Atmospheric Environment (v.41, #4)

Emission inventory for the road transport sector in Sardinia (Italy) by R. Bellasio; R. Bianconi; G. Corda; P. Cucca (677-691).
Atmospheric emission inventories are important tools for studying air quality and to set up possible remediation plans in areas characterised by nonattainment of the limit values established by legislation. In industrialised countries a considerable fraction of the emissions is due to road traffic, in particular in urban areas. For this reason emissions from road traffic must be estimated as accurately as possible, a task that can be performed, for the European vehicle fleet, thanks to the availability of the COPERT III methodology. This methodology is powerful and accurate, even if its algorithms can be difficult to apply in a regional emission inventory; moreover the collection of the necessary input data requires a lot of resources and time. This paper describes the road traffic emission inventory estimated for Region Sardinia (Italy) with a bottom-up approach. The estimation has been done by means of a software tool (EMITRA—EMIssions from road TRAnsport) which implements the COPERT III methodology. The resulting emission inventory has been compared against another emission inventory for Sardinia and against emission inventories for other Italian regions, to evaluate its reliability.
Keywords: COPERT III; CORINAIR; Emission inventory; Air pollution; Traffic; Sardinia;

This paper examines the role of meteorology in linking near surface emissions of particulate matter and associated ambient concentrations in urban areas. The examination is conducted with two models: a steady state model based on urban dispersion models developed earlier, and an unsteady state model that accounts for time varying meteorological and emission inputs. After conducting sensitivity studies with the models, they are applied in Pune, India to (a) check consistency between estimates of surface emissions of particulate matter (with aerodynamic diameters of less than 10 μ m, referred to as PM 10 ) and observed ambient concentrations and (b) identify the variables that govern air quality. Results from the modeling exercise indicate that (1) nighttime meteorology governs both hourly as well as 24 h averaged concentrations and (2) because the wind speeds in urban areas are typically low, concentration estimates from the steady state model differ substantially from those of the unsteady state model during the nighttime hours both in magnitude and in timing of the peaks; however, the difference between the 24 h averaged concentrations from the two models is less than 5% for the cases considered here. Because our understanding of nighttime meteorology in urban areas is limited, there is a need for experimental programs to relate the diurnal variation of concentrations with associated meteorology, especially during the night.
Keywords: Urban pollution; Dispersion models; Nighttime boundary layer; Particulate concentrations; PM 10 ; Pune; India;

Assessing the influence of abatement efforts and other human activities on ozone levels is complicated by the atmosphere's changeable nature. Two statistical methods, the dynamic linear model (DLM) and the generalized additive model (GAM), are used to estimate ozone trends in the eastern United States and to adjust for meteorological effects. The techniques and resulting estimates are compared and contrasted for four monitoring locations chosen through principal components analysis to represent regional patterns of ozone concentrations. After adjustment for meteorological influence, overall downward trends are evident at all four locations from 1997 to 2004. The results indicate that the two methods’ estimates of ozone changes agree well. When such estimates are needed quickly, or when many similar, but separate analyses are required, the ease of implementation and relative simplicity of the GAMs are attractive. The DLMs are much more flexible, readily addressing such issues as autocorrelation, the presence of missing values, and estimation of long-term trends or cyclical patterns. Implementation of DLMs, however, is typically more difficult, and especially in the absence of an experienced practitioner, they may be better reserved for in-depth analyses.
Keywords: Ozone trends; Dynamic linear model; Generalized additive model; Meteorological adjustment; Principal components analysis;

