Atmospheric Environment (v.43, #10)

Organic and inorganic sampling artefacts assessment by R. Vecchi; G. Valli; P. Fermo; A. D'Alessandro; A. Piazzalunga; V. Bernardoni (1713-1720).
During collection on filter-based aerosol samplers, organic and inorganic aerosol compounds both contribute to positive and negative artefacts, significantly affecting chemical analyses results for single species and PM mass concentrations. Up to now, studies on organic or inorganic artefacts have been conducted in Europe but very scarce data are available for both in a single study.The field study was carried out in Milan, which is located in the Po valley (Northern Italy) one of the major pollution hot spots in Europe. As sampling artefacts depend on many factors, such as filter type, face velocity, sampling duration, and ambient conditions, in this field study two different filter types have been considered (i.e. quartz fibre filters and Teflon filters) for the assessment of both inorganic and organic artefacts during two different seasons (performing also some samplings at different flow-rates).Results showed that positive artefacts due to OC adsorption on quartz filters accounted for 39% of the OC measured concentration in summer, and 23% in winter. Negative artefact due to nitrate volatilisation by the filters was 51% on Teflon and 22% on the quartz filters in summer, and no or negligible losses were observed in winter. A significant improvement in the PM mass comparability obtained in parallel samplings on different filters was obtained taking into account the artefact estimates performed in this study.
Keywords: Organic carbon; Nitrates; Denuder; Filter pack; Milan;

Flow and dispersion in an urban cubical cavity by Young-Hee Ryu; Jong-Jin Baik (1721-1729).
Flow and dispersion in an urban cubical cavity are numerically investigated using a Reynolds-averaged Navier–Stokes equations (RANS) model with the renormalization group (RNG) kɛ turbulence closure model. The urban cubical cavity is surrounded by flank walls that are parallel to the streamwise direction, called end-walls, as well as upstream and downstream walls. A primary vortex and secondary vortices including end-wall vortices are formed in the cavity. Because of the end-wall drag effect, the averaged mean-flow kinetic energy in the cavity is smaller than that in an urban street canyon that is open in the along-canyon direction. A trajectory analysis shows that the end-wall vortices cause fluid particles to move in the spanwise direction, indicating that flow in the cavity is essentially three-dimensional. The iso-surfaces of the Okubo–Weiss criterion capture cavity vortices well. The pollutant concentration is high near the bottom of the upstream side in the case of continuous pollutant emission, whereas it is high near the center of the primary vortex in the case of instantaneous pollutant emission. To get some insight into the degree of pollutant escape from the cavity according to various meteorological factors, extensive numerical experiments with different ambient wind speeds and directions, inflow turbulence intensities, and cavity-bottom heating intensities are performed. For each experiment, we calculate the time constant, which is defined as the time taken for the pollutant concentration to decrease to e −1 of its initial value. The time constant decreases substantially with increasing ambient wind speed, and tends to decrease with increasing inflow turbulence intensity and cavity-bottom heating intensity. The time constant increases as the ambient wind direction becomes oblique. High ambient wind speed is found to be the most crucial factor for ventilating the cavity, thus improving air quality in an urban cubical cavity.
Keywords: Reynolds-averaged Navier–Stokes equations (RANS) model; Flow and dispersion; Urban cubical cavity; End-walls; Time constant;

Identifying source regions for the atmospheric input of PCDD/Fs to the Baltic Sea by Ulla Sellström; Anna-Lena Egebäck; Michael S. McLachlan (1730-1736).
PCDD/F contamination of the Baltic Sea has resulted in the European Union imposing restrictions on the marketing of several fish species. Atmospheric deposition is the major source of PCDD/Fs to the Baltic Sea, and hence there is a need to identify the source regions of the PCDD/Fs in ambient air over the Baltic Sea. A novel monitoring strategy was employed to address this question. During the winter of 2006–2007 air samples were collected in Aspvreten (southern Sweden) and Pallas (northern Finland). Short sampling times (24 h) were employed and only samples with stable air mass back trajectories were selected for analysis of the 2,3,7,8-substituted PCDD/F congeners. The range in the PCDD/F concentrations from 40 samples collected at Aspvreten was a factor of almost 50 (range 0.6–29 fg TEQ/m3). When the samples were grouped according to air mass origin into seven compass sectors, the variability was much lower (typically less than a factor of 3). This indicates that air mass origin was the primary source of the variability. The contribution of each sector to the PCDD/F contamination over the Baltic Sea during the winter half year of 2006/2007 was calculated from the average PCDD/F concentration for each sector and the frequency with which the air over the Baltic Sea came from that sector. Air masses originating from the south–southwest, south–southeast and east segments contributed 65% of the PCDDs and 75% of the PCDFs. Strong correlations were obtained between the concentrations of most of the PCDD/F congeners and the concentration of soot. These correlations can be used to predict the PCDD/F concentrations during the winter half year from inexpensive soot measurements.
Keywords: PCDD/F; Baltic Sea; Monitoring; Ambient air; Trajectory;

