Regional contributions to airborne particulate matter in central California during a severe pollution episode

The externally-mixed source-oriented UCD/CIT air quality model was applied to determine the significance of inter-regional transport for primary and secondary particulate matter (PM) in California's Central Valley during a severe wintertime PM pollution episode from December 15, 2000 to January 7, 2001. The gases and primary PM emitted from eight different geographical sub-regions were tracked separately in a model simulation that included transport, physical and chemical transformation and deposition processes. The model results directly predict the contribution that each sub-region makes to PM concentrations throughout the entire model domain. The boundary layer was relatively stagnant during the simulated 3-week air quality episode, and no consistent transport pattern for primary PM was predicted. Several significant inter-regional transport events were identified that each lasted a few days. Each of these inter-regional events was characterized by transport of gas-phase precursors of nitrate that combined with local emissions of ammonia to produce particulate nitrate. Nitrate already in the particle phase was not transported efficiently due to higher dry deposition rates for particles relative to gas-phase nitrogen oxides. The distinctive pattern of transport for nitrate precursors reflects the relatively long timescales required to convert NO_x emissions to nitrate during winter conditions characterized by low temperatures, weak photolysis rates, and low oxidant concentrations. The equilibrium partitioning of nitrate and ammonia to the particle phase is relatively fast once the nitrate has been produced. The most-likely transport distance for nitrate during the current episode varied from 130–140 km for the northern portion of the Central Valley to 50–60 km in the southern portion of the Central Valley. Sub-regions further south in the Valley have smaller transport distances because of slower wind speeds and the greater abundance of ammonia in these areas, leading to faster conversion of gas-phase reactive nitrogen into particulate nitrate, which has a higher dry deposition rate than the gas-phase species. The most-likely transport distance for primary organic compounds (OC) was found to be less than that for nitrate, varying from 50 to 60 km for the northern portion of the Valley to 20–30 km for southern portion of the Valley. Overall, 68% of the particulate nitrate formed in the most polluted sub-regions of the Central Valley originates from emissions in those same sub-regions. Local emissions controls should therefore provide an effective strategy to reduce airborne particulate matter concentrations to acceptable levels.     

Dilution and aerosol dynamics within a diesel car exhaust plume—CFD simulations of on-road measurement conditions

Vehicle particle emissions are studied extensively because of their health effects, contribution to ambient PM levels and possible impact on climate. The aim of this work was to obtain a better understanding of secondary particle formation and growth in a diluting vehicle exhaust plume using 3-d information of simulations together with measurements. Detailed coupled computational fluid dynamics (CFD) and aerosol dynamics simulations have been conducted for H₂SO₄–H₂O and soot particles based on measurements within a vehicle exhaust plume under real conditions on public roads.Turbulent diffusion of soot and nucleation particles is responsible for the measured decrease of number concentrations within the diesel car exhaust plume and decreases coagulation rates. Particle size distribution measurements at 0.45 and 0.9 m distance to the tailpipe indicate a consistent soot mode (particle diameter D_p∼50 nm) at variable operating conditions. Soot mode number concentrations reached up to 10¹³ m⁻³ depending on operating conditions and mixing.For nucleation particles the simulations showed a strong sensitivity to the spatial dilution pattern, related cooling and exhaust H₂SO_4(g). The highest simulated nucleation rates were about 0.05–0.1 m from the axis of the plume. The simulated particle number concentration pattern is in approximate accordance with measured concentrations, along the jet centreline and 0.45 and 0.9 m from the tailpipe. Although the test car was run with ultralow sulphur fuel, high nucleation particle (D_p⩽15 nm) concentrations (>10¹³ m⁻³) were measured under driving conditions of strong acceleration or the combination of high vehicle speed (>140 km h⁻¹) and high engine rotational speed (>3800 revolutions per minute (rpm)).Strong mixing and cooling caused rapid nucleation immediately behind the tailpipe, so that the highest particle number concentrations were recorded at a distance, x=0.45 m behind the tailpipe. The simulated growth of H₂SO₄–H₂O nucleation particles was unrealistically low compared with measurements. The possible role of low and semi-volatile organic components on the growth processes is discussed. Simulations for simplified H₂SO₄–H₂O–octane–gasoil aerosol resulted in sufficient growth of nucleation particles.     

