Characterization of aging wood chip combustion aerosol in an environmental chamber

Aging of aerosol from wood chip combustion in a stoker burner was monitored in an outdoor environmental chamber for 19–27 h in order to study the size, volatility and organic carbon (OC) content of the combustion aerosol particles during aging. A scanning mobility particle sizer, a volatility tandem differential mobility analyzer (VTDMA), and a thermal–optical carbon analyzer were utilized. The VTDMA and carbon analyses were performed at the beginning, after 17–24 h of aging and at one intermediate point. The size decrease of freshly emitted particles was 6–10% when heated to $360{}^{\circ }\mathrm{C}$, and was found to depend on the experiment start time. For particles aged for 24 h, a 74–86% decrease in particle size at $360{}^{\circ }\mathrm{C}$ was observed. The more volatile OC fraction and the total OC fraction in the particles increased and the less volatile OC fraction decreased with aging. This suggests that during aging more volatile compounds condense on or heavier compounds photodegrade into lighter ones in the particles. Occasionally, new particle formation and growth were observed in the following day. The new particles were found to be composed mainly of volatile material.     

Mercury emissions from automobiles using gasoline,diesel, and LPG

Mercury (Hg) emissions from gasoline, diesel, and liquefied petroleum gas (LPG) vehicles were measured and speciated (particulate, oxidized, and elemental mercury). First, three different fuel types were analyzed for their original Hg contents; 571.1±4.5 ng L⁻¹ for gasoline, 185.7±2.6 ng L⁻¹ for diesel, and 1230.3±23.5 ng L⁻¹ for LPG. All three vehicles were then tested at idling and driving modes. Hg in the exhaust gas was mostly in elemental form (Hg⁰), and no detectable levels of particulate (Hg^p) or oxidized (Hg²⁺) mercury were measured. At idling modes, Hg concentrations in the exhaust gas of gasoline, diesel, and LPG vehicles were 1.5–9.1, 1.6–3.5, and 10.2–18.6 ng m⁻³, respectively. At driving modes, Hg concentrations were 3.8–16.8 ng m⁻³ (gasoline), 2.8–8.5 ng m⁻³ (diesel), and 20.0–26.9 ng m⁻³ (LPG). For all three vehicles, Hg concentrations at driving modes were higher than at idling modes. Furthermore, Hg emissions from LPG vehicle was highest of all three vehicle types tested, both at idling and driving modes, as expected from the fact that it had the highest original fuel Hg content.     

Aerosol number size distributions within the exhaust plume of a diesel and a gasoline passenger car under on-road conditions and determination of emission factors

A new setup has been developed and built to measure number size distributions of exhaust particles and thermodynamic parameters under real traffic conditions. Measurements have been performed using a diesel and a gasoline passenger car driving with different speeds and engine conditions. Significant number of nucleation mode particles was found only during high load conditions, i.e. high car and engine speeds behind the diesel car. The number concentration of soot mode particles varied within a factor of two for different engine conditions while the concentration of nucleation mode particles varied up to two orders of magnitude. The results show that roadside measurements are still quite different from those behind the tailpipe. Beside dilution transformation processes within the first meter behind the tailpipe also play an important role, such as nucleation and growth. Emission factors were calculated and compared with those obtained by other studies. Emission factors for particles larger than 25 nm (primary emissions) varied within 1.1 × 10¹⁴ km^?1 and 2.7 × 10¹⁴ km^?1 for the diesel car and between 0.6 × 10¹² km^?1 and 3.5 × 10¹² km^?1 for the gasoline car. The advantage of these measurements is the exhaust dilution under atmospheric conditions and the size-resolved measurement technique to divide into primary emitted and secondary formed particles.     

Measurement of nucleation and soot mode particle emission from a diesel passenger car in real world and laboratory in situ dilution

Uncertainties still remain in the size and number emission of nucleation and soot mode particles from diesel vehicles and understanding of the nucleation process under different ambient conditions. Particle emission measurements were carried out with a EURO-3 certified European diesel passenger car running on low (<10 ppm S) and high (310 ppm S) sulfur fuel. A newly developed in situ diluter which sampled exhaust continuously from the tailpipe and diluted in two steps by a factor of 500–6000 was employed to study nucleation particle formation under well-controlled temperature and humidity conditions. Particle emission measurements were also carried out with a mobile laboratory chasing the exhaust plume of the same vehicle in summer (19–25 °C) and winter (9 °C), with no significant difference of the nucleation or soot mode particle emission found. The particle size distributions compared well with those measured in the laboratory with the same vehicle under identical driving conditions. Simple nucleation and coagulation calculations were compared with the atmospheric and laboratory measurements. It was shown that the primary dilution step had the largest impact on the nucleation mode formation, while the model overpredicted the influence of temperature and humidity. No nucleation mode particles were observed running the diesel vehicle on low (<10 ppm S) fuel.     

