Atmospheric Environment (v.40, #7)

In recent years, photochemical air pollution has become a significant problem in the São Paulo Metropolitan Area (SPMA). For some air pollutants, especially ozone and particulate matter, concentrations in excess of national air quality standards have been registered. According to data published by the State Environmental Agency (CETESB), approximately 90% of ozone precursors are emitted into the atmosphere by the vehicle fleet [CETESB, 2000. Relatório de Qualidade do ar do Estado de Sao Paulo, 1999; CETESB, 2002. Relatório de Qualidade do ar do Estado de Sao Paulo, 2004].The estimation of precursor emissions speciation is a rather complex task. Estimating spatial and temporal variation of vehicle emissions is the greatest source of uncertainty.As in other locales, data regarding motor vehicle emissions are scarce. Due to the considerable discrepancies in emission inventories reported in various regions of the world, we evaluated the official emission inventories of non-methane organic gas (NMOG) and nitrogen oxides (NO x ) using an observation-based approach. Ratios of NO x /carbon monoxide (CO) and NMOG/CO were calculated from ambient measurements taken in the early morning (0700–0800) during July and August of 1999. This top-down approach assumes that early morning ambient concentrations of CO, NO x and NMOG are dominated by motor vehicle emissions, and that the photochemical process has not substantially affected the concentrations. Based on these ratios and on the assumption that official inventory of CO emissions is reasonably accurate, on-road motor vehicle emissions of NO x seem to be significantly overestimated and NMOG emissions slightly underestimated. An Eulerian photochemical model, using both the revised motor vehicle emission inventory and the original official emissions provided by CETESB, was applied to an episodic air pollution event in the SPMA (9–12 August 1999). Meteorology fields were obtained from the CALMET model. When the revised, rather than the official, emission inventories are used, ozone and NO concentrations predicted by the California Institute of Technology (CIT) airshed model more closely match observed values.
Keywords: Ozone; Ozone precursors; Photochemical modeling; Vehicle emissions;

Mass conservation in the Community Multiscale Air Quality model by Yongtao Hu; M. Talat Odman; Armistead G. Russell (1199-1204).
Mass conservation errors were discovered when the Community Multiscale Air Quality (CMAQ) model (version 4.3) was coupled with the Fifth-Generation PSU/NCAR Mesoscale Model (MM5). These errors can be severe particularly over complex terrain. A recent correction made to the vertical advection module (in version 4.4) reduces the mass conservation errors, but does not completely eliminate them. This means that the method of renormalizing concentrations according to air density, which is currently applied to address the inconsistency problem, is not an ideal solution. Reconstruction of the wind fields by adjusting the vertical wind is proposed as a simple remedy to make CMAQ strictly mass conservative.
Keywords: Regional air quality modeling; Inconsistency of meteorological fields; Mass conservation error; Source-receptor relationship; Emissions control strategy;

Coarse and accumulation mode particles associated with Asian dust in southwestern Japan by Daizhou Zhang; Yasunobu Iwasaka; Atsushi Matsuki; Kazunori Ueno; Tatsuya Matsuzaki (1205-1215).
Number and mass concentrations of atmospheric particles were measured at a surface site on the southwestern Japan coast from March to May 2002. Particles were collected when Asian dust appeared at the site in this period, and later characterized with their morphology and elemental composition from electron microscopic analysis. The mass concentration of suspended particulate matters with diameter smaller than 10 μm (SPM10) during dust episodes was predominated by particles larger than 1.0 μm (coarse particles), which were mainly mineral dust with a small fraction of sea salt. As dust-loading low-pressure systems were approaching, SPM10 and the number concentration of coarse particles decreased gradually until the arrival of cold fronts. After that, they increased due to dust arrival except during rainfall. Time series of the number concentration of coarse particles during dust plume passages was not in parallel with that of accumulation mode particles in the range of 0.1–0.3 μm and they were even inverse in some episodes, reflecting a horizontal structure with multiple intervals of dust and secondary particles. The electron microscopic analysis confirmed the frequent mixture of sea salt in dust particles and suggested that the probability for dust particles to become mixtures with sea salt was likely dependent on the vertical thermodynamic structure of the marine boundary layer, through which aloft dust particles descended to the ground. More mineral dust particles mixed with sea salt in cases with deep mixing layers than with shallow mixing layers. No correlation between the mixture degree and the transport time for dust particles to travel in the marine atmosphere from the Asian continent to southwestern Japan was found.
Keywords: Particle number concentration; Dust; Pollutant; Low-pressure passage;