Chemical composition of aerosols during a major biomass burning episode over northern Europe in spring 2006: Experimental and modelling assessments

The long-range transported smokes emitted by biomass burning had a strong impact on the PM_2.5 mass concentrations in Helsinki over the 12 days period in April and May 2006. To characterize aerosols during this period, the real-time measurements were done for PM_2.5, PM_2.5–10, common ions and black carbon. Moreover, the 24-h PM₁ filter samples were analysed for organic and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), ions and levoglucosan. The Finnish emergency and air quality modelling system SILAM was used for the forecast of the PM_2.5 concentration generated by biomass burning. According to the real-time PM_2.5 data, the investigated period was divided into four types of PM situations: episode 1 (EPI-1; 25–29 April), episode 2 (EPI-2; 1–5 May), episode 3 (EPI-3; 5–6 May) and a reference period (REF; 24 March–24 April). EPI-3 included a local warehouse fire and therefore it is discussed separately. The PM₁ mass concentrations of biomass burning tracers—levoglucosan, potassium and oxalate—increased during the two long-range transport episodes (EPI-1 and EPI-2). The most substantial difference between the episodes was exhibited by the sulphate concentration, which was 4.9 (±1.4) μg m⁻³ in EPI-2 but only 2.4 (±0.31) μg m⁻³ in EPI-1 being close to that of REF (1.8±0.54 μg m⁻³). The concentration of particulate organic matter in PM₁ was clearly higher during EPI-1 (11±3.3 μg m⁻³) and EPI-2 (9.7±4.0 μg m⁻³) than REF (1.3±0.45 μg m⁻³). The long-range transported smoke had only a minor impact on the WSOC-to-OC ratio. According to the model simulations, MODIS detected the fires that caused the first set of concentration peaks (EPI-1) and the local warehouse fire (EPI-3), but missed the second one (EPI-2) probably due to dense frontal clouds.     

Effects of soil dust episodes and mixed fuel sources on source apportionment of PM10 particles in Kuopio,Finland

A receptor modeling study was carried out in Kuopio, Finland, between January and April 1994. Near the center of town, the daily mean concentrations were measured for PM10, sulphur dioxide, carbon monoxide and Black Smoke. Elemental concentrations of PM10 samples for 38 days were analyzed by ICP-MS. The main sources and their contributions to the measured concentrations of PM10 particles were solved by receptor modeling using a factor analysis-multiple linear regression (FA-MLR) model. Because a dust episode was very strong during two sampling days, the FA analysis was strongly influenced by this episode and did not give main factors. The factor analysis, when the two episode days were omitted, gave credible factors related to the sources in the study area. The four major sources and their estimated contributions to the average PM10 concentration of 27.2 μg m^-3 were: soil and street dust 46–48%, heavy fuel oil burning 12–18%, traffic exhaust 10–14%, wood burning ca. 11% and unidentified sources 15–25%. However, during spring dust episode days, with maximum PM10 concentration of 150 μg m^-3, the main source of PM10 was soil.     

Fine,ultrafine and nanoparticle trace element compositions near a major freeway with a high heavy-duty diesel fraction

Trace elements and metals in the ultrafine (<0.18 μm) and accumulation (0.18–2.5 μm) particulate matter (PM) modes were measured during the winter season, next to a busy Southern California freeway with significant (∼20%) diesel traffic. Both ambient and concentrated size-segregated impactor samples were taken in order to collect enough mass for chemical analysis. Data at this location were compared to a site located 1 mile downwind of the freeway, which was reflective of urban background. The most abundant trace elements in the accumulation mode detected by inductively coupled plasma mass spectroscopy (ICPMS) were S (138 ng m⁻³), Na (129 ng m⁻³), and Fe (89 ng m⁻³) while S (35 ng m⁻³) and Fe (35 ng m⁻³) were the most abundant in the ultrafine mode. The concentrations of several trace elements, including Mg, Al, and Zn, and in particular Ca, Cu, and Pb, did not uniformly increase with size within fine PM, an indication that various roadway sources exist for these elements. Calculation of crustal enrichment factors for the two sites indicates that the freeway traffic contributed to enriched levels of ultrafine Cu, Ba, P and Fe and possibly Ca. The results of this study show that trace elements constitute a small fraction of PM mass in the nanoparticle size range, but these can and should be characterized due to their likely importance to human health.     