Vertical profiles of ultrafine to supermicron particles measured by aircraft over Osaka metropolitan area in Japan by Shuichi Hasegawa; Shinji Wakamatsu; Toshimasa Ohara; Yasuyuki Itano; Katsumi Saitoh; Masamitsu Hayasaki; Shinji Kobayashi (717-729).
Intensive aircraft- and ground-based measurements of ultrafine to supermicron particles in the Osaka metropolitan area, Japan, were carried out on 17–19 March 2003, in order to investigate vertical profiles of size-resolved particles in the urban atmosphere. Differently sized particles were observed at different altitudes on 19 March. Relatively higher concentrations of ultrafine particles (31 nm) and submicron particles (0.3–0.5 μm) were measured (100–200 cm−3) at altitudes of 300 and 600 m, whereas supermicron particles (2–5 μm) were present (300–600 cm−3) at higher altitudes (1300 m in the morning and 2200 m in the afternoon). The chemical composition analysis showed that supermicron particles evidently comprised mainly soil particles mixed internally with anthropogenic species such as carbonaceous components and sulfate. Numerical simulation using the Chemical weather FORecasting System (CFORS) suggested the long-range transport of soil dust and black carbon from the Asian continent. Total number concentrations of particles sized 10–875 nm ranged from 4.8×103 to 3.0×104  cm−3 at an altitude of 300 m and from 7.3×102 to 4.8×103  cm−3 at an altitude of 1300 m. Total number concentrations of particles sized 10–875 nm correlated very well with NO X concentrations, and, therefore, ultrafine and submicron particles were likely emitted from urban activities such as car traffic and vertically transported. Number size distributions at lower altitudes obtained by aircraft measurements were similar to those obtained by ground measurements, with modal diameters of 20–30 nm on 18 March and about 50 nm on 19 March.
Keywords: Ultrafine particles; Submicron particles; Supermicron particles; Chemical composition; Long-range transport;

Origin of the exceedances of the European daily PM limit value in regional background areas of Spain by Miguel Escudero; Xavier Querol; Anna Ávila; Emilio Cuevas (730-744).
The origin of the daily exceedances of 50 μg PM10 m−3 (daily limit value or DLV of the EU air quality directive) and of an arbitrary daily value (DV) 35 μg PM2.5 m−3 recorded in 2001–2003 in 13 regional background stations of the Iberian Peninsula were interpreted. This was carried out by means of back-trajectory analysis, available PM model outputs, satellite data and meteorological maps. This allows the detection of high PM episodes on a regional scale and the study of their seasonal and geographical variability.The number of exceedances of the PM10 DLV ranged in 2001–2003 from 6 to 41 depending on the monitoring site. For the selected PM2.5 DV, the range of daily exceedances was 0–10 in the study period.The majority of the PM10 (>70% in most stations) and PM2.5 (17–55% in most stations) exceedances in regional background monitoring stations are caused by African dust outbreaks. These exceedances were less frequent in winter than in summer due to: (a) the frequent long range transport of dust in the warm seasons over Iberia, (b) the re-suspension associated with convective atmospheric dynamics, and (c) the relative low rainfall favouring re-suspension and high residence time of PM. Moreover, a regional contribution of secondary aerosols derived from the efficient photochemical transformation of gaseous precursors may coincide with African transport in summer.Episodes with lack of advective conditions caused 2–29% and 20–50% of the PM10 and PM2.5 exceedances. These occurred mainly in summer due to poor renovation of air masses, increased convective re-suspension, dispersion of pollutants towards rural areas and regional re-circulation and aging of air masses which result in the proliferation of secondary inorganic species.Long-range transport of PM from continental Europe caused exceedances (9–40% and 18–38% of the PM10 and PM2.5 exceedances, respectively), only in northern Iberia because, as the European air masses evolve towards the south, the pollutants suffer dispersion/dilution. Local exceedances are associated with the advection of the clean Atlantic air masses, which cannot increase PM levels to a great extent without the influence of a local source of PM. The proportion of local exceedances of PM10 and PM2.5 ranged 6–33% and 17–40%, respectively.
Keywords: PM10; PM2.5; Spain; Regional background; African dust;