The aim of the present work is to evaluate the potential of various developed neural network models to provide reliable predictions of PM10 hourly concentrations, a task that is known to present certain difficulties. The modeling study involves 4 measurement locations within the Greater Athens Area which experiences a significant PM-related air pollution problem. The PM10 data used cover the period of 2001–2002. Artificial neural network models were developed using a combination of meteorological and time-scale input variables. A genetic algorithm optimization procedure for the selection of the input variables was also evaluated. The results of the neural network models were rather satisfactory, with values of the coefficient of determination (r 2) for independent test sets ranging between 0.50 and 0.67 for the four sites and values of the index of agreement between 0.80 and 0.89. The performance of examined neural network models was superior in comparison with multiple linear regression models that were developed in parallel (r 2 for regression models ranging between 0.29 and 0.35). Their performance was also found adequate in the case of high-concentration events, with acceptable probabilities of detection and low false alarm rates. The suitability of the developed neural network models for use at real-time conditions was further evaluated for PM10 hourly concentrations recorded during the days of the 2004 Athens Olympic Games.
Keywords: Particulate matter; Neural networks; Genetic algorithms; Prediction; Air pollution modeling;

Replicable experimental studies using a novel experimental facility and a machine-based odour quantification technique were conducted to demonstrate the relationship between odour emission rates and pond loading rates. The odour quantification technique consisted of an electronic nose, AromaScan A32S, and an artificial neural network. Odour concentrations determined by olfactometry were used along with the AromaScan responses to train the artificial neural network. The trained network was able to predict the odour emission rates for the test data with a correlation coefficient of 0.98. Time averaged odour emission rates predicted by the machine-based odour quantification technique, were strongly correlated with volatile solids loading rate, demonstrating the increased magnitude of emissions from a heavily loaded effluent pond. However, it was not possible to obtain the same relationship between volatile solids loading rates and odour emission rates from the individual data. It is concluded that taking a limited number of odour samples over a short period is unlikely to provide a representative rate of odour emissions from an effluent pond. A continuous odour monitoring instrument will be required for that more demanding task.
Keywords: Odour; Electronic nose; Effluent pond; Olfactometry; Swine; Manure; Neural network;

Concentration measurement in a road tunnel as a method to assess “real-world” vehicles exhaust emissions by G. Zanini; M. Berico; F. Monforti; L. Vitali; S. Zambonelli; S. Chiavarini; T. Georgiadis; M. Nardino (1242-1254).
An experiment aimed at comparing particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) concentrations produced in a road tunnel by buses is described. The experiment took place in 2001 in Bologna when a couple of buses belonging to the public transport fleet where driven backwards and forwards in a road tunnel closed to all other vehicles. Buses run in the tunnel for 8 h a day for 4 experiment days, each day using a different fuel: biodiesel, diesel–water emulsion, diesel–water emulsion with low sulphur content and commercial diesel. Average daily concentrations of PM of different sizes and of 12 PHAs were measured and comparison between different fuels was attempted in order to assess “real-world” exhaust emissions of different fuels. Due to heterogeneity of experimental conditions in different days and the relatively large measurement uncertainties, the effort was only partially successful, and it was not possible to state any firm conclusion on fuels reliability even if some indications in agreement with literature were found. Nevertheless, the experiment and the data analysis method developed could be of interest as a methodological approach for future experiments aimed at evaluating “real-world” exhaust emissions of single vehicles.
Keywords: Particulate matter; Bus engines; PAHs; Biodiesel blend; Water diesel emulsion; Lungs deposition; Real-world experiment;

