Atmospheric Environment (v.40, #17)

Windblown dust can have significant impacts on local air pollution levels, and in cases such as dust from Africa or Asia, can have global impacts on our environment. Models to estimate particulate matter emissions from windblown dust are generally based on the local wind speed, the threshold wind speed to initiate erosion, and the soil texture of a given surface. However, precipitation, soil crusting, and soil disturbance can dramatically change the threshold wind speed and erosion potential of a surface, making modeling difficult. A low-cost sampling and analysis method was developed to account for these surface changes in a wind erosion model. Windblown dust emissions measured as PM10 (particulate matter less than a nominal 10 μm aerodynamic diameter) have been found to be generally proportional to sand flux (also known as saltation flux). In this study, a model was used to estimate sand flux using the relationship Q=AρG/g, where Q is horizontal sand flux, A is a surface erosion potential factor, ρ is air density, g is the gravitational constant, and G = ∫ u * ( u * 2 - u * t 2 ) d t , where u * is friction velocity and u * t is the threshold friction velocity of the surface. The variable A in the model was derived by comparing the measured sand flux for a given period and area to G for the same period. Sand flux was monitored at Owens Lake, CA using low-cost Cox Sand Catchers (CSCs) for monthly measurements, and more expensive electronic sensors (Sensits) to measure hourly flux rates and u * t . Monitors were spaced 1 km apart at 114 sites, covering one clay and three sand-dominated soil areas. Good model results relied primarily on the erosion potential A, which could be determined from CSC measurements and wind speed data. Annual values for A were found to range from 1.3 to 3.5 in the three sand areas. The value of A was an order of magnitude lower (0.2) in the less erodible clay area. Previous studies showed similar values for A of 0.7 and 2.9 for a sandy site at Owens Lake, and 1.1 for a site in the Chihuahuan desert in New Mexico. The model performed well using annual values for A and better with monthly values, with R 2 ranging from 0.74 to 0.87 for hourly sand flux rates in the four study areas. Monthly changes in A accounted for temporal surface changes, such as precipitation and surface crusting in the model predictions. This study demonstrated that low-cost periodic sand flux sampling using CSCs can provide a practical method to determine values for A in a simple wind erosion model, and that this model can provide good hourly and monthly estimates of sand flux rates in windblown dust areas.
Keywords: Wind erosion; Particulate matter; Sand flux; Sensit; Threshold friction velocity;

Hydrogen cyanide in ambient air near a gold heap leach field: Measured vs. modeled concentrations by Kenneth G. Orloff; Brian Kaplan; Peter Kowalski (3022-3029).
To extract gold from low-grade ores, a solution of sodium cyanide is trickled over pads of crushed ore. During this operation, small quantities of hydrogen cyanide gas may escape to the ambient air. To assess these emissions, we collected air samples at monitoring stations located on opposite sides of a gold heap leach field at distances ranging from 1100 to 1500 ft from the center of the field. Hydrogen cyanide was detected in 6 of 18 ambient air samples at concentrations ranging from 0.26 to 1.86 parts per billion (ppb). Ambient air samples collected at residential properties located within 2600 ft of the leach field did not contain detectable concentrations of cyanide (detection level of 0.2 ppb). We used site-specific data and two steady-state air dispersion models, ISCST3 and AERMOD, to predict ambient air concentrations of cyanide at the sampling points. The ISCST3 model over-predicted the measured 8-h concentrations of hydrogen cyanide by a factor of 2.4, on average, and the AERMOD model under-predicted the air concentrations of hydrogen cyanide by a factor of 0.76, on average. The major sources of uncertainty in the model predictions were the complex terrain of the area and the uncertainty in the emission rates of cyanide from the leach field. The measured and predicted concentrations of cyanide in the air samples were not at levels that would pose a human health hazard for acute or chronic exposures.
Keywords: Air monitoring; ISCST3; AERMOD;

