Atmospheric Environment (v.43, #4)
Editorial board (i).
Compilation and application of a primary PM2.5 emissions inventory with high sectoral resolution in Japan by Toshiharu Sugiyama; Keisuke Nansai; Susumu Tohno; Kouhei Yamamoto (759-768).
To elucidate the macro-structure of the PM2.5 emissions generated by Japan's economic activities, this paper presents an emission inventory of primary particles of PM2.5 with high sectoral resolution based on the Japanese Input–Output Tables, comprising some 400 sectors. These primary PM2.5 emissions were estimated by multiplying the estimated energy consumption associated with each fuel type by a PM10 emission factor incorporating the technological level of dust collection in each sector and the mass ratio of PM2.5 to PM10. Non-energy emissions from agricultural open burning were also determined. Total PM2.5 emissions in 2000 were 252 kt, 49% of which were due to mobile emission sources. Changes in total PM2.5 emissions between 1990 and 2000 were also calculated. This showed that a substantial increase in energy sector emissions due to rising coal consumption was offset by a sharp decline in emissions from road vehicles and shipping vessels, resulting in an overall decrease in total emissions. In addition, the emissions induced by economic demand in each sector were quantified by means of input–output analysis, which revealed that demand for construction, foods and communications and services constituted the principal causes of real domestic emissions. An assessment of sectoral contributions to PM2.5 emissions that takes into account the effects of human exposure, expressed as external costs, suggests that the contribution of transportation is greater than indicated on the grounds of direct emissions alone.
Keywords: Anthropogenic source; Emission inventory; Input–output analysis; Exposure; External cost;
Interpretation of air quality in relation to monitoring station's surroundings by Jason Lau; W.T. Hung; C.S. Cheung (769-777).
This study explores the appropriateness of the locality of air monitoring stations which are meant to indicate air quality in the area. Daily variations in NO2 and PM10 concentrations at 14 monitoring stations in Hong Kong are examined. The daily variations in NO2 at a number of background monitoring stations exhibit patterns similar to variations in traffic volume while variations in PM10 concentration exhibit less discernible pattern. Principal component analysis (PCA) and cluster analysis (CA) are applied to analyse NO2 and PM10 measurements between January 2001 and December 2005. The results show that NO2 concentrations at background stations within the urban area are highly influenced by vehicle emissions. The effect vehicle emission has on NO2 at stations within new towns is smaller. CA results also show that variations in PM10 concentrations are distinguished by the area the station is located in. PCA results show that there are two principal components (PC's) associated with variations in roadside concentration of PM10. The strong influence of roadside emissions towards concentrations of NO2 and PM10 at a number of urban background stations may be due to their close proximity to busy roadways and the high density of surrounding tall buildings, which creates an enclosure that hinders dispersion of roadside emissions and results in air pollution behaviour that reflects variation in traffic.
Keywords: NO2; PM10; Roadside emission; Monitoring station location; Dispersion process;
A simple urban dispersion model tested with tracer data from Oklahoma City and Manhattan by Steven Hanna; Emmanuel Baja (778-786).
A simple urban dispersion model is tested that is based on the Gaussian plume model and modifications to the Briggs urban dispersion curves. An initial dispersion coefficient (σ o) of 40 m is assumed to apply in built-up downtown areas, and the stability is assumed to be slightly unstable during the day and slightly stable during the night. Observations from tracer experiments during the Joint Urban 2003 (JU2003) field study in Oklahoma City and the Madison Square Garden 2005 (MSG05) field study in Manhattan are used for model testing. The tracer SF6 was released during JU2003 near ground level in the downtown area and concentrations were observed at over 100 locations within 4 km from the source. Six perfluorocarbon tracer (PFT) gases were released near ground level during MSG05 and sampled by about 20 samplers at the surface and on building roofs. The evaluations compare concentrations normalized by source release rate, C/Q, for each sampler location and each tracer release, where data were used only if both the observed and predicted concentrations exceeded threshold levels. At JU2003, for all samplers and release times, the fractional mean bias (FB) is about 0.2 during the day (20% mean underprediction) and 0.0 during the night. About 45 –50% of the predictions are within a factor of two (FAC2) of the observations day and night at JU2003. The maximum observed C/Q is about two times the maximum predicted C/Q both day and night. At MSG05, for all PFTs, surface samplers, and release times, FB is 0.14 and FAC2 is about 45%. The overall 60 min-averaged maximum C/Q is underpredicted by about 40% for the surface samplers and is overpredicted by about 25% for the building-roof samplers.
Keywords: Urban dispersion; Simple urban dispersion model; Joint Urban 2003 (JU2003) field experiment; Madison Square Garden 2005 (MSG05) field experiment; Air quality model evaluation; New York City air pollution;
Development of a distance-to-roadway proximity metric to compare near-road pollutant levels to a central site monitor by Timothy M. Barzyk; Barbara Jane George; Alan F. Vette; Ronald W. Williams; Carry W. Croghan; Carvin D. Stevens (787-797).