Dry deposition of particles and canopy exchange: Comparison of wet, bulk and throughfall deposition at five forest sites in Italy by Raffaella Balestrini; Silvia Arisci; Maria Cristina Brizzio; Rosario Mosello; Michela Rogora; Antonio Tagliaferri (745-756).
The contribution of dry deposition to the total atmospheric input of acidifying compounds and base cations is of overwhelming importance. Throughfall measurements provide an estimate of the total deposition to forest soils, including dry deposition, but some uncertainties, related to the canopy interaction processes, affect this approach. We compared the concentrations and the fluxes of the main ions determined in wet-only, bulk and throughfall samples collected at five forest sites in Italy. The contribution of coarse particles deposited onto the bulk samplers was of prime importance for base cations, representing on average from 16% to 46% of the bulk deposition. The extent of this dry deposition depended on some geographical features of the sites, such as the distance from the sea and the annual rainfall. The possibility of applying specific bulk/wet ratios to estimate the wet deposition proved to be limited by the temporal variability of these ratios, which must be considered together with the spatial variability. A direct comparison of the dry contribution deriving from the bulk–wet and the throughfall–wet demonstrated that an extensive natural surface (forest canopy) performs better than a small synthetic surface (funnel of the bulk sampler) in collecting dry deposition of SO4 2−, NO3 and Na+. The canopy exchange model was applied to both bulk and wet data to estimate the contribution of dry deposition to the total input of base cations, and the uncertainty associated to the model discussed. The exclusive use of bulk data led to a considerable underestimation of base cation dry deposition, which varies among the study sites.
Keywords: Wet-only; Bulk; Throughfall; Dry deposition; Canopy exchange model;

The phase-in and phase-out of European emissions of HCFC-141b and HCFC-142b under the Montreal Protocol: Evidence from observations at Mace Head, Ireland and Jungfraujoch, Switzerland from 1994 to 2004 by R.G. Derwent; P.G. Simmonds; B.R. Greally; S. O’doherty; A. McCulloch; A. Manning; S. Reimann; D. Folini; M.K. Vollmer (757-767).
The mixing ratios of HCFC-141b (1,1-dichlorofluoroethane) and HCFC-142b (1-chloro-1,1-difluoroethane) have been rising steadily in baseline air at Mace Head, Ireland over the 10-year period from 1994 to 2004. These HCFCs are widely used replacements for the chlorofluorocarbons phased out under the Montreal Protocol and its subsequent amendments. Analysis of the HCFC content of regionally-polluted air arriving at Mace Head from the European continent shows that European emissions reached a peak during 2000–2001 and have declined subsequently, following the phase-out in their usage. European emissions of HCFC-141b have been further constrained by observations at the High-Alpine Jungfraujoch site. The reductions are consistent with the phase-out of HCFC production and use from the year 2001 onwards mandated by European regulations designed to exceed the requirements of the Montreal Protocol.
Keywords: HCFC-141b; HCFC-142b; Hydrochlorofluorocarbons; European emissions; Montreal protocol;

Chiral organochlorine pesticides in the atmosphere by Marta Venier; Ronald A. Hites (768-775).
We measured the enantiomeric fractions (EF) of various organochlorine pesticides in air samples from Indiana, Arkansas, and Louisiana collected in 2002–2003. Enantiomeric fractions for o,p′-DDD are reported here for the first time, and they suggest preferential depletion of one enantiomer over the other, with a mean value of 0.44. For the chlordanes, the EFs followed the same trends as reported in previous studies. EF values for trans-chlordane (TC) were slightly below 0.5, and values for cis-chlordane (CC) were slightly above 0.5. For cis-heptachlor epoxide (HEPX), the EF values averaged 0.65, indicating a clear preferential depletion of the (−)-enantiomer. For TC and CC, no clear distinction could be made between the values measured among the three sites, suggesting that it is not possible to use these EF values as “source signatures”. For HEPX, the Indiana site had significantly higher EF values than did the Arkansas site; this difference may reflect differences in the historic use of heptachlor in these two regions.
Keywords: Enantiomers; Source signature; Chlordane; Heptachlor epoxide; Atmospheric transport; DDD;