Dicarboxylic acids, ketocarboxylic acids and dicarbonyls in the urban roadside area of Hong Kong by K.F. Ho; S.C. Lee; J.J. Cao; Kimitaka Kawamura; Tomomi Watanabe; Y. Cheng; Judith C. Chow (3030-3040).
Homologous dicarboxylic acids (C2–C12), ketocarboxylic acids (ωC2–ωC9, pyruvic acid) and dicarbonyls (glyoxal and methylglyoxal) have been studied in the urban aerosol samples (PM2.5) collected from the Hong Kong roadside atmosphere during winter and summer of 2003 using a capillary GC and GC-MS method. The concentrations of total dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls were higher in winter than in summer (except for some species like phthalic acid, Ph). Oxalic (C2) acid was found as the most abundant species in summer, followed by Ph. Oxalic (C2) acid was also found as the most abundant species in winter, but followed by malonic (C3) acid. The C2 diacid comprised 28–66% of the total diacid concentrations. The diacids with higher carbon numbers were less abundant, although C9 diacid was relatively abundant (2%). Glyoxylic acid (ωC2) and methylglyoxal were found as the most abundant ketocarboxylic acid and dicarbonyl in both seasons, respectively. The concentrations of the total diacids, total ketoacids and total dicarbonyls ranged from 224 to 1381 ng m−3, 10 to 89 ng m−3 and 5 to 21 ng m−3, respectively. Their relative abundances in PM2.5 mass were 1.18%, 0.06% and 0.02%, respectively. High concentrations of toluene (winter: 33.8 μg m−3; summer: 41.3 μg m−3) and naphthalenes (winter: 1.2 μg m−3; summer: 1.9 μg m−3) observed were one possible source for the abundant phthalic and also methylmaleic acids detected.
Keywords: Dicarboxylic acids; Ketocarboxylic acids; Dicarbonyls; Seasonal variations; Hong Kong;

This study evaluates the ability of the Community Multiscale Air Quality (CMAQ) model to simulate the spatial variability of summertime ozone (O3) at the surface and in the free troposphere over the continental United States. Simulated surface O3 concentrations are compared with 987 Air Quality System (AQS) sites and 123 Clean Air Status and Trends Network (CASTNet) sites. CMAQ's ability to reproduce surface observations varies with O3 concentration. The model best simulates observed O3 for intermediate concentrations (40–60 ppbv), while over-(under-) predicting at lower (higher) levels. CMAQ reproduces surface O3 for a wide range of conditions (30–80 ppbv) with a normalized mean error (NME) less than 35% and normalized mean bias (NMB) lying between ±15% for the whole domain. Although systematically over-predicting O3 in the east and under-predicting it in the western United States, CMAQ is able to reproduce 1- and 8-h daily maxima with a cross-domain mean bias (MB) of 1 and 8 ppbv, or NMB of 8% and 25%, respectively. The model underestimates observed O3 at rural sites (MB=−5 ppbv, NMB=−5% and NME=23% with a 40 ppbv cut-off value) and over-predicts it at urban and suburban sites by a similar magnitude (MB=6 ppbv, NMB=7% and NME=25%). Apparent errors and biases decrease when data is averaged over longer periods, suggesting that most evaluation statistics are dependent on the time scale of data aggregation. Therefore, performance criteria should specify an averaging period (e.g., 1- or 8- h) and not be independent of averaging period as some current model evaluation studies imply. Comparisons of vertical profiles of simulated O3 with ozonesonde data show both overestimation and underestimation by 10–20 ppbv in the lower troposphere and a consistent under-prediction in the upper troposphere. Vertical O3 distributions are better simulated when lateral boundary conditions obtained from the global Model of Ozone and Related Tracers version 2 (MOZART-2) are used, but under-prediction remains. The assumption of zero-flux at the top boundary and the resulting exclusion of the contribution of stratosphere–troposphere exchange to tropospheric O3 concentrations limit the ability of CMAQ to reproduce O3 concentrations in the upper troposphere.
Keywords: CMAQ; Model evaluation; Ozone; Ozonesonde; Vertical profile; Air quality model;

Photochemical ozone production in the Eastern Mediterranean by Evangelos Gerasopoulos; Giorgos Kouvarakis; Mihalis Vrekoussis; Christos Donoussis; Nikolaos Mihalopoulos; Maria Kanakidou (3057-3069).
A 7 year time series (1997–2004) of surface ozone at Finokalia, Crete, in the Eastern Mediterranean, was analysed to investigate the factors that control the diurnal variability of ozone, and evaluate seasonally distributed ozone production/destruction rates in the area. The observed diurnal evolution of related chemical/physical parameters indicates that ozone morning built-up is driven by photochemistry while during summer the entrainment from the free troposphere is the dominant process in the afternoon. The observed similar behaviour of ozone maxima and Radon-222 minima supports that entrainment from the free troposphere affects the ozone diurnal pattern. Ozone nighttime depletion is mainly attributed to deposition and to a lesser extent to chemical reactions. On an annual basis the role of local photochemistry is found to be limited (−1–1.7 ppbv d−1) contributing by less than 4% to the observed ozone levels. During summer the enhanced ozone destruction via deposition and chemistry are almost balanced by the chemical production and the entrainment of ozone rich air masses from the free troposphere that maximizes in summer (4–6% of the observed ozone levels). Chemical box model simulations also indicate low net chemical production in the area throughout the year that results from high chemical production and destruction terms. Especially during summer photochemical ozone depletion over the area is revealed both by model results and observations (0.5–1.0 ppbv d−1).
Keywords: Ozone photochemical production; Eastern Mediterranean; Marine boundary layer; Diurnal cycle;