Vertical profiles of ultrafine to supermicron particles measured by aircraft over Osaka metropolitan area in Japan

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.     

Aqueous-phase reactive uptake of dicarbonyls as a source of organic aerosol over eastern North America

We use a global 3-D atmospheric chemistry model (GEOS-Chem) to simulate surface and aircraft measurements of organic carbon (OC) aerosol over eastern North America during summer 2004 (ICARTT aircraft campaign), with the goal of evaluating the potential importance of a new secondary organic aerosol (SOA) formation pathway via irreversible uptake of dicarbonyl gases (glyoxal and methylglyoxal) by aqueous particles. Both dicarbonyls are predominantly produced in the atmosphere by isoprene, with minor contributions from other biogenic and anthropogenic precursors. Dicarbonyl SOA formation is represented by a reactive uptake coefficient γ = 2.9 × 10^?3 and takes place mainly in clouds. Surface measurements of OC aerosol at the IMPROVE network in the eastern U.S. average 2.2 ± 0.7 μg C m^?3 for July–August 2004 with little regional structure. The corresponding model concentration is 2.8 ± 0.8 μg C m^?3, also with little regional structure due to compensating spatial patterns of biogenic, anthropogenic, and fire contributions. Aircraft measurements of water-soluble organic carbon (WSOC) aerosol average 2.2 ± 1.2 μg C m^?3 in the boundary layer (<2 km) and 0.9 ± 0.8 μg C m^?3 in the free troposphere (2–6 km), consistent with the model (2.0 ± 1.2 μg C m^?3 in the boundary layer and 1.1 ± 1.0 μg C m^?3 in the free troposphere). Source attribution for the WSOC aerosol in the model boundary layer is 27% anthropogenic, 18% fire, 28% semi-volatile SOA, and 27% dicarbonyl SOA. In the free troposphere it is 13% anthropogenic, 37% fire, 23% semi-volatile SOA, and 27% dicarbonyl SOA. Inclusion of dicarbonyl SOA doubles the SOA contribution to WSOC aerosol at all altitudes. Observed and simulated correlations of WSOC aerosol with other chemical variables measured aboard the aircraft suggest a major SOA source in the free troposphere compatible with the dicarbonyl mechanism.     

Generation and growth of aerosols over Pune,India

The measured physical size distributions of sub-micron particles during cold season at Pune, India are analyzed to explore the characteristics of nucleation and growth properties. Preliminary analysis of aerosol size distribution in time-series shows large increase in number concentration due to nucleation events between 0800 h and 1030 h at this location. The observable quantities such as condensable vapor concentration (C), its source rate (Q), growth rate (GR) and condensable sink (CS) are estimated from the time-series evolutions of aerosol size distributions. The concentration of vapor and its source rate were about 19.8 ± 2.15 × 10⁷ molecules cm^?3 and 1.28 ± 0.084 × 10⁷ cm^?3 s^?1 respectively. The average condensation sink and growth rate were 7.1 ± 0.4 × 10^?2 s^?1 and 16.95 ± 1.86 nm h^?1 respectively during the growth period. The values are high enough to trigger the nucleation bursts and enhance subsequent growth rates of nucleation mode particles at this location. The magnitudes are in the range of those observed at New Delhi, India and much higher than those of European cities. The ratio of apparent to real nucleation rate is found to be a measure of number concentration of freshly produced particles by photo-chemical nucleation. The predicted number concentrations corresponding to measured distributions of mid-point diameter increases with the size for both 1 nm nucleated clusters and 3 nm particles. The database of all the possible event days and the event characteristics forms the basis for future works into the causes and implications of atmospheric particle formation at this location.     

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.     