Demonstrating attainment in Atlanta using urban airshed model simulations: impact of boundary conditions and alternative forms of the NAAQS

Urban Airshed Model-Version IV (UAM-IV) simulations on 7–8 July, 1988 for the Atlanta, Georgia, nonattainment area are used to investigate how recent changes in the National Ambient Air Quality Standard (NAAQS) and changes in boundary concentrations may affect attempts to comply with the standard through local emissions reductions. According to model results, the recently promulgated 8 h NAAQS at a level of 0.08 ppmv will require larger emission reductions to comply with the standard than those that are necessary to comply with the previous 1 h/0.12 ppmv NAAQS. Regardless of the form of the NAAQS or the magnitude of the concentrations of O₃ and its precursors at the model domain boundary, UAM-IV simulations for Atlanta predict that NO_x (NO+NO₂) emission reductions are more effective than volatile organic compound reductions in mitigating O₃ pollution. Moreover, the simulations indicate that NO_x emission reductions greater than 60–75% would be required to demonstrate attainment under either form of the standard, even if boundary concentrations of O₃ and its precursors were substantially reduced. Further research is necessary to determine if this weak response to emission controls is truly representative of the real atmosphere, or is a result of the meteorological conditions specific to this episode, or is an artifact of the UAM-IV model or its inputs.     

The physical characteristics of sulfur aerosols

A review of the physical characteristics of sulfur-containing aerosols, with respect to size distribution of the physical distributions, sulfur distributions, distribution modal characteristics, nuclei formation rates, aerosol growth characteristics, and in situ measurement, has been made.Physical size distributions can be characterized well by a trimodal model consisting of three additive lognormal distributions.When atmospheric physical aerosol size distributions are characterized by the trimodal model, the following typical modal parameters are observed:1. Nuclei mode – geometric mean size by volume, DGV_n, from 0.015 to 0.04 μm. σ_gn=1.6, nucler mode volumes from 0.0005 over the remote oceans to 9 μm³ cm⁻³ on an urban freeway.2. Accumulation mode – geometric mean size by volume, DGV_a, from 0.15 to 0.5 μm, σ_ga=1.6–2.2 and mode volume concentrations from 1 for very clean marine or continental backgrounds to as high as 300 μm³ cm⁻³ under very polluted conditions in urban areas.3. Coarse particle mode – geometric mean size by volume, DGV_c, from 5 to 30 μm, σ_gn=2–3, and mode volume concentrations from 2 to 1000 μm³ cm⁻³.It has also been concluded that the fine particles (D_p<2 μm) are essentially independent in formation, transformation and removal from the coarse particles (D_p>2 μm).Modal characterization of impactor-measured sulfate size distributions from the literature shows that the sulfate is nearly all in the accumulation mode and has the same size distribution as the physical accumulation mode distribution.Average sulfate aerodynamic geometric mean dia. was found to be 0.48±0.1 μm (0.37±0.1 μm vol. dia.) and σ_g=2.00±0.29. Concentrations range from a low of about 0.04 μg m⁻³ over the remote oceans to over 8 μg m⁻³ under polluted conditions over the continents.Review of the data on nucleation in smog chambers and in the atmosphere suggests that when SO₂, is present, SO₂-to-aerosol conversion dominates the Aitken nuclei count and, indirectly, through coagulation and condensation, the accumulation mode size and concentration. There are indications that nucleation is ubiquitous in the atmosphere, ranging from values as low as 2 cm⁻³ h⁻¹ over the clean remote oceans to a high of 6×10⁶ cm⁻³ h⁻¹ in a power plant plume under sunny conditions.There is considerable theoretical and experimental evidence that even if most of the mass for the condensational growth of the accumulation mode comes from hydrocarbon conversion, sulfur conversion provides most of the nuclei.     

