Check out our New Publishers' Select for Free Articles

Atmospheric Environment (v.43, #37)

Editorial board (pp. i).

A review of current knowledge concerning dry deposition of atmospheric mercury by Leiming Zhang; L. Paige Wright; Pierrette Blanchard (pp. 5853-5864).

The status of the current knowledge concerning the dry deposition of atmospheric mercury, including elemental gaseous mercury (Hg⁰), reactive gaseous mercury (RGM), and particulate mercury (Hg_p), is reviewed. The air–surface exchange of Hg⁰ is commonly bi-directional, with daytime emission and nighttime deposition over non-vegetated surfaces and vegetated surfaces with small leaf area indices under low ambient Hg⁰ conditions. However, daytime deposition has also been observed, especially when the ambient Hg⁰ is high. Typical dry deposition velocities ( V_d) for Hg⁰ are in the range of 0.1–0.4 cm s⁻¹ over vegetated surfaces and wetlands, but substantially smaller over non-vegetated surfaces and soils below canopies. Meteorological, biological, and soil conditions, as well as the ambient Hg⁰ concentrations all play important roles in the diurnal and seasonal variations of Hg⁰ air–surface exchange processes. Measurements of RGM deposition are limited and are known to have large uncertainties. Nevertheless, all of the measurements suggest that RGM can deposit very quickly onto any type of surface, with its V_d ranging from 0.5 to 6 cm s⁻¹. The very limited data for Hg_p suggest that its V_d values are in the range of 0.02–2 cm s⁻¹.A resistance approach is commonly used in mercury transport models to estimate V_d for RGM and Hg_p; however, there is a wide range of complexities in the dry deposition scheme of Hg⁰. Although resistance-approach based dry deposition schemes seem to be able to produce the typical V_d values for RGM and Hg⁰ over different surface types, more sophisticated air–surface exchange models have been developed to handle the bi-directional exchange processes. Both existing and newly developed dry deposition schemes need further evaluation using field measurements and intercomparisons within different modelling frameworks.

Keywords: Air–surface exchange; Dry deposition velocity; Measurement and modelling; Speciated mercury

Temporal variability of soil-atmospheric CO₂ and CH₄ fluxes from different land uses in mid-subtropical China by Javed Iqbal; Shan Lin; Ronggui Hu; Minglei Feng (pp. 5865-5875).

Different land uses in subtropics play an important role in regulating the global environmental changes. To reduce uncertainties of greenhouse gas (GHG) emissions of agricultural soils in subtropical ecosystem, a four years campaign was started to determine the temporal GHG (CO₂ and CH₄) fluxes from seven sites of four land use types (1 vegetable field, 3 uplands, 2 orchards, 1 pine forest). The mean annual budgets of CO₂, and CH₄ were 6.5∼10.5 Mg CO₂ ha⁻¹ yr⁻¹, and +0.47 ∼ −2.37 kg CH₄ ha⁻¹ yr⁻¹, respectively. Pine forest had significantly lower CO₂ emission and higher CH₄ uptake than agriculture land uses. Tilled orchard emitted more CO₂ and oxidized less CH₄ than non-tilled orchard. Upland crops had higher CO₂ emissions than orchards, while abrupt differences of CH₄ uptake were observed between upland crops and orchards. Every year, the climate was warm and wet from April to September (the hot–humid season) and became cool and dry from October to March (the cool–dry season). Driven by seasonality of temperature and WFPS, CO₂ fluxes were significantly higher in the hot–humid season than in cool–dry season. Soil temperature, WFPS, NO₃⁻–N and NH₄⁺–N contents interactively explained CH₄ uptake which was significantly higher in cool–dry season than in hot–humid season. We conclude that soil C fluxes from different land uses are strongly under control of different climatic predictors along with soil nutrient status, which interact in conjunction with each other to supply the readily available substrates.

