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Atmospheric Environment (v.42, #2)
Measurements and predictors of on-road ultrafine particle concentrations and associated pollutants in Los Angeles by S. Fruin; D. Westerdahl; T. Sax; C. Sioutas; P.M. Fine (pp. 207-219).
Motor vehicles are the dominant source of oxides of nitrogen (NO x), particulate matter (PM), and certain air toxics (e.g., benzene, 1,3-butadiene) in urban areas. On roadways, motor vehicle-related pollutant concentrations are typically many times higher than ambient concentrations. Due to high air exchange rates typical of moving vehicles, this makes time spent in vehicles on roadways a major source of exposure. This paper presents on-road measurements for Los Angeles freeways and arterial roads taken from a zero-emission electric vehicle outfitted with real-time instruments. The objective was to characterize air pollutant concentrations on roadways and identify the factors associated with the highest concentrations. Our analysis demonstrated that on freeways, concentrations of ultrafine particles (UFPs), black carbon, nitric oxide, and PM-bound polycyclic aromatic hydrocarbons (PM-PAH) are generated primarily by diesel-powered vehicles, despite the relatively low fraction (∼6%) of diesel-powered vehicles on Los Angeles freeways. However, UFP concentrations on arterial roads appeared to be driven primarily by proximity to gasoline-powered vehicles undergoing hard accelerations. Concentrations were roughly one-third of those on freeways. By using a multiple regression model for the freeway measurements, we were able to explain 60–70% of the variability in concentrations of UFP, black carbon, nitric oxide, and PM-PAH using measures of diesel truck density and hour of day (as an indicator of wind speed). Freeway concentrations of these pollutants were also well correlated with readily available annual average daily truck counts, potentially allowing improved population exposure estimates for epidemiology studies. Based on these roadway measurements and average driving time, it appears that 33–45% of total UFP exposure for Los Angeles residents occurs due to time spent traveling in vehicles.
Keywords: In-vehicle exposures; Roadway concentrations; Diesel emissions; Nanoparticles
Long-term changes in emissions of nitrogen oxides and particulate matter from on-road gasoline and diesel vehicles by George A. Ban-Weiss; John P. McLaughlin; Robert A. Harley; Melissa M. Lunden; Thomas W. Kirchstetter; Andrew J. Kean; Anthony W. Strawa; Eric D. Stevenson; Gary R. Kendall (pp. 220-232).
Gas- and particle-phase pollutants were measured separately for (a) light-duty (LD) vehicles and (b) medium-duty (MD) and heavy-duty (HD) diesel trucks. Measurements were made during summer 2006 at the Caldecott Tunnel in the San Francisco Bay area as part of a continuing campaign to track changes in vehicle emissions over time. When normalized to fuel consumption, NO x emission factors were found to be 3.0±0.2 and 40±3gkg−1 for LD vehicles and MD/HD diesel trucks, respectively. Corresponding particulate matter (PM2.5) emission factors were 0.07±0.02 and 1.4±0.3gkg−1. The ratio of particulate black carbon to organic mass (BC/OM) for LD vehicles was 0.71±0.15. For diesel trucks, BC/OM was 2±1, indicating that PM2.5 was dominated by BC. Results from 2006 are compared to similar measurements made at the same site in 1997. For LD vehicles, NO x and PM2.5 emission factors decreased by 67±3% and 36±17%, respectively. Corresponding decreases for diesel trucks were 30±9% for NO x and 48±12% for PM2.5. The ratio of HD to LD emission factor for NO x increased from 6±1 to 13±1 between 1997 and 2006, which indicates an increase in the relative importance of diesel trucks as a source of NO x emissions. The absorption, scattering, and extinction cross-section emission factors parameters relevant to climate change and atmospheric visibility, were an order of magnitude higher for diesel trucks than LD vehicles. Single-scattering albedo, measured at λ=675nm, was 0.31±0.06 and 0.20±0.05 for LD vehicle and diesel truck PM emissions, respectively.