Modeling air quality during the California Regional PM10/PM2.5 Air Quality Study (CPRAQS) using the UCD/CIT source-oriented air quality model – Part III. Regional source apportionment of secondary and total airborne particulate matter

A comprehensive air quality modeling project was carried out to simulate regional source contributions to secondary and total (=primary + secondary) airborne particle concentrations in California's Central Valley. A three-week stagnation episode lasting from December 15, 2000 to January 7, 2001, was chosen for study using the air quality and meteorological data collected during the California Regional PM₁₀/PM_2.5 Air Quality Study (CRPAQS). The UCD/CIT mechanistic air quality model was used with explicit decomposition of the gas phase reaction chemistry to track source contributions to secondary PM. Inert artificial tracers were used with an internal mixture representation to track source contributions to primary PM. Both primary and secondary source apportionment calculations were performed for 15 size fractions ranging from 0.01 to 10 μm particle diameters. Primary and secondary source contributions were resolved for fugitive dust, road dust, diesel engines, catalyst equipped gasoline engines, non-catalyst equipped gasoline engines, wood burning, food cooking, high sulfur fuel combustion, and other anthropogenic sources.Diesel engines were identified as the largest source of secondary nitrate in central California during the study episode, accounting for approximately 40% of the total PM_2.5 nitrate. Catalyst equipped gasoline engines were also significant, contributing approximately 20% of the total secondary PM_2.5 nitrate. Agricultural sources were the dominant source of secondary ammonium ion. Sharp gradients of PM concentrations were predicted around major urban areas. The relative source contributions to PM_2.5 from each source category in urban areas differ from those in rural areas, due to the dominance of primary OC in urban locations and secondary nitrate in the rural areas. The source contributions to ultra-fine particle mass PM_0.1 also show clear urban/rural differences. Wood smoke was found to be the major source of PM_0.1 in urban areas while motor vehicle sources were the major contributor of PM_0.1 in rural areas, reflecting the influence from two major highways that transect the Valley.     

Characteristics of vertical profiles and sources of PM2.5, PM10 and carbonaceous species in Beijing

In August 2003 during the anticipated month of the 2008 Beijing Summer Olympic Games, we simultaneously collected PM₁₀ and PM_2.5 samples at 8, 100, 200 and 325 m heights up a meteorological tower and in an urban and a suburban site in Beijing. The samples were analysed for organic carbon (OC) and elemental carbon (EC) contents. Particulate matter (PM) and carbonaceous species pollution in the Beijing region were serious and widespread with 86% of PM_2.5 samples exceeding the daily National Ambient Air Quality Standard of the USA (65 μg m⁻³) and the overall daily average PM₁₀ concentrations of the three surface sites exceeding the Class II National Air Quality Standard of China (150 μg m⁻³). The maximum daily PM_2.5 and PM₁₀ concentrations reached 178.7 and 368.1 μg m⁻³, respectively, while those of OC and EC reached 22.2 and 9.1 μg m⁻³ in PM_2.5 and 30.0 and 13.0 μg m⁻³ in PM₁₀, respectively. PM, especially PM_2.5, OC and EC showed complex vertical distributions and distinct layered structures up the meteorological tower with elevated levels extending to the 100, 200 and 300 m heights. Meteorological evidence suggested that there exist fine atmospheric layers over urban Beijing. These layers were featured by strong temperature inversions close to the surface (<50 m) and more stable conditions aloft. They enhanced the accumulation of pollutants and probably caused the complex vertical distributions of PM and carbonaceous species over urban Beijing. The built-up of PM was accompanied by transport of industrial emissions from the southwest direction of the city. Emissions from road traffic and construction activities as well as secondary organic carbon (SOC) are important sources of PM. High OC/EC ratios (range of 1.8–5.1 for PM_2.5 and 2.0–4.3 for PM₁₀) were found, especially in the higher levels of the meteorological tower suggesting there were substantial productions of SOC in summer Beijing. SOC is estimated to account for at least 33.8% and 28.1% of OC in PM_2.5 and PM₁₀, respectively, with higher percentages at the higher levels of the tower.     

