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Atmospheric Environment (v.43, #38)

Editorial board (pp. i).

Determination of elemental carbon in lake sediments using a thermal–optical transmittance (TOT) method by A.J. Khan; Kamal Swami; Tanveer Ahmed; A. Bari; Akhtar Shareef; Liaquat Husain (pp. 5989-5995).

An improved chemical oxidation pretreatment method has been developed for the determination of elemental carbon (EC) [also known as black carbon (BC) or soot] in lake sediments, using a thermal–optical transmittance (TOT) carbon analyzer. The method employs six steps: (1) removal of carbonates by treatment with HCl; (2) removal of silicates by treatment with HF + HCl; (3) removal of any remaining carbonates by treatment with HCl; (4) removal of humic acids by treatment with NaOH; and (5) oxidation of kerogens by K₂Cr₂O₇ + H₂SO₄. A critical step of zinc chloride treatment was added; this apparently changes EC's morphology and enhances retention on quartz fiber filter, resulting in several-fold increased chemical yield. EC was determined using the TOT method with modified combustion timings. Carbon black (acetylene) and four NIST standard reference materials (SRMs) were used for quality control, and to assess the precision of the analysis. The EC recoveries from 18 carbon black samples varied from 90 to 111%, with a mean value of 99 ± 6%. The high EC recoveries confirmed the validity of the method. Char reference materials (i.e. chestnut wood and grass char) were used to determine potential contribution to EC in our measurements. The char references containing about 700 mg total organic carbon (OC) contributed ∼1.5% EC. The measured EC values from four NIST standards were 17.0 ± 0.6, 24.2 ± 3.2, 5.6, and 1.9 ± 0.1 mg g_dw⁻¹ for SRM-1648, SRM-1649a, SRM-1941b and SRM-8704, respectively. These values in SRMs were in agreement (<±4%) with the previously reported values. The method was applied to determine the EC in sediment cores from an urban lake and a remote mountain lake in the Northeastern United States. The EC concentrations in two lakes mimic the model EC emissions from the industrial revolution in United States.

Keywords: Lake sediment, elemental carbon; Black carbon; Chemical oxidation method; Thermal–optical (TOT) method; Global warming

Temperature-dependent rate coefficients for the reactions of Cl atoms with methyl methacrylate, methyl acrylate and butyl methacrylate at atmospheric pressure by María B. Blanco; Iustinian Bejan; Ian Barnes; Peter Wiesen; Mariano A. Teruel (pp. 5996-6002).

Rate coefficients for the gas-phase reactions of Cl atoms with a series of unsaturated esters CH₂C(CH₃)C(O)OCH₃ (MMA), CH₂CHC(O)OCH₃ (MAC) and CH₂C(CH₃)C(O)O(CH₂)₃CH₃ (BMA) have been measured as a function of temperature by the relative technique in an environmental chamber with in situ FTIR detection of reactants. The rate coefficients obtained at 298 K in one atmosphere of nitrogen or synthetic air using propene, isobutene and 1,3-butadiene as reference hydrocarbons were (in units of 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹) as follows: k_(Cl+MMA) = 2.82 ± 0.93, k_(Cl+MAC) = 2.04 ± 0.54 and k_(Cl+BMA) = 3.60 ± 0.87. The kinetic data obtained over the temperature range 287–313 K were used to derive the following Arrhenius expressions (in units of cm³ molecule⁻¹ s⁻¹): k_(Cl+MMA) = (13.9 ± 7.8) × 10⁻¹⁵ exp[(2904 ± 420)/ T], k_(Cl+MAC) = (0.4 ± 0.2) × 10⁻¹⁵ exp[(3884 ± 879)/ T], k_(Cl+BMA) = (0.98 ± 0.42) × 10⁻¹⁵ exp[(3779 ± 850)/ T]. All the rate coefficients display a slight negative temperature dependence which points to the importance of the reversibility of the addition mechanism for these reactions. This work constitutes the first kinetic and temperature dependence study of the reactions cited above.An analysis of the available rates of addition of Cl atoms and OH radicals to the double bond of alkenes and unsaturated and oxygenated volatile organic compounds (VOCs) at 298 K has shown that they can be related by the expression: log k_OH = 1.09 log k_Cl − 0.10. In addition, a correlation between the reactivity of unsaturated VOCs toward OH radicals and Cl atoms and the HOMO of the unsaturated VOC is presented. Tropospheric implications of the results are also discussed.