Keywords: Motor vehicles; Tunnel study; Aerosol optical properties; Nitrogen oxides; Exhaust particulate matter
Evaluation and intercomparison of meteorological predictions by five MM5-PBL parameterizations in combination with three land-surface models by Zhiwei Han; Hiromasa Ueda; Junling An (pp. 233-249).
In this study, MM5 predictions with five PBL parameterizations in combination with three land-surface models (LSMs) are intercompared and evaluated by using a wide variety of observations derived from WMO routine surface weather stations, TRACE-P aircraft experiments, intense radiosonde soundings and satellite measurements. Six scenarios with various PBL schemes and LSMs are designed to investigate the similarities and differences in model predictions. For near-surface variables, all scenarios yield good correlation between prediction and observation for 2m-temperature (T2) and 2m-water vapor mixing ratio (Q2), and relatively poor ones for wind fields. On average, T2 was consistently underpredicted by all scenarios, whereas Q2 was overpredicted by five of the six scenarios. It is found that the application of Noah land-surface model instead of the five-layer soil model is able to enhance the prediction accuracy of Q2. For 10m-wind speed, the GSE scenario (Gayno–Seaman scheme with the five-layer soil model) produces somewhat smaller correlation, but better consistency in magnitude than those of the other scenarios. Model predictions are more consistent for upper air as a result of using FDDA reanalysis nudging and the reducing influence of underlying surface with altitude. All scenarios show the tendencies to underpredict temperature and to overpredict wind speed at altitudes <1km and to underpredict wind speed at altitudes >3km. The correlations for water vapor mixing ratio are much smaller at altitudes >3km than that in the boundary layer. The differences in predicted PBL height among scenarios are large. GSE scenario performs best for phase (correlation), whereas PCX scenario (Pleim–Chang scheme with Pleim–Xiu LSM) produces the best statistics for magnitude of PBL height. Diurnal variation of PBL height over the western Pacific region during the study period is characterized by the typical day and night cycling superimposed by occasional expansion associated with cold front passage. The scenarios similarly predict precipitation spatial variability, but the difference in absolute magnitude is comparatively large among them, even for the scenarios using the same LSM, suggesting the important impact of PBL turbulence parameterization on precipitation. All scenarios predict larger precipitation amount averaged over the entire domain with the exception of GSE scenario. The statistics for satellite estimates are better than those for model predictions, but satellite data tends to underpredict observation by a similar range to that of GSE scenario. In the study period, latent heat fluxes are about twice the sensible heat fluxes over the western Pacific region, with maximum being 300–600 and 100–300Wm−2, respectively. The differences in surface fluxes among scenarios are mainly determined by various LSMs rather than different PBL schemes applied.
Keywords: Planetary boundary layer parameterization; Land-surface model; Sensitivity simulation; Evaluation; Intercomparison; Mesoscale model MM5
Semi-continuous mass closure of the major components of fine particulate matter in Riverside, CA by Brett D. Grover; Norman L. Eatough; Woods R. Woolwine; Justin P. Cannon; Delbert J. Eatough; Russell W. Long (pp. 250-260).
The application of newly developed semi-continuous aerosol monitors allows for the measurement of all the major species of PM2.5 on a 1-h time basis. Temporal resolution of both non-volatile and semi-volatile species is possible. A suite of instruments to measure the major chemical species of PM2.5 allows for semi-continuous mass closure. A newly developed dual-oven Sunset carbon monitor is used to measure non-volatile organic carbon, semi-volatile organic carbon and elemental carbon. Inorganic species, including sulfate and nitrate, can be measured with an ion chromatograph based sampler. Comparison of the sum of the major chemical species in an urban aerosol with mass measured by an FDMS resulted in excellent agreement. Linear regression analysis resulted in a zero-intercept slope of 0.98±0.01 with an R2=0.86. One-hour temporal resolution of the major species of PM2.5 may reduce the uncertainty in receptor based source apportionment modeling, will allow for better forecasting of PM2.5 episodes, and may lead to increased understanding of related health effects.
Keywords: PM; 2.5; mass and components; Semi-volatile material; Closure
Chemical markers for sea salt in IMPROVE aerosol data by Warren H. White (pp. 261-274).
