is aimed at understanding the characteristics and sources of the serious haze pollution in the southern Hebei area using the Mesoscale Modeling System Generation 5 (MM5) and the Models-3/Community Multiscale Air Quality Model (CMAQ). The haze frequencies in the cities of southern Hebei, including Shijiazhuang, Xingtai, and five other urban centers in the surrounding regions, are analyzed for a ten-year period from 2001 to 2010, which shows a very similar and clear seasonal variation. The contributions of the local and regional anthropogenic emissions to the concentration of fine particulate matter (PM2.5, particles with an aerodiameter of less than or equal to 2.5 μm) and the light extinction coefficient (B ext) are estimated by conducting simulations of seven scenarios. The results show that approximately 65% of the PM2.5 in Shijiazhuang and Xingtai originated from the local emissions of the southern Hebei area, followed by Shanxi Province and the northern area of Hebei (13.8% and 7.3% to Shijiazhuang and 10.4% and 5.2% to Xingtai, respectively). The contributions of the emissions from the local area, Shanxi Province and the northern Hebei area to B ext are approximately 59.4%, 13.8% and 6.8% for Shijiazhuang and 58.2%, 10.1% and 5.0% for Xingtai, respectively. Moreover, an analysis of a typical pollution episode indicates that the contributions from the Shandong and Henan provinces are also significant. Further investigations are still required because of the complexity of the haze pollution over the southern Hebei area.► We model the area which has the most severe haze pollution in China. ► We model the most polluted month out of the 120 months from 2001 to 2010. ► We analyze the haze frequencies of the seven urban centers in North China Plain for 2001–2010. ► Transboundary air pollution plays an important role in the haze formation over North China Plain.
Keywords: Haze; Visibility; PM2.5; Southern Hebei; Models-3/CMAQ;

Greenhouse gas (GHG) emissions have exacerbated global warming, and consequently are the focus of worldwide reduction efforts. Reducing emissions involves accurately estimating GHG emissions and the uncertainty associated with such estimates. The uncertainty of GHG emission estimates is often assessed using the 95% confidence interval. Given a small sample size and non-normal distribution of the underlying population, the uncertainty estimate obtained using the 95% confidence interval may lead to significant bias. Bootstrap confidence interval is an effective means of reducing bias. This work presents a procedure for estimating the uncertainty of GHG emission estimation using bootstrap confidence intervals. Numerical simulation is performed for GHG emission estimates under three distributions (namely normal, log-normal and uniform) to find the 95% confidence intervals and bootstrap confidence intervals. Finally, the accuracy and sensitivity of the uncertainty of various interval estimations are examined by comparing the coverage performance, interval mean and interval standard deviation. Simulation results indicate that the bootstrap intervals are more applicable than the 95% confidence interval given non-normal dataset and small sample size. Moreover, when sample size n is less than 30, the bootstrap confidence interval has a smaller interval length with a smaller deviation than that of the classical 95% confidence interval regardless of whether the data distribution is normal or non-normal. This study recommends a sample size greater than or equal to 9 for estimating the uncertainty of emission estimates. When the sample size n exceeds 30, either the normality-based 95% confidence interval or bootstrap confidence intervals may be used regardless of whether the data distribution is normal or non-normal. A case study of carbon stock from Taiwan demonstrates the feasibility of the proposed procedure.► Emission estimates data generated by Monte Carlo Method. ► Bootstrap Samples are selected by bootstrap Simulation. ► Computed Emission estimates sorted to find BCa Confidence Interval. ► Various parameter combinations and Distributions are considered. ► Validity and Sensitivity are tested by coverage percentage.
Keywords: Bootstrap confidence intervals; Bootstrap simulation; Greenhouse gas emissions; Uncertainty;

Long-term features of cloud microbiology at the puy de Dôme (France) by Mickaël Vaïtilingom; Eléonore Attard; Nicolas Gaiani; Martine Sancelme; Laurent Deguillaume; Andrea I. Flossmann; Pierre Amato; Anne-Marie Delort (88-100).
Despite the enormous volume they represent and the importance they have for Earth’s climate, clouds remain environments where the microbiological features are still poorly understood. Studies of the microbial content existing in the atmosphere have demonstrated extreme quantitative and qualitative variability, of which the drivers yet need to be determined. Between 2007 and 2010, we collected cloud water from the puy de Dôme summit in France (1465 m a.s.l.) for chemical and microbiological analysis. These data were combined with cloud data collected between 2004 and 2005 following similar protocols. Overall, the cultivable community of chemotrophic aerobic microorganisms was dominated by pigmented colonies and accounted for <1% of the 3.3 × 103 to 2.5 × 105 total bacteria mL−1, but up to 41% of the 8.9 × 102 to 3.2 × 104 fungal cells mL−1. None of the concentrations of the chemical compounds measured was linked to the variations observed for the microbiological content, suggesting distinct sources and/or distinct modes of incorporation into cloud water. However, the overall dataset indicated that microorganisms in clouds were mostly originating from continental areas, especially from vegetation. We isolated and identified 185 heterotrophic bacteria and 150 yeasts from our samples (including -Alpha, -Beta and Gamma-Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria, and Basidiomycetous and Ascomycetous yeasts), the corresponding 16S and 26S rRNA gene sequences of which have been deposited in GenBank. A few genera largely dominated the pool of cultivable microorganisms in clouds, such as Pseudomonas and Sphingomonas for bacteria, which were detected in more than 40% of the clouds sampled, and Dioszegia and Udeniomyces for yeasts, detected in more than 60% of the samples. The recurring presence of some groups of microorganisms suggests that they have elaborated strategies of increased survival in the atmosphere and clouds.► Microbiological content in 34 cloud water samples collected in 8 years. ► The concentration of microorganisms was linked to the origin of the air mass. ► The main source of viable microorganisms for clouds is probably vegetation. ► Presence of recurring groups (Pseudomonas, Sphingomonas…). ► Certain microorganisms seem better fitted for living in the atmosphere than others.
Keywords: Cloud water; Microorganism; Bacteria; Yeast; Atmosphere;