Keywords: Acrylate-esters; Chlorine atoms; Arrhenius parameters; Troposphere; Marine environment

Road fugitive dust emission characteristics in Beijing during Olympics Game 2008 in Beijing, China by Fan Shou-bin; Tian Gang; Li Gang; Huang Yu-hu; Qin Jian-ping; Cheng Shui-yuan (pp. 6003-6010).

Eighty road dust-fall (DF) monitoring sites and 14 background monitoring sites were established in the Beijing metropolitan area, and monitoring was conducted from January 2006 to December 2008. The dust-fall attributable to roads (ΔDF) showed a clear decline from 2006 to 2008. Dust-fall levels decreased across different road types from freeway > major arterial roads > minor arterial roads > collector roads > background sites. The ΔDF showed declines of 65%, 55%, 65% and 84% respectively for freeways, major arterial, minor arterial and collector roads from August 2007 to August 2008, and declines of 77%, 76%, 82% and 82% between August 2006 and August 2008. The ΔDF declined by 80%, 79%, 82% and 69% for freeways, major arterial, minor arterial and collector roads respectively between September 2007 and September 2008, and declined by 84%, 88%, 80% and 81% between September 2006 and September 2008.Eighty samples were collected in August 2007 and August 2008 and analyzed for silt loading. PM₁₀ emission factors and emission strengths were calculated using the AP-42 model. The silt loading reduced by 77%, 35%, 61%, 59% and 75% for freeways, major arterial, minor arterial, collector and local roads respectively. The PM₁₀ emission factors were reduced by 57%, 15%, 36%, 51% and 61% and the PM₁₀ emission strength declined by 70%, 40%, 55%, 65% and 72% for freeways, major arterial, minor arterial, collector and local roads respectively between August 2007 and August 2008. The decline is consistent with the reduction in road dust-fall.

Keywords: Paved road; Fugitive dust; Silt loading; Dust-fall; Olympic Games 2008; Beijing

Pollutant dispersion in idealized city models with different urban morphologies by Jian Hang; Mats Sandberg; Yuguo Li; Leif Claesson (pp. 6011-6025).

The mechanism of pollutant dispersion in idealized city models is investigated numerically by the introduction of a uniformly distributed pollutant source at street pedestrian level. We first study three short city forms with a single main street or two crossing streets, characterized by street length/street height ratios of L/ H = 6 or 7 and a street height/street width ratio of H/ W = 1, including a sharp-edged round city model, a smooth-edged round city model, and a sharp-edged square city model. For short city models with a single street and a parallel approaching wind, pollutant dilution mainly depends on the horizontal flow rate which decreases along the street. This decreasing rate is smallest for the smooth-edged round city model, which results in the lowest street concentrations. For city models with two crossing streets and the approaching wind parallel to the main street, the differences in overall city form result in different dispersion processes. For a sharp-edged round city model with two crossing streets, an approaching wind slightly non-parallel to the main street generates a lower pollutant concentration in the entire street volume. We also studied a sharp-edged round city model with one narrow street ( L/ H = 6; H/ W = 6.7), finding that the uniformly distributed pollutants are transported from two street entries to the city centre, and are then removed out across the street roof. In contrast to the short city models we studied a single-street sharp-edged long rectangular city model ( L/ H = 21.7; H/ W = 1) in which the horizontal flow rate remained nearly constant in a region far from the two entries. Within this region the turbulence across the street roof contributed more to the pollutant removal than vertical mean flows.

Keywords: Urban morphology; City form; CFD simulation; Pollutant dispersion

Indoor–outdoor concentrations of RSPM in classroom of a naturally ventilated school building near an urban traffic roadway by Radha Goyal; Mukesh Khare (pp. 6026-6038).

A study on indoor–outdoor RSPM (PM₁₀, PM_2.5 and PM_1.0) mass concentration monitoring has been carried out at a classroom of a naturally ventilated school building located near an urban roadway in Delhi City. The monitoring has been planned for a year starting from August 2006 till August 2007, including weekdays (Monday, Wednesday and Friday) and weekends (Saturday and Sunday) from 8:0 a.m. to 2:0 p.m., in order to take into account hourly, daily, weekly, monthly and seasonal variations in pollutant concentrations. Meteorological parameters, including temperature, rH, pressure, wind speed and direction, and traffic parameters, including its type and volume has been monitored simultaneously to relate the concentrations of indoor–outdoor RSPM with them. Ventilation rate has also been estimated to find out its relation with indoor particulate concentrations. The results of the study indicates that RSPM concentrations in classroom exceeds the permissible limits during all monitoring hours of weekdays and weekends in all seasons that may cause potential health hazards to occupants, when exposed. I/O for all sizes of particulates are greater than 1, which implies that building envelop does not provide protection from outdoor pollutants. Further, a significant influence of meteorological parameters, ventilation rate and of traffic has been observed on I/O. Higher I/O for PM₁₀ is indicating the presence of its indoor sources in classroom and their indoor concentrations are strongly influenced by activities of occupants during weekdays.

