Atmospheric Environment (v.44, #17)

Volatile aldehydes in libraries and archives by Ann Fenech; Matija Strlič; Irena Kralj Cigić; Alenka Levart; Lorraine T. Gibson; Gerrit de Bruin; Konstantinos Ntanos; Jana Kolar; May Cassar (2067-2073).
Volatile aldehydes are produced during degradation of paper-based materials. This may result in their accumulation in archival and library repositories. However, no systematic study has been performed so far. In the frame of this study, passive sampling was carried out at ten locations in four libraries and archives. Despite the very variable sampling locations, no major differences were found, although air-filtered repositories were found to have lower concentrations while a non-ventilated newspaper repository exhibited the highest concentrations of volatile aldehydes (formaldehyde, acetaldehyde, furfural and hexanal). Five employees in one institution were also provided with personal passive samplers to investigate employees’ exposure to volatile aldehydes. All values were lower than the presently valid exposure limits.The concentration of volatile aldehydes, acetic acid, and volatile organic compounds (VOCs) in general was also compared with that of outdoor-generated pollutants. It was evident that inside the repository and particularly inside archival boxes, the concentration of VOCs and acetic acid was much higher than the concentration of outdoor-generated pollutants, which are otherwise more routinely studied in connection with heritage materials. This indicates that further work on the pro-degradative effect of VOCs on heritage materials is necessary and that monitoring of VOCs in heritage institutions should become more widespread.
Keywords: Air quality; Health and safety; Indoor emission; Paper degradation; VOC;

Ambient formaldehyde and its contributing factor to ozone and OH radical in a rural area by Wang Xiaoyan; Wang Huixiang; Wang Shaoli (2074-2078).
Formaldehyde (HCHO), as well as correlative pollutants was measured from 1 to 31 July in 2007 at Mazhuang, a rural site located in the east of China. Gaseous HCHO was scrubbed from the air with an acidic 2,4-dinitrophenylhydrazine (DNPH) solution, which leaded to the reaction of HCHO with DNPH and produced a stable product, 2,4-dinitrophenylhydrazone, followed by online analysis by high-performance liquid chromatography (HPLC) coupled with Ultraviolet detector. During the observation period, mixing ratios of HCHO ranged from 0.2 ppbv to 6.2 ppbv, with an average of 1.5 ± 0.67 ppbv. HCHO shows an evident diurnal variation, the maximum appeared during 12:00–14:00. The average concentration diurnal variations of measured HCHO, ozone (O3), Methylhydroperoxides (MHP, CH3OOH), hydrogen peroxide (H2O2), nitrogen oxides (NOx) and meteorological parameters were compared. The similar variations of HCHO, O3 and radiation imply that photo-oxidation of hydrocarbons might be the major source for HCHO. Based on the maximum incremental reactivity (MIR) coefficient of HCHO, the calculation shows that HCHO contributes about 20% to total observed O3 during the study period. In order to compare the contributions of O3, HCHO and HONO to OH radical, photolysis rate parameters (J-values) of the three compounds were calculated by the Tropospheric Ultraviolet and Visible (TUV) Radiation Model (4.4 version). Based on the comparison, this study reaches the conclusion that O3 is the dominant source of OH radical at Mazhuang. This study also uses P(HCHO)/P(O3) which represents the ratio of contrbutions of HCHO and O3 to OH radical, to discuss the action of HCHO in OH radical soucers. The result shows that P(HCHO)/P(O3) is 12.5% on average, with the maximum of 21.0% at 13:00P.M. and minimum of 7.5% before 9:00A.M. and after 17:00P.M..Therefore HCHO is also an important source of OH radical and cannot be ignored.
Keywords: Formaldehyde; Contribution factor; OH radical; Rural area; China;