In order to investigate seasonal and diurnal variation of primary organic carbon (POC) and secondary organic carbon (SOC) concentrations in a megacity, hourly measurements of particulate and gaseous pollutants were carried out in Seoul from January to December 2010. The EC Tracer Method (ECTM) and the Multiple Regression Method (MRM) have been used to estimate seasonal and diurnal concentrations of POC and SOC concentrations. Annual mean SOC concentrations estimated by ECTM (SOCECTM) and MRM (SOCMRM) accounted for 14.61 and 17.21% of TOC concentrations, respectively. Seasonal patterns in SOCMRM were comparable to those of SOCECTM, but the annual average SOCMRM was about 15% greater than that of SOCECTM. In spring, however, a large discrepancy was observed between SOCECTM and SOCMRM, which is thought to be due to a high ozone concentration and primary TOC/EC ratio. Regarding the annual mean diurnal characteristics, POC concentration showed peaks around 10:00 and 00:00 local time that were also observed in diurnal variations of TOC and EC concentrations. Annual mean SOC concentration, however, showed peaks at around 15:00. In the morning over all seasons, we found discrepancies between SOCECTM and SOCMRM due to overestimated SOCECTM concentration. The diurnal variations in SOC concentrations were found to have seasonal characteristics. The diurnal pattern of SOC concentration in spring was similar to that in autumn, and SOC concentrations in all seasons with the exception of winter showed a peak at around 15:00. In summer, however, the SOC concentration peak at around 15:00 was greater by 70%, 81%, and 54% than the peaks seen in spring, autumn, and winter, respectively, which could be explained by the high ozone concentration and strong UV radiation in summer. From 10:00 to 15:00 in summer, the average increase rates in SOCECTM and SOCMRM were 0.39 and 0.24 μg m−3 h−1, respectively. In winter, negligible diurnal variations of estimated SOC concentrations demonstrate that SOC formation is less active than in other seasons. The high concentration level of mean SOC in winter could be attributed to a low mixing height or stagnant atmospheric condition.► First estimation of diurnal SOC variations was carried out in a megacity site. ► Enhanced SOC concentration was estimated in summer. ► The diurnal variations in SOC concentrations show seasonal characteristics. ► SOC concentrations were peaked at 3:00 PM for all seasons with different magnitudes. ► The results from EC tracer and multiple regression methods show slight discrepancy.
Keywords: Secondary organic carbon; Primary organic carbon; Diurnal variation; EC tracer method; Multiple regression method;

Temperature inversions influence the local air quality at smaller scales and the pollution transport at larger spatio-temporal scales and are one of the most commonly observed meteorological phenomena over Scandinavia (54°N–70°N, 0–30°E) during winter. Here, apart from presenting key statistics on temperature inversions, a large-scale co-variation of inversion strength and carbon monoxide (CO), an ideal pollution tracer, is further quantified at six vertical levels in the free troposphere during three distinct meteorological regimes that are identified based on inversion strength. Collocated temperature and CO profiles from Atmospheric Infrared Sounder (AIRS) are used for this purpose. Higher values of CO (up to 15%) are observed over Scandinavia during weakly stable regimes at all vertical levels studied, whereas lower CO values (up to 10%) are observed when inversions become stronger and elevated. The observed systematic co-variation between CO and inversion strength in three meteorological regimes is most likely explained by the efficacy of long-range transport to influence tropospheric composition over Scandinavia. We argue that this large-scale co-variation of temperature inversions and CO would be a robust metric to test coupling of large-scale meteorology and chemistry in transport models.► The key statistics on temperature inversions over Scandinavia is presented. ► The link between carbon monoxide and temperature inversions is investigated. ► Pollution transport signal based solely on satellite observations is inferred.
Keywords: Carbon monoxide; Pollution transport; AIRS; Chemistry transport models; Temperature inversions;