Keywords: Classroom; Natural ventilation; RSPM; Meteorology; Occupant's activity; Traffic

Effect of typhoon on atmospheric particulates in autumn in central Taiwan by Guor-Cheng Fang; Shin-Jay Lin; Shih-Yu Chang; Charles-C.K. Chou (pp. 6039-6048).

Previous studies have suggested that the ongoing global climate change will likely increase the intensity and frequency of extreme weather, such as typhoons. Since the beginning of global warming, it has become necessary to understand the influence of typhoons on air quality. Rare data, especially particulate measurements data could be used to establish the relationship between the air pollution and typhoons. One of main limiting factors is that most of the previous chemical analyses of particulates used a relatively long sampling time, which could dilute the temporal impact of particulate characteristics and their sources. This work, depending more time-resolved measurements, focus on the characteristics and sources of high particulate matter levels and the influence of typhoons and the Pacific high system. Depending on the measurements, two pollutant groups were clearly identified in this work. The first pollutant group was the emissions from neighboring riverbeds under the strong circulation of the typhoon in the driest season and characterized as high coarse particle concentrations with high mass fraction of Ca²⁺. The second pollutant group was characterized as the formation and transport of secondary particles with prevalent ions of NH₄⁺, NO₃⁻, and SO₄²⁻ and occurred in the sea-land breeze circulation under the influence the Pacific high system.

Keywords: Extreme weather; Pacific high; sea-land breeze; continuous measurement; Chemical species

Increasing interannual and altitudinal ozone mixing ratios in the Catalan Pyrenees by Maria Díaz-de-Quijano; Josep Peñuelas; Àngela Ribas (pp. 6049-6057).

Interannual, seasonal, daily and altitudinal patterns of tropospheric ozone mixing ratios, as well as ozone phytotoxicity and the relationship with NO_x precursors and meteorological variables were monitored in the Central Catalan Pyrenees (Meranges valley and Forest of Guils) over a period of 5 years (2004–2008). Biweekly measurements using Radiello passive samplers were taken along two altitudinal transects comprised of thirteen stations ranging from 1040 to 2300 m a.s.l. Visual symptoms of ozone damage in Bel-W3 tobacco cultivars were evaluated biweekly for the first three years (2004–2006). High ozone mixing ratios, always above forest and vegetation protection AOT40 thresholds, were monitored every year. In the last 14 years, the AOT40 (Apr–Sept.) has increased significantly by 1047 μg m⁻³ h per year. Annual means of ozone mixing ratios ranged between 38 and 67 ppb_v (38 and 74 ppb_v during the warm period) at the highest site (2300 m) and increased at a rate of 5.1 ppb_v year⁻¹. The ozone mixing ratios were also on average 35–38% greater during the warm period and had a characteristic daily pattern with minimum values in the early morning, a rise during the morning and a decline overnight, that was less marked the higher the altitude. Whereas ozone mixing ratios increased significantly with altitude from 35 ppb_v at 1040 m–56 ppb_v at 2300 m (on average for 2004–2007 period), NO₂ mixing ratios decreased with altitude from 5.5 ppb_v at 1040 m–1 ppb_v at 2300 m. The analysis of meteorological variables and NO_x values suggests that the ozone mainly originated from urban areas and was transported to high-mountain sites, remaining aloft in absence of NO. Ozone damage rates increased with altitude in response to increasing O₃ mixing ratios and a possible increase in O₃ uptake due to more favorable microclimatic conditions found at higher altitude, which confirms Bel-W3 as a suitable biomonitor for ozone concentrations during summer time. Compared to the valley-bottom site the annual means of ozone mixing ratios are 37% larger in the higher sites. Thus the AOT40 for the forest and vegetation protection threshold is greatly exceeded at higher sites. This could have substantial effects on plant life at high altitudes in the Pyrenees.

Keywords: AOT40; Bel-W3; Biomonitoring; Mediterranean region; Nitrogen oxides; Phytotoxicity

Weekly periodicities of meteorological variables and their possible association with aerosols in Korea by Byung-Gon Kim; Min-Hyeok Choi; Chang-Hoi Ho (pp. 6058-6065).