Atmospheric pollutants, gases as well as particulate, have been pointed out as a major cause of weathering of historic stained glass windows. Although conservators did not succeed in stopping or reversing the ensuing damage up to date, a slower rate of destruction to maintain the grandeur of the artifact is certainly achievable, by installing a protective glazing (PG). Measurements were carried out for a period of 1 year in the Sainte Chapelle in Paris, France, in order to integrate the influence of some major pollutants and acidifying substances indoors, and outdoors, as well as in the interspace, created by the PG. The concentrations of SO2, NO2 and O3 were assessed using passive diffusion tubes. The PG reduced SO2 and O3 pollutant exposure of the stained glass windows by 80% relative to the outdoor concentrations. NO2 concentrations remained almost the same inside, outside and in the interspace; however, previous studies showed that even in high concentrations of NO2 accompanied by low concentrations of SO2 the degradation of this kind of glass is modest. The results of bulk particle analyses by energy-dispersive X-ray fluorescence indicated the accumulation and re-suspension of particles as the main factor of elevated concentration of elements inside of Sainte Chapelle. The abundance and type of particles obtained by electron probe X-ray micro analysis were slightly different in the three measured areas. The main distinction is the occurrence of CaSO4 particles inside and in the interspace. In conclusion, the installation of a PG in Sainte Chapelle seems to be appropriate.
Keywords: Protective glazing; Stained glass windows; Sainte Chapelle; Single particles; gases;

Source identification and size distribution of atmospheric polycyclic aromatic hydrocarbons during rice straw burning period by Hsi-Hsien Yang; Cheng-Hsien Tsai; Mu-Rong Chao; Yi-Ling Su; Shu-Mei Chien (1266-1274).
Atmospheric particulate and polycyclic aromatic hydrocarbon (PAH) size distributions were measured at a suburban area in central Taiwan during the rice straw burning and non-burning periods. Samples were acquired using a semi-volatile sampling train (PS-1 sampler) and a micro-orifice uniform deposit impactor (MOUDI). The collected materials were extracted and then analyzed by gas chromatograph/mass selective detector for 21 PAHs. The average total PAH concentrations of particulate and gaseous phases were 33.0 and 1160 ng m−3, respectively, in the rice straw burning period, which were higher than those on the non-burning days. Potential sources of PAHs were identified using the characteristic ratios. Benzo[a]pyrene/benzo[ghi]perylene ratio indicates the burning of rice straw is a significant source for PAH contribution at the sampling area. It also suggests that the rice straw burning primarily contribute fine particulate PAHs. Bimodal size distributions are obtained with a predominance of total PAHs in the accumulation mode during rice straw burning periods and in ultra-fine mode during non-burning periods. The particulate and particulate phase PAHs from rice straw burning are coarser than those from vehicle exhaust. The results also suggest that the amounts of PAHs per unit mass of particulate are less for the burning of rice straw than those of vehicle emissions.
Keywords: PAHs; Mass median diameter; Respirable particulate; Biomass burning; Characteristic ratio;

Present and future acid deposition to ecosystems: The effect of climate change by Michael G. Sanderson; William J. Collins; Colin E. Johnson; Richard G. Derwent (1275-1283).
A global chemistry-transport model has been used to study the deposition of acidic nitrogen and sulphur species in the present day (1990s) and future (2090s). For the oxidised nitrogen species, climate change increases the amount of nitric acid produced and deposited to soils. However, for reduced nitrogen species, both climate change and pollutant emission increases act to convert more ammonia to ammonium sulphate which in turn may result in further acidification of soils. This change occurs via increased aqueous phase oxidation of sulphur dioxide, indicating that the sulphur and reduced nitrogen cycles are closely linked. The modelled acid deposition fluxes have been used with estimates of base cation deposition fluxes to identify areas with excess deposition above the critical loads. These data show an increasing risk of acidification in parts of the USA and South-East Asia. Certain areas, especially in Asia, remain at risk even when higher values of critical loads and base cation deposition fluxes are used.
Keywords: Critical loads; Deposition; Modelling; Ammonium; Sulphate;