The Interagency Monitoring of PROtected Visual Environments (IMPROVE) network monitors chemically speciated fine-particle concentrations at about 170 rural or remote sites in the United States, including several in coastal settings. Sea salt is a major component of marine aerosols, and can have significant optical effects on both global and local scales. Sodium is the most commonly employed chemical marker for sea salt, but the ion is not a target of IMPROVE's routine chromatography and the element is poorly detected by IMPROVE's routine X-ray fluorescence analysis. This paper examines data from six coastal sites where sea salt is abundant, to identify more reliable signatures of fresh sea salt in routine IMPROVE data. The chloride ion measurement, by ion chromatography on a Nylon filter sampling behind a carbonate denuder, appears to represent the total concentration of this reactive species at the selected sites. It is shown to be a good predictor of conserved sea salt markers such as non-crustal strontium, calcium and potassium, as well as the portion of gravimetric mass not explained by terrestrial fractions. These conclusions may not extend to other locations where sea salt is a smaller and more aged fraction of the aerosol mix.
Keywords: Sea salt; IMPROVE network; Chloride; Depletion; Sodium; Accuracy
Correlation of nitrogen dioxide with other traffic pollutants near a major expressway by Bernardo Beckerman; Michael Jerrett; Jeffrey R Brook; Dave K Verma; Muhammad A Arain; Murray M Finkelstein (pp. 275-290).
This study addresses three objectives: (1) to assess the correlation of NO2 to other ambient pollutants measured with passive samplers; (2) to explore peak traffic particulate matter air pollution correlations with passively measured NO2; and (3) to pilot an advanced mobile air pollution laboratory to supply supplementary information on correlations between NO2 and other air pollutants.Active and passive monitoring was conducted at two transects perpendicular to an expressway with nearly 400,000 vehicles per day. NO2, NO x, O3, VOCs, fine-particles and ultrafine particles were measured at increasing distance away from the expressway. The measurement equipment included Ogawa, TraceAir and 3M organic vapor monitors (OVM-3500) passive samplers, and an array of active measurement equipment: Dust-Trak and P-Trak monitors, chemoluminescent analyzer, aethalometer, tapered element oscillating microbalance, Grimm condensation particle counter, and an Ionicon analytik proton transfer reaction mass spectrometer.Levels of NO2 were observed to decay with increasing distance from the expressway, declining to background levels by 300m. Moderate to high correlations were observed between passive NO2 measurements and passive NO x, O3 ( r∼0.60–0.86). The correlations with active PM measurements made with Dust-Trak and P-Trak monitors were in the range 0.64–0.78; correlations between NO2 and VOCs were more variable. Active measurements of NO2 and PM2.5, ultrafine particles, O3 and black carbon, had high correlations ( r∼0.7–0.96).The variability of many traffic-related pollutants around an expressway is characterized well by passive measurements of NO2. Further research is needed to assess whether these relationships hold in different traffic and land-use environments.
Keywords: Traffic; Air pollution; NO; 2; VOC; Fine particulate matter; Ultrafine particles; Toronto; Distance decay
N2O emission from the semi-arid ecosystem under mineral fertilizer (urea and superphosphate) and increased precipitation in northern China by Jinfeng Zhang; Xingguo Han (pp. 291-302).