In this paper, we describe two advanced statistical techniques suited to address the following questions: which source categories of emissions affect given areas and where do these source categories come from? A source category is defined as a combination of volatile organic compounds (VOCs) associated with a specific industrial process. A discussion of the positive matrix factorization (PMF) multivariate receptor model is presented, and this PMF technique applied to hourly average concentrations of VOCs measured at five Photochemical Assessment Monitoring Stations (PAMS) located near the emission-rich Houston Ship Channel region in Texas. The observations were made between June and October 2003, and the PMF analysis was limited to nighttime measurements (21:00–06:00 CDT) to remove the complexity of photochemical processing and associated changes in the concentrations of primary and secondary VOCs. Six to eight VOCs source categories were identified for the five Ship Channel sites. Specific geographic areas associated with each source category were identified through the use of conditional probability functions that identify source regions when superimposed on maps of VOC emissions.
Keywords: Receptor modeling; VOC; Positive matrix factorization (PMF); Conditional probability function (CPF); Houston; Air quality;

Numerical experiments on MM5–CMAQ sensitivity to various PBL schemes by Qi Mao; Larry L. Gautney; Toree M. Cook; Mary E. Jacobs; Shandon N. Smith; Jimmie J. Kelsoe (3092-3110).
The Community Multiscale Air Quality (CMAQ) modeling system developed by the United States Environmental Protection Agency (USEPA) was used along with the PSU/NCAR mesoscale modeling system MM5 to study air quality modeling sensitivity to various planetary boundary layer (PBL) schemes implemented in MM5. Two 37-day periods, representing typical summer and winter periods, were selected for the simulations. The MM5 domain covered the continental US while the CMAQ domain covered much of the central and eastern US. There were 34 vertical layers in MM5 and 18 in CMAQ. The horizontal resolution was 36 km for both. MM5 was run with five of the seven commonly used PBL schemes to generate a series of gridded meteorological fields. The data were then processed and converted by the meteorology–chemistry interface processor (MCIP) to produce meteorological input for CMAQ, in conjunction with the emissions data prepared by the Sparse Matrix Operator Kernel Emissions (SMOKE) System.The sensitivity of MM5–CMAQ modeling to the various PBL schemes was assessed and quantified by comparing model output against observations from the meteorological and the air quality monitoring networks within the CMAQ domain. The meteorological variables evaluated included surface (2-m) and 850-mb temperature, 10-meter and 850 mb wind speed and direction, 2-m mixing ratio, surface pressure, and cloud fraction over 50 surface sites and 21 upper air sounding sites. The CMAQ variables included gaseous species O3, NO2, NO x , SO2 and fine particulate matter PM2.5 for over 2000 monitoring stations. A new 3-2-1 objective evaluation approach was developed to enhance the model sensitivity analysis. Results of evaluation of these variables indicate that domain-wide the performance of neither model was sensitive to the PBL schemes. Although large differences of PBL height existed across the meteorological simulations, they did not appreciably affect the CMAQ performance. On an urban scale, differences across the CMAQ simulations were large enough for the model to be considered sensitive, although no favorable PBL scheme was identified. It is suggested that domain-wide the lack of sensitivity of the MM5–CMAQ modeling system to the PBL schemes was mainly attributed to the parameterization of vertical eddy diffusivity in CMAQ and the four-dimensional data assimilation (FDDA) in MM5.
Keywords: Model sensitivity; Planetary boundary layer; Air quality simulation; FDDA; Aspect ratios of error;