Production and removal of aerosol in a polluted fog layer: model evaluation and fog effect on PM

A radiation fog physics, gas- and aqueous-phase chemistry model is evaluated against measurements in three sites in the San Joaquin Valley of California (SJV) during the winter of 1995. The measurements include for the first time vertically resolved fog chemical composition measurements. Overall the model is successful in reproducing the fog dynamics as well as the temporal and spatial variability of the fog composition (pH, sulfate, nitrate, and ammonium concentrations) in the area. Sulfate production in the fog layer is relatively slow (1–4 μg m⁻³ per fog episode) compared to the episodes in the early 1980s because of the low SO₂ concentrations in the area and the lack of oxidants inside the fog layer. Sulfate production inside the fog layer is limited by the availability of oxidants in the urban areas of the valley and by SO₂ in the more remote areas. Nitrate is produced in the rural areas of the valley by the heterogeneous reaction of N₂O₅ on fog droplets, but this reaction is of secondary importance for the more polluted urban areas. The gas-phase production of HNO₃ during the daytime is sufficient to balance the nitrate removed during the nighttime fog episodes. Entrainment of air from the layer above the fog provides another source of reactants for the fog layer. Wet removal is one of most important processes inside the fog layer in SJV. We estimate based on the three episodes investigated during IMS95 that a typical fog episode removes 500–2000 μg m⁻² of sulfate, 2500–6500 μg m⁻² of nitrate, and 2000–3500 μg m⁻² of ammonium. For the winter SJV valley the net fog effect corresponds to reductions in ground ambient concentrations of 0.05–0.2 μg m⁻³ for sulfate, 3–6 μg m⁻³ for total nitrate, and 1–3 μg m⁻³ for total ammonium.     

Spatial representativeness and scales of transport during the 1995 integrated monitoring study in California's San Joaquin Valley

Daily measurements of PM₁₀ mass and chemical composition were obtained for the period 1–14 November 1995 from a saturation monitoring network around Corcoran, and for varying portions of the period 9 December 1995–6 January 1996 for three networks around Bakersfield, Fresno, and the Kern Wildlife Refuge, in California's San Joaquin Valley. During the latter period, monitoring locations were also operated along the boundaries and across the width of the Valley. The Corcoran, Bakersfield, and Fresno networks consisted of 12–25 sites, located in areas of about 300–800 km². Each network also included one core site, situated at a pre-existing monitoring location, with more extensive and more temporally resolved measurements. Mean concentrations of PM₁₀ and its constituents varied from core-site concentrations by 20% or more over distances ranging from 4 to 14 km. Local source influences were observed to affect sites over distances of less than 1 km, but primary particulate emissions were also transported over urban or sub-regional scales of approximately 10–30 km during the winter and greater than 30 km in the fall. During winter, gas-phase precursors of secondary aerosol may have been transported over distances of approximately 100 km, but little evidence was found for transport of primary PM on such a scale.     

Concentrations of ethene and formaldehyde at a valley and a mountain top site in the Austrian Alps

Ethene and formaldehyde concentrations were measured at two forest sites (valley, mountain top) in the Achen Valley (Austrian Alps, Tyrol) during three campaigns in 2001 and 2002. During the June/July campaign mean concentrations of ethene were above 9 ppb_v at the valley station and 1.9 ppb_v at the mountain top site; lower ethene concentrations were observed at the valley site during the April (1.4 ppb_v) and the May campaign (3.1 ppb_v). As 9 ppb_v is the effect-related limiting value (= concentration of pollutants in the atmosphere, above which direct adverse effects on receptors may occur according to the present knowledge) of the Austrian Academy of Sciences for plants (1997) we found that ethene levels in valleys may come close to the limiting value. Formaldehyde concentrations were far below the effect-related limiting value of 16 ppb_v. On the basis of the actual knowledge, ethene could be relevant as a phytotoxic component in alpine valleys.     