The primary objective of the Detroit Exposure and Aerosol Research Study (DEARS) was to compare air pollutant concentrations measured at various neighborhoods, or exposure monitoring areas (EMAs), throughout a major metropolitan area to levels measured at a central site or community monitor. One of the EMAs was located near a busy freeway (annual average daily traffic (AADT) of ∼130,000) so that impacts of mobile sources could be examined. Air pollution concentrations from the roadway-proximate sites were compared to the central site monitor. The volatile organic compounds (VOCs) selected (benzene, toluene, ethylbenzene, m,p- and o-xylene, 1,3 butadiene, 1,3,5-trimethylbenzene and 4-ethyltoluene) are typically associated with mobile sources. Gradients were also evident that demonstrated the amplification of pollutant levels near the roadway compared to the community monitor. A novel distance-to-roadway proximity metric was developed to plot the measurements and model these gradients. Effective distance represents the actual distance an air parcel travels from the middle of a roadway to a site and varies as a function of wind direction, whereas perpendicular distance is a fixed distance oriented normal to the roadway. Perpendicular distance is often used as a proxy for exposures to traffic emissions in epidemiological studies.Elevated concentrations of all the compounds were found for both a summer and winter season. Effective distance was found to be a statistically significant (p < 0.05) univariate predictor for concentrations of toluene, ethylbenzene, m,p-xylene and o-xylene for summer 2005. For each of these pollutants, effective distance yielded lower p-values than the corresponding perpendicular distance models, and model fit improved. Results demonstrate that this near-road EMA had elevated levels of traffic-related VOCs compared to the community monitor, and that effective distance was a more accurate predictor of the degree to which they were elevated as a function of distance. Effective distance produced a range of distance-to-roadway values for a single site based on wind direction, thus increasing the number and range of values that could be used to plot and predict relative differences in pollutant concentrations between two sites.
Keywords: Near-road; VOC; Effective distance; Central site monitor;
Gas-phase chemistry of benzyl alcohol: Reaction rate constants and products with OH radical and ozone by Joel C. Harrison; J.R. Wells (798-804).
A bimolecular rate constant, k OH+Benzyl alcohol, of (28 ± 7) × 10−12 cm3 molecule−1 s−1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with benzyl alcohol, at (297 ± 3) K and 1 atm total pressure. Additionally, an upper limit of the bimolecular rate constant, k O3+Benzyl alcohol, of approximately 6 × 10−19 cm3 molecule−1 s−1 was determined by monitoring the decrease in benzyl alcohol concentration over time in an excess of ozone (O3). To more clearly define part of benzyl alcohol's indoor environment degradation mechanism, the products of the benzyl alcohol + OH were also investigated. The derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) were used to positively identify benzaldehyde, glyoxal and 4-oxopentanal as benzyl alcohol/OH reaction products. The elucidation of other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible benzyl alcohol/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms.
Keywords: OH rate constant; Ozone rate constant; Benzyl alcohol; Indoor chemistry;
Organic matter in the bulk precipitations in Zagreb and Šibenik, Croatia by Palma Orlović-Leko; Marta Plavšić; Elvira Bura-Nakić; Zlatica Kozarac; Božena Ćosović (805-811).
Dissolved organic carbon (DOC), surface active substances (SAS) and copper complexing capacity (CuCC) were studied in bulk precipitations collected periodically from 2003 to 2007 in the continental city of Croatia (Zagreb: n = 27) and in the city at the Adriatic coast (Šibenik: n = 38). DOC concentrations (Zagreb: 0.67–4.03 mgC/L with average concentration of 1.93 ± 0.76 mgC/L; Šibenik: 0.44–4.13 mgC/L with average concentration of 1.83 ± 0.83 mgC/L) are similar to those measured in other samples of continental rainwater in the northern hemisphere. The concentrations of SAS in samples from Zagreb ranged from 0.055 to 0.45 eq. Triton-X-100 mg/L with average concentration of (0.14 ± 0.06) eq. Triton-X-100 mg/L. SAS fractions were of a similar range in Šibenik (0.02–0.60 eq. Triton-X-100 mg/L) with an average concentration of 0.11 ± 0.06 eq. Triton-X-100 mg/L. However, the lowest values of SAS (between 0.02 and 0.04 eq. Triton-X-100 mg/L) were observed only in Šibenik (27%). We have estimated that the higher pH values were responsible for lower surface activity of organic matter in bulk samples from Šibenik. DOC may form complexes that control the transport and solubility of heavy metals in natural water. CuCC measured in Šibenik in the range 0.066–1.4 μM Cu2+ was in general higher, compared to the one in Zagreb (0.010–0.586 μM Cu2+) which is the result of biogenically driven organic contribution to the precipitation, especially in the warmer period of the year.
Keywords: Dissolved organic carbon (DOC); Surface active substances (SAS); Complexing capacity (CuCC); Bulk precipitation;
Global atmospheric emission inventory of polycyclic aromatic hydrocarbons (PAHs) for 2004 by Yanxu Zhang; Shu Tao (812-819).