The late sea breeze (LSB), defined as a sea breeze with an onset time later than 1200 LST, and its impact on O3 concentration distributions have been investigated both observationally and numerically over the Busan metropolitan area in Korea. The observed LSB mostly occurred under weak offshore synoptic flows during mid-day, and was found with late but apparent transitions in wind direction along with lower wind speed. The observed O3 concentrations associated with the LSB demonstrated more significant enhancement of maximum O3 concentrations than those of the early sea breeze by a factor of approximately 1.5. The main meteorological feature associated with the LSB was also reproduced by MM5 for typical cases. The numerically derived backward trajectories suggested that the increase of O3 at the coastal site is mainly due to recirculated polluted air mass. The numerical simulation of O3 concentrations from MM5/UAM-V shows that offshore winds of northwesterly synoptic flow swept the precursors of O3 that were emitted by the urban area toward the sea during the early morning. As the development of the LSB was suppressed by the synoptic flow, a large near-stagnant wind field formed over the sea with intense photochemical activity at mid-day. However, the subsequent LSB with low wind speed was simulated in order to slowly re-advect the photochemically produced air parcels toward the inland area, resulting in both a significant enhancement of O3 concentrations and high concentrations over the coastal area lasting for relatively longer hours. This result implies that the LSB plays an important role in the recirculation/accumulation of O3 concentrations over the Busan metropolitan area, Korea.
Keywords: Late sea breeze; Ozone distribution; Synoptic flow; MM5/UAM-V; Recirculation;

Determinants of indoor air concentrations of PM2.5, black smoke and NO2 in six European cities (EXPOLIS study) by H.K. Lai; L. Bayer-Oglesby; R. Colvile; T. Götschi; M.J. Jantunen; N. Künzli; E. Kulinskaya; C. Schweizer; M.J. Nieuwenhuijsen (1299-1313).
EXPOLIS was a large-scale population-based study of urban adult exposures to multiple pollutants, and was conducted between 1996 and 2000 in six European cities. Measurements made using standardised protocols in Athens (Greece), Basel (Switzerland), Helsinki (Finland), Milan (Italy), Oxford (UK), and Prague (Czech Republic), allow similarities and differences between contrasting European regions, climates and populations to be identified. Two consecutive days of home indoor and home outdoor measurements of fine particulate matter (PM2.5), black smoke (BS), and nitrogen dioxide (NO2) were carried out at the homes of adult participants on different dates and seasons during the sampling period. Regression models with interactions searched by all-possible subset method were used to assess the city effects and the determinants of home indoor PM2.5 (adj R 2 = 0.60 , n = 413 ), BS (adj R 2 = 0.79 , n = 382 ) and NO2 (adj R 2 = 0.67 , n = 302 ) levels. Both bi-directional (positive and negative signs of associations) and unidirectional (consistently either positive or negative sign of associations) city effects on different determinants in each indoor model were shown. Smoking, gas-stove usage, outdoor temperature, and wind speed were the common determinants in all three indoor models. Other determinants, including the presence of wooden material, heating, and being located in suburb area, were also identified. They were likely linked to cultural and socio-economic factors.
Keywords: Black smoke; Exposure assessment; Indoor air pollution; Nitrogen dioxide; Particulate matter;

Traffic-generated emissions of ultrafine particles from pavement–tire interface by Andreas Dahl; Arash Gharibi; Erik Swietlicki; Anders Gudmundsson; Mats Bohgard; Anders Ljungman; Göran Blomqvist; Mats Gustafsson (1314-1323).
In a road simulator study, a significant source of sub-micrometer fine particles produced by the road–tire interface was observed. Since the particle size distribution and source strength is dependent on the type of tire used, it is likely that these particles largely originate from the tires, and not the road pavement. The particles consisted most likely of mineral oils from the softening filler and fragments of the carbon-reinforcing filler material (soot agglomerates). This identification was based on transmission electron microscopy studies of collected ultrafine wear particles and on-line thermal treatment using a thermodesorber.The mean particle number diameters were between 15–50 nm, similar to those found in light duty vehicle (LDV) tail-pipe exhaust. A simple box model approach was used to estimate emission factors in the size interval 15–700 nm. The emission factors increased with increasing vehicle speed, and varied between 3.7×1011 and 3.2×1012  particles vehicle−1  km−1 at speeds of 50 and 70 km h−1. This corresponds to between 0.1–1% of tail-pipe emissions in real-world emission studies at similar speeds from a fleet of LDV with 95% gasoline and 5% diesel-fueled cars. The emission factors for particles originating from the road–tire interface were, however, similar in magnitude to particle number emission factors from liquefied petroleum gas-powered vehicles derived in test bench studies in Australia 2005. Thus the road–tire interface may be a significant contributor to particle emissions from ultraclean vehicles.
Keywords: Road wear; Size distribution; Light duty vehicle; Nanoparticle; Emission factor;