Soil management and climate change affect N2O emission significantly. The semi-arid grassland in northern China is under strong anthropogenic disturbance (fertilization and land use) and toward a 30% increase in precipitation in future. To investigate their impacts on N2O emission, N2O fluxes were measured monthly in the grassland and abandoned cropland under mineral fertilizer (urea and superphosphate) and increased precipitation during the growing season. During the measured period, WFPS (water filled pore space) from all the treatments never exceeded 70%, suggesting that nitrification was the predominant source of N2O for all the treatments. Increased precipitation induced an additional growing season emission of 0.28–0.30kgN2O-Nha−1y−1. N2O emission increased linearly with nitrogen application rate and emission factors (EFs) for grassland and abandoned cropland averaged 0.35% and 0.52%, respectively. Superphosphate addition induced N2O emission from abandoned cropland ( P<0.05), but had no significant effect in the grassland ( P>0.05). Despite of substantial differences in soil properties, N2O emissions were not significantly different between the grassland and abandoned cropland ( P>0.05). Increased precipitation and nitrogen application at 15gNm−2y−1 across the grassland and abandoned cropland of northern China will increase the growing season emissions of 71.4–76.5 and 139.23GgN2O-N into atmosphere annually. These increased emissions are about 40% and 75% of the annual emission of 186.15GgN2O-N from untreated soils, respectively. Therefore, in the temperate semi-arid ecosystem, abandoned cropland does not constitute a potent source for increasing N2O while the effect of nitrogen fertilization and increased precipitation cannot be neglected from the regional or national emission.
Keywords: Nitrous oxide; Precipitation; Nitrogen; Phosphorus; Grassland; Abandoned
Determination of ambient gas-particle partitioning constants of non-polar and polar organic compounds using inverse gas chromatography by Hans Peter H. Arp; R.P. René P. Schwarzenbach; K.-U. Kai-Uwe Goss (pp. 303-312).
Gas-particle equilibrium partition coefficients for organic compounds,K ip, are traditionally determined using sample-and-extract methods, in which particles and the surrounding air are simultaneously sampled and concentrations are determined from extracts. Though these techniques are necessary for determining actual ambient concentrations, they have several shortcomings when they are used to gain insight on the sorption properties of ambient particles. Some examples are that (i) the role of relative humidity and temperature are difficult to account for due to fluctuating conditions, (ii) only compounds that are present in ambient air can be studied, and (iii) extracts themselves do not directly indicate if particle-bound compounds are in equilibrium with the air phase or not. An alternative approach that could overcome these shortcomings is inverse gas chromatography (IGC). In this work, we developed an IGC method that uses particle-loaded fiber filters as a stationary phase. The measured retention of analytes injected into the IGC system is a direct measure of the collected particle's sorption behavior. A validation study that used particles with known sorption properties indicates that this approach gives reliableK ip values for a wide variety of compounds. Further, ambient particles from a suburban and urban location were found to be stable over time and to exhibit equilibrium sorption in the IGC, showing that this method is suitable for studying ambient particles. The IGC method presented here is a promising new tool for gaining deeper insights into the gas-particle partitioning behavior of polar and non-polar organic compounds.
Keywords: Ambient; Gas-particle partitioning; Fiber filters; IGC
Effects of potassium nitrate on the solid phase transitions of ammonium nitrate particles by Hong Bo Wu; Chak K. Chan (pp. 313-322).
Ammonium nitrate (NH4NO3) is a common constituent of atmospheric particulate pollutants. It exists in five stable polymorphic forms, designated as phases V, IV, III, II and I, below its melting point of 170°C. In atmospheric research, very little attention has been paid to the solid phase transitions of NH4NO3 because phase IV NH4NO3 particles are stable over a wide range of tropospheric temperatures. Potassium nitrate (KNO3) is often found to co-exist with NH4NO3 in atmospheric aerosols, and it can change the phase transition behaviors of solid NH4NO3 particles. In this study, we investigated the effects of KNO3 on the solid phase transitions of NH4NO3 particles using in situ microscopic Raman spectroscopy. Both the transition path and transition temperature of NH4NO3 single particles (40–700μm) depend on the KNO3 mass percentage and the particle size. With the addition of KNO3, the IV→II transition, which appears at 52°C for pure NH4NO3 particles, is replaced by the IV→III transition. The KNO3 mass percentage required for this change in transition path increases with decreasing particle size and the transition temperature decreases with increasing KNO3 mass percentage. At a relatively high mass percentage of KNO3 (⩾7.4wt%), the KNO3/NH4NO3 mixed particles undergo the IV→III transition under ambient temperatures, or even crystallize directly in phase III from droplets with a further increase in the mass percentage of KNO3. Submicron KNO3/NH4NO3 particles crystallize to phase IV at low KNO3 mass percentages (⩽5.7wt%) but to phase III at higher KNO3 mass percentages (⩾7.4wt%). These results suggest that atmospheric solid NH4NO3 particles may exist in phase III and the phase transitions should not be ignored in atmospheric chemical models.