Dioxins,furans and polycyclic aromatic hydrocarbons emissions from a hospital and cemetery waste incinerator

An experimental campaign was carried out on a hospital and cemetery waste incineration plant in order to assess the emissions of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polycyclic aromatic hydrocarbons (PAHs). Raw gases were sampled in the afterburning chamber, using a specifically designed device, after the heat recovery section and at the stack. Samples of slags from the combustion chamber and fly ashes from the bag filter were also collected and analyzed. PCDD/Fs and PAHs concentrations in exhaust gas after the heat exchanger (200–350 °C) decreased in comparison with the values detected in the afterburning chamber. Pollutant mass balance regarding the heat exchanger did not confirm literature findings about the de novo synthesis of PCDD/Fs in the heat exchange process. In spite of a consistent reduction of PCDD/Fs in the flue gas treatment system (from 77% up to 98%), the limit of 0.1 ng ITEQ Nm⁻³ at the stack was not accomplished. PCDD/Fs emission factors for air spanned from 2.3 up to 44 μg ITEQ t⁻¹ of burned waste, whereas those through solid residues (mainly fly ashes) were in the range 41–3700 μg ITEQ t⁻¹. Tests run with cemetery wastes generally showed lower PCDD/F emission factors than those with hospital wastes. PAH total emission factors (91–414 μg kg⁻¹ of burned waste) were in the range of values reported for incineration of municipal and industrial wastes. In spite of the observed release from the scrubber, carcinogenic PAHs concentrations at the stack (0.018–0.5 μg Nm⁻³) were below the Italian limit of 10 μg Nm⁻³.     

Inventory of aerosol and sulphur dioxide emissions from India: I—Fossil fuel combustion

A comprehensive, spatially resolved (0.25°×0.25°) fossil fuel consumption database and emissions inventory was constructed, for India, for the first time. Emissions of sulphur dioxide and aerosol chemical constituents were estimated for 1996–1997 and extrapolated to the Indian Ocean Experiment (INDOEX) study period (1998–1999). District level consumption of coal/lignite, petroleum and natural gas in power plants, industrial, transportation and domestic sectors was 9411 PJ, with major contributions from coal (54%) followed by diesel (18%). Emission factors for various pollutants were derived using India specific fuel characteristics and information on combustion/air pollution control technologies for the power and industrial sectors. Domestic and transportation emission factors, appropriate for Indian source characteristics, were compiled from literature. SO₂ emissions from fossil fuel combustion for 1996–1997 were 4.0 Tg SO₂ yr⁻¹, with 756 large point sources (e.g. utilities, iron and steel, fertilisers, cement, refineries and petrochemicals and non-ferrous metals), accounting for 62%. PM_2.5 emitted was 0.5 and 2.0 Tg yr⁻¹ for the 100% and the 50% control scenario, respectively, applied to coal burning in the power and industrial sectors. Coal combustion was the major source of PM_2.5 (92%) primarily consisting of fly ash, accounting for 98% of the “inorganic fraction” emissions (difference between PM_2.5 and black carbon+organic matter) of 1.6 Tg yr⁻¹. Black carbon emissions were estimated at 0.1 Tg yr⁻¹, with 58% from diesel transport, and organic matter emissions at 0.3 Tg yr⁻¹, with 48% from brick-kilns. Fossil fuel consumption and emissions peaked at the large point industrial sources and 22 cities, with elevated area fluxes in northern and western India. The spatial resolution of this inventory makes it suitable for regional-scale aerosol-climate studies. These results are compared to previous studies and differences discussed. Measurements of emission factors for Indian sources are needed to further refine these estimates.     

Organic trace gas composition of the marine boundary layer over the northwest Indian Ocean in April 2000

In April 2000 atmospheric trace gas measurements were performed on the western Indian Ocean on a cruise of the Dutch research vessel Pelagia from the Seychelles (5°S, 55°E) to Djibouti (12°N, 43°E). The measurements included analysis of dimethyl sulfide (DMS), acetone and acetonitrile every 40 s using PTR-MS (proton-transfer-reaction mass spectrometry) and gas chromatographic analyses of C₂–C₇ hydrocarbons in air samples taken during the cruise. The measurements took place at the end of the winter monsoon season and the sampled air masses came predominantly from the Southern Hemisphere, resulting in low concentrations of some long-lived hydrocarbons, halocarbons, acetone (350 pptv) and acetonitrile (120 pptv). On three consecutive days a diurnal cycle in DMS concentration was observed, which was used to estimate the emission of DMS (1.5±0.7×10¹³ molecules m⁻² s⁻¹) and the 24 h averaged concentration of hydroxyl (OH) radicals (1.4±0.7×10⁶ molecules cm⁻³). A strongly increased DMS concentration was found at a location where upwelling of deeper ocean waters took place, coinciding with a marked decrease in acetone and acetonitrile. In the northwestern Indian Ocean a slight increase of some trace gases was noticed showing a small influence of pollution from Asia and from northeast Africa as indicated with back trajectory calculations. The air masses from Asia had elevated acetonitrile concentrations showing some influence of biomass burning as was also found during the 1999 Indian Ocean Experiment, whereas the air masses from northeast Africa seemed to have other sources of pollution.     