The global atmospheric emissions of the 16 polycyclic aromatic hydrocarbons (PAHs) listed as the US EPA priority pollutants were estimated using reported emission activity and emission factor data for the reference year 2004. A database for emission factors was compiled, and their geometric means and frequency distributions applied for emission calculation and uncertainty analysis, respectively. The results for 37 countries were compared with other PAH emission inventories. It was estimated that the total global atmospheric emission of these 16 PAHs in 2004 was 520 giga grams per year (Gg y−1) with biofuel (56.7%), wildfire (17.0%) and consumer product usage (6.9%) as the major sources, and China (114 Gg y−1), India (90 Gg y−1) and United States (32 Gg y−1) were the top three countries with the highest PAH emissions. The PAH sources in the individual countries varied remarkably. For example, biofuel burning was the dominant PAH source in India, wildfire emissions were the dominant PAH source in Brazil, while consumer products were the major PAH emission source in the United States. In China, in addition to biomass combustion, coke ovens were a significant source of PAHs. Globally, benzo(a)pyrene accounted for 0.05% to 2.08% of the total PAH emission, with developing countries accounting for the higher percentages. The PAH emission density varied dramatically from 0.0013 kg km−2 y in the Falkland Islands to 360 kg km−2 y in Singapore with a global mean value of 3.98 kg km−2 y. The atmospheric emission of PAHs was positively correlated to the country's gross domestic product and negatively correlated with average income. Finally, a linear bivariate regression model was developed to explain the global PAH emission data.
Keywords: PAHs; Emission inventory; Global;
Generation and growth of aerosols over Pune, India by P. Murugavel; D.M. Chate (820-828).
The measured physical size distributions of sub-micron particles during cold season at Pune, India are analyzed to explore the characteristics of nucleation and growth properties. Preliminary analysis of aerosol size distribution in time-series shows large increase in number concentration due to nucleation events between 0800 h and 1030 h at this location. The observable quantities such as condensable vapor concentration (C), its source rate (Q), growth rate (GR) and condensable sink (CS) are estimated from the time-series evolutions of aerosol size distributions. The concentration of vapor and its source rate were about 19.8 ± 2.15 × 107 molecules cm−3 and 1.28 ± 0.084 × 107 cm−3 s−1 respectively. The average condensation sink and growth rate were 7.1 ± 0.4 × 10−2 s−1 and 16.95 ± 1.86 nm h−1 respectively during the growth period. The values are high enough to trigger the nucleation bursts and enhance subsequent growth rates of nucleation mode particles at this location. The magnitudes are in the range of those observed at New Delhi, India and much higher than those of European cities. The ratio of apparent to real nucleation rate is found to be a measure of number concentration of freshly produced particles by photo-chemical nucleation. The predicted number concentrations corresponding to measured distributions of mid-point diameter increases with the size for both 1 nm nucleated clusters and 3 nm particles. The database of all the possible event days and the event characteristics forms the basis for future works into the causes and implications of atmospheric particle formation at this location.
Keywords: Nucleation; Nucleated aerosols; Photo-chemical; Gas precursors;
Measurement of aerosol number size distributions in the Yangtze River delta in China: Formation and growth of particles under polluted conditions by Jian Gao; Tao Wang; Xuehua Zhou; Waishing Wu; Wenxing Wang (829-836).
Particle size distribution is important for understanding the sources and effects of atmospheric aerosols. In this paper we present particle number size distributions (10 nm–10 μm) measured at a suburban site in the fast developing Yangtze River Delta (YRD) region (near Shanghai) in summer 2005. The average number concentrations of ultrafine (10–100 nm) particles were 2–3 times higher than those reported in the urban areas of North America and Europe. The number fraction of the ultrafine particles to total particle count was also 20–30% higher. The sharp increases in ultrafine particle number concentrations were frequently observed in late morning, and the particle bursts on 5 of the 12 nucleation event days can be attributed to the homogeneous nucleation leading to new particle formation. The new particle formation events were characterized with a larger number of nucleation-mode particles, larger particle surface area, and larger condensational sink than usually reported in the literature. These suggest an intense production of sulfuric acid from photo-oxidation of sulfur dioxide in the YRD. Overall, the growth rate of newly formed particles was moderate (6.4 ± 1.6 nm h−1), which was comparable to that reported in the literature.
Keywords: New particle formation; Sulfur dioxide; Photochemical activity; Shanghai;
Heterogeneous reactivity of pyrene and 1-nitropyrene with NO2: Kinetics, product yields and mechanism by K. Miet; K. Le Menach; P.-M. Flaud; H. Budzinski; E. Villenave (837-843).
The heterogeneous reactivity of nitrogen dioxide with pyrene and 1-nitropyrene (1NP) adsorbed on silica particles has been investigated using a fast-flow-tube in the absence of light. Reactants and products were extracted from particles using pressurised fluid extraction (PFE) and concentration measurements were performed using gas chromatography/mass spectrometry (GC/MS). The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate polycyclic compound concentrations versus reaction time. Experiments were performed at three different NO2 concentrations and second order rate constants were calculated considering the oxidant concentration. The following rate constant values were obtained at room temperature: k(NO2 + pyrene) = (9.3 ± 2.3) × 10−17 cm3 molecule−1 s−1 and k(NO2 + 1NP) = (6.2 ± 1.5) × 10−18 cm3 molecule−1 s−1, showing that the reactivity of 1NP was slower by a factor of 15 than that of pyrene. 1NP was identified as the only NO2-initiated oxidation product of pyrene and all the three dinitropyrenes were identified in the case of the 1NP reaction. The product quantification allowed showing that the kinetics of oxidation product formation was equal to that measured for parent compounds degradation, within uncertainties, confirming the validity of the reaction kinetics measurements.