Keywords: Ammonium nitrate; Potassium nitrate; Phase transition; Polymorphs; Raman spectroscopy
Modelling the impact of elevated primary NO2 and HONO emissions on regional scale oxidant formation in the UK by M.E. Jenkin; S.R. Utembe; R.G. Derwent (pp. 323-336).
Recent increases in the fractional contribution of NO2 to NO x emissions from the road transport sector in Europe are well documented in the literature. A photochemical trajectory model has been used to simulate the impact of increasing the NO2 fraction on the chemical evolution of air masses arriving at the TORCH field campaign site in the southern UK during late July and August 2003, a period which included a widespread photochemical pollution episode associated with a heat-wave. The impact of partial emissions of NO x in the form of nitrous acid (HONO) has also been considered. The model incorporates emissions of NO x, CO, SO2, methane and a detailed speciation of non-methane volatile organic compounds (VOC), coupled with a comprehensive description of the chemistry of secondary pollutant formation. An increase in the fractional contribution of NO2 to NO x emissions from 0% to 30% (v/v) results in a 2.49ppb increase in the simulated campaign mean mixing ratio of oxidant (defined as the sum of O3 and NO2). This is almost exclusively in the form of O3, and represents a ca. 7% increase in the simulated campaign mean O3 mixing ratio. Consideration of 156 events, at 6-hourly resolution throughout the campaign period, indicates that oxidant increments during the heat-wave period are generally simulated to be greater than those for the remainder of the campaign, with a maximum increment of ca. 12ppb. The increases in oxidant mixing ratios are shown to derive from both the direct effect of increased NO2 input, and indirectly from the enhanced regional-scale chemical processing that this promotes. An illustrative increase in the fractional contribution of HONO to NO x emissions from 0% to 5% (v/v) results in increases in the simulated campaign mean mixing ratios of O3 and oxidant of 1.51 and 1.15ppb, respectively, with the smaller increment for oxidant reflecting a decrease in the NO2 mixing ratio resulting from a notably enhanced NO x oxidation rate. The oxidant increments during the heat-wave period are once again simulated to be greater than those for the remainder of the campaign, with a maximum increment of ca. 11ppb, which results exclusively from the enhanced regional-scale chemical processing that the HONO emissions promote. The impact of increased fractional NO2 and HONO emissions on the rate of oxidation of NO x to nitrate is also illustrated and discussed.
Keywords: Photochemical pollution; Primary pollutant; Secondary pollutant; Ozone; Ozone episode; Nitrogen oxides; Volatile organic compounds
An estimation of the global emission of methyl bromide from rapeseed ( Brassica napus) from 1961 to 2003 by M. Iqbal Mead; Iain R. White; Graham Nickless; Kuo-Ying Wang; Dudley E. Shallcross (pp. 337-345).
Gan et al. [Gan, J., Yates, S.R., Ohr, H.D., Sims, J.J., 1998. Production of methyl bromide by terrestrial higher plants. Geophysical Research Letters 25 (19), 3595–3598] have reported that plants of the family Brassicaceae take up bromide from soils and subsequently release methyl bromide (CH3Br) to the atmosphere deriving a significant emission from this source of about 7Gg(109g)yr−1. In this study, we determine a yearly global emission rate for CH3Br from one such species, rapeseed, from 1961 to 2003 using data on crop harvest index and growth rate in conjunction with global production data. This study suggests that CH3Br emissions from rapeseed have increased 10-fold from 1961 to 2003 and by a factor of 3–4 since 1980. It also suggests that the geographical distribution of emissions has also changed substantially in the last 40yr. The annual emission of CH3Br from mustard and cabbage is also estimated; whilst relative levels emitted from these species are less significant, as these crops are continually exploited for new applications CH3Br emissions are set to increase.