Uptake of gaseous nitrous acid (HONO) by several plant species by Ralf Schimang; Achim Folkers; Jörg Kleffmann; Einhard Kleist; Marco Miebach; Jürgen Wildt (1324-1335).
Uptake of gaseous nitrous acid (HONO) by sunflower (Heliantus annuus L. var. gigantheus), tobacco (Nicotiana tabacum L. var. Bel W3), castor (Rhicinus communis L. var. Carmencita), and birch (Betula pendula L.) was studied under controlled conditions in a continuously stirred tank reactor. Exposing plants to HONO at concentrations between 60 ppt and 10 ppb led to significant uptake by the plants. The uptake was proportional to HONO concentrations and linearly related to stomatal conductivity. HONO losses at the cuticle were of minor importance. Our data imply a quick metabolism of HONO and it is concluded that the uptake of HONO by plants is only limited by diffusion of HONO through the plants stomata.Comparing results from measurements with and without plants in the chamber it is furthermore concluded that a compensation point for HONO uptake is below 20 ppt if it exists at all. Heterogeneous formation of HONO by reactions of NO2 on the plant surfaces was either not effective or compensated by the stomatal uptake of HONO. The data of the present study imply that plant surfaces represent a sink for HONO. Therefore, it was concluded that processes on plant surfaces cannot explain HONO formation on ground surfaces as observed in field studies.
Keywords: HONO; Foliar uptake; Stomatal conductivity; Deposition velocity; Heterogeneous reactions;

Aldehyde measurements in indoor environments in Strasbourg (France) by C. Marchand; B. Bulliot; S. Le Calvé; Ph. Mirabel (1336-1345).
Formaldehyde and acetaldehyde concentrations have been measured in indoor environments of various public spaces (railway station, airport, shopping center, libraries, underground parking garage, etc.) of Strasbourg area (east of France). In addition, formaldehyde, acetaldehyde propionaldehyde and hexanal concentrations have been measured in 22 private homes in the same area. In most of the sampling sites, indoor and outdoor formaldehyde and acetaldehyde concentrations were measured simultaneously. Gaseous aldehydes levels were quantified by a conventional DNHP-derivatization method followed by liquid chromatography coupled to UV detection. Outdoor formaldehyde and acetaldehyde concentrations were both in the range 1–10 μg m−3, the highest values being measured at the airport and railway station. Indoor concentrations were strongly dependant upon the sampling sites. In homes, the average concentrations were 37 μg m−3 (living rooms) and 46 μg m−3 (bedrooms) for formaldehyde, 15 μg m−3 (living rooms) and 18 μg m−3 (bedrooms) for acetaldehyde, 1.2 μg m−3 (living rooms) and 1.6 μg m−3 (bedrooms) for propionaldehyde, 9 μg m−3 (living rooms) and 10 μg m−3 (bedrooms) for hexanal. However, concentrations as high as 123, 80 and 47 μg m−3 have been found for formaldehyde, acetaldehyde and hexanal respectively. In public spaces, the highest formaldehyde concentration (62 μg m−3) was found in a library and the highest concentration of acetaldehyde (26 μg m−3) in the hall of a shopping center. Additional measurements of formaldehyde and acetaldehyde were made inside a car both at rest or in a fluid or heavy traffic as well as in a room where cigarettes were smoked. Our data have been discussed and compared with those of previous studies.
Keywords: Aldehyde measurements; Indoor pollutants; Homes; Airport; Shopping centre;