Keywords: PAH; Pyrene; 1-nitropyrene; Silica particles; NO2; Kinetics; Oxidation products;
Quantitative trace analysis of polyfluorinated alkyl substances (PFAS) in ambient air samples from Mace Head (Ireland): A method intercomparison by Annika Jahnke; Jonathan L. Barber; Kevin C. Jones; Christian Temme (844-850).
A method intercomparison study of analytical methods for the determination of neutral, volatile polyfluorinated alkyl substances (PFAS) was carried out in March, 2006. Environmental air samples were collected in triplicate at the European background site Mace Head on the west coast of Ireland, a site dominated by ‘clean’ westerly winds coming across the Atlantic. Extraction and analysis were performed at two laboratories active in PFAS research using their in-house methods. Airborne polyfluorinated telomer alcohols (FTOHs), fluorooctane sulfonamides and sulfonamidoethanols (FOSAs/FOSEs) as well as additional polyfluorinated compounds were investigated. Different native and isotope-labelled internal standards (IS) were applied at various steps in the analytical procedure to evaluate the different quantification strategies. Field blanks revealed no major blank problems. European background concentrations observed at Mace Head were found to be in a similar range to Arctic data reported in the literature. Due to trace-levels at the remote site, only FTOH data sets were complete and could therefore be compared between the laboratories. Additionally, FOSEs could partly be included. Data comparison revealed that despite the challenges inherent in analysis of airborne PFAS and the low concentrations, all methods applied in this study obtained similar results. However, application of isotope-labelled IS early in the analytical procedure leads to more precise results and is therefore recommended.
Keywords: Polyfluorinated alkyl substances (PFAS); Air analysis; Method intercomparison; Isotope-labelled internal standards; European background levels;
Sensitivity of ozone concentrations to diurnal variations of surface emissions in Mexico City: A WRF/Chem modeling study by Zhuming Ying; Xuexi Tie; Guohui Li (851-859).
Sensitivity of ozone (O3) concentrations in the Mexico City area to diurnal variations of surface air pollutant emissions is investigated using the WRF/Chem model. Our analysis shows that diurnal variations of nitrogen oxides (NO x = NO + NO2) and volatile organic compound (VOC) emissions play an important role in controlling the O3 concentrations in the Mexico City area. The contributions of NO x and VOC emissions to daytime O3 concentrations are very sensitive to the morning emissions of NO x and VOCs. Increase in morning NO x emissions leads to decrease in daytime O3 concentrations as well as the afternoon O3 maximum, while increase in morning VOC emissions tends to increase in O3 concentrations in late morning and early afternoon, indicating that O3 production in Mexico City is under VOC-limited regime. It is also found that the nighttime O3 is independent of VOCs, but is sensitive to NO x . The emissions of VOCs during other periods (early morning, evening, and night) have only small impacts on O3 concentrations, while the emissions of NO x have important impacts on O3 concentrations in the evening and the early morning.This study suggests that shifting emission pattern, while keeping the total emissions unchanged, has important impacts on air quality. For example, delaying the morning emission peak from 8 am to 10 am significantly reduced the morning peaks of NO x and VOCs, as well as the afternoon O3 maxima. It suggests that without reduction of total emission, the daytime O3 concentrations can be significantly reduced by changing the diurnal variations of the emissions of O3 precursors.
Keywords: WRF/Chem; Ozone; Emissions; Diurnal variation; Mexico City;
Link between aerosol optical, microphysical and chemical measurements in an underground railway station in Paris by J.-C. Raut; P. Chazette; A. Fortain (860-868).
Measurements carried out in Paris Magenta railway station in April–May 2006 underlined a repeatable diurnal cycle of aerosol concentrations and optical properties. The average daytime PM10 and PM2.5 concentrations in such a confined space were approximately 5–30 times higher than those measured in Paris streets. Particles are mainly constituted of dust, with high concentrations of iron and other metals, but are also composed of black and organic carbon. Aerosol levels are linked to the rate at which rain and people pass through the station. Concentrations are also influenced by ambient air from the nearby streets through tunnel ventilation. During daytime approximately 70% of aerosol mass concentrations are governed by coarse absorbing particles with a low Angström exponent (∼0.8) and a low single-scattering albedo (∼0.7). The corresponding aerosol density is about 2 g cm−3 and their complex refractive index at 355 nm is close to 1.56–0.035 i. The high absorption properties are linked to the significant proportion of iron oxides together with black carbon in braking systems. During the night, particles are mostly submicronic, thus presenting a greater Angström exponent (∼2). The aerosol density is lower (1.8 g cm−3) and their complex refractive index presents a lower imaginary part (1.58–0.013 i), associated to a stronger single-scattering albedo (∼0.85–0.90), mostly influenced by the ambient air. For the first time we have assessed the emission (deposition) rates in an underground station for PM10, PM2.5 and black carbon concentrations to be 3314 ± 781(−1164 ± 160), 1186 ± 358(−401 ± 66) and 167 ± 46(−25 ± 9) μg m−2 h−1, respectively.