Keywords: Land use; Seasonal difference; Soil C fluxes; Soil inorganic N; Subtropical

Correlation between PM concentrations and aerosol optical depth in eastern China by Jian-Ping Guo; Xiao-Ye Zhang; Hui-Zheng Che; Sun-Ling Gong; Xingqin An; Chun-Xiang Cao; Jie Guang; Hao Zhang; Ya-Qiang Wang; Xiao-Chun Zhang; Min Xue; Xiao-Wen Li (pp. 5876-5886).

Using one year of Aerosol Optical Depth (AOD) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite and particular matter (PM) contents measured at eleven sites located mostly in the eastern China in 2007, the relationship between columnar AOD and hourly and daily average (DA) PM were established. The peak AOD observed from MODIS was generally consistent with the surface PM measurements in eastern China, where Zhengzhou had the maximum annual mean PM₁₀ of 182.1 μg m⁻³, while Longfengshan had the minimum annual mean of 38.1 μg m⁻³. Ground level observations indicated that PM concentration varies widely across different regions, which was mainly due to the difference in weather conditions and anthropogenic emissions. The coarse particles accounted for the main air pollution in Zhengzhou and Benxi whiles the fine particles, however, were the main constituents in other sites. Results showed that MODIS AOD (averaged over the box of 5 × 5 and 3 × 3 pixels) had a better positive correlation with the coincident hourly average (HA) PM concentration than with DA due to diurnal variation in PM mass measurements. After correcting AOD for relative humidity (RH), the correlation did not improve significantly, suggesting that the RH was not the main factor affecting the correlation of PM with AOD. The statistical regression analysis between MODIS AOD and PM mass suggested that the satellite-derived AOD is a useful tool for mapping PM distribution over large spatial domains.

Keywords: AOD; PM; Correlation; MODIS

Detection of Asian dust ( Hwangsa) over the Yellow Sea by decomposition of unpolarized infrared reflectivity by Sungwook Hong (pp. 5887-5893).

The periodical occurrence of Asian dust ( Hwangsa) in East Asia during every spring and winter is of great consequence to regional human health and visibility. One weakness of the previous methods based on the brightness temperature (BT) differences or optical depths is that they can not accurately detect the dust events over the Yellow Sea. This study proposes a unique technique of decomposing unpolarized reflectivities to distinguish between dust and clouds over the sea surface. Many current infrared (IR) satellite instruments such as MTSAT-1R measure the unpolarized radiance. In this process, an approximate relationship between vertically and horizontally polarized reflectivities is validated for the IR wavelengths of 3–12 μm. The radiances observed from an IR geostationary satellite and the simulated sea surface temperature (SST) are used for a case study of Asian dust events. The results show qualitatively the reasonable spatial agreements with MODIS true color images for these Asian dust events. The proposed method in this study can be utilized for the operational purpose to detect the signal of Asian dust over sea surface.

Keywords: Dust aerosol; Polarization; Reflectivity; Infrared; Sea surface

Contribution of transboundary air pollution to ionic concentrations in fog in the Kinki Region of Japan by Hikari Shimadera; Akira Kondo; Akikazu Kaga; Kundan Lal Shrestha; Yoshio Inoue (pp. 5894-5907).

To estimate the contribution of transboundary transported air pollutants from other Asian countries to Japan in ionic concentrations in fog water in March 2005, the Community Multiscale Air Quality (CMAQ) modeling system was utilized with meteorological fields produced by the 5th generation Mesoscale Model (MM5). For meteorological predictions, the model well reproduced the surface meteorological variables, particularly temperature and humidity, and generally captured fog occurrence. For chemical predictions, most of the model-predicted monthly mean concentrations were approximately within a factor of 2 of the observations, indicating that the model well simulated the long-range atmospheric transport from the Asian Continent to Japan. For SO₄²⁻, NO₃⁻ and NH₄⁺, the contribution rates of the transboundary air pollution in the Kinki Region of Japan ranged from 69 to 82% for aerosols, from 47 to 87% for ionic concentrations in rain, and from 55 to 79% for ionic concentrations in fog. The study found that the transboundary air pollution also affected ionic concentrations in fog as well as aerosol concentrations and ionic concentrations in rain.