A global three-dimensional (3D) transport–dispersion model was used to simulate Krypton-85 (85Kr) background concentrations at five sampling locations along the US east coast during 1982–1983. The samplers were established to monitor the 85Kr plume downwind of the Savannah river plant (SRP), a nuclear fuel reprocessing facility. The samplers were located 300–1000 km downwind of the SRP. In the original analyses of the measurements, a constant background concentration, representing an upper-limit and different for each sampling station, was subtracted from the measurements to obtain the part of the measurement representing the SRP plume. The use of a 3D global model, which includes all major 85Kr sources worldwide, was able to reproduce the day-to-day concentration background variations at the sampling locations with correlation coefficients of 0.36–0.46. These 3D model background predictions, without including the nearby SRP source, were then subtracted from the measured concentrations at each sampler, the result representing the portion of the measurement that can be attributed to emissions from the SRP. The revised plume estimates were a factor of 1.3–2.4 times higher than from the old method using a constant background subtraction. The greatest differences in the SRP plume estimates occurred at the most distant sampling stations.
Keywords: Global dispersion model; Long-range transport; Krypton-85; Savannah river plant; ACURATE; HYSPLIT;

Importance of wet precipitation as a removal and transport process for atmospheric water soluble carbonyls by Sou N. Matsunaga; Alex B. Guenther; Yusuke Izawa; Christine Wiedinmyer; Jim P. Greenberg; Kimitaka Kawamura (790-796).
Carbonyl compounds exist in the atmosphere as either gases or aerosols. Some of them are water soluble and known as oxidation products of biogenic and/or anthropogenic hydrocarbons. Five carbonyl compounds, glyoxal (GO), 4-oxopentanal (4-OPA), glycolaldehyde (GA), hydroxyacetone (HA) and methylglyoxal (MG) have been identified in a temporal series of 12 rain samples. The concentrations of the compounds in the samples were high at the beginning of the rain event and decreased with time to relatively low and fairly constant levels, indicating that the compounds were washed out from the atmosphere at the start of the rain event. Possibly, these compounds also existed in the cloud condensation nuclei (CCN). Wet deposition rates of the carbonyl compounds were calculated for nine samples collected during a 20 h period. The deposition rates ranged from 0 (4-OPA) to 1.2×10−1  mg C m−2  h−1 (MG) with the average of 2.9×10−2  mg C m−2  h−1. Production rates of isoprene oxidation products (GA, HA and MG) in the area surrounding the sampling site were estimated with a chemical box model. The deposition rates exceeded the production rates in most samples. This indicates that the rainfall causes a large net flux of the water soluble compounds from the atmosphere to the ground. Insoluble carbonyl compounds such as n-nonanal and n-decanal were expected to be present in the atmosphere, but were not detected in the rain during the sampling period, suggesting that an aerosol containing these insoluble compounds does not effectively act as a CCN.
Keywords: Deposition rate; Production rate; Aerosol; Cloud condensation nuclei; Isoprene oxidation products;

Numerical study on adjusting and controlling effect of forest cover on PM10 and O3 by Shiyong Du; Daiwen Kang; Xiaoen Lei; Liren Chen (797-808).
A new-coupled air quality numerical modeling system has been developed and applied to the study on the adjusting and controlling effect of forest cover on air quality. The modeling system is composed of Plant Canopy Layer Model (PCLM), Urban Scale Meteorological Model (USMM), and High-Resolution Chemical Model (HRCM). The system was applied to the study on the ecological adjusting and controlling effects on PM10 and O3 in Jinan City, China. The results show that the forest cover can adjust and control PM10 and O3 significantly by reducing the concentrations of PM10 while increasing the concentrations of O3 with the increase of forest cover.
Keywords: Numerical simulation; Forest cover; Adjusting and controlling effect; PM10; O3; Air quality;

In this study, a comprehensive analysis was made to describe the environmental behavior and pollution status of lead (Pb) in 13 major cities in Korea in a 14-year time span (1991–2004). The results clearly indicate that spatial distribution of Pb is clearly distinguished between different city types and between different temporal intervals. The Pb concentration levels in the cities of strong industrial activities are found to be higher than those of relatively clean ones by approximately an order of magnitude. Examination of the seasonal patterns indicated a strong consistency in almost all cities so that Pb concentration peaked during spring and winter, while it dropped noticeably during summer. If the long-term trend of Pb pollution is examined for the entire study period (14 years), it appears to contrast between different city types in relation with the relative intensity of Pb pollution. In cities of strong industrial activities, the reduction of Pb seemed to occur more effectively due to the stringent measures implemented to ban metal emissions over the past decades. In contrast, such temporal patterns appear to be more complicated in cities with moderately or fairly clean environments. This is possibly due to the fact that the effect induced by the phase-out of the dominant source (i.e., leaded gasoline) became less significant, while other sources were further diversified and/or intensified through time. The overall results of this comprehensive study confirm the fact that the status of Pb pollution in most city areas can be reflected fairly sensitively by changes in social and environmental conditions.
Keywords: Lead (Pb); Atmospheric; Industrial emission; Spatial; Korea;