Roadside measurements of fine and ultrafine particles at a major road north of Gothenburg

Particle measurements were conducted at a road site 15 km north of the city of Gothenburg for 3 weeks in June 2000. The size distribution between 10 and 368 nm was measured continuously by using a differential mobility particle sizer (DMPS) system. PM_2.5 was sampled on a daily basis with subsequent elemental analysis using EDXRF-spectroscopy. The road is a straight four-lane road with a speed limit of 90 kph. The road passing the site is flat with no elevations where the vehicles run on a steady workload and with constant speed. The traffic intensity is about 20,000 cars per workday and 13,000 vehicles per day during weekends. The diesel fuel used in Sweden is low in sulphur content (<10 ppm) and therefore the diesel vehicles passing the site contribute less to particle emissions in comparison with other studies. A correlation between PM_2.5 and accumulation mode particles (100–368 nm) was observed. However, no significant correlation was found between number concentrations of ultrafine particles (10–100 nm) and PM_2.5 or the accumulation mode number concentration. The particle distribution between 10 and 368 nm showed great dependency on wind speed and wind direction, where the wind speed was the dominant factor for ultrafine (10–100 nm) particle concentrations. The difference in traffic intensity between workday and weekend together with wind data made it possible to single out the traffic contribution to particle emissions and measure the size distribution. The results presented in combination with previous studies show that both PM_2.5 and the mass of accumulation mode particles are bad estimates for ultrafine particles.     

Ozone uptake by citrus trees exposed to a range of ozone concentrations

The Citrus genus includes a large number of species and varieties widely cultivated in the Central Valley of California and in many other countries having similar Mediterranean climates. In the summer, orchards in California experience high levels of tropospheric ozone, formed by reactions of volatile organic compounds (VOC) with oxides of nitrogen (NO_x). Citrus trees may improve air quality in the orchard environment by taking up ozone through stomatal and non-stomatal mechanisms, but they may ultimately be detrimental to regional air quality by emitting biogenic VOC (BVOC) that oxidize to form ozone and secondary organic aerosol downwind of the site of emission. BVOC also play a key role in removing ozone through gas-phase chemical reactions in the intercellular spaces of the leaves and in ambient air outside the plants. Ozone is known to oxidize leaf tissues after entering stomata, resulting in decreased carbon assimilation and crop yield. To characterize ozone deposition and BVOC emissions for lemon (Citrus limon), mandarin (Citrus reticulata), and orange (Citrus sinensis), we designed branch enclosures that allowed direct measurement of fluxes under different physiological conditions in a controlled greenhouse environment. Average ozone uptake was up to 11 nmol s^?1 m^?2 of leaf. At low concentrations of ozone (40 ppb), measured ozone deposition was higher than expected ozone deposition modeled on the basis of stomatal aperture and ozone concentration. Our results were in better agreement with modeled values when we included non-stomatal ozone loss by reaction with gas-phase BVOC emitted from the citrus plants. At high ozone concentrations (160 ppb), the measured ozone deposition was lower than modeled, and we speculate that this indicates ozone accumulation in the leaf mesophyll.     