Keywords: Fog; Long-range transport; East Asia; CMAQ; MM5

The impact of wood stove technology upgrades on indoor residential air quality by Ryan W. Allen; Sara Leckie; Gail Millar; Michael Brauer (pp. 5908-5915).

Fine particulate matter (PM_2.5) air pollution has been linked to adverse health impacts, and combustion sources including residential wood-burning may play an important role in some regions. Recent evidence suggests that indoor air quality may improve in homes where older, non-certified wood stoves are exchanged for lower emissions EPA-certified alternatives. As part of a wood stove exchange program in northern British Columbia, Canada, we sampled outdoor and indoor air at 15 homes during 6-day sampling sessions both before and after non-certified wood stoves were exchanged. During each sampling session two consecutive 3-day PM_2.5 samples were collected onto Teflon filters, which were weighed and analyzed for the wood smoke tracer levoglucosan. Residential PM_2.5 infiltration efficiencies ( F_inf) were estimated from continuous light scattering measurements made with nephelometers, and estimates of F_inf were used to calculate the outdoor- and indoor-generated contributions to indoor air. There was not a consistent relationship between stove technology and outdoor or indoor concentrations of PM_2.5 or levoglucosan. Mean F_inf estimates were low and similar during pre- and post-exchange periods (0.32 ± 0.17 and 0.33 ± 0.17, respectively). Indoor sources contributed the majority (∼65%) of the indoor PM_2.5 concentrations, independent of stove technology, although low indoor-outdoor levoglucosan ratios (median ≤ 0.19) and low indoor PM_2.5-levoglucosan correlations ( r ≤ 0.19) suggested that wood smoke was not a major indoor PM_2.5 source in most of these homes. In summary, despite the potential for extensive wood stove exchange programs to reduce outdoor PM_2.5 concentrations in wood smoke-impacted communities, we did not find a consistent relationship between stove technology upgrades and indoor air quality improvements in homes where stoves were exchanged.

Keywords: Wood stove; Intervention; Particulate matter; Levoglucosan; Infiltration

Evaluation of retrofit crankcase ventilation controls and diesel oxidation catalysts for reducing air pollution in school buses by Kim Trenbath; Michael P. Hannigan; Jana B. Milford (pp. 5916-5922).

This study evaluates the effect of retrofit closed crankcase ventilation filters (CCFs) and diesel oxidation catalysts (DOCs) on the in-cabin air quality in transit-style diesel school buses. In-cabin pollution levels were measured on three buses from the Pueblo, CO District 70 fleet. Monitoring was conducted while buses were driven along their regular routes, with each bus tested three times before and three times after installation of control devices. Ultrafine number concentrations in the school bus cabins were 33–41% lower, on average, after the control devices were installed. Mean mass concentrations of particulate matter less than 2.5 μm in diameter (PM2.5) were 56% lower, organic carbon (OC) 41% lower, elemental carbon (EC) 85% lower, and formaldehyde 32% lower after control devices were installed. While carbon monoxide concentrations were low in all tests, mean concentrations were higher after control devices were installed than in pre-retrofit tests. Reductions in number, OC, and formaldehyde concentrations were statistically significant, but reductions in PM2.5 mass were not. Even with control devices installed, during some runs PM2.5 and OC concentrations in the bus cabins were elevated compared to ambient concentrations observed in the area. OC concentrations inside the bus cabins ranged from 22 to 58 μg m⁻³ before and 13 to 33 μg m⁻³ after control devices were installed. OC concentrations were correlated with particle-bound organic tracers for lubricating oil emissions (hopanes) and diesel fuel and tailpipe emissions (polycyclic aromatic hydrocarbons (PAH) and aliphatic hydrocarbons). Mean concentrations of hopanes, PAH, and aliphatic hydrocarbons were lower by 37, 50, and 43%, respectively, after the control devices were installed, suggesting that both CCFs and DOCs were effective at reducing in-cabin OC concentrations.