An inventory of biogenic volatile organic compounds for a subtropical urban–rural complex by Jie Chang; Yuan Ren; Yan Shi; Yimei Zhu; Ying Ge; Shengmao Hong; Li Jiao; Fengmei Lin; Changhui Peng; Tomoki Mochizuki; Akira Tani; Ying Mu; Chengxin Fu (115-123).
Increases in atmospheric volatile organic compounds (VOC), especially in relation to biogenic VOC (BVOC), and haze days that affect the built-up areas are believed to be closely correlated. The present study aims to provide a spatially and temporally resolved BVOC inventory of a subtropical urban–rural complex, the Greater Hangzhou Area (GHA) in China. Urban green space was subdivided into block green space and linear green space; rural areas were classified into four primary forest types. A field survey was conducted to assess the vegetation composition (species, size) and foliar mass of each tree species. BVOC emission potentials were obtained from measurement and literature. Results showed (1) the emission intensity (annual BVOC emissions per land area) in the entire GHA is 3.37 × 106 g C km−2 yr−1, and rural forest (excluding bamboo forest) exhibits lower average emission intensity (2.74 × 106 g C km−2 yr−1) than that of urban green space (3.13 × 106 g C km−2 yr−1); (2) Within the built-up area, the block green space has higher emission intensity (3.93 × 106 g C km−2 yr−1) than the linear green space (2.63 × 106 g C km−2 yr−1); (3) in Hangzhou city, BVOC emissions of native and exotic trees exhibited no differences; and (4) in rural areas, bamboo forests and coniferous forests were the major contributors of BVOC emissions, whereas the original vegetation type of this region, evergreen broad-leaved forest, possessed lower BVOC emissions. The results suggest that total BVOC emission can be controlled to low levels by planting low-emitting species in built-up areas while restoring original broad-leaved forest vegetation in rural areas.► Bamboo forest is the major contributor to the BVOC emissions of the GHA. ► Average BVOC emission intensity of urban green space is higher than that of rural forest (not including bamboo forest). ► Native and exotic tree species exhibit no difference in BVOC emissions in the GHA. ► BVOC emissions intensity increases from north to south in eastern costal China.
Keywords: Greater Hangzhou Area; Green space; Isoprene; Monoterpenes; Tree; Exotic species;

Origin and degradation of lipids in aeolian particles from a coastal area of the north-western Mediterranean Sea by J.-F. Rontani; B. Charriere; F. Vaultier; N. Garcia; R. Sempéré; P. Raimbault (124-135).
The lipid content of eight samples of aeolian particles collected on the Frioul Islands (north-western Mediterranean Sea) during the year 2010 was investigated. Lipid analyses indicated a significant contribution of terrestrial higher plant debris to some of the samples, while meat cooking residues were also found. Specific degradation products of sterols and monounsaturated fatty acids were employed to assess the importance of biotic and abiotic degradation processes on land and during aeolian transport. Degradation of higher plant lipids on land appears to involve Type II (i.e., singlet oxygen-mediated) photooxidation during senescence and bacterial degradation processes in soils, while during aeolian transport this terrestrial material mainly undergoes autoxidation and/or Type I (i.e., radical-mediated) photooxidation and is relatively well preserved towards bacterial degradation. In contrast, bacteria play a significant role in the degradation of meat cooking residues in these particles.► Lipids of aeolian particles collected in NW Mediterranean Sea were analyzed. ► Biotic and abiotic degradation state of lipids in these particles was examined. ► Degradation of higher plants on land involves photooxidation and biodegradation. ► During aeolian transport higher plant debris mainly undergo free radical oxidation. ► Bacteria play a significant role in the degradation of meat cooking residues.
Keywords: Aeolian particles; North-western Mediterranean Sea; Lipids; Higher plant debris; Biotic and abiotic degradation; Autoxidation; Photooxidation; Bacterial degradation;

Emissions of carbon monoxide and carbon dioxide from uncompressed and pelletized biomass fuel burning in typical household stoves in China by Wen Wei; Wei Zhang; Dan Hu; Langbo Ou; Yindong Tong; Guofeng Shen; Huizhong Shen; Xuejun Wang (136-142).
Carbon dioxide (CO2) and carbon monoxide (CO) impact climate change and human health. The uncertainties in emissions inventories of CO2 and CO are primarily due to the large variation in measured emissions factors (EFs), especially to the lack of EFs from developing countries. China's goals of reducing CO2 emissions require a maximum utilization of biomass fuels. Pelletized biomass fuels are well suited for the residential biomass market, providing possibilities of more automated and optimized systems with higher modified combustion efficiency (MCE) and less products from incomplete combustion. However, EFs of CO2 and CO from pellet biomass fuels are seldom reported, and a comparison to conventional uncompressed biomass fuels has never been conducted. Therefore, the objectives of this study were to experimentally determine the CO2 and CO EFs from uncompressed biomass (i.e., firewood and crop residues) and biomass pellets (i.e., pine wood pellet and corn straw pellet) under real residential applications and to compare the influences of fuel properties and combustion conditions on CO2 and CO emissions from the two types of biomass fuels. For the uncompressed biomass examples, the CO2 and CO EFs were 1649.4 ± 35.2 g kg−1 and 47.8 ± 8.9 g kg−1, respectively, for firewood and 1503.2 ± 148.5 g kg−1 and 52.0 ± 14.2 g kg−1, respectively, for crop residues. For the pellet biomass fuel examples, the CO2 and CO EFs were 1708.0 ± 3.8 g kg−1 and 4.4 ± 2.4 g kg−1, respectively, for pellet pine and 1552.1 ± 16.3 g kg−1 and 17.9 ± 10.2 g kg−1, respectively, for pellet corn. In rural China areas during 2007, firewood and crop residue burning produced 721.7 and 23.4 million tons of CO2 and CO, respectively.► Emission factors of CO2 and CO for uncompressed and pelletized biomass fuels. ► CO2 and CO emissions reduced by pellet fuels compared with uncompressed biomass. ► Inventory on CO2 and CO emissions from biomass burning in China rural areas.
Keywords: Emissions factors; Pellet biomass fuels; Biomass burning; Carbon monoxide; Carbon dioxide;