Keywords: Subway; Mass concentrations; Chemical analyses; Optical properties; Emission rates;
Effect of urban morphology on wind condition in idealized city models by Jian Hang; Mats Sandberg; Yuguo Li (869-878).
Wind conditions in urban environments are important for a number of reasons. They can serve to transport air pollutants out of the urban environment and to moderate urban microclimatic conditions if satisfactory, yet can compromise pedestrian comfort and safety if not. We aim to study experimentally and numerically the effects of urban morphology (e.g., overall city form (skyline), street orientation, and street configuration) on wind conditions in cities. This report considers our initial investigations of two idealized city forms that are coincidentally similar to ancient Roman cities that were organized on one or two primary streets – a main north–south street, the cardus maximus, and a secondary east–west street, the decumanus maximus – and contained within a well-defined perimeter.We first consider round and square city models with one main street set parallel to the approaching wind and a secondary street producing an intersection at city centre. Not surprisingly, wind conditions in the two city models are dissimilar due to their shape differences. We then consider a long rectangular city model with a fully developed steady flow region along the main street. If the main street of the round city model is narrow, the parallel approaching wind cannot blow through the entire street and a penetrating inflow exists at the leeward opening. For the round city model with two crossing streets, a slightly non-parallel wind to the main street generates a stronger wind level in the entire street volume.
Keywords: Wind conditions; Urban morphology; City form; Numerical simulation; Wind tunnel;
Optical and microphysical properties of severe haze and smoke aerosol measured by integrated remote sensing techniques in Gwangju, Korea by Young M. Noh; Detlef Müller; Dong H. Shin; Hanlim Lee; Jin S. Jung; Kwon H. Lee; Maureen Cribb; Zhanqing Li; Young J. Kim (879-888).
Aerosol optical and microphysical parameters from severe haze events observed in October 2005 at Gwangju, Korea (35.10°N, 126.53°E) were determined from the ground using a multi-wavelength Raman lidar, a sunphotometer, and a real-time carbon particle analyzer and from space using satellite retrievals. Two different aerosol types were identified based on the variability of optical characteristics for different air mass conditions. Retrievals of microphysical properties of the haze from the Raman lidar indicated distinct light-absorbing characteristics for different haze aerosols originating from eastern and northern China (haze) and eastern Siberia (forest-fire smoke). The haze transported from the west showed moderately higher absorbing characteristics (SSA = 0.90 ± 0.03, 532 nm) than from the northern direction (SSA = 0.96 ± 0.02). The organic/elemental carbon (OC/EC) ratio varied between 2.5 ± 0.4 and 4.1 ± 0.7.
Keywords: Haze; Raman lidar; Satellite; Single-scattering albedo;
Monitoring of dust emission on gravel roads: Development of a mobile methodology and examination of horizontal diffusion by Karin Edvardsson; Rolf Magnusson (889-896).
Traffic-generated fugitive dust on gravel roads impairs visibility and deposits on the adjacent environment. Particulate matter smaller than 10 μm in diameter (PM10) is also associated with human health problems. Dust emission strength depends on the composition of granular material, road moisture, relative humidity, local climate (precipitation, wind velocity, etc.), and vehicle characteristics.The objectives of this study were to develop a reliable and rapid mobile methodology to measure dust concentrations on gravel roads, evaluate the precision and repeatability of the methodology and correspondence with the currently used visual assessment technique. Downwind horizontal diffusion was studied to evaluate the risk of exceeding the maximum allowed particulate matter concentration in ambient air near gravel roads according to European Council Directive [European Council Directive 1999/30/EC of 22 April 1999 relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air. Official Journal of the European Communities. L163/41.].A TSI DustTrak Aerosol Monitor was mounted on an estate car travelling along test sections treated with various dust suppressants. Measured PM10 concentrations were compared to visual assessments performed at the same time. Airborne particles were collected in filters mounted behind the vehicle to compare the whole dust fraction with the PM10 concentration. For measuring the horizontal diffusion, DustTraks were placed at various distances downwind of a dusty road section.The mobile methodology was vehicle and speed dependent but not driver dependent with pre-specified driving behaviours. A high linear correlation between PM10 of different vehicles makes relative measurements of dust concentrations possible. The methodology gives continuous data series, mobility, and easy handling and provides fast, reliable and inexpensive measurements for estimating road conditions to make road maintenance more efficient.Good correlations between measured PM10-values, visually assessed dust generation and dust collected in filters were obtained. PM10 seems to be correlated to the whole dust fraction that impairs visibility on gravel roads.A decay in PM10 concentration as a function of distance from the road was observed. Measured particles principally did not travel further than 45 m from the road. The risk of exceeding the PM10 concentration stated in the EC-directive seems small.
Keywords: Gravel roads; Dust emission; PM10; Methodology evaluation; European Council Directive;
Effect of high concentrations of inorganic seed aerosols on secondary organic aerosol formation in the m-xylene/NO x photooxidation system by Zifeng Lu; Jiming Hao; Hideto Takekawa; Lanhua Hu; Junhua Li (897-904).