Size-resolved,real-time measurement of water-insoluble aerosols in metropolitan Atlanta during the summer of 2004

During the month of August 2004, the size-resolved number concentration of water-insoluble aerosols (WIA) from 0.25 to 2.0 μm was measured in real-time in the urban center of Atlanta, GA. Simultaneous measurements were performed for the total aerosol size distribution from 0.1 to 2.0 μm, the elemental and organic carbon mass concentration, the aerosol absorption coefficient, and the aerosol scattering coefficient at a dry (RH=30%) humidity. The mean aerosol number concentration in the size range 0.1–2.0 μm was found to be 360±175 cm⁻³, but this quantity fluctuated significantly on time scales of less than one hour and ranged from 25 to 1400 cm⁻³ during the sample period. The mean WIA concentration (0.25–2.0 μm) was 13±7 cm⁻³ and ranged from 1 to 60 cm⁻³. The average insoluble fraction in the size range 0.25–2.0 μm was found to be 4±2.5% with a range of 0.3–38%. The WIA population was found to follow a consistent diurnal pattern throughout the month with concentration maxima concurring with peaks in vehicular traffic flow. WIA concentration also responded to changes in meteorological conditions such as boundary layer depth and precipitation events. The temporal variability of the absorption coefficient followed an identical pattern to that of WIA and ranged from below the detection limit to 55 Mm⁻¹ with a mean of 8±6 Mm⁻¹. The WIA concentration was highly correlated with both the absorption coefficient and the elemental carbon mass concentration, suggesting that WIA measurements are dominated by fresh emissions of elemental carbon. For both the total aerosol and the WIA size distributions, the maximum number concentration was observed at the smallest sizes; however the WIA size distribution also exhibited a peak at 0.45 μm which was not observed in the total population. Over 60% of the particles greater than 1.0 μm were observed to be insoluble in the water sampling stream used by this instrumentation. Due to the refractive properties of black carbon, it is highly unlikely that these particles could be composed of elemental carbon, suggesting a crustal source for super-micron WIA.     

Measurements of JNO3− in snow by nitrate-based actinometry

Chemical actinometry was used to measure nitrate photolysis rate coefficients, J_NO3⁻, on and in snowpack at Summit, Greenland. Sealed glass tubes containing nitrate and a hydroxyl radical trapping system were buried in snow and exposed for between 2 and 24 h. Average J_NO3⁻ values for 2-h midday exposures in early June on surface snow were 10–14×10⁻⁷ s⁻¹. Averages over 24 h were 3.5–4.5×10⁻⁷ s⁻¹. These values reflect the integrated photon flux and also any variation of the nitrate photolysis rate with temperature. Attenuation of J_NO3⁻ within the firn was 0.03–0.04 cm⁻¹ for 24-h exposures and 0.08 cm⁻¹ for a 2-h exposure. Different attenuation coefficients may relate to differential light penetration due to changes in sun angle over the course of 24 h.     

Nitro-PAH formation studied by interacting artificially PAH-coated soot aerosol with NO2 in the temperature range of 295–523 K