Wintertime aerosol dynamics and chemical composition across the mixing layer over basin valleys by L. Ferrero; D. Cappelletti; B. Moroni; G. Sangiorgi; M.G. Perrone; S. Crocchianti; E. Bolzacchini (143-153).
Aerosol size distributions and chemical compositions were characterized during extensive balloon soundings over the Terni valley (central Italy). The evolution of aerosol size distributions across the mixing layer, and further up, revealed features similar in many aspects to those observed over Milan (the Po Valley) and attributed to sedimentation and ageing dynamics.Sedimentation led to a lower vertical mixing of coarse particles than of fine ones. This also resulted in a decline in the mean volume of coarse particles across the mixing height (−50.5 ± 15.1% and −47.2 ± 12.4% over Terni and Milan, respectively) accompanied by a reduction in crustal components.Conversely, fine particles were subject to ageing, resulting in an increase in their mean volume above the mixing height (+10.9 ± 4.8% and +4.0 ± 3.1% over Terni and Milan, respectively); this process was accompanied by an increase in secondary aerosol components, and a greater correlation between different aerosol size-classes.These results were obtained over basins of different sizes and geographical location; as such, they corroborate the presence of common forms of behaviour driven by comparable meteorological and orographic conditions, which seem to characterize polluted basin valleys in general.Display Omitted► Vertical aerosol profiles were measured over basin valleys using a tethered balloon. ► The vertical mixing of fine and coarse particles reached different altitudes. ► The mean volume of coarse particles and, crustal components, decreased with height. ► The mean volume of fine particles and, secondary components, increased with height. ► Common aerosol dynamics occurred in winter: sedimentation and ageing.
Keywords: Aerosol vertical profile; Size distribution; Chemical composition; Sedimentation; Ageing; Optical particle counter; Scanning electron microscopy;

Modeling the effect of humidity on the threshold friction velocity of coal particles by Xiaochun Zhang; Weiping Chen; Chun Ma; Shuifen Zhan (154-160).
Coal particles emission could cause serious air pollution in coal production region and transport region. In coal mining industry, large amounts of water are regularly spayed to coal piles to prevent dust emission from the coal particles. The mechanism behind this measure is to manage the threshold friction velocity, which is an important parameter in controlling wind erosion and dust emission. Bagnold has developed a threshold friction velocity model for soil particles. However, the Bagnold model cannot be applied directly to coal particles as coal particles are quite different from soils in physical and chemical properties. We studied and modeled threshold friction velocity of coal particles under different humidities by using a wind tunnel. Results showed that the effects of humidity on coal particles’ threshold friction velocity are related to the hydrophilic effect and adhesive effect. Bagnold model can be corrected by two new parameter items which explained the two effects. The new model, agreed well with wind tunnel measurements for coal particles with different size categories. Despite the fact the new model was developed for coal particles, its physical basis may allow the model application to other wind susceptible particles.► We modeled threshold friction velocity for humidity influenced coal particles. ► It is questionable to apply the soil TFV model to coal, as different properties. ► Humidity effects on coal TFV are attributed to hydrophilic and adhesive effects. ► Hydrophilic and adhesive effect were explained by two new parameter items. ► The new model performances well for coal particles.
Keywords: Threshold friction velocity; Mathematical model; Coal particles; Humidity content; Wind tunnel;

While it is well known that combustion of ethanol as a biofuel will lead to enhanced emissions of methane, ethene (ethylene), acetaldehyde, formaldehyde, and oxides of nitrogen (primarily NO) when compared to gasoline alone, especially during cold starts or if catalytic converters are not operating properly, the impacts of increases in atmospheric ethene levels from combustion of fuels with higher ethanol content has not received much attention. Ethene is a well known and potent plant growth hormone and exposure to agricultural crops and natural vegetation results in yield reductions especially when combined with higher levels of PAN and ozone also expected from the increased use of ethanol/gasoline blends. We report here some baseline measurements of ethene obtained in 2002 in the southwestern and south central United States. These data indicate that current ethene background levels are less than 1 ppb. Anticipated increases in fuel ethanol content of E30 or greater is expected to lead to higher atmospheric levels of ethene on regional scales due to its atmospheric lifetime of 1.5–3 days. These background measurements are discussed in light of the potential enhancement of ethene levels expected from the anticipated increases in ethanol use as a renewable biofuel.► Baseline ethene in 2002 for the South Central U.S. found at a <0.5 ppb level. ► Arid land ethene levels were ∼0.1 ppb while grasslands and forests were ∼0.3 ppb. ► E85 and biomass burning C2H4 emissions may lead to much higher ethene levels. ► Ethene, PAN, and Ozone increases from E85 and fires need to be better evaluated.
Keywords: Ethanol; Biofuel; Ethene; Ethylene; Air quality; Climate change; Peroxyacetyl nitrate; Ozone; Benzene; Toluene; Ethyne;