Size distributions and formation of dicarboxylic acids in atmospheric particles

The PM2.5 concentrations and the size distributions of dicarboxylic acids in Hong Kong were studied. Eleven sets of daily PM2.5 samples were obtained at a downtown sampling site during the period of 5–16 December 2000 using an R&P speciation PM2.5 sampler. About 6–12% of the total oxalic acid was found in the gas phase in some samples. A good correlation between succinate and sulfate (R²=0.88) and a moderate correlation between oxalate and sulfate (R²=0.74) were found. Sampling artifacts of oxalate, malonate and succinate were found to be negligible. A total of 18 sets of 48–96 h size distribution data on dicarboxylic acids, sulfate, nitrate and sodium at an urban site and a rural site from June 2000 to May 2001 were obtained using a Micro-Orifice Uniform Deposit Impactor. Data from both sites show similar size distribution characteristics of the dicarboxylic acids. The condensation mode of oxalate was usually observed at 0.177–0.32 μm. The location of the peak of the droplet mode of oxalate was associated with that of sulfate. When the peak of sulfate in the droplet mode appeared at 0.32–0.54 μm, the peak of oxalate sometimes appeared at 0.32–0.54 μm and sometimes shifted to 0.54–1.0 μm. When the peak of sulfate in the droplet mode appeared at 0.54–1.0 μm, the peak of oxalate sometimes appeared at 0.54–1.0 μm and sometimes shifted to 1.0–1.8 μm. Oxalate, succinate and sulfate found in the droplet mode were attributed to in-cloud formation. The slight shift of the oxalate peak from 0.32–0.54 to 0.54–1.0 μm or from 0.54–1.0 to 1.0–1.8 μm was ascribed to minor oxalate evaporation after in-cloud formation. The maximum peak of malonate sometimes appeared in the droplet mode and sometimes appeared at 3.1–6.2 μm. The formation of malonate is associated to the reactions between sea salt and malonic acid.     

Middle and lower troposphere aerosol characteristics and ozone concentrations over northwestern Greece during STAAARTE 1997

Accumulation aerosol particle distributions were measured on 14 June 1997 during two research flights over northwestern Greece, including the greater Thessaloniki area (GTA). At flight altitudes of about 5000 m (<550 mb), accumulation mode number particle size distributions appeared to be unimodal with a maximum in the first bin of the measured number size distribution with a mid-point of 0.11 μm. At lower altitudes and over the GTA, accumulation mode particle size distributions were bimodal with a first mode peak at 0.125 μm and a second mode peak at 0.275 μm. The second mode was more pronounced in areas of higher relative humidity, thus indicating the presence of deliquescent aerosols, but also in areas where high O₃ concentrations were measured. Ozone concentrations ranged between 25 and 60 ppb at high altitudes east of GTA and between 50 and 110 ppb over the city of Thessaloniki with the maximum measured at an altitude of about 500 m. This is consistent with the local topographical and meteorological conditions, mainly due to the nocturnal inversion and the development of local circulation flows (land and sea breeze) over the city.     

Particulate matter in the indoor air of classrooms—exploratory results from Munich and surrounding area

Numerous epidemiological studies have demonstrated the association between particle mass (PM) concentration in outside air and the occurrence of health related problems and/or diseases. However, much less is known about indoor PM concentrations and associated health risks. In particular, data are needed on air quality in schools, since children are assumed to be more vulnerable to health hazards and spend a large part of their time in classrooms.On this background, we evaluated indoor air quality in 64 schools in the city of Munich and a neighbouring district outside the city boundary. In winter 2004–2005 in 92 classrooms, and in summer 2005 in 75 classrooms, data on indoor air climate parameters (temperature, relative humidity), carbon dioxide (CO₂) and various dust particle fractions (PM₁₀, PM_2.5) were collected; for the latter both gravimetrical and continuous measurements by laser aerosol spectrometer (LAS) were implemented. In the summer period, the particle number concentration (PNC), was determined using a scanning mobility particle sizer (SMPS). Additionally, data on room and building characteristics were collected by use of a standardized form. Only data collected during teaching hours were considered in analysis. For continuously measured parameters the daily median was used to describe the exposure level in a classroom.The median indoor CO₂ concentration in a classroom was 1603 ppm in winter and 405 ppm in summer. With LAS in winter, median PM concentrations of 19.8 μg m⁻³ (PM_2.5) and 91.5 μg m⁻³ (PM₁₀) were observed, in summer PM concentrations were significantly reduced (median PM_2.5=12.7 μg m⁻³, median PM₁₀=64.9 μg m⁻³). PM_2.5 concentrations determined by the gravimetric method were in general higher (median in winter: 36.7 μg m⁻³, median in summer: 20.2 μg m⁻³) but correlated strongly with the LAS-measured results. In explorative analysis, we identified a significant increase of LAS-measured PM_2.5 by 1.7 μg m⁻³ per increase in humidity by 10%, by 0.5 μg m⁻³ per increase in CO₂ indoor concentration by 100 ppm, and a decrease by 2.8 μg m⁻³ in 5–7th grade classes and by 7.3 μg m⁻³ in class 8–11 compared to 1–4th class. During the winter period, the associations were stronger regarding class level, reverse regarding humidity (a decrease by 6.4 μg m⁻³ per increase in 10% humidity) and absent regarding CO₂ indoor concentration. The median PNC measured in 36 classrooms ranged between 2622 and 12,145 particles cm⁻³ (median: 5660 particles cm⁻³).The results clearly show that exposure to particulate matter in school is high. The increased PM concentrations in winter and their correlation with high CO₂ concentrations indicate that inadequate ventilation plays a major role in the establishment of poor indoor air quality. Additionally, the increased PM concentration in low level classes and in rooms with high number of pupils suggest that the physical activity of pupils, which is assumed to be more pronounced in younger children, contributes to a constant process of resuspension of sedimented particles. Further investigations are necessary to increase knowledge on predictors of PM concentration, to assess the toxic potential of indoor particles and to develop and test strategies how to ensure improved indoor air quality in schools.     