In situ measurements of NO, NO2, NO y , and O3 in Dinghushan (112°E, 23°N), China during autumn 2008 by Yang Sun; Lili Wang; Yuesi Wang; Deqiang Zhang; Liu Quan; Xin Jinyuan (2079-2088).
Measurements of O3, NO, NO2, and NOy mixing ratios were carried out at a station-Dinghushan in Guangdong province of China from Oct. 18th, 2008 to Nov. 7th, 2008. This research shows that under conditions of a strong subtropical high (temperature high, relative humidity low), on Oct. 29th, 2008 the Dinghushan station observed severe photochemical pollution. The Maximum hour average concentration of O3 reached 128 ppbv, and the serious photochemical pollution is caused by superposition of local photochemical reaction and regional transport. The observation that NO x ozone production efficiency (OPE) values for high O3 pollution on Oct. 29–30th, 2008 were 10.5 and 15, which were more than the values of the city source region and lower than that of the surrounding clean areas. It means the sensitivity of O3 generated was transitioning from VOCs limited condition to NOx-limited regime. By applying a Smog Production Model, the results show that the extent of reaction values less than 0.6 were occurred on 17 days during campaign, and 13 days for the extents of reactions more than 0.6. However, there were no data with values over 0.8, which indicates that the observation station represent a VOCs sensitive system during campaign. Analysis of the extents of reactions and wind data show that the pollution is mostly subject to a southeasterly airflow influence.
Keywords: NO; NO2; NOz; OPE; SPM;

A methodology to urban air quality assessment during large time periods of winter using computational fluid dynamic models by M.A. Parra; J.L. Santiago; F. Martín; A. Martilli; J.M. Santamaría (2089-2097).
The representativeness of point measurements in urban areas is limited due to the strong heterogeneity of the atmospheric flows in cities. To get information on air quality in the gaps between measurement points, and have a 3D field of pollutant concentration, Computational Fluid Dynamic (CFD) models can be used. However, unsteady simulations during time periods of the order of months, often required for regulatory purposes, are not possible for computational reasons. The main objective of this study is to develop a methodology to evaluate the air quality in a real urban area during large time periods by means of steady CFD simulations. One steady simulation for each inlet wind direction was performed and factors like the number of cars inside each street, the length of streets and the wind speed and direction were taken into account to compute the pollutant concentration. This approach is only valid in winter time when the pollutant concentrations are less affected by atmospheric chemistry. A model based on the steady-state Reynolds-Averaged Navier–Stokes equations (RANS) and standard k-ɛ turbulence model was used to simulate a set of 16 different inlet wind directions over a real urban area (downtown Pamplona, Spain). The temporal series of NOx and PM10 and the spatial differences in pollutant concentration of NO2 and BTEX obtained were in agreement with experimental data. Inside urban canopy, an important influence of urban boundary layer dynamics on the pollutant concentration patterns was observed. Large concentration differences between different zones of the same square were found. This showed that concentration levels measured by an automatic monitoring station depend on its location in the street or square, and a modelling methodology like this is useful to complement the experimental information. On the other hand, this methodology can also be applied to evaluate abatement strategies by redistributing traffic emissions.
Keywords: Ambient wind direction; Computational fluid dynamics; Experimental measurements; Pamplona; Urban flow and dispersion;

Carbonyl compounds in urban ambient air and street canyons were measured from December 2008 to August 2009 in a mountainous city in southwest China (Guiyang). The formaldehyde yield from the photo-oxidation of isoprene emitted by vegetation was estimated to be in the range of 0.63–3.62 μg m−3 from May to August, which accounted for 28.8–33.4% of ambient formaldehyde. Based on the calculation of photolysis rates and rates of reaction with the OH radical, it was found that photolysis was the predominant sink for formaldehyde and acetone in both summer and winter. For acetaldehyde, photo-oxidation by OH radicals and photolysis were the major sinks in summer while photo-oxidation by OH radicals was the dominant sink in winter. Wet precipitation was found to be an important removal process for the atmospheric carbonyls. In the urban ambient air, the average concentrations of formaldehyde, acetaldehyde, acetone and all carbonyls were 4.8 ± 2.1, 5.7 ± 3.3, 5.1 ± 2.5, and 25.1 ± 9.2 μg m−3 (n  = 139), respectively. The average concentrations of these species in street canyons were 18.8 ± 6.5, 9.4 ± 3.2, 10.9 ± 2.1, and 64.1 ± 16.3 μg m−3 (n  = 62), respectively. The significantly higher carbonyl levels on weekdays (compared to weekends) highlight the contribution of vehicle emissions to carbonyls in the street canyons.
Keywords: Carbonyls; Street canyon; Urban ambient air; Photo-oxidation; Methacrolein (MACR);