Diesel particulate matter poses a threat to human health, and in particular nitrated polycyclic aromatic hydrocarbons (NPAHs) found within and on the surface of these particles. Although diesel particulate filters (DPFs) have been designed and implemented to reduce these and other harmful diesel emissions, the particle loaded filters may act as a reaction chamber for the enhanced production of NPAHs from the nitration of PAHs with NO₂.Focus is on the investigation of the heterogeneous reactions that occur on soot particles by exposing laboratory produced pyrene- or benzo(a)pyrene-coated spark discharge soot particles to varying concentrations of NO₂ and temperatures while following the formation of products over time. The sole nitration product that was observed throughout the experiments with pyrene-coated soot was 1-nitropyrene (1-NPYR), which increased linearly with reaction time for all NO₂ concentrations chosen (0.11, 1.0, 2.0, 4.0 ppm, m m^?1). Resulting 1-NPYR formation rate increased exponentially with [NO₂]. Throughout the 3-h experiments less than 10% of pyrene has been converted to 1-NPYR and the partial reaction order with regard to [NO₂] was estimated to 1.52. Benzo(a)pyrene (BaP) was more reactive than pyrene. After 3 h reaction time almost 80% of the BaP has been converted to 6-NBaP.Highest 1-NPYR concentrations on particles were detected at 373 K, and at higher temperatures a considerable decrease in particulate 1-NPYR was observed. A similar trend was observed in a DPF simulation system (PM-Kat^®-like) with BaP-coated soot. In this case, highest 6-NBaP concentration on particles was detected at 423 K. Backed by corroborating results from separate gas/solid-phase partition experiments with 1-NPYR and 6-NBaP, it is likely that the newly formed 1-NPYR and 6-NBaP became transferred from particle to gas phase at higher temperatures. Results from this study confirm the presence of 1-NPYR and 6-NBaP in particulate and gas phase under conditions encountered in DPFs, especially when operated at low temperature situations of the aftertreatment system.     

Reactions between ozone and building products: Impact on primary and secondary emissions

Reactions of ozone on common building products were studied in a dedicated emission test chamber system. Fourteen new and unused products were exposed to 100–160 ppb of ozone at 23 °C and 50% RH during 48 h experiments. Ozone deposition velocities calculated at steady state were between 0.003 cm s⁻¹ (alkyd paint on polyester film) and 0.108 cm s⁻¹ (pine wood board). All tested product showed modified emissions when exposed to ozone and secondary emissions of several aldehydes were identified. Carpets and wall coverings emitted mainly C₅–C₁₀ n-aldehydes, typical by-products of surface reactions. Linoleum, polystyrene tiles and pine wood boards also showed increased emissions of formaldehyde, benzaldehyde and hexanal associated with reduced emissions of unsaturated compounds suggesting the occurrence of gas-phase reactions. The ozone removal on the different tested products was primarily associated with surface reactions. The relative contribution of gas-phase reactions to the total ozone removal was estimated to be between 5% and 30% for pine wood boards depending on relative humidity (RH) and on the incoming ozone concentration and 2% for polystyrene tiles. On pine wood board, decreasing ozone deposition velocities were measured with increasing ozone concentrations and with RH increasing in the range 30–50%.     

Density of foliage mass and area in the boreal forest cover in Finland,with applications to the estimation of monoterpene and isoprene emissions

The distribution of the density of foliage mass and area in forest canopies throughout Finland (60–70°N) were determined on the basis of the permanent sample plots used in the Finnish National Forest Inventory. These parameters were linked to the long-term monthly mean air temperatures for 1961–1990, which had been converted to hourly temperature and radiation values with the help of a weather simulator in order to calculate the spatial distribution of mean yearly emissions of monoterpene and isoprene over Finland. The mean total density of foliage mass in southern Finland (60°⩽latitude<65°N) was around 500 g m⁻², equivalent to 4–5 m² of total foliage area per m² of land area. In northern Finland (65°⩽latitude<70°N), the maximum values remained below 200–300 g m⁻², or 2–3 m² m⁻². The highest values were achieved in forests dominated by mature Norway spruces. The higher temperatures and longer growing season in southern Finland led to greater emissions than in the rest of the country. Total annual emissions of monoterpene were 1070 kg km⁻² yr⁻¹ in southern Finland and 460 kg km⁻² yr⁻¹ in the north, and those of isoprene from Norway spruce canopies 150 and 40 kg km⁻² yr⁻¹, respectively.     

Emissions of PCDD/Fs,PCBs, and PAHs from legacy on-road heavy-duty diesel engines

Exhaust emissions of seventeen 2,3,7,8-substituted polychlorinated dibenzo-p-dioxin/furan (PCDD/F) congeners, tetra–octa PCDD/F homologues, 12 WHO 2005 polychlorinated biphenyl (PCB) congeners, mono–nona chlorinated biphenyl homologues, and 19 polycyclic aromatic hydrocarbons (PAHs) from three legacy diesel engines were investigated. The three engines tested were a 1985 model year GM 6.2 J-series engine, a 1987 model year Detroit Diesel Corporation 6V92 engine, and a 1993 model year Cummins L10 engine. Results were compared to United States’ mobile source inventory for on-road diesel engines, as well as historic and modern diesel engine emission values. The test fuel contained chlorine at 9.8 ppm which is 1.5 orders of magnitude above what is found in current diesel fuel and 3900 ppm sulfur to simulate fuels that would have been available when these engines were produced. Results indicate PCDD/F emissions of 13.1, 7.1, and 13.6 pg International Toxic Equivalency (I-TEQ) L⁻¹ fuel consumed for the three engines respectively, where non-detects are equal to zero. This compares with a United States’ mobile source on-road diesel engine inventory value of 946 pg I-TEQ L⁻¹ fuel consumed and 1.28 pg I-TEQ L⁻¹ fuel consumed for modern engines equipped with a catalyzed diesel particle filter and urea selective catalytic reduction. PCB emissions are 2 orders of magnitude greater than modern diesel engines. PAH results are representative of engines from this era based on historical values and are 3–4 orders of magnitude greater than modern diesel engines.     