High concentrations (>15 μm3 cm−3) of CaSO4, Ca(NO3)2 and (NH4)2SO4 were selected as surrogates of dry neutral, aqueous neutral and dry acidic inorganic seed aerosols, respectively, to study the effects of inorganic seeds on secondary organic aerosol (SOA) formation in irradiated m-xylene/NO x photooxidation systems. The results indicate that neither ozone formation nor SOA formation is significantly affected by the presence of neutral aerosols (both dry CaSO4 and aqueous Ca(NO3)2), even at elevated concentrations. The presence of high concentrations of (NH4)2SO4 aerosols (dry acidic) has no obvious effect on ozone formation, but it does enhance SOA generation and increase SOA yields. In addition, the effect of dry (NH4)2SO4 on SOA yield is found to be positively correlated with the (NH4)2SO4 surface concentration, and the effect is pronounced only when the surface concentration reaches a threshold value. Further, it is proposed that the SOA generation enhancement is achieved by particle-phase heterogeneous reactions induced and catalyzed by the acidity of dry (NH4)2SO4 seed aerosols.
Keywords: Secondary organic aerosol; Aerosol yield; Calcium sulfate; Calcium nitrate; Ammonium sulfate;
Deposition rates on smooth surfaces and coagulation of aerosol particles inside a test chamber by Tareq Hussein; Aleš Hruška; Pavla Dohányosová; Lucie Džumbová; Jiří Hemerka; Markku Kulmala; Jiří Smolík (905-914).
Because aerosol particle deposition is an important factor in indoor air quality, many empirical and theoretical studies have attempted to understand the process. In this study, we estimated the deposition rate of aerosol particles on smooth aluminum surfaces inside a test chamber. We investigated the influence of turbulent intensity due to ventilation and fan operation. We also investigated two important processes in particle deposition: turbophoresis, which is significant for micron particles, and coagulation, which is relevant to ultrafine particles (UFP diameter <0.1 μm) at high particle concentrations. Our analysis included semi-empirical estimates of the deposition rates that were compared to available deposition models and verified with simulations of an aerosol dynamics model. In agreement with previous studies, this study found that induced turbulent intensity greatly enhanced deposition rates of fine particles (FP diameter <1 μm). The deposition rate of FP was proportional to the ventilation rate, and it increased monotonically with fan speed. With our setup, turbophoresis was very important for coarse particles larger than 5 μm. The coagulation of aerosol particles was insignificant when the particle concentration was less than 104 cm−3 during fan operation. The model simulation results verified that the aerosol dynamics module incorporated in our Multi-Compartment and Size-Resolved Indoor Aerosol Model (MC-SIAM) was valid. The behavior of aerosol particles inside our chamber was similar to that found in real-life conditions with the same ventilation rates (0.018–0.39 h−1) and similar air mixing modes. Therefore, our findings provide insight into indoor particle behavior.
Keywords: Deposition rate; Turbophoresis; Coagulation; Turbulent intensity; Modeling;
Validation of model calculation of ammonia deposition in the neighbourhood of a poultry farm using measured NH3 concentrations and N deposition by S.G. Sommer; H.S. Østergård; P. Løfstrøm; H.V. Andersen; L.S. Jensen (915-920).
Substantial emission of ammonia (NH3) from animal houses and the related high local deposition of NH3-N are a threat to semi-natural nitrogen-deficient ecosystems situated near the NH3 source. In Denmark, there are regulations limiting the level of NH3 emission from livestock houses near N-deficient ecosystems that are likely to change due to nitrogen (N) enrichment caused by NH3 deposition. The models used for assessing NH3 emission from livestock production, therefore, need to be precise, as the regulation will affect both the nature of the ecosystem and the economy of the farmer. Therefore a study was carried out with the objective of validating the Danish model used to monitor NH3 transport, dispersion and deposition from and in the neighbourhood of a chicken farm. In the study we measured NH3 emission with standard flux measuring methods, NH3 concentrations at increasing distances from the chicken houses using passive diffusion samplers and deposition using 15N-enriched biomonitors and field plot studies. The dispersion and deposition of NH3 were modelled using the Danish OML-DEP model. It was also shown that model calculations clearly reflect the measured NH3 concentration and N deposition. Deposition of N measured by biomonitors clearly reflected the variation in NH3 concentrations and showed that deposition was not significantly different from zero (P < 0.05) at distances greater than 150–200 m from these chicken houses. Calculations confirmed this, as calculated N deposition 320 m away from the chicken farm was only marginally affected by the NH3 emission from the farm. There was agreement between calculated and measured deposition showing that the model gives true estimates of the deposition in the neighbourhood of a livestock house emitting NH3.
Keywords: Ammonia; Dispersion; Deposition; Biomonitors; OML-DEP model;
A fluctuating plume model for concentration fluctuations in a plant canopy by L. Mortarini; P. Franzese; E. Ferrero (921-927).