Estimation of NH3 bi-directional flux from managed agricultural soils by Ellen J. Cooter; Jesse O. Bash; John T. Walker; M.R. Jones; Wayne Robarge (2107-2115).
The Community Multi-Scale Air Quality model (CMAQ) is used to assess regional air quality conditions for a wide range of chemical species throughout the United States (U.S.). CMAQ representation of the regional nitrogen budget is limited by its treatment of ammonia (NH3) soil emission from, and deposition to underlying surfaces as independent rather than tightly coupled processes, and by its reliance on soil emission estimates that do not respond to variable meteorology and ambient chemical conditions. The present study identifies an approach that addresses these limitations, lends itself to regional application, and will better position CMAQ to meet future assessment challenges. These goals were met through the integration of the resistance-based flux model of with elements of the United States Department of Agriculture EPIC (Environmental Policy Integrated Climate) model. Model integration centers on the estimation of ammonium and hydrogen ion concentrations in the soil required to estimate soil NH3 flux. The EPIC model was calibrated using data collected during an intensive 2007 field study in Lillington, North Carolina. A simplified process model based on the nitrification portion of EPIC was developed and evaluated. It was then combined with the model and measurements of near-surface NH3 concentrations to simulate soil NH3 flux at the field site. Finally, the integrated flux (emission) results were scaled upward and compared to recent national ammonia emission inventory estimates. The integrated model results are shown to be more temporally resolved (daily), while maintaining good agreement with established soil emission estimates at longer time-scales (monthly). Although results are presented for a single field study, the process-based nature of this approach and NEI comparison suggest that inclusion of this flux model in a regional application should produce useful assessment results if nationally consistent sources of driving soil and agricultural management information are identified.
Keywords: Bi-directional flux; Ammonia emissions; Agricultural soils; Fertilizer emissions; EPIC; CMAQ;

Part II presents a comprehensive evaluation of CMAQ for August of 2002 on twenty-one sensitivity simulations (detailed in Part I) in MM5 to investigate the model performance for O3 SIPs (State Implementation Plans) in the complex terrain. CMAQ performance was quite consistent with the results of MM5, meaning that accurate meteorological fields predicted in MM5 as an input resulted in good model performance of CMAQ. In this study, PBL scheme plays a more important role than its land surface models (LSMs) for the model performance of CMAQ. Our results have shown that the outputs of CMAQ on eighteen sensitivity simulations using two different nudging coefficients for winds (2.5 and 4.5 × 10−4 s−1, respectively) tend to under predict daily maximum 8-h ozone concentrations at valley areas except the TKE PBL sensitivity simulations (ETA M-Y PBL scheme with Noah LSMs and 5-layer soil model and Gayno-Seaman PBL) using 6.0 × 10−4 s−1 with positive MB (Mean Bias). At mountain areas, none of the sensitivity simulations has presented over predictions for 8-h O3, due to relatively poor meteorological model performance. When comparing 12-km and 4-km grid resolutions for the PX simulation in CMAQ statistics analysis, the CMAQ results at 12-km grid resolution consistently show under predictions of 8-h O3 at both of valley and mountain areas and particularly, it shows relatively poor model performance with a 15.1% of NMB (Normalized Mean Bias). Based on our sensitivity simulations, the TKE PBL sensitivity simulations using a maximum value (6 × 10−4) among other sensitivity simulations yielded better model performance of CMAQ at all areas in the complex terrain. As a result, the sensitivity of RRFs to the PBL scheme may be considerably significant with about 1–3 ppb in difference in determining whether the attainment test is passed or failed. Furthermore, we found that the result of CMAQ model performance depending on meteorological variations is affected on estimating RRFs for attainment demonstration, indicating that it is necessary to improve model performance. Overall, G_c (Gayo-Seaman PBL scheme) using the coefficient for winds, 6 × 10−4 s−1, sensitivity simulation predicts daily maximum 8-h ozone concentration closer to observations during a typical summer period from May to September and provides generally low future design values (DVFs) at valley and mountain areas compared to other simulations.
Keywords: Model performance; CMAQ; Planetary boundary layer; SIPs; RRFs;