Keywords: CH; 3; Br; Rapeseed; Brassica; Ozone; Biosphere
Geochemical properties of airborne particulate matter (PM10) collected by automatic device and biomonitors in a Mediterranean urban environment by P. Adamo; S. Giordano; D. Naimo; R. Bargagli (pp. 346-357).
The mineralogy and geochemistry (major and trace elements) of particulate matter collected from 14 April to 29 May 2003 by automatic device (PM10) and entrapped by moss and lichen exposed in bags in a monitoring site of Naples urban area were studied with the aim to obtain useful information for risk assessment and control measures feasibility.PM10 concentrations were generally above the threshold values fixed by the 1999/30/EC directive. Constant and low intensity winds enhanced re-suspension of fine particles and dispersion of gaseous pollutants. PM10 samples contained trace elements in relatively lower amounts compared to literature reports from other Mediterranean monitoring sites. Significant correlations between Al, Ca, Cu, Fe, K, Mg and Mn indicated that soil dust largely contributed to the accumulation of fine particles on filters and exposed mosses and lichens. Highly significant correlations were also found between Ni and V, indicative of oil combustion processes, Fe, Cu and Cr, indicative of vehicle emissions and mechanical components abrasion, and Na and Mg, indicative of marine aerosols. Lead and Hg did not correlate significantly with any other element.Comparison of element EFs, calculated with respect to the composition of Naples surface soils, indicated higher contribution of soil dust to PM and moss chemical composition compared with lichens, which in turn, according with their better preserved vitality, intercepted/absorbed more efficiently anthropogenic particles and elements of metabolic interest.Crystalline and amorphous detrital components (quartz, calcite, feldspars, volcanic glass, mica, kaolinite and smectite) and sea-bearing salts phases (halite, gypsum, Mg–K sulphates, Mg–Ca carbonates) were the main minerals in PM10, along with silica fibers and tuff particles.
Keywords: PM; 10; composition; Geochemistry; Urban air; Naples; Automatic sampler; Biomonitors; SEM/EDS
Locating and quantifying the impact of local sources of air pollution by Ronald C. Henry (pp. 358-363).
A new hybrid receptor model is described, which uses 1-min observations of pollutant concentrations along with back trajectories to estimate the average concentration at the receptor given that air has passed over a nearby area. The points on each back trajectory are associated with the pollutant concentration when the trajectory arrives at the monitor. The average value of the pollutant at the monitor given that air has passed near a geographical point on a grid is calculated by nonparametric regression of the pollutant concentrations over all the back trajectories passing near the point for the period of interest. A method is given of apportioning the average pollutant concentrations to local sources in geographically distinct regions and is illustrated by application to 1-min sulfur dioxide data from Long Beach, CA for May, June, and July 2005. Limitations of the model are discussed.
Keywords: Air pollution; Data analysis; Receptor model; Nonparametric regression; Back trajectory; Los Angeles; Long beach
Spatial variation in vehicle-derived metal pollution identified by magnetic and elemental analysis of roadside tree leaves by B.A. Maher; C. Moore; J. Matzka (pp. 364-373).
Exposure to metal-rich particulate pollution is associated with adverse health outcomes. In particular, lead has recently been shown to be toxic in young children even at low levels previously considered ‘safe’. Lead poisoning from vehicle pollution has been addressed internationally by removal of leaded petrol but toxic blood lead levels in children continue to be reported in urban areas, the source suggested to be resuspended roadside soil, enriched in lead due to previous leaded fuel usage. Here, we use paired geochemical and magnetic analyses of natural biomonitors—kerbside tree leaves—and of air sample filters to examine contemporary sources of particulate pollution, and show that co-associated, fine (<1μm) lead- and iron-rich particles are emitted as vehicle-derived pollutants. Higher and strongly correlated lead, iron and magnetic remanence values were found closer to roads and on the road-proximal rather than road-distal sides of trees. Critically, highest pollutant values occurred on tree leaves next to uphill rather than downhill road lanes. The lead content of the leaf particulates was associated only with sub-micrometre, combustion-derived spherical particles. These results indicate that vehicle exhaust emissions, rather than resuspended soil dust, or tyre, brake or other vehicle wear are the major source of the lead, iron and magnetic loadings on roadside tree leaves. Analysis of leaves at different heights showed that leaf particulate lead and iron concentrations are highest at ∼0.3m (i.e. small child height) and at 1.5–2m (adult head height) above ground level; monitoring station collectors placed at 3m above the surface thus significantly under-estimate kerbside, near-surface lead concentrations. These results indicate that vulnerable groups, especially young children, continue to be exposed to fine, lead- and iron-rich, vehicle-derived particulates.