Particle volatility in the vicinity of a freeway with heavy-duty diesel traffic

During February–March 2006, a major field sampling campaign was conducted adjacent to the Interstate 710 (I-710) freeway in Los Angeles, CA. I-710 has high traffic volumes (ca. 11,000 vehicles h⁻¹) and a high percentage (17–18%) of heavy-duty diesel vehicle (HDDV) traffic. The volatility of ambient particles of 20, 40, 80 and 120 nm in diameter was investigated using a Tandem Differential Mobility Analyzer (TDMA) at two locations—close to the freeway (10 m) and approximately 150 m downwind. The smallest particles (20 nm) are largely volatile at both locations. Larger particles, e.g., ⩾40 nm) showed evidence of external mixing, with the non-volatile fraction increasing with particle size. Particle volatility increased with decreasing ambient temperature. The HDDVs contribute to relatively larger non-volatile particle number and volume fractions and greater external mixing than earlier observations at a pure light-duty gasoline vehicle freeway [Kuhn et al., 2005c. Atmospheric Environment 39, 7154–7166]. Finally, the fraction of externally mixed soot particles decreased as the downwind distance increased from the I-710, due to atmospheric processes such as vapor adsorption and condensation as well as particle coagulation.     

Polycyclic aromatic hydrocarbons in the urban atmospheric particulate matter in the city of Naples (Italy)

An investigation on PAH in the atmospheric particulate matter of the city of Naples has been carried out. Urban atmospheric particulate matter was sampled in three sampling sites (West, East and central areas of the city), whose characteristics were representative of the prevailing conditions. In each site, 24 h samplings for 7 consecutive days were performed during three sampling campaigns, in 1996–1997. The results were comparable with those reported in literature for similar investigations. Total PAH were in the range 2–130 ng m⁻³, with a seasonal variation (autumn/winter vs. summer) in the range 1.5–4.5. The relative contribution of diesel engines vs. gasoline fuelled engines was evidenced.     

Responses of two birch (Betula pendula Roth) clones to different ozone profiles with similar AOT40 exposure

Saplings of two clones of European white birch (Betula pendula Roth) were exposed to three different ozone profiles resulting in same AOT40 value of 13–14 ppm h in a chamber experiment. The sensitive clone 5 and the more tolerant clone 2 were growing (1) under filtered air (=control), or (2) were exposed to 70 ppb ozone for 24 h d⁻¹ (=profile 1), (3) to 100 ppb ozone for 12 h d⁻¹ at 8:00–20:00 (=profile 2), or (4) to 200 ppb ozone for 4.5 h d⁻¹ at 9:30–14:00 (=profile 3) for 20 d. The saplings were determined for growth, visible leaf injuries, stomatal conductance, and concentrations of Rubisco, chlorophyll and carotenoids. Growth responses and induction of visible foliar injuries under different ozone profiles were variable, resulting in 4–17% lower dry mass of shoot, 16–46% reduction in stem height increment and 11–43% increase in visible injuries in clone 5, which was accompanied by higher leaf turnover rate under profile 3 indicating compensation growth. In clone 2, ozone-induced responses ranged from slight stimulation in stem height growth to 13% decrease in dry mass of shoot and 2–16% increase in visible injuries. Daytime stomatal conductance rates were lowered by 14–54% in clone 5 and 9–74% in clone 2, depending on profile. The additional power-weighted analyses revealed that high peak concentrations and exposure shape were important for induction of visible injuries in both clones and reduction in stomatal conductance in clone 5, whereas growth reductions were rather related to total cumulative exposure. The results indicate that profile of ozone exposure, night-time stomatal conductance (24 h flux), and recovery time for defence and compensations reactions should not be ignored in plant response and ozone flux modelling.