Air quality in Brunei Darussalam during the 1998 haze episode

Regional haze from biomass burning in SE Asia is a recurring air pollution phenomenon with a potential impact on the health of several hundred million people. Air quality data in Brunei Darussalam during the 1998 haze episode revealed that only particulate matter is a significant pollutant. The WHO guideline of 70 μg m⁻³ for PM₁₀ (24 h average) was exceeded on 54 days during the haze episode which lasted from 1 February to 30 April 1998. Concentrations of SO₂, NO₂, and O₃ were all below WHO guidelines and the 8 h guideline for CO was exceeded on only seven occasions. Average daily PM₁₀ concentrations were below 450 μg m⁻³ but concentrations greater than 600 μg m⁻³ persisted for several hours at a time and total exposure to such high concentrations could add up to several days over the course of a haze episode. Airborne particles exhibited diurnal variation, typically rising through the night to very high levels in the early morning and thereafter decreasing due largely to meteorological factors. The pollutant standards index (PSI), widely used to report urban air quality, may not be suitable for haze from forest fires as it does not take into account short-term exposure to extremely high particle concentrations of up to 1 mg m⁻³.     

Surface ozone and NOx concentrations at a high altitude Mediterranean site,Greece

Ozone was measured in six- and NO_x in five sampling periods in 1996–97, mostly during summer, at a 1070 m altitude site in northern Peloponnese. Mean values in each sampling period ranged from 43–48 ppb exceeding the European Union 24 h plant protection standard. The background ozone concentration of 43 ppb derived from the correlation of ozone with NO^′_x also exceeded the EU plant protection standard. Ozone exhibited maxima in the afternoon and minima during the night; in certain 24–48 h periods, however, the ozone concentrations remained practically constant; in these short periods air mass back trajectories indicated air masses which originated in north Africa. NO^′_x concentrations had maximum of 24 h around noon. Their mean concentrations ranged from 0.5–0.7 ppb, smaller than respective concentrations in north-central Europe.     

Quantification on source/receptor relationship of primary pollutants and secondary aerosols from ground sources—Part I. Theory

A new algorithm has been derived for trajectory models to determine the transfer coefficient of each source along or adjacent to a trajectory and to calculate the concentrations of SO₂, NO_x, sulfate, nitrate, fine particulate matter (PM) and coarse PM at a receptor. The transfer coefficient t_f (s m⁻¹) is defined to be the ratio between the contributed concentration ΔC (μg m⁻³) to the receptor from a ground source and the emission rate of the source q (μg m⁻² s⁻¹) at a grid, i.e. t_f≡ΔC/q. The model is developed by combining with a backward trajectory scheme and a circuit-type's parameterization. First, the transfer coefficients of grids along or adjacent a back-trajectory are calculated. Then, the contributed concentration of each emission grid is determined by multiplying its emission rate with the transfer coefficient of the grid. Finally, the concentration at the receptor is determined by the summation of all the contributed concentrations within the domain of simulation.