The weekly periodicities in meteorological variables and its association with aerosols in Korea are investigated using long-term surface measurements of meteorology (1975–2005) and aerosols (1999–2005). Through an analysis of the annual (and/or seasonal) values averaged over 10 stations, we identified distinct weekly periodicities in the daily minimum temperature ( T_min), diurnal temperature range (DTR), cloud fraction, and solar insolation, although they have different characteristics from each other. The weekly association among variables is discussed in this study. Positive anomalies of the cloud fraction and T_min and negative anomalies of solar insolation and DTR are seen for the second half of the week and the reverse for the first half of the week, i.e., more cloudiness and less insolation for Wednesday−Thursday and less cloudiness and more insolation for Monday−Tuesday. Furthermore, seasonal dependence of weekly anomalies shows that the weekly periodicities are enhanced especially in autumn, more than 2–3 times as great as those of the annual mean. The weekly cycles in such variables are most likely driven by changes in cloud fraction, possibly through aerosol–cloud interactions induced by aerosol variations between working weekdays and Sunday, which are clearly identified in PM10 weekly cycles. This study also suggests that the weekly periodicities in meteorological variables are possibly associated with long-range transport of weekly periodicities, as well as aerosol–cloud-precipitation interactions over the region.

Keywords: Weekly periodicities; Diurnal temperature range; Meteorological variables; Aerosols; Korea

Spatial distribution and seasonal variation of char-EC and soot-EC in the atmosphere over China by Y.M. Han; S.C. Lee; J.J. Cao; K.F. Ho; Z.S. An (pp. 6066-6073).

A previous study on PM_2.5 carbonaceous aerosols measured with the thermal optical reflectance (TOR) method in fourteen Chinese cities is extended by subdividing total EC into char-EC and soot-EC. Average char-EC concentrations show great differences between the fourteen cities and between winter and summer periods, with concentrations of 8.67 and 2.41 μg m⁻³ in winter and summer, respectively. Meanwhile spatial and seasonal soot-EC variations are small, with average concentrations of 1.26 and 1.21 μg m⁻³ in winter and summer, respectively. Spatial and temporal distributions of char-EC, similar to EC, are mainly influenced by local fuel consumption, as well as the East Asian monsoon and some meteorological factors such as the mixing height and wet precipitation. The small spatial and seasonal variation of soot-EC is consistent with its regional-to-global dispersion, which may suggest that soot carbon is not local carbon, but regional carbon. Char-EC/soot-EC ratios show summer minimum and winter maximum in all cities, which is in good agreement with the difference in source contributions between the two periods. As OC/EC ratio is affected by the formation of the secondary organic aerosol (SOA), char-EC/soot-EC ratio is a more effective indicator for source identification of carbonaceous aerosol than previously used OC/EC ratio.

Keywords: Carbonaceous aerosols; Char; Soot; Spatial distribution; China

Particulate mercury emissions in regional wildfire plumes observed at the Mount Bachelor Observatory by B.D. Finley; P.C. Swartzendruber; D.A. Jaffe (pp. 6074-6083).

Atmospheric mercury is composed primarily of Hg⁰ (>95%), but Hg⁺² and particle bound mercury are also found in some environments. The three forms of mercury were measured at the Mount Bachelor Observatory beginning in 2005. Using data gathered from 2005 to 2007, 15 periods were identified during which PHg was above the instrument detection limit of 3 pg m⁻³ for nine or more consecutive hours. Peak PHg concentrations ranged from 6.0 to 44.3 pg m⁻³. During these events, PHg is strongly correlated with CO and sub-micron aerosol scatter coefficient (typically R² > 0.6). Our data suggest that the 15 PHg events were likely due to regional wildfires in California and Oregon. Wildfires were identified as the primary PHg source using a combination of air-mass back-trajectories, MODIS satellite data, and chemical and physical tracers of combustion. Slopes of the PHg/σ_sp and PHg/CO relationships ranged from 0.20 to 1.57 pg (Mm⁻¹)⁻¹ and 0.11 to 0.61 pg m⁻³ ppb⁻¹, respectively. The range of slopes may indicate different types of burning (e.g. flaming vs. smoldering), differing amounts of chemical processing, different fuel sources, or different physical parameters such as the plume injection height. The slopes provide constraints for the relationship between PHg, CO, and aerosol scatter from wildfires. Asian long-range transport was not a source of PHg but we cannot rule out the possibility of local U.S. industrial sources of PHg for some of the events. Assuming our observations are representative of global fire emissions, we estimate that PHg represents 15% of the total mercury released from wildfires and is a source of PHg comparable to anthropogenic sources.