Uncertainty in health risks due to anthropogenic primary fine particulate matter from different source types in Finland by M. Tainio; J.T. Tuomisto; J. Pekkanen; N. Karvosenoja; K. Kupiainen; P. Porvari; M. Sofiev; A. Karppinen; L. Kangas; J. Kukkonen (2125-2132).
The emission-exposure and exposure-response (toxicity) relationships are different for different emission source categories of anthropogenic primary fine particulate matter (PM2.5). These variations have a potentially crucial importance in the integrated assessment, when determining cost-effective abatement strategies. We studied the importance of these variations by conducting a sensitivity analysis for an integrated assessment model. The model was developed to estimate the adverse health effects to the Finnish population attributable to primary PM2.5 emissions from the whole of Europe. The primary PM2.5 emissions in the whole of Europe and in more detail in Finland were evaluated using the inventory of the European Monitoring and Evaluation Programme (EMEP) and the Finnish Regional Emission Scenario model (FRES), respectively. The emission-exposure relationships for different primary PM2.5 emission source categories in Finland have been previously evaluated and these values incorporated as intake fractions into the integrated assessment model. The primary PM2.5 exposure-response functions and toxicity differences for the pollution originating from different source categories were estimated in an expert elicitation study performed by six European experts on air pollution health effects. The primary PM2.5 emissions from Finnish and other European sources were estimated for the population of Finland in 2000 to be responsible for 209 (mean, 95% confidence interval 6–739) and 357 (mean, 95% CI 8–1482) premature deaths, respectively. The inclusion of emission-exposure and toxicity variation into the model increased the predicted relative importance of traffic related primary PM2.5 emissions and correspondingly, decreased the predicted relative importance of other emission source categories. We conclude that the variations of emission-exposure relationship and toxicity between various source categories had significant impacts for the assessment on premature deaths caused by primary PM2.5.
Keywords: Fine particulate matter; Intake fraction; Exposure-response; Integrated assessment; Sensitivity analysis;

Scavenging of soluble trace gases by falling rain droplets in inhomogeneous atmosphere by Tov Elperin; Andrew Fominykh; Boris Krasovitov (2133-2139).
We analyze non-isothermal absorption of trace gases by the rain droplets with internal circulation which is caused by interfacial shear stresses. It is assumed that the concentration of soluble trace gases and temperature in the atmosphere varies in a vertical direction. The rate of scavenging of soluble trace gases by falling rain droplets is determined by solving heat and mass transfer equations. In the analysis we accounted for the accumulation of the absorbate in the bulk of the falling rain droplet. The problem is solved in the approximation of a thin concentration and temperature boundary layers in the droplet and in the surrounding air. We assumed that the bulk of a droplet, beyond the diffusion boundary layer, is completely mixed and concentration of the absorbate and temperature are homogeneous and time-dependent in the bulk. By combining the generalized similarity transformation method with Duhamel's theorem, the system of transient conjugate equations of convective diffusion and energy conservation for absorbate transport in liquid and gaseous phases with time-dependent boundary conditions is reduced to a system of linear convolution Volterra integral equations of the second kind which is solved numerically. Calculations are performed using available experimental data on concentration and temperature profiles in the atmosphere.It is shown than if concentration of a trace gas in the atmosphere is homogeneous and temperature in the atmosphere decreases with height, beginning from some altitude gas absorption is replaced by gas desorption. Neglecting temperature inhomogenity in the atmosphere described by adiabatic lapse rate leads to essential overestimation of the trace gas concentration in a droplet on the ground.
Keywords: Precipitation scavenging; Trace gases; Rain droplets; Gas absorption; Heat transfer; Mass transfer;

Impact of particle emissions of new laser printers on modeled office room by Antti J. Koivisto; Tareq Hussein; Raimo Niemelä; Timo Tuomi; Kaarle Hämeri (2140-2146).
In this study, we present how an indoor aerosol model can be used to characterize particle emitter and predict influence of the source on indoor air quality. Particle size-resolved emission rates were quantified and the source’s influence on indoor air quality was estimated by using office model simulations. We measured particle emissions from three modern laser printers in a flow-through chamber. Measured parameters were used as input parameters for an indoor aerosol model, which we then used to quantify the particle emission rates. The same indoor aerosol model was used to simulate the effect of the particle emission source inside an office model. The office model consists of a mechanically ventilated empty room and the particle source. The aerosol from the ventilation air was a filtered urban background aerosol. The effect of the ventilation rate was studied using three different ventilation ratios 1, 2 and 3 h−1. According to the model, peak emission rates of the printers exceeded 7.0 × 108 s−1 (2.5 × 1012 h−1), and emitted mainly ultrafine particles (diameter less than 100 nm). The office model simulation results indicate that a print job increases ultrafine particle concentration to a maximum of 2.6 × 105 cm−3. Printer-emitted particles increased 6-h averaged particle concentration over eleven times compared to the background particle concentration.
Keywords: Indoor aerosol model; Emission rate; Indoor air quality; Aerosol; Laser printer;