Exposure to particulate matter in a mosque by Yılmaz Ocak; Akın Kılıçvuran; Aykut Balkan Eren; Aysun Sofuoglu; Sait C. Sofuoglu (169-176).
Indoor air quality in mosques during prayers may be of concern for sensitive/susceptible sub-groups of the population. However, no indoor air pollutant levels of potentially toxic agents in mosques have been reported in the literature. This study measured PM concentrations in a mosque on Friday when the mid-day prayer always receives high attendance. Particle number and CO2 concentrations were measured on nine sampling days in three different campaigns before, during, and after prayer under three different cleaning schedules: vacuuming a week before, a day before, and on the morning of the prayer. In addition, daily PM2.5 concentrations were measured. Number concentrations in 0.5–1.0, 1.0–5.0, and > 5.0 μm diameter size ranges were monitored. In all campaigns the maximum number concentrations were observed on the most crowded days. The lowest number concentrations occurred when vacuuming was performed a day before the prayer day in two of the three size ranges considered. PM2.5 concentrations (four-hour samples that integrated before, during, and after the prayer) were comparable to the other indoor environments reported in the literature. CO2 concentrations suggested that ventilation was not sufficient in the mosque during the prayers. The results showed that better ventilation, a preventive cleaning strategy, and a more detailed study are needed.► Particle number and PM2.5 concentrations were measured in a mosque. ► Resuspension from a carpeted surface is important for exposure to coarse particles. ► Lower concentrations occurred when carpet was vacuumed a day before the prayer. ► IAQ should be safe for healthy worshippers based on 1-h PM2.5 exposure. ► PM exposure may be important for sensitive/susceptible people among worshippers.
Keywords: Indoor air quality; Mosque; Particulate matter; Cleaning; Human activity;

This study highlights the influence of dry and wet deposition on concentrations of chlorinated organophosphate flame retardants (OFR) in soil. Soil samples were collected in 2010/11 during a period of snow falling to snow melting, a period of rainfall and a dry period. Snow and rainwater samples were also collected from the soil sampling site. Tris(2-chloroethyl)phosphate (TCEP), tris(2-chloroisopropyl)phosphate (TCPP) and tris(1,3-dichloro-2-propyl)phosphate (TDCP) were analysed in soil samples using a combination of Twisselmann extraction and solid-phase microextraction (SPME), followed by gas chromatography-mass spectrometry (GC-MS). SPME/GC-MS was applied to analyse TCEP, TCPP and TDCP in aqueous samples.Concentrations of TCEP were between 236 and 353 ng L−1 in snow and 78 and 234 ng L−1 in rain. TCPP concentrations were between 226 and 284 ng L−1 in snow and 371 and 385 ng L−1 in rain. In soil samples, concentrations ranged from 5.07 to 23.48 ng g−1 dry weight (dwt) for TCEP and 5.66 to 19.82 ng g−1 dwt for TCPP. Concentrations of TDCP in rainwater and snow samples were rather low (46 and 100 ng L−1, respectively); concentrations of TDCP were below the limit of detection in soil samples.Snow melting caused enhanced soil concentrations of TCEP and TCPP, but greater effect of snow melting was observed for TCEP than for TCPP soil concentrations. No significant correlation between precipitation amounts and soil concentrations was observed. The influence of wet deposition on soil contents of TCEP and TCPP may be covered by volatilisation or by the mobility of both compounds in soil and their transport to deeper soil zones with seepage water. Snow was found to be a more efficient scavenger and transporter of chlorinated OFR into soil than rainwater. During dry weather, the soil concentrations of both compounds seemed to be driven mainly by air concentrations, which are determined by source emission strengths and photochemical degradation in the atmosphere.Values of calculated air concentrations were between 0.0034 ng m−3 for TCEP and 0.99 ng m−3 for TCPP. Total OFR specific loads were 3756 ng m-2 day-1 within the first 24 h and 3028 ng m-2 day-1 within the next 24 h. Fugacity calculations (0.011 to 0.103 for TCPP and 0.005 to 0.073 for TCEP) indicated net deposition from air to soil for both compounds.► Chlorinated OFR e.g. TCEP and TCPP were detected in snow, rainwater and soil samples. ► No significant correlation between precipitation amounts and soil concentrations was observed. ► Air concentrations were calculated from rainwater concentrations. ► Fugacity calculations indicated net deposition from air to soil for both chlorinated OFR.
Keywords: Precipitation; Snow; Rainwater; Dry and wet deposition; Fugacity fraction;

Trends in ozone concentrations in the Iberian Peninsula by quantile regression and clustering by A. Monteiro; A. Carvalho; I. Ribeiro; M. Scotto; S. Barbosa; A. Alonso; J.M. Baldasano; M.T. Pay; A.I. Miranda; C. Borrego (184-193).
In this paper, 10-years of ozone (O3) hourly concentrations collected over the period 2000–2009 in the Iberian Peninsula (IP) are analyzed using records from 11 background sites. All the selected monitoring stations present an acquisition efficiency above 85%. The changes in surface ozone over the Iberian Peninsula are examined by means of quantile regression, which allows to analyse the trends not only in the mean but in the overall data distribution. In addition, the ozone hourly concentrations records are clustered on the basis of their resulting distributions.The analysis showed that high altitude stations (>900 m) have higher background O3 concentrations (∼80 μg m−3). The same magnitude of background O3 concentrations is found in stations near the Mediterranean Sea. On the other hand, the rural stations near the Atlantic coast present lower background values (∼50–60 μg m−3) than those of Mediterranean influence. The two sub-urban stations exhibit the lowest background concentrations (∼45 μg m−3). The results of the quantile regression show a very distinct behaviour of the data distribution, the slopes for a fixed quantile are not the same over IP, reflecting the spatial dependence of O3 trends. Hence the rate of temporal change is not the same for all parts of the data distribution, as implicitly assumed in ordinary regression. The lower quantile (percentile 5) presents higher rates of change than the middle (percentile 50) and the upper quantile (percentile 95). The clustering procedure reveals what has been already detected in the quantile regression. The station with highest rates of decrease on the O3 concentrations (easternmost station of IP) is isolated and then other clusters are formed among the moderately positive/negative O3 trends around the IP. The clustering procedure highlighted that the largest trends are found for the lower ozone O3 values, with largest negative trend at the easternmost station of IP, and also in northern and mainland stations, and an opposite behaviour, with positive O3 trends, is observed at the Atlantic coast stations.► 10-years of O3 data collected in the Iberian Peninsula are analysed. ► The O3 changes are examined by means of quantile regression and clustering analysis. ► Very distinct behaviour of the data distribution. ► The largest trends (negative/positive) are found for the lower ozone O3 values. ► Positive trend is observed at the Atlantic coast stations.
Keywords: Iberian Peninsula; Tropospheric ozone; Spatial and temporal analysis; Quantile regression; Cluster analysis; Ozone trend;