A one-particle Lagrangian model for continuous releases in the non-Gaussian inhomogeneous turbulence of a canopy layer is derived based on the fluctuating plume model of Franzese [2003. Lagrangian stochastic modeling of a fluctuating plume in the convective boundary layer. Atmos. Environ. 37, 1691–1701.]. The model equations are filtered by a time-dependent low-pass filter applied to the turbulent kinetic energy in order to obtain a fluctuating plume model able to simulate the vertical meandering of the cloud centroid through non-stationary Lagrangian equations. The model satisfies the well-mixed condition. The relative dispersion of particles and the concentration fluctuation statistics of a passive tracer inside a modeled vegetal canopy are studied. The probability density function of the concentration relative to the plume centroid is parameterized and the mean and variance fields of concentration are simulated and compared with wind-tunnel data and numerical simulations. A skewed, reflected probability density function for the vertical position of the plume centroid is considered.
Keywords: Lagrangian stochastic model; Fluctuating plume; Meandering; Relative dispersion; Concentration fluctuations; Canopy flow;
Past and future trends in concentrations of sulphur and nitrogen compounds in the Arctic by Lars R. Hole; Jesper H. Christensen; Tuija Ruoho-Airola; Kjetil Tørseth; Veronica Ginzburg; Piotr Glowacki (928-939).
Recent trends in nitrogen and sulphur compounds in air and precipitation from a range of Arctic monitoring stations are presented, with seasonal data from the late 70s to 2004 or 2005. Earlier findings of declining sulphur concentrations are confirmed for most stations, while the pattern is less clear for reduced and oxidized nitrogen. In fact there are positive trends for nitrogen compounds in air at several stations. Acidity is generally reduced at many stations while the precipitation amount is either increasing or stable. Variability of sulphate concentrations in air for the period 1991–2000 is reasonably well reproduced at most stations using an Eulerian, hemispherical model. Results for nitrogen compounds are weaker. Scenario studies show that even if large sulphur emission reductions take place in important source regions in South-East Asia in the coming decades, only small changes in Arctic deposition can be expected. This is because South-East Asian emissions have small influence north of the Arctic circle.
Keywords: Arctic; NO x ; NH x , SO x ; Monitoring; Deposition; Precipitation; AMAP; Trends;
ATR-FTIR characterization of organic functional groups and inorganic ions in ambient aerosols at a rural site by Charity Coury; Ann M. Dillner (940-948).
An Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopic method was used to measure organic functional groups and inorganic ions at Tonto National Monument (TNM), an Interagency Monitoring of Protected Visual Environments (IMPROVE) sampling site in a rural area near Phoenix, Arizona. Functional groups and ions from common aerosol compound classes such as aliphatic and aromatic CH, methylene, methyl, aldehydes/ketones, carboxylic acids, ammonium sulfate and nitrate as well as functional groups from difficult to measure compound classes such as esters/lactones, acid anhydrides, carbohydrate hydroxyl and ethers, amino acids, and amines were quantified. On average, ∼33% of the PM1.0 mass was composed of organic aerosol. The average (standard deviation) composition of the organic aerosol at TNM was 34% (6%) biogenic functional groups, 21% (5%) oxygenated functional groups, 28% (7%) aliphatic hydrocarbon functional groups (aliphatic CH, methylene and methyl) and 17% (1%) aromatic hydrocarbon functional groups. Compositional analysis, functional group correlations, and back trajectories were used to identify three types of events with source signatures: primary biogenic-influenced, urban-influenced, and regional background. The biogenic-influenced event had high concentrations of amino acids and carbohydrate hydroxyl and ether, as well as aliphatic CH and aromatic CH functional groups and qualitatively high levels of silicate. The urban-influenced events had back trajectories traveling directly from the Phoenix area and high concentrations of hydrocarbons, oxygenated functional groups, and inorganic ions. This aerosol characterization suggests that both primary emissions in Phoenix and secondary formation of aerosols from Phoenix emissions had a major impact on the aerosol composition and concentration at TNM. The regional background source had low concentrations of all functional groups, but had higher concentrations of biogenic functional groups than the urban source.
Keywords: Oxygenated organic particulate matter; Biogenic aerosols; Carbohydrates; Amino acids; Acid anhydrides;
Comparative study of measured and modelled number concentrations of nanoparticles in an urban street canyon by Prashant Kumar; Andrew Garmory; Matthias Ketzel; Ruwim Berkowicz; Rex Britter (949-958).
This study presents a comparison between measured and modelled particle number concentrations (PNCs) in the 10–300 nm size range at different heights in a canyon. The PNCs were modelled using a simple modelling approach (modified Box model, including vertical variation), an Operational Street Pollution Model (OSPM) and Computational Fluid Dynamics (CFD) code FLUENT. All models disregarded any particle dynamics. CFD simulations have been carried out in a simplified geometry of the selected street canyon. Four different sizes of emission sources have been used in the CFD simulations to assess the effect of source size on mean PNC distributions in the street canyon. The measured PNCs were between a factor of two and three of those from the three models, suggesting that if the model inputs are chosen carefully, even a simplified approach can predict the PNCs as well as more complex models. CFD simulations showed that selection of the source size was critical to determine PNC distributions. A source size scaling the vehicle dimensions was found to better represent the measured PNC profiles in the lowest part of the canyon. The OSPM and Box model produced similar shapes of PNC profile across the entire height of the canyon, showing a well-mixed region up to first ≈2 m and then decreasing PNCs with increased height. The CFD profiles do correctly reproduce the increase from road level to a height of ≈2 m; however, they do not predict the measured PNC decrease higher in the canyon. The PNC differences were largest between idealised (CFD and Box) and operational (OSPM) models at upper sampling heights; these were attributed to weaker exchange of air between street and roof-above in the upper part of the canyon in the CFD calculations. Possible reasons for these discrepancies are given.