A comparative study of the elemental composition of the exhaust emissions of cars powered by liquefied petroleum gas and unleaded petrol by McKenzie C.H. Lim; Godwin A. Ayoko; Lidia Morawska; Zoran D. Ristovski; E. Rohan Jayaratne; Serge Kokot (3111-3122).
Elements emitted from the exhausts of new Ford Falcon Forte cars powered by unleaded petrol (ULP) and liquefied petroleum gas (LPG) were measured on a chassis dynamometer. The measurements were carried out in February, June and August 2001, and at two steady state driving conditions (60 and 80 km h−1). Thirty seven elements were quantified in the exhaust samples by inductively coupled plasma mass spectrometry (ICPMS). The total emission factors of the elements from the exhausts of ULP cars were higher than those of LPG cars at both engine speeds even though high variability in the exhaust emissions from different cars was noted. The effect of the operating conditions such as mileage of the cars, engine speed, fuel and lubricating oil compositions on the emissions was studied. To investigate the effects of these conditions, multivariate data analysis methods were employed including exploratory principal component analysis (PCA), and the multi-criteria decision making methods (MCDM), preference ranking organization method for enrichment evaluation (PROMETHEE) and geometrical analysis for interactive aid (GAIA), for ranking the cars on the basis of the emission factors of the elements. PCA biplot of the complete data matrix showed a clear discrimination of the February, June and August emission test results. In addition, (i) platinum group elements (PGE) emissions were separated from each other in the three different clusters viz. Pt with February, Pd with June and Rh with August; (ii) the motor oil related elements, Zn and P, were particularly associated with the June and August tests (these vectors were also grouped with V, Al and Cu); and (iii) highest emissions of most major elements were associated with the August test after the cars have recorded their highest mileage. Extensive analysis with the aid of the MCDM ranking methods demonstrated clearly that cars powered by LPG outperform those powered by ULP. In general, cars tested in June perform better than those tested in August, which suggested that mileage was the key criterion of car performance on the basis of elemental emission factors.
Keywords: ULP- and LPG-powered cars; Chemical elements; Emission factors; Multivariate analyses;

Nitrous acid in the urban area of Rome by Karin Acker; Antonio Febo; Sebastian Trick; Cinzia Perrino; Paolo Bruno; Peter Wiesen; Detlev Möller; Wolfgang Wieprecht; Renate Auel; Marco Giusto; Andreas Geyer; Ulrich Platt; Ivo Allegrini (3123-3133).
Nitrous acid (HNO2) and a large variety of other components were simultaneously measured in the city centre of Rome (Italy) during the NITROCAT ground based field experiment in May/June 2001. The highest HNO2 concentrations were found under high-pressure conditions with high nocturnal atmospheric stability and high values of pollutants. After night time formation and accumulation up to 2 ppb HNO2 were observed. The measurements confirm that during the first hours after sunrise, when hydroxyl radical (OH) production rates from other sources (photolysis of ozone and formaldehyde (HCHO)) are slow, HNO2 photolysis is the most important primary OH source in the lowest part of the troposphere; up to 1–4×107  OH cm−3  s−1 were estimated for that time from this source. This contributes considerably to the initiation of the photochemistry for the day. The unexpected high daytime concentrations of few hundred ppt observed by DOAS as well as by the two in situ wet collection techniques (wet denuder/IC, coil sampling/HPLC) possibly influence ozone chemistry during the entire day. The heterogeneous on-surface production of HNO2 (and consequently of HNO3) provides also a new-type acidity formation influencing directly the biosphere and the materials. About 20% of the total nitrite was found on atmospheric aerosols. The HNO2 measurements agree well for the different in situ measurement techniques and the spatial integration DOAS simultaneously performed over several weeks in the real atmosphere and during reaction chamber experiments.
Keywords: Air pollution; Atmospheric chemistry; Heterogeneous processes; Nitrous acid;

Semi-permeable membrane devices (SPMDs) were deployed at 12 sites in the Pearl River Delta (PRD) during 2001–2002 to elucidate the spatial distribution and seasonal variations of polycyclic aromatic hydrocarbons (PAHs) in the subtropical region. Pine needles from the same sites were also analyzed for PAHs for a comparison with SPMDs. In Guangzhou, high volume active air sampling (HiVol) was carried out weekly through out the year-round sampling campaign. The PAHs sequestered in SPMDs (in ng SPMD−1  day−1) were found to be higher in winter than in summer. Using the HiVol data, SPMD sampling rates were calculated seasonally for some dominant gas-phase PAH compounds (Fluorene to Pyrene). These sampling rates ranged from 0.7 to 2.8 m3  day−1, which were used to determine the atmospheric PAH concentrations at other sites. The calculated PAH concentrations, based on different temperature-dependant SPMD sampling rates, in the air were higher in summer than in winter. The PAH compounds sampled with SPMDs and pine needle were mainly associated with gaseous PAHs, while pine needles accumulated more high molecular weight (HW) PAHs. Good agreements were found in the spatial distribution of atmospheric PAHs measured by SPMDs and pine needles. The potential of using SPMDs for seasonal monitoring of atmospheric organic pollutants at a regional scale was demonstrated.
Keywords: Semi-permeable membrane device (SPMD); Polycyclic aromatic hydrocarbons (PAHs); Passive air sampling; Seasonal variations; Pearl River Delta;