Monitoring atmospheric levels and deposition of dioxin-like pollutants in sub-alpine Northern Italy by J. Castro-Jiménez; S.J. Eisenreich; G. Mariani; H. Skejo; G. Umlauf (194-202).
The objective of this work was to assess the atmospheric occurrence, seasonal variations and deposition of dioxin-like pollutants (17 PCDD/Fs + 12 DL-PCBs) in sub-alpine northern Italy. A total of 108 weekly integrated samples (aerosol + gas phases) were collected during a 1-year period (2005–2006) at the Ispra EMEP site (Northern Italy, 45°49′N, 8°38′E). Atmospheric loadings into Lake Maggiore were also estimated by implementing a deposition model. ∑2,3,7,8-PCDD/F atmospheric total concentrations were dominated by the aerosol-bound fraction which ranged from 50 to 3080 (1–215 WHO98 TEQ) fg m−3. In contrast DL-PCB levels were dominated by the gas phase concentrations and varied from 1800 to 14800 (1–5 WHO98 TEQ) fg m−3. The aerosol and gas phase concentrations of PCDD/Fs and DL-PCBs exhibited a similar seasonality (higher values in winter time for aerosol-bound contaminants and lower concentrations for gas phase contaminants) in spite of their different environmental sources and properties. Estimated total atmospheric (dry + wet) depositional fluxes of dioxin-like pollutants in sub-alpine northern Italy were ∼0.2–∼9.5 ng m−2 d−1, with wet deposition dominating. Total atmospheric inputs (2,3,7,8-PCDD/Fs + DL-PCBs) into Lake Maggiore ranged from 14 to 304 g y−1. Higher environmental concentrations of dioxin-like pollutants in sub-alpine northern Italy are expected in the cold season and in rainy days due to a combined effect of stagnant atmospheric conditions (low winds), household wood burning in the region and higher pollutant loads via rainfall in winter.Display Omitted► PCDD/F levels are in the range of those in rural/semi-rural areas world-wide. ► DL-PCB levels are in the range of those in moderate urban/industrial impacted areas. ► Contaminant burden in winter precipitation events is higher than in summer rains. ► Up to 300 g of PCDD/F + DL-PCB can be deposited into Lake Maggiore waters yearly.
Keywords: PCDD/Fs; DL-PCBs; Deposition fluxes; Air concentration; Lake Maggiore; Environmental exposure;

Multiple air monitoring campaigns were conducted from 2003 to 2007 during the months of December through April in which time-integrated monitoring of PM2.5 was performed during 55 prescribed burn (PB) events administered under select meteorological conditions. The data were analyzed using a generalized additive mixed-model (GAMM) where the logarithm of PM2.5 concentrations were modeled as the sum of linear and non-linear functions of our covariates of interest after accounting for the confounding associated with the grouping structure of our data and spatial dependency. Our model explained 61% of the variance of log transformed PM2.5. The GAM component of the model (i.e. our covariates of interest) explained 40% of that variance and the mixed-model component (i.e. random-effects and spatial correlation) explained 21%. Within burn events, concentrations across our air monitoring grid were significantly influenced by the distance from burn perimeter to air monitor and the proportion of time the air monitor was in line with the wind field over the burn. Among burns, variation was significantly influenced by burn duration, burn size, mode of ignition, and regional background PM2.5; indicating the importance of these for fire management. Measures of burn intensity and meteorology were found to be insignificant in our model; however, it is possible that some of these effects were absorbed by the random-effects of our model. These findings demonstrate that downwind exposure is largely a function of wind direction combined with distance from the burn and that emissions from one burn to the next are dependent on burn size, duration, and mode of ignition.► This study presents short-range emissions from prescribed forest burns. ► Influences of meteorology and burn characteristics on downwind smoke are examined. ► Decreasing distance to burn perimeter and downwindedness explained the most PM. ► Burn size, ignition type, and duration were also significant but of less importance.
Keywords: Air pollution; Generalized additive models; Mixed-models; Particulate matter; Prescribed burning; Smoke;