The fine particulate matter (PM) emissions from nine commercial aircraft engine models were determined by plume sampling during the three field campaigns of the Aircraft Particle Emissions Experiment (APEX). Ground-based measurements were made primarily at 30 m behind the engine for PM mass and number concentration, particle size distribution, and total volatile matter using both time-integrated and continuous sampling techniques. The experimental results showed a PM mass emission index (EI) ranging from 10 to 550 mg kg−1 fuel depending on engine type and test parameters as well as a characteristic U-shaped curve of the mass EI with increasing fuel flow for the turbofan engines tested. Also, the Teflon filter sampling indicated that ∼40–80% of the total PM mass on a test-average basis was comprised of volatile matter (sulfur and organics) for most engines sampled. The number EIs, on the other hand, varied from ∼1015 to 1017 particles kg−1 fuel with the turbofan engines exhibiting a logarithmic decay with increasing fuel flow. Finally, the particle size distributions of the emissions exhibited a single primary mode that were lognormally distributed with a minor accumulation mode also observed at higher powers for all engines tested. The geometric (number) mean particle diameter ranged from 9.4 to 37 nm and the geometric standard deviation ranged from 1.3 to 2.3 depending on engine type, fuel flow, and test conditions.
Keywords: Particulate matter; Emissions; Gas turbine engines; Aircraft; Ground measurements;

Woody stem methane emission in mature wetland alder trees by Vincent Gauci; David J.G. Gowing; Edward R.C. Hornibrook; Joanna M. Davis; Nancy B. Dise (2157-2160).
Methane (CH4) is an important greenhouse gas that is predominantly emitted to the atmosphere from anoxic wetland ecosystems. Understanding the sources and emissions of CH4 is crucially important for climate change predictions; however, there are significant discrepancies between CH4 source estimates derived via so-called bottom-up and top-down methods. Here we report CH4 emission from the stems of mature wetland alder (Alnus glutinosa) trees in the UK, a common tree of northern hemisphere floodplains and wetlands. The alder stems most likely behave as conduits for soil-produced CH4 either in the gaseous or aqueous phase, and may, therefore, help to reconcile methodological differences in the way the wetland CH4 source is estimated.Alder tree stems emitted average peak CH4 fluxes of 101 μg CH4 m−2 h−1 (on a stem area basis) in early October, a rate that is similar to that obtained from mature Japanese ash (Fraxinus mandshurica var. japonica) in Japan and amounting to approximately 20% of the measured CH4 flux from the soil surface. The finding suggests that trees, which occupy 60% of Earth's wetlands and are normally excluded from the measurement programmes that form the basis for bottom-up estimates of the global wetland source, could be important contributors to overall terrestrial ecosystem CH4 flux.
Keywords: Fluxes; Emission pathway; Wetlands; Forest; Anaerobic;

A solid phase extraction cleanup step substantially improved analytical efficiency and data quality for measurements of non-polar and moderately polar organic molecular marker concentrations in airborne particulate matter. Rapid gas chromatography column deterioration was evident after very few samples in the absence of a cleanup step, resulting in the need for frequent recalibration. High molecular weight polycyclic aromatic hydrocarbons, were among the species most strongly impacted by the deterioration, exhibiting deviations as high as 30–40% from expected calibration verification standard values after only a few injections. Column deterioration and calibration verification failure were eliminated by introducing a solid phase extraction step prior to analysis and a total of 58 samples were analyzed with no unacceptable deviation of calibration verification standards from target values
Keywords: Aerosol; Particulate matter; Orgranic; Analysis; Source apportionment; Hopane; Polycyclic aromatic hydrocarbon;