Speciated hourly mercury measurements were made in Detroit, Michigan during four sampling campaigns from 2000 to 2002. In addition, other chemical and meteorological parameters were measured concurrently. These data were analyzed using principal components analysis (PCA) in order to develop source receptor relationships for mercury species in urban Detroit. Reactive gaseous mercury (RGM) was found to cluster on two main factors; photochemistry and a coal combustion factor. Particulate phase mercury, Hgp, tended to cluster with RGM on the same factor. The photochemistry factor corroborates previous observations of the presence of RGM in highly oxidizing atmospheres and does not point to a specific source emission type. Instead, it likely represents local emissions and regional transport of photochemically processed air masses. The coal combustion factor is indicative of emissions from coal-fired power plants near the receptor site. Elemental mercury was found on a factor for combustion from automobiles and points to the influence these emissions have on the receptor site, which was located proximate to two major interstate highways and the largest border crossing in the United States. This analysis reveals that the receptor site which is located in an industrialized sector of the city of Detroit experienced impacts from both stationary and point sources of mercury that are both local and regional in nature.
Keywords: Gaseous elemental mercury (GEM); Reactive gaseous mercury (RGM); Particulate phase mercury (Hgp); Source–receptor relationships; Photochemistry; Coal burning; Automobile emissions;

Long-term changes in tropospheric ozone by S.J. Oltmans; A.S. Lefohn; J.M. Harris; I. Galbally; H.E. Scheel; G. Bodeker; E. Brunke; H. Claude; D. Tarasick; B.J. Johnson; P. Simmonds; D. Shadwick; K. Anlauf; K. Hayden; F. Schmidlin; T. Fujimoto; K. Akagi; C. Meyer; S. Nichol; J. Davies; A. Redondas; E. Cuevas (3156-3173).
Tropospheric ozone changes are investigated using a selected network of surface and ozonesonde sites to give a broad geographic picture of long-term variations. The picture of long-term tropospheric ozone changes is a varied one in terms of both the sign and magnitude of trends and in the possible causes for the changes. At mid latitudes of the S.H. three time series of ∼20 years in length agree in showing increases that are strongest in the austral spring (August–October). Profile measurements show this increase extending through the mid troposphere but not into the highest levels of the troposphere.In the N.H. in the Arctic a period of declining ozone in the troposphere through the 1980s into the mid-1990s has reversed and the overall change is small. The decadal-scale variations in the troposphere in this region are related in part to changes in the lowermost stratosphere.At mid latitudes in the N.H., continental Europe and Japan showed significant increases in the 1970s and 1980s. Over North America rises in the 1970s are less than those seen in Europe and Japan, suggesting significant regional differences. In all three of these mid latitude, continental regions tropospheric ozone amounts appear to have leveled off or in some cases declined in the more recent decades. Over the North Atlantic three widely separated sites show significant increases since the late-1990s that may have peaked in recent years.In the N.H. tropics both the surface record and the ozonesondes in Hawaii show a significant increase in the autumn months in the most recent decade compared to earlier periods that drives the overall increase seen in the 30-year record. This appears to be related to a shift in the transport pattern during this season with more frequent flow from higher latitudes in the latest decade.
Keywords: Trends; Surface ozone; Ozonesondes; Tropospheric chemistry; Ozone transport;