Study of aerosol transport through precipitation chemistry over Arabian Sea during winter and summer monsoons by P.S. Praveen; P.S.P. Rao; P.D. Safai; P.C.S. Devara; D.M. Chate; K. Ali; G.A. Momin (825-836).
Precipitation samples over the Arabian Sea collected during Arabian Sea Monsoon Experiment (ARMEX) in 2002–2003 were examined for major water soluble components and acidity of aerosols during the period of winter and summer monsoon seasons. The pH of rain water was alkaline during summer monsoon and acidic during winter monsoon. Summer monsoon precipitation showed dominance of sea-salt components (∼90%) and significant amounts of non-sea salt (nss) Ca2+ and SO4 2−. Winter monsoon precipitation samples showed higher concentration of NO3 and NH4 + compared to that of summer monsoon, indicating more influence of anthropogenic sources. The rain water data is interpreted in terms of long-range transport and background pollution. In summer monsoon, air masses passing over the north African and Gulf continents which may be carrying nss components are advected towards the observational location. Also, prevailing strong southwesterly winds at surface level produced sea-salt aerosols which led to high sea-salt contribution in precipitation. While in winter monsoon, it was observed that, air masses coming from Asian region towards observational location carry more pollutants like NO3 and nss SO4 2− that acidify the precipitation.
Keywords: Precipitation; Monsoon; Acidity; Transport; ARMEX;

A high ozone event in the Houston–Galveston–Brazoria area was utilized to study the shortcomings of the current air quality models. To improve the baseline simulations with the Comprehensive Air quality Model with Extensions (CAMx) for developing the state implementation plan, the Texas Commission on Environmental Quality (TCEQ) imputed emissions of highly reactive volatile organic compounds (HRVOCs) by scaling the amount of fugitive emissions of olefins to co-emitted NO x from selected point sources, effectively multiplying by 3–12 times over the regular inventory values. In this paper, CAMx and the Community Multiscale Air Quality (CMAQ) model were used to determine if the imputed HRVOC emissions were consistent with the observed atmospheric conditions. With the base emissions, CMAQ and CAMx both with the Carbon-Bond 4 (CB-4) mechanism simulated similar ozone concentrations. But with the imputed HRVOC emissions, CMAQ predicted lower ozone peaks than CAMx in the vicinity and downwind of the Ship Channel and other highly HRVOC-rich areas. Based on analyses of sensitivity simulations of CMAQ with different emission inputs and vertical diffusion algorithms in the model, we found that the modeled atmosphere lacked reactivity to produce the observed high ozone event. Although the imputed HRVOC emissions improved ozone prediction at the surface sites, but the ethylene concentrations were not consistent with the measurements at the super sites (La Porte and Clinton) and by NOAA aircraft. Several sensitivity tests designed to provide additional radicals into the system and other research results suggested that the lack of reactivity may need to be corrected by targeted, and probably of episodic, increase of HRVOC emissions, from the sources in the Houston Ship Channel. Additional investigation of the ozone production efficiency for different chemical mechanisms is necessary to pinpoint the emissions uncertainty issues.
Keywords: Emissions uncertainty; Ground level ozone; Air quality model evaluation; Vertical mixing; Highly reactive volatile organic compounds;

Particulate matter in the indoor air of classrooms—exploratory results from Munich and surrounding area by H. Fromme; D. Twardella; S. Dietrich; D. Heitmann; R. Schierl; B. Liebl; H. Rüden (854-866).
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, PM2.5) 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 (PM2.5) and 91.5 μg m−3 (PM10) were observed, in summer PM concentrations were significantly reduced (median PM2.5=12.7 μg m−3, median PM10=64.9 μg m−3). PM2.5 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 PM2.5 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.
Keywords: Indoor; Schools; Classrooms; Particulate matter; Carbon dioxide; Particle number concentration; Ultrafine particles;