Keywords: Diesel emissions; Organic tracers; Air pollution exposure; Diesel control technology

Atmospheric hydrogen peroxide: Evidence for aqueous-phase formation from a historic perspective and a one-year measurement campaign by Detlev Möller (pp. 5923-5936).

H₂O₂ is produced in the atmospheric gas phase only through a single pathway, the HO₂ radical recombination. Its main role has been identified in oxidizing SO₂ dissolved in hydrometeors to sulphate. Thus aqueous-phase chemistry has been considered to be a main sink (apart from dry deposition and scavenging) but rarely a source of H₂O₂ despite early findings of its heterogeneous and aqueous-phase production. The aim of this paper is to discuss the atmospheric budget of H₂O₂ from the multiphase chemistry approach with special emphasis on new sources other than gas-phase HO₂ recombination. After providing a brief historic view on H₂O₂ chemistry, often unknown to young atmospheric chemists but important for a complete understanding, the results of a one-year study of simultaneous measurements of H₂O₂ in rain and air are presented that show strong evidence for aqueous-phase H₂O₂ formation. Implications for future changes in atmospheric chemistry are discussed from the viewpoint of an “interfacial chemistry”.

Keywords: Hydrogen peroxide; Air chemistry; Multiphase chemistry; Rain water; Monitoring; Ozone; Sulphur dioxide; History; Aqueous-phase chemistry

Effects of post-sampling conditions on ambient carbon aerosol filter measurements by Ann M. Dillner; Chin H. Phuah; Jay R. Turner (pp. 5937-5943).

Ambient carbonaceous material collected on quartz filters is prone to measurement artifacts due to material gained or lost during post-sampling field latency, shipping, and storage. In seventeen sampling events over a one year period, ambient PM_2.5 aerosols were collected on quartz filters (without denuders) and subjected to various filter treatments to assess the potential for and extent of artifacts. The filter treatments simulated post-sampling environments that filters may be exposed to and included: storage at 40 °C for up to 96 h, storage at −16 °C for 48 h, and storage at room temperature (∼21 °C) for 48 h. Carbon mass on the filters was measured using a thermal-optical method. The total carbon (TC), total organic carbon (TOC) and total elemental carbon (TEC) as well as carbon thermal fraction masses were obtained. Statistical analyses were performed to identify significant differences in carbon fraction concentrations between filters analyzed immediately after sampling and after being subjected to treatment.TOC and TC concentrations decreased by on average 15 ± 5% and 10 ± 4%, respectively, for filters maintained at 40 °C for 96 h but did not change for filters stored at room temperature or frozen for 48 h. TEC did not change for any of the filter treatments. The mass concentration for the organic carbon thermal fraction that evolves at the lowest temperature step (OC1) decreased with increasing storage time at 40 °C with average losses of 70 ± 7% after 96 h. Therefore, OC1 is not a stable measurement due to post-sampling conditions that may be encountered. This work demonstrates that TOC and TC can have substantial measurement artifacts on filters subjected to field latency and other non-temperature controlled post-sampling handling, compared to the carbon loadings on the filter at the end of the sampling period.

Keywords: OCEC; Organic carbon artifact; Carbon fractions; Semi-volatile organic compounds; Thermal-optical method

Polycyclic aromatic hydrocarbon exhaust emissions from different reformulated diesel fuels and engine operating conditions by Esther Borrás; Luis A. Tortajada-Genaro; Monica Vázquez; Barbara Zielinska (pp. 5944-5952).