Diurnal and seasonal variation of monoterpene and sesquiterpene emissions from Scots pine (Pinus sylvestris L.) by C. Holzke; T. Hoffmann; L. Jaeger; R. Koppmann; W. Zimmer (3174-3185).
Recent research pointed out the question of missing OH reactivity in a forest system and the question for unknown highly reactive biogenic emissions. In this study we show that coniferous forests are an important source of highly reactive hydrocarbons, the sesquiterpenes. We investigated the seasonality of terpene emissions from Scots pine to work out influences on atmospheric chemistry in different seasons for both mono- and sesquiterpenes. Especially sesquiterpenes (C15) change dramatically in their contribution to the terpene emissions of Scots pine. Fourteen sesquiterpenes and oxygenated compounds were found in the emissions. In spring, the pattern was most complex with all 14 compounds being emitted, whereas in summer and fall it was reduced to 1,8-cineol and camphor. The emission pattern of the monoterpenes varied only slightly. The main compounds emitted were α-pinene, β-pinene, and 3-carene representing up to 90% of the total terpene emission. The total monoterpene emission rates varied from below detection limit to 460 pmol m−2  s−1 with highest emission rates found in June. Standard emission rates of the main compounds calculated from the monthly measured diurnal emission courses varied considerably over the year. Highest values were found in spring and early summer with up to 700 pmol m−2  s−1.
Keywords: Emission; Long-term variation; Monoterpenes; Scots pine; Seasonality; Sesquiterpenes; VOCs;

The GILTT solution of the advection–diffusion equation for an inhomogeneous and nonstationary PBL by D.M. Moreira; M.T. Vilhena; D. Buske; T. Tirabassi (3186-3194).
In this work, we present an analytical solution for the nonstationary two-dimensional advection–diffusion equation to simulate the pollutant dispersion in the planetary boundary layer. In this method the advection–diffusion equation is solved by the application of the Laplace transform technique and the solution of the resulting stationary problem by the generalised integral Laplace transform technique (GILTT). We also report numerical simulations and statistical comparison with experimental data available in the literature.
Keywords: GILTT; Laplace transform; Atmospheric dispersion; Analytical solution; Time-dependent advection–diffusion equation; Planetary boundary layer; Air pollution modeling;

Mass concentration and elemental composition of indoor PM2.5 and PM10 in University rooms in Thessaloniki, northern Greece by Panagiotis Gemenetzis; Panagiotis Moussas; Anastasia Arditsoglou; Constantini Samara (3195-3206).
The mass concentration and the elemental composition of PM2.5 and PM10 were measured in 40 rooms (mainly offices or mixed office-lab rooms, and photocopying places) of the Aristotle University of Thessaloniki, northern Greece. A total of 27 major, minor and trace elements were determined by ED-XRF analysis. The PM2.5/PM10 concentration ratios averaged 0.8±0.2, while the corresponding elemental ratios ranged between 0.4±0.2 and 0.9±0.2. The concentrations of PM2.5 and PM10 were significantly higher (by 70% and 50%, respectively) in the smokers’ rooms compared to the non-smokers’ places. The total elemental concentrations were also higher in the smokers’ rooms (11.5 vs 8.2 μg m−3 for PM2.5, and 10.3 vs 7.6 μg m−3 for PM2.5−10). Fine particle concentrations (PM2.5) were found to be quite proportional to smoking strength. On the contrary, the two environments exhibited similar coarse (PM2.5−10) particle fractions not related to the number of cigarettes smoked. A slight decrease of particle concentrations with increasing the floor level was also observed, particularly for PM2.5, suggesting that high-level floors are less impacted by near ground-level sources like traffic emissions. Finally, the removal efficiency of air purification systems was evaluated.
Keywords: Air purification system; ETS; Enrichment factors; Heavy metals; Offices; Particulate matter;

A 12-month study of PM10 and gases in the industrial Spanish town of Puertollano reveals striking variations in pollutant concentrations. The normal daily pollution pattern is characterised by a daily double peak for NO x and CO and associated double trough for ozone (morning and evening), a midday atmospheric fumigation peak for SO2 and PM10 (1–2 h later in winter), and a late morning through afternoon maximum for ozone (shorter and lower in winter). Superimposed upon this are: (1) seasonal variations, which accentuate the PM10 and SO2 mid-morning peaks in winter (when the peak occurs later than in summer), raise NO2, ozone and background particulate levels during the summer, and favour enhanced levels of NO during the winter; (2) local pollution spikes, particularly those associated with SO2 release from nearby industrial sources; (3) regional atmospheric stagnation episodes, which enhance concentrations of all pollutants and (4) intrusion of exotic pollutants, notably desert dust from North Africa. Given that air pollutants are known adversely to influence human health, understanding and predicting such diurnal variations in concentrations of inhalable pollutants is especially relevant to susceptible individuals such as asthmatics.
Keywords: PM10; SO2; NO x ; Industry; Fumigation; Spain;

New Directions: Rich in CO2 by Malamo Korbetis; David S. Reay; John Grace (3219-3220).