A simplified chemistry module for atmospheric transport and dispersion models: Proof-of-concept using SCIPUFF by Douglas S. Burns; Shawn D. Rottmann; Angela B.L. Plitz; Floyd L. Wiseman; William Moore; Veeradej Chynwat (212-221).
An atmospheric chemistry module was developed to predict the fate of environmentally hazardous compounds discharged into the atmosphere. The computationally efficient model captures the diurnal variation within the environment and in the degradation rates of the released compounds, follows the formation of toxic degradation products, runs rapidly, and in principle can be integrated with any atmospheric transport and dispersion model. To accomplish this, a detailed atmospheric chemistry mechanism for a target toxic industrial compound (TIC) was reduced to a simple empirical effective degradation rate term (k eff). Empirically derived decay functions for k eff were developed as a function of important meteorological parameters such as solar flux, temperature, humidity, and cloud cover for various land uses and locations by statistically analyzing data generated from a detailed chemistry mechanism run over a wide range of (typical) atmospheric conditions. 1-Butene and two degradation products (propanal and nitrooxybutanone) were used as representative chemicals in the algorithm development for this proof-of-concept demonstration of the capability of the model. The quality of the developed model was evaluated via comparison with experimental chamber data and the results (decay rates) compared favorably for ethene, propene, and 1-butene (within a factor of two 75% or more of the time).► A methodology for the development of a simplified atmospheric chemistry module. ► The model captures the diurnal variation of decay rates over large parameter spaces. ► The module provides better real-time assessment without increasing runtime. ► The module has been integrated into the SCIPUFF model. ► The module is designed for easy integration into other models.
Keywords: Atmospheric chemistry; SCIPUFF; Toxic industrial compound; Carbon Bond Mechanism; 1-Butene;

Temporal trends of polychlorinated biphenyls in precipitation in Beijing, China by Guosheng Yang; Lingling Ma; Diandou Xu; Liyan Liu; Hongliang Jia; Yang Chen; Yongbao Zhang; Zhifang Chai (222-227).
Temporal trend of polychlorinated biphenyls (PCBs) was determined in precipitation and monthly depositional fluxes were calculated in Beijing for the first time from February 2009 to March 2011. Total PCBs concentrations ranged from 7.00 to 993 ng L−1 in dissolved phase and from 1.00 to 133 ng L−1 in particulate phase, with a two orders of magnitude variation. Concentrations of PCBs were dominated by dissolved phase, which accounted for 82.5% of the total PCBs in precipitation, implying PCBs enrichment in rainwater due to efficient scavenging of highly contaminated gas phase and nonfilterable submicron particles which easily adsorbed organic contaminants in urban atmosphere. Highest concentrations of PCBs were measured in snow, which were about two times higher than those in rainwater, demonstrating more efficient scavenging of PCBs by snow. The sum of bi-, tri- and tetrachlorinated congeners accounted for 70.5% of total PCBs in precipitation, suggesting that PCBs mainly come from the historical usage of domestic PCB product, e.g., trichlorobiphenyl. PCBs concentrations in both dissolved and particulate phases showed slow rate of decline, with a half-life of 16.9 years in precipitation, suggesting that the atmospheric concentrations of PCBs were decreasing slowly in Beijing. The wet deposition flux of ∑PCBs ranged from 0.240 to 6.55 μg m−2 month−1 (mean: 1.41 μg m−2 month−1), indicating a relatively high level of PCBs contamination in Beijing atmosphere.► We determine the characters of PCBs in precipitation in Beijing from February 2009 to March 2011. ► Wide concentration variations in both phases are found. ► High portions of dissolved phase in precipitation are exhibited. ► The sum of low weighted congeners accounts for 70.5%. ► The wet deposition flux of ∑PCBs is 16.9 μg m−2 yr−1.
Keywords: Polychlorinated biphenyls; Precipitation; Flux; Beijing;

Monitoring marine persistent organic pollutants (POPs) is important because oceans play a significant role in the cycling of POPs. The South China Sea (SCS) is surrounded by developing countries in Southeast Asia which are centers of e-waste recycling and the ship dismantling industry. In this study, shipboard air samples collected over the SCS between September 6 and 22, 2005 were analyzed for polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs). The levels of ∑12PCBs ranged from 32.3 to 167 pg m−3, with a mean value of 98.4 ± 36.0 pg m−3. Tetra-CBs were the predominant congeners. The concentrations of ∑18PCNs ranged from N.D. to 26.0 pg m−3, with a mean value of 10.5 ± 7.16 pg m−3, and tri-CNs were predominant. The gaseous concentrations of PCBs and PCNs over the SCS were consistent with those over other seas and oceans. Compared with previous studies, it was found that the concentrations of PCBs exhibited an obviously declining trend. The measured PCB and PCN concentrations in the atmosphere over the SCS were influenced by their proximity to source regions and air mass origins. The highest gaseous PCB and PCN concentrations were found at sampling sites adjacent to the continental South China. E-waste recycling, ship dismantling and combustion in South China and some Southeast Asian countries might contribute PCBs and PCNs to the atmosphere of the SCS.► Gaseous samples were collected over the northern South China Sea. ► The concentration of PCBs exhibited an obviously declining trend comparison with previous study. ► Tetra-CBs and tri-CNs were the predominant congeners overall. ► PCB and PCN concentrations were influenced by the proximity to source areas.
Keywords: PCBs; PCNs; South China Sea; Atmosphere;