Variation of surface electric field with special thrust to atmospheric inversion condition is studied for the tropical station Pune (18°32′N, 73°51′E, 550 m ASL) for the year 1993 considering average meteorological conditions. The study aims to understand the relative effect of space charge density variation modulated by vertical temperature gradient (lapse rate) Vs conductivity variations controlled by radionuclide concentration on modification of electric field close to surface. Electric field is predominantly controlled by lapse rate (space charge density variation) and radon progeny concentration (conductivity modification) in summer and winter respectively. An empirical relation developed elsewhere is evaluated for the present observations.
Keywords: Atmospheric inversion; Atmospheric electric field; Radon progeny concentration; Pollutant dispersion;

Iron, manganese and copper emitted by cargo and passenger trains in Zürich (Switzerland): Size-segregated mass concentrations in ambient air by Nicolas Bukowiecki; Robert Gehrig; Matthias Hill; Peter Lienemann; Christoph N. Zwicky; Brigitte Buchmann; Ernest Weingartner; Urs Baltensperger (878-889).
Particle emissions caused by railway traffic have hardly been investigated in the past, due to their obviously minor influence on air quality compared to automotive traffic. In this study, emissions related to particle abrasion from wheels and tracks were investigated next to a busy railway line in Zürich (Switzerland), where trains run nearly exclusively with electrical locomotives. Hourly size-segregated aerosol samples (0.1–1, 1–2.5 and 2.5–10 μm) were collected with a rotating drum impactor (RDI) and subsequently analyzed by synchrotron radiation X-ray fluorescence spectrometry (SR-XRF). In this way, hourly elemental mass concentrations were obtained for chromium, manganese, iron and copper, which are the elements most relevant for railway abrasion. Additionally, daily aerosol filters were collected at the same site as well as at a background site for subsequent analysis by gravimetry and wavelength dispersive XRF (WD-XRF). Railway related ambient air concentrations of iron and manganese were calculated for the coarse (2.5–10 μm) and fine (<2.5 μm) particle fraction by means of a Mn/Fe ratio investigation. The comparison to train type and frequency data showed that 75% and 60% of the iron and manganese mass concentrations related to cargo and passenger trains, respectively, were found in the coarse mode. The railway related iron mass concentration normalized by the train frequency ranges between 10 and 100 ng m−3  h iron in 10 m distance to the tracks, depending on train type. It is estimated that the personal exposure next to a busy railway line above ground is more than a magnitude lower than inside a subway station.
Keywords: Railway; Aerosol; Emissions; Abrasion; Trace metals; Iron;

Bus, minibus, metro inter-comparison of commuters’ exposure to air pollution in Mexico City by J.E. Gómez-Perales; R.N. Colvile; A.A. Fernández-Bremauntz; V. Gutiérrez-Avedoy; V.H. Páramo-Figueroa; S. Blanco-Jiménez; E. Bueno-López; R. Bernabé-Cabanillas; F. Mandujano; M. Hidalgo-Navarro; M.J. Nieuwenhuijsen (890-901).
Commuters’ exposure measurements were taken for PM2.5, carbon monoxide (CO) and benzene in minibuses, buses and metro during morning and evening rush hours during January–March 2003 in Mexico City. For PM2.5, the chemical composition was characterized. Total carbon was the most abundant species in fine particles (approximately 50%). Minibuses (49 μg m−3) and buses had similar concentrations of exposure for PM2.5 (53 μg m−3). For CO and benzene the concentrations were higher in minibuses. Morning rush hour was the commuting period with the highest concentrations for minibuses and buses. Metro was the mode of transport with lower concentrations for all pollutants. Carbon monoxide concentrations were similar to those identified in a previous campaign in 2002 and approximately 3.5 times lower than those in a study conducted in 1991. Benzene was characterized systematically in the selected modes of transport. A strong association was observed between wind speed and pollutant concentrations in buses.
Keywords: Transport users’ exposure; PM2.5; CO; Benzene; Chemical composition;