In this work the possibility of measuring real-time concentrations of PM2.5 and the corresponding vertical turbulent fluxes using the optical detector Mie pDR-1200, operating synchronously with an ultrasonic anemometer, is investigated. This detector is known to be sensitive to high values of relative humidity (RH) and a new procedure to correct the effect of RH on concentration measurements is presented. Results of optical measurements have been compared with gravimetric detections of PM2.5 and results show a reasonable correlation between them and an improvement of the agreement when RH-correction is used. Results presented have been collected at two measurement sites that can be representative of urban background environments but in one of them was present an industrial area nearby. Post-processing of data has been performed with the eddy-correlation technique that allows evaluation of vertical turbulent fluxes of PM2.5 as well as sensible heat and momentum fluxes. The turbulent mass fluxes, together with the analysis of real-time concentrations and their correlation with meteorology proved to be an useful tool to infer details about the local aerosol dynamics helping to interpret traditional gravimetric analysis of aerosol that is usually performed on a 24 h basis. Results show that the methodology can be useful in identifying the contribution of local sources like ground level emissions or industrial plumes with respect to the contribution of sources located far away from the measurement site.
Keywords: PM2.5; Aerosol turbulent flux; Optical instrumentation; Aerosol dynamics; Hygroscopicity;

Dispersion from ground-level sources in a shoreline urban area by Jing Yuan; Akula Venkatram; Vlad Isakov (1361-1372).
We present results from a field study conducted in Wilmington, a suburb of Los Angeles, during 8 days of the period 26 August–10 September 2004. The tracer, sulfur hexafluoride, was released at a height of 3 m from a power plant site on the shoreline, and the concentrations of the tracer were sampled on five arcs at 100, 400, 1000, 3000, and 5000 m from the source during 6 h of the day starting at 7 a.m. This resulted in 40-h-long experiments, out of which, 21 had concentration measurements that could be interpreted with models. The meteorological conditions that governed dispersion were measured using sonic anemometers and sodars. The data analysis indicates that even during summer, the stability of the onshore flow is strong enough to keep the height of the convective internal boundary layer below 150 m at distances of 5000 m from the shoreline. However, the turbulence levels in the stable boundary layer are not smaller than those in the surface convective layer suggesting the presence of a shear generated boundary layer, which is advected with the onshore flow.A simple Gaussian dispersion model was used to interpret the ground-level concentrations measured in the experiment. The model uses expressions for plume spreads that depend on meteorological information at a height of 50 m from the surface. The vertical spread of the plume is limited to the height of the shear generated boundary layer. The height of this boundary layer is proportional to σ w / N , where σ w is the standard deviation of the vertical velocity fluctuations, and N is the Brunt–Vaisala frequency of the stable layer capping the surface-based convective layer. This result is based on indirect evidence: model performance improves significantly when vertical plume spread is limited to this height.
Keywords: Shoreline dispersion; Shear generated boundary layer; Field experiment; Tracer study; Plume spread; Dispersion model; Data analysis; Wilmington; Urban dispersion; Thermal internal boundary layer;

The exchange rates of carbonyl sulfide (COS) and dimethyl sulfide (DMS) between 19 tree species and the atmosphere were investigated under natural field conditions using a static enclosure. Most of the investigated trees acted as sinks for atmospheric COS and a few trees, such as Salix matsudana Koidz. and Ulmus pumila L. could emit COS. The distinct diurnal variations of COS uptake for the investigated trees indicated that COS uptake strongly depended on photosynthetically active radiation (PAR). The average COS uptake rates for most species were much higher in summer than in autumn, indicating leaf age and temperature also might be the important influencing factors for COS uptake. Platanus orientalis L., Sophara japonica var. P. loud., Magnolia denudata Desr. and Sophora japonica L. were capable of continuously absorbing COS in daytime as well as in nighttime. For Platanus orientalis L., the maximal COS uptake rate and DMS emission rate on a single leaf area basis were −15.29 and 0.42 pmol m−2  s−1, respectively. The COS exchange fluxes for the investigated tree species depended strongly on the ambient COS mixing ratios. Significant correlation between DMS emissions and temperature was observed in summer.
Keywords: Carbonyl sulfide; Dimethyl sulfide; Exchange rate; Trees;

Erratum to “Measurements of atmospheric mercury species during an international study of mercury depletion events at Ny-Alesund, Svalbard, spring 2003. How reproducible are our present methods?” by Katrine Aspmo; Pierre-Alexis Gauchard; Alexandra Steffen; Christian Temme; Torunn Berg; Enno Bahlmann; Cathy Banic; Aurelien Dommergue; Ralf Ebinghaus; Christophe Ferrari; Nicola Pirrone; Francesca Sprovieri; Grethe Wibetoe (1384).