Keywords: Dispersion; Modelling; Nanoparticles; Particle number concentration; Street canyon;
Carbonaceous aerosol over a Pinus taeda forest in Central North Carolina, USA by Chris Geron (959-969).
Organic aerosol is the least understood component of ambient fine particulate matter (PM2.5). In this study, organic and elemental carbon (OC and EC) within ambient PM2.5 over a three-year period at a forested site in the North Carolina Piedmont are presented. EC exhibited significant weekday/weekend effects and less significant seasonal effects, in contrast to OC, which showed strong seasonal differences and smaller weekend/weekday effects. Summer OC concentrations are about twice as high as winter concentrations, while EC was somewhat higher in the winter. OC was highly correlated with EC during cool periods when both were controlled by primary combustion sources. This correlation decreased with increasing temperature, reflecting higher contributions from secondary organic aerosol, likely of biogenic origin. PM2.5 radiocarbon data from the site confirms that a large fraction of the carbon in PM2.5 is indeed of biogenic origin, since modern (non-fossil fuel derived) carbon accounted for 80% of the PM2.5 carbon over the course of a year. OC and EC exhibited distinct diurnal profiles, with summertime OC peaking in late evening and declining until midday. During winter, OC peaked during the early morning hours and again declined until midday. Summertime EC peaked during late morning hours except on weekends. Wintertime EC often peaked in late PM or early AM hours due to local residential wood combustion emissions. The highest short term peaks in OC and EC were associated with wildfire events. These data corroborate recent source apportionment studies conducted within 20 km of our site, where oxidation products of isoprene, α-pinene, and β-caryophyllene were identified as important precursors to organic aerosols. A large fraction of the carbon in rural southeastern ambient PM2.5 appears to be of biogenic origin, which is probably difficult to reduce by anthropogenic controls.
Keywords: Organic carbon; Particulate matter; Southeastern U.S.; Biogenic VOC; Biomass burning; Secondary organic aerosol;
Laser induced fluorescence instrument for NO2 measurements: Observations at a central Italy background site by Cesare Dari-Salisburgo; Piero Di Carlo; Franco Giammaria; Yoshizumi Kajii; Alfonso D'Altorio (970-977).
A laser induced fluorescence (LIF) instrument has been developed to measure tropospheric NO2 with low detection limit. The instrument design, development and first measurements are reported. There are also details of the temporal gate system built for the fluorescence acquisition. The instrument is able to make fast measurements (up to 4 Hz) and shows a limit of detection of 10 pptv/60 s. Continuous observations (2 weeks in summer 2007) in a small town in central Italy were used to test the performance of the instrument and to study the photochemistry of ozone in a background site. LIF and a commercial chemiluminescence (CL) instrument simultaneous observations of NO2 show a good linearity (LIF = 1.02 CL + 0.6 (ppb), R 2 = 0.98) but there is a bias of the commercial instrument of about 0.60 ppbv on average. The overestimation of the CL system is probably due to conversion of NO y species into NO by the molybdenum converter used in the CL instrument to detect NO2. Analysis of 1 s data is used to test the instrument response and the coupling between nitrogen oxides and ozone.
Keywords: Nitrogen dioxide; Ozone; Boundary layer; Urban pollution; Laser induced fluorescence;
Polycyclic aromatic hydrocarbon emission from straw burning and the influence of combustion parameters by Hao Lu; Lizhong Zhu; Nali Zhu (978-983).
A simulated burning experiment was conducted in a tubular furnace system to examine the emission of polycyclic aromatic hydrocarbons (PAHs) from the burning of rice and bean straw, and the influence of combustion parameters was investigated. Total emission amounts of 16 PAHs (∑PAHs) from the burning of rice and bean straw ranged from 9.29 to 23.6 μg g−1 and from 3.13 to 49.9 μg g−1, respectively, which increased with the increase of temperatures from 200 to 700 °C. The contribution of combustion to individual PAH yields was about 80.6–100%, which was generally increased with the increase of burning temperature. Moisture content in straw had a negative effect on PAH formation, especially on PAHs with low molecular weight. ∑PAHs emission amounts decreased by 78.2% for bean straw with a moisture content of 30% in comparison with that for dried straw. In addition, PAH emission amounts increased with the increase of O2 content in supplied air and then decreased, which showed a maximum emission at O2 content of 40%. The source fingerprint of PAHs in emission from straw burning was established, which showed that naphthalene accounted for 35.0 ± 7.4% of ∑PAHs. Based on the experimental data, emission amounts of ∑PAHs from the burning of rice and bean straw were estimated to be 320–357 and 32.5–76.0 tons to ambient air per year in China, respectively.
Keywords: Polycyclic aromatic hydrocarbons; Straw; Combustion parameters; Fingerprint;