A set of experiments carried out at the EUPHORE smog chamber have been simulated using a simplified version of the Community Multiscale Air Qualtity model version 4.7 (CMAQv4.7). First, the terpene parameterizations included in the model have been tested against the experimental data, showing a general overprediction of the aerosol mass formed. Experimental differences between the experiments presented here and those from which the model parameters were obtained, such as the NO:NO2 ratio and the type of OH-initiator seem to be the reason of the overprediction observed. In the second part of the work, new parameterizations have been calculated for the two different set of conditions defined: CALTECH conditions, based on the experiments by and (low NO:NO2 ratio and propene as OH-inititator) and EUPHORE conditions, based on the experiments of this work (high NO:NO2 ratio and HONO as OH-initiator). We have estimated increases of 11% and 82% in the stoichiometric coefficients α i of the surrogate semivolatile products when the conditions change from EUPHORE to CALTECH conditions. Finally, the parameterizations are tested against an independent set of experiments published by . Results indicate that the parameters derived for the EUPHORE conditions simulate well experiments carried out under similar conditions. However, the parameters tend to overpredict SOA formation under high NOx conditions.► We modeled SOA formation from biogenic VOCs photooxidation using CMAQv4.7. ► CMAQv4.7 simulations show overpredictions of the smog chamber experimental data. ► New parameterizations are calculated in order to explain the differences observed. ► NO:NO2 ratio and type of OH-initiator play an important role on SOA formation. ► Parameters derived in this work closely simulate experiments by other authors.
Keywords: Secondary organic aerosol; SOA modeling; CMAQv4.7; Parameter estimation; α-pinene; Limonene;

2-(4-Morpholinyl) benzothiazole (24MoBT) and N-cyclohexyl-2-benzothiazolamine (NCBA), which are present in automobile tires, are impurities of the vulcanisation accelerators OBS and CBS, respectively, as defined by the Japan Industrial Standard. To assess 24MoBT and NCBA as markers to trace the usage patterns of OBS and CBS in developing countries, urban dusts were collected from five representative cities of China and India for the analysis of 24MoBT and NCBA. The concentrations in these dust samples were found to be within the range of 3.40–151 ng g−1 for 24MoBT and nd–56.9 ng g−1 for NCBA. The higher levels of 24MoBT may indicate that the traditional accelerator OBS is still used in vehicle tires, whereas the relatively lower contents of NCBA are mainly related to the lesser use of CBS tires. The individual fractions of 24MoBT and NCBA in BTs (24MoBT + NCBA) are compared among cities, and the results show that the fraction sequence is consistent with the number of vehicles and the cities' economic development. This study indicates not only that 24MoBT is presently more suitable for tracing tire wear emissions than NCBA in China but also that there is a potential to assess the impact of traffic sources on urban environments using BTs.
Keywords: 2-(4-Morpholinyl) benzothiazole (24MoBT); N-cyclohexyl-2-benzothiazolamine (NCBA); Traffic source; China; India;

Modeling secondary organic aerosol formation from xylene and aromatic mixtures using a dynamic partitioning approach incorporating particle aqueous-phase chemistry (II) by Harshal M. Parikh; Annmarie G. Carlton; Yang Zhou; Haofei Zhang; Richard M. Kamens; William Vizuete (250-260).
Formation of secondary organic aerosol (SOA) is simulated for 14 outdoor smog chamber experiments using condensed gas-phase regulatory mechanisms and a new SOA framework. This framework is based on empirical parameterizations of independent chamber experiments and includes role of glyoxal and methylglyoxal in formation of particle aqueous-phase. To evaluate for regulatory applications, the chamber experiments include an urban non-SOA VOC mixture and NOx, with either injections of o/p-xylenes or toluene. The experiments are performed under varying conditions of relative humidity (RH) and in the presence of low initial background seed. Gas-particle partitioning of semi-volatile products into particle organic-phase is modeled using a dynamic partitioning approach with reactive uptake coefficient as the principal transport and kinetic parameter. Aqueous-phase SOA is predicted using formulations that describe the irreversible loss of both glyoxal and methylglyoxal to particle aqueous-phase. The predicted SOA mass in the new framework is evaluated using two regulatory gas-phase mechanisms – CB05 or SAPRC07 and, two regulatory parameterization schemes to predict semi-volatile product formation – an Odum-type two-product model and volatility basis-set (VBS). Predictions from the new SOA framework reproduce SOA mass within the uncertainty range of observations, irrespective of the choice of gas-phase mechanism and SOA parameterization scheme (root mean square error [RMSE] range of 0.18–3.08 μg m−3). Further, model results suggest strong possibility of dominance of bulk-process under low seed conditions and surface-uptake process under high seed for aqueous-phase SOA formation. Sensitivity analysis to the hygroscopic nature of aqueous-phase SOA indicates an uncertainty of a factor of 2 in bulk-process and surface-uptake rates. In summary, the results strongly point to considering mass-transfer and kinetic limitations in regulatory air quality models at low ambient seed concentrations and highlight the importance of aqueous-phase SOA for aromatics under high-RH conditions.► SOA framework with dynamic partitioning and aerosol aqueous-phase processes. ► Mass-transfer limitation to partitioning in presence of non-SOA-forming HC mixture. ► Substantial aqueous-phase SOA contribution at high RH from aromatic oxidation. ► Aqueous-phase SOA: bulk-process at low seed and surface-uptake at high seed.
Keywords: Secondary organic aerosol; Xylene; Glyoxal uptake; Thermodynamic equilibrium; Dynamic partitioning;

New Directions: Airborne ultrafine particle dust from building activities – A source in need of quantification by Prashant Kumar; Mike Mulheron; Bernard Fisher; Roy M. Harrison (262-264).