Keywords: Vehicle pollution; Magnetism; Lead pollution; Biomonitoring
Apportionment of sources of fine and coarse particles in four major Australian cities by positive matrix factorisation by Yiu-Chung Chan; David D. Cohen; Olga Hawas; Eduard Stelcer; Rod Simpson; Lyn Denison; Neil Wong; Mary Hodge; Eva Comino; Stewart Carswell (pp. 374-389).
In this study, 437 days of 6-daily, 24-h samples of PM2.5, PM2.5–10 and PM10 were collected over a 12-month period during 2003–2004 in Melbourne, Sydney, Brisbane and Adelaide. The elemental, ionic and polycyclic aromatic hydrocarbon composition of the particles were determined. Source apportionment was carried out by using the positive matrix factorisation software (PMF2). Eight factors were identified for the fine particle samples including ‘motor vehicles’, ‘industry’, ‘other combustion sources’, ‘ammonium sulphates’, ‘nitrates’, ‘marine aerosols’, ‘chloride depleted marine aerosols’ and ‘crustal/soil dust’. On average combustion sources, secondary nitrates/sulphates and natural origin dust contributed about 46%, 25% and 26% of the mass of the fine particle samples, respectively. ‘Crustal/soil dust’, ‘marine aerosols’, ‘nitrates’ and ‘road side dust’ were the four factors identified for the coarse particle samples. On average natural origin dust contributed about 76% of the mass of the coarse particle samples. The contributions of the sources to the sample mass basically reflect the emission source characteristics of the sites. Secondary sulphates and nitrates were found to spread out evenly within each city. The average contribution of secondary nitrates to fine particles was found to be rather uniform in different seasons, rather than higher in winter as found in other studies. This could be due to the low humidity conditions in winter in most of the Australian cities which made the partitioning of the particle phase less favourable in the NH4NO3 equilibrium system. A linear relationship was found between the average contribution of marine aerosols and the distance of the site from the bay side. Wind erosion was found associated with higher contribution of crustal dust on average and episodes of elevated concentration of coarse particles in spring and summer.
Keywords: PM; 2.5; PM; 2.5–10; Source apportionment; Positive matrix factorisation; PIXE; PAH
Impact of the transport of aerosols from the free troposphere towards the boundary layer on the air quality in the Paris area by Augustin Colette; Laurent Menut; Martial Haeffelin; Yohann Morille (pp. 390-402).
We propose a quantification of the downward transport of aerosols from the free troposphere (FT) to the planetary boundary layer (PBL). Aerosols are originally released at the surface as a consequence of anthropogenic activities, biomass burning, soil mobilization, etc. After being vertically transported into the FT, they are exposed to the long-range transport (LRT) and may subside to impact, in turn, surface air pollution in remote places. Using 5400h of routine Lidar observations conducted at the SIRTA observatory in the Paris area (France), we identified 154 free tropospheric aerosol layers continuously monitored during their downward transport into the local PBL. One of these events—associated to a Saharan dust outbreak—is thoroughly documented in a case study. And a climatological analysis of surface PM10 levels recorded at air quality monitoring stations allows the impact of FT to PBL transport of aerosols to be quantified. This source is found to be significant for 15 out of the 16 stations, with average PM10 concentrations 2.14μgm−3 (i.e. 12%) above climatological values after the injection of free tropospheric aerosols into the PBL.
Keywords: Aerosols; Air quality; Long-range transport; Free troposphere–boundary layer coupling; Lidar