The study of light-duty diesel engine exhaust emissions is important due to their impact on atmospheric chemistry and air pollution. In this study, both the gas and the particulate phase of fuel exhaust were analyzed to investigate the effects of diesel reformulation and engine operating parameters. The research was focused on polycyclic aromatic hydrocarbon (PAH) compounds on particulate phase due to their high toxicity. These were analyzed using a gas chromatography–mass spectrometry (GC–MS) methodology.Although PAH profiles changed for diesel fuels with low-sulfur content and different percentages of aromatic hydrocarbons (5–25%), no significant differences for total PAH concentrations were detected. However, rape oil methyl ester biodiesel showed a greater number of PAH compounds, but in lower concentrations (close to 50%) than the reformulated diesel fuels. In addition, four engine operating conditions were evaluated, and the results showed that, during cold start, higher concentrations were observed for high molecular weight PAHs than during idling cycle and that the acceleration cycles provided higher concentrations than the steady-state conditions. Correlations between particulate PAHs and gas phase products were also observed.The emission of PAH compounds from the incomplete combustion of diesel fuel depended greatly on the source of the fuel and the driving patterns.

Keywords: Polycyclic aromatic hydrocarbons; Reformulated diesel; Rape oil methyl ester biodiesel; Diesel exhaust emissions

Growing season total gaseous mercury (TGM) flux measurements over an Acer rubrum L. stand by Jesse O. Bash; David R. Miller (pp. 5953-5961).

Relaxed eddy accumulation (REA) measurements of the total gaseous mercury (TGM) flux measurements were taken over a deciduous forest predominantly composed of Red Maple ( Acer rubrum L.) during the growing season of 2004 and the second half of the growing season of 2005. The magnitudes of the flux estimates were in the range of published results from other micrometeorological mercury fluxes taken above a tall canopy and larger than estimates from flux chambers. The magnitude and direction of the flux were not static during the growing season. There was a significant trend ( p < 0.001), from net deposition of TGM in early summer to net evasion in the late summer and early fall before complete senescence. A growing season atmosphere-canopy total mercury (TGM) compensation point during unstable daytime conditions was estimated at background ambient concentrations (1.41 ng m⁻³). The trend in the seasonal net TGM flux indicates that long term dry deposition monitoring is needed to accurately estimate mercury loading over a forest ecosystem.

Keywords: Biogeochemical cycling; Relaxed eddy accumulation; Micrometeorological fluxes; Mercury dry deposition; Natural mercury emissions

Effects of 10% biofuel substitution on ground level ozone formation in Bangkok, Thailand by Austin Milt; Aaron Milano; Savitri Garivait; Richard Kamens (pp. 5962-5970).

The Thai Government's search for alternatives to imported petroleum led to the consideration of mandating 10% biofuel blends (biodiesel and gasohol) by 2012. Concerns over the effects of biofuel combustion on ground level ozone formation in relation to their conventional counterparts need addressing. Ozone formation in Bangkok is explored using a trajectory box model. The model is compared against O₃, NO, and NO₂ time concentration data from air monitoring stations operated by the Thai Pollution Control Department. Four high ozone days in 2006 were selected for modeling. Both the traditional trajectory approach and a citywide average approach were used. The model performs well with both approaches but slightly better with the citywide average. Highly uncertain and missing data are derived within realistic bounds using a genetic algorithm optimization. It was found that 10% biofuel substitution will lead to as much as a 16 ppb peak O₃ increase on these four days compared to a 48 ppb increase due to the predicted vehicle fleet size increase between 2006 and 2012. The approach also suggests that when detailed meteorological data is not available to run three dimensional airshed models, and if the air is stagnant or predominately remains over an urban area during the day, that a simple low cost trajectory analysis of O₃ formation may be applicable.

Keywords: Bangkok; Modeling ground level ozone; Biodiesel; Ethanol substitution; Genetic algorithm optimization

Simulating PM concentration during a winter episode in a subtropical valley: Sensitivity simulations and evaluation methods by P.L. Livingstone; K. Magliano; K. Gürer; P.D. Allen; K.M. Zhang; Q. Ying; B.S. Jackson; A. Kaduwela; M. Kleeman; L.F. Woodhouse; K. Turkiewicz; L.W. Horowitz; K. Scott; D. Johnson; C. Taylor; G. O'Brien; J. DaMassa; B.E. Croes; F. Binkowski; D. Byun (pp. 5971-5977).