Keywords: Mercury; Wildfire; Biomass burning

Precipitation scavenging of particle-bound contaminants – A case study of PCDD/Fs by Michael S. McLachlan; Ulla Sellström (pp. 6084-6090).

Precipitation scavenging of particles is a major mechanism for atmospheric deposition of organic contaminants, but there have been few field studies. We studied precipitation scavenging of PCDD/Fs with the aim of deepening understanding of environmental variables influencing this process. Bulk deposition of PCDD/Fs and their concentrations in ambient air measured at a background site in Sweden were used to calculate precipitation scavenging ratios. Contrary to expectations, increasing scavenging ratios with decreasing degree of chlorination of the PCDD/F congeners were observed when the particle-associated PCDD/F concentrations in air were used for the calculation. This was attributed to differences in temperature and thereby in the gas – particle partitioning of the PCDD/Fs between ground level and clouds where much of the particle scavenging occurs. When the particle-associated PCDD/F concentrations were recalculated for a 10–20 °C lower temperature, the scavenging ratios of the different PCDD/F congeners were similar. Hence differences between ground level and in-cloud temperature should be considered when calculating scavenging ratios from field observations and when modeling this process. The scavenging ratios averaged ∼200 000, with lower values when the particle-associated PCDD/F concentration in air was lower. The soot concentration in air was a good predictor of bulk deposition of PCDD/Fs.

Keywords: Precipitation scavenging; Scavenging factor; PCDD/F; Soot; Bulk deposition

Three-dimensional characterization of the ammonia plume from a beef cattle feedlot by Ralf M. Staebler; Sean M. McGinn; Brian P. Crenna; Thomas K. Flesch; Katherine L. Hayden; Shao-Meng Li (pp. 6091-6099).

In Canada approximately 45% of ammonia (NH₃) emissions are attributed to dairy and beef cattle industries. The present study focused on NH₃ emissions from a beef feedlot with a one-time capacity of 17,220 head. The aim was to improve the Canadian NH₃ emission inventories and air quality forecasting capabilities. A Cessna 207, equipped with a fast-response NH₃/NO_y detector and a quadrupole aerosol mass spectrometer, was flown in a grid pattern covering an area of 8 × 8 km centered on a feedlot (800 × 800 m) at altitudes ranging from 30 to 300 m above ground. Stationary ground measurements of NH₃ concentration and turbulence parameters were made downwind of the feedlot. Three flights were conducted under varying meteorological conditions, ranging from very calm to windy with near-neutral stratification. NH₃ mixing ratios up to 100 ppbv were recorded on the calm day, up to 300 m above ground. An average feedlot NH₃ emission rate of 76 ± 4 μg m⁻² s⁻¹ (equivalent to 10.2 g head⁻¹ h⁻¹) was estimated. Characteristics of the measured NH₃ plume were compared to those predicted by a Lagrangian dispersion model. The spatially integrated pattern of NH₃ concentrations predicted and measured agreed but the measured was often more complex than the predicted spatial distribution. The study suggests that the export of NH₃ through advection accounted for about 90% of the emissions from the feedlot, chemical transformation was insignificant, and dry deposition accounted for the remaining 10%.

Keywords: Ammonia; Beef feedlot emissions; Airborne measurements; Local ammonia budget; Backward Lagrangian stochastic model; Alberta

Organic aerosol characterization by complementary measurements of chemical bonds and molecular fragments by Lynn M. Russell; Ranjit Bahadur; Lelia N. Hawkins; James Allan; Darrel Baumgardner; Patricia K. Quinn; Timothy S. Bates (pp. 6100-6105).

Organic aerosol chemical markers from normalized concentrations of independent measurements of mass fragments (using Aerosol Mass Spectrometry, AMS) are compared to bond-based functional groups (from Fourier Transform Infrared spectroscopy, FTIR) during eight field projects in the western hemisphere. Several field projects show weak correlations between alcohol group fractions and m/ z 60 fractions, consistent with the organic hydroxyl groups and the fragmentation of saccharides, but the weakness of the correlations indicate chemical differences among the relationships for ambient aerosols in different regions. Carboxylic acid group fractions and m/ z 44 fractions are correlated weakly for three projects, with correlations expected for aerosols dominated by di-acid compounds since their fragmentation is typically dominated by m/ z 44. Despite differences for three projects with ratios of m/ z 44 to m/ z 57 fragments less than 10, five projects showed a linear trend between the project-average m/ z 44 to m/ z 57 ratio and the ratio of acid and alkane functional groups. While this correlation explains only a fraction of the fragment and bond variability measured, the consistency of this relationship at multiple sites indicates a general agreement with the interpretation of the relative amount of m/ z 44 as a carboxylic acid group marker and m/ z 57 as an alkane group marker.