We investigated a two-week episode with high PM concentrations in California Central Valley during the Christmas–New Year of 2000–2001 using a modeling system that consists of a computationally efficient, 3-D photochemical–microphysical transport model, a mesoscale meteorological model, emission models, and an evaluation package. One hundred simulations were conducted with fine resolutions and observational constraints, to reproduce spatial and temporal features of observed PM concentrations and to understand the formation mechanism of the episode. Simulated PM concentrations consist of secondary inorganic components, mainly ammonium nitrate, and total carbon in areas with elevated concentrations in the accumulation mode, and consist of mainly dust and sea salt in the coarse mode. Simulated oxidants and nitrate were significantly elevated over the valley, and the latter showed much less amplitude than the former. Simulated PM concentrations were evaluated with observations systematically with spatially and temporally paired method, a more restrictive multivariate method (NMFROC), and a more flexible “gradient evaluation” method. The paired evaluation shows that high correlation coefficient ( R=∼0.8) and low fractional error (FE=∼0.1) could be achieved at stations with elevated 24-h concentration of PM in the accumulation mode in some simulations. The NMFROC method was used to extract useful information from seemingly failed simulations. A “gradient evaluation” method is introduced here to extract additional information from simulations. We found that emission reductions of NO _x and AVOC showed similar effects on percentage basis in different areas, and both are more effective than reducing NH₃ for abating elevated concentrations of accumulation mode PM in California Central Valley during the winter episode.

Keywords: Aerosol; Photochemical–microphysical transport model; Gradient evaluation

The effects of parametric uncertainties in simulations of a reactive plume using a Lagrangian stochastic model by Tilo Ziehn; Nick S. Dixon; Alison S. Tomlin (pp. 5978-5988).

A combined Lagrangian stochastic model with micro-mixing and chemical sub-models is used to investigate a reactive plume of nitrogen oxides (NO_x) released into a turbulent grid flow doped with ozone (O₃). Sensitivities to the model input parameters are explored for different source NO_x scenarios. The wind tunnel experiments of provide the simulation conditions for the first case study where photolysis reactions are not included and the main uncertainties occur in parameters defining the turbulence scales, source size and reaction rate of NO with O₃. Using nominal values of the parameters from previous studies, the model gives a good representation of the radial profile of the conserved mean scalarΓ¯NOx although slightly over predicts peak mean NO₂ concentrationsΓ¯NO2 compared to the experiments. The high dimensional model representation (HDMR) method is used to investigate the effects of uncertainties in model inputs on the simulation of chemical species concentrations. For this scenario, the Lagrangian velocity structure function coefficient has the largest impact on simulatedΓ¯NOx profiles. Photolysis reactions are then included in a chemical scheme consisting of eight reactions between species NO, O, O₃ and NO₂. Independent and interactive effects of 22 input parameters are studied for two source NO_x scenarios using HDMR, including turbulence parameters, temperature dependant rate parameters, photolysis rates, temperature, fraction of NO in total NO_x at the source and background ozone concentration [O₃]. For this reactive case, the variance in the predicted mean plume centreΓ¯O3 is caused by parameters describing both physical (mixing time-scale coefficient) and chemical processes (activation energy for the reaction O₃+NO). The variance in predicted plume centreΓ¯NO2 and root mean square NO₂ concentrationγNO2′, is strongly influenced by the fraction of NO in the source NO_x, and to a lesser extent the mixing time-scale coefficient. Adjusting the latter gives improved agreement with the Brown and Bilger experiment. Some weak parameter interactions are observed.

Keywords: Global sensitivity analysis; High dimensional model representation; HDMR; NO; ₂; Ozone; Lagrangian structure function coefficient

Sections

Personal tools

Atmospheric Environment (v.43, #37)

Sections

Personal tools

Local resources

Atmospheric Environment (v.43, #37)