Keywords: Organic aerosols; Aerosol mass spectrometry; Infrared spectroscopy; Chemical composition

Simultaneous measurements of formaldehyde and nitrous acid in dews and gas phase in the atmosphere of Santiago, Chile by María A. Rubio; Eduardo Lissi; Guillermo Villena; Y.F. Elshorbany; Jörg Kleffmann; Ralf Kurtenbach; Peter Wiesen (pp. 6106-6109).

The amounts of formaldehyde and nitrous acid (HONO) in gas phase and dews of Santiago de Chile were simultaneously measured. Formaldehyde concentrations values in the liquid phase (dews) correlate fairly well with those in the gaseous phase and are even higher than those expected from gas–dew equilibrium. On the other hand, nitrite concentrations in dews were considerably smaller (ca. 15 times) than those expected from the gas-phase concentrations. This under-saturation is attributed to diffusion limitations due to the relatively large HONO solubility. In agreement with this, under-saturation increases with the rate of dew formation and the pH of the collected waters, factors that should increase the rate of gas to liquid HONO transfer required to reach equilibrium.

Keywords: Nitrous acid; Formaldehyde; Dews; Santiago de Chile; Henry's constant

Fast response measurements of the dispersion of nanoparticles in a vehicle wake and a street canyon by Prashant Kumar; Alan Robins; Rex Britter (pp. 6110-6118).

The distributions of nanoparticles (below 300 nm in diameter) change rapidly after emission from the tail pipe of a moving vehicle due to the influence of transformation processes. Information on this time scale is important for modelling of nanoparticle dispersion but is unknown because the sampling frequencies of available instruments are unable to capture these rapid processes. In this study, a fast response differential mobility spectrometer (Cambustion Instruments DMS500), originally designed to measure particle number distributions (PNDs) and concentrations in engine exhaust emissions, was deployed to measure particles in the 5–1000 nm size range at a sampling frequency of 10 Hz. This article presents results of two separate studies; one, measurements along the roadside in a Cambridge (UK) street canyon and, two, measurements at a fixed position (20 cm above road level), centrally, in the wake of a single moving diesel-engined car. The aims of the first measurements were to test the suitability and recommend optimum operating conditions of the DMS500 for ambient measurements. The aim of the second study was to investigate the time scale over which competing influences of dilution and transformation processes (nucleation, condensation and coagulation) affect the PNDs in the wake of a moving car. Results suggested that the effect of transformation processes was nearly complete within about 1 s after emission due to rapid dilution in the vehicle wake. Furthermore, roadside measurements in a street canyon showed that the time for traffic emissions to reach the roadside in calm wind conditions was about 45 ± 6 s. These observations suggest the hypothesis that the effects of transformation processes are generally complete by the time particles are observed at roadside and the total particle numbers can then be assumed as conserved. A corollary of this hypothesis is that complex transformation processes can be ignored when modelling the behaviour of nanoparticles in street canyons once the very near-exhaust processes are complete.

Keywords: Dispersion; Fast response particle measurements; Nanoparticles; Particle number distribution; Street canyon; Vehicle wake

Erratum to “New Directions: Nanodust – A source of metals in the atmospheric environment?” [Atmos. Environ. 43 (2009) 4666–4667] by Vicki H. Grassian (pp. 6119-6119).

Corrigendum to “Rapid measurement of emissions from military aircraft turbine engines by downstream extractive sampling of aircraft on the ground: Results for C-130 and F-15 aircraft” [Atm. Environ. 43 (2009) 2612–2622] by Chester W. Spicer; Michael W. Holdren; Kenneth A. Cowen; Darrell W. Joseph; Jan Satola; Bradley Goodwin; Howard Mayfield; Alexander Laskin; M. Lizabeth Alexander; John V. Ortega; Matthew Newburn; Robert Kagann; Ram Hashmonay (pp. 6120-6120).

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Atmospheric Environment (v.43, #38)