Black carbon aerosols in urban air in South Asia by Vincent A. Dutkiewicz; Sofia Alvi; Badar M. Ghauri; M. Iqbal Choudhary; Liaquat Husain (1737-1744).
We report data from a yearlong (2006–2007) study of black carbon concentrations ([BC]) measured at 5-min intervals with an Aethalometer in Karachi, Pakistan. Daily mean [BC] varied from about 1 to 15 μg m−3. However, short-term spikes exceeding 40 μg m−3 were common, occurring primarily during the morning and evening rush-hour periods. The [BC] values were highest during November through February, ∼10 μg m−3, and lowest during June through September, ∼2 μg m−3. Diurnal, seasonal, and day-of-the-week trends are discussed. It is demonstrated that these trends are strongly affected by meteorological patterns. A simple expression is applied to the concentration profiles to separate the effects of meteorological conditions and elucidate the underlying emissions patterns. Daily emissions varied from 14,000 to 22,000 kg of BC per day. When integrated over the year emissions for Karachi Proper were estimated at 6.7 kilometric tons per year and emissions for greater Karachi were 17.5 kilometric tons per year. Folding in the populations of each area yields BC emissions of 0.74 and 1.1 kg per person per year, respectively. Applying the model to previously collected data at Lahore, Pakistan yields emissions during November–January that are around a factor of two higher than those in Karachi, but because the BC measurements in Lahore covered only three months, no estimates of annual emissions were attempted. Given the large populations of these cities the local health impact from PM alone is expected to be severe but because of the high [BC] emissions the impact on the global climate may be equally significant.
Keywords: Carbonaceous aerosols; Black carbon; BC emissions; South Asia; Urban air;

This paper presents the regulated and unregulated exhaust emissions of a diesel passenger vehicle, operated with low sulphur automotive diesel and soy methyl ester blends. Emission and fuel consumption measurements were conducted under real driving conditions (Athens Driving Cycle, ADC) and compared with those of a modified New European Driving Cycle (NEDC) using a chassis dynamometer. A Euro II compliant diesel vehicle was used in this study, equipped with an indirect injection diesel engine, fuelled with diesel fuel and biodiesel blends at proportions of 5, 10, and 20% respectively. Unregulated emissions of 11 polycyclic aromatic hydrocarbons (PAHs), 5 nitro-PAHs, 13 carbonyl compounds (CBCs) and the soluble organic fraction (SOF) of the particulate matter were measured. Qualitative hydrocarbon analysis was also performed on the SOF. Regulated emissions of NO x , CO, HC, CO2, and PM were also measured over the two test cycles. It was established that some of the emissions measured over the (hot-start) NEDC differed from the real-world cycle. Significant differences were also observed in the vehicle's fuel consumption between the two test cycles. The addition of biodiesel reduced the regulated emissions of CO, HC and PM, while an increase in NO x was observed over the ADC. Carbonyl emissions, PAHs and nitro-PAHs were reduced with the addition of biodiesel over both driving cycles.
Keywords: Biodiesel; Driving cycles; Carbonyl compounds; PAH; Nitro-PAHs;

Improved measurements of ammonia losses from cattle feedlots are needed to quantify the national NH3 emissions inventory and evaluate management techniques for reducing emissions. Speciation cartridges composed of glass honeycomb denuders and filter packs were adapted to measure gaseous NH3 and aerosol NH4 + fluxes using relaxed eddy accumulation (REA). Laboratory testing showed that a cartridge equipped with four honeycomb denuders had a total capture capacity of 1800 μg of NH3. In the field, a pair of cartridges was deployed adjacent to a sonic anemometer and an open-path gas analyzer on a mobile tower. High-speed valves were attached to the inlets of the cartridges and controlled by a datalogger so that up- and down-moving eddies were independently sampled based on direction of the vertical wind speed and a user-defined deadband. Air flowed continuously through the cartridges even when not sampling by means of a recirculating air handling system. Eddy covariance measurement of CO2 and H2O, as measured by the sonic and open-path gas analyzer, were used to determine the relaxation factor needed to compute REA-based fluxes. The REA system was field tested at the Beef Research Unit at Kansas State University in the summer and fall of 2007. Daytime NH3 emissions ranged between 68 and 127 μg m−2  s−1; fluxes tended to follow a diurnal pattern correlated with latent heat flux. Daily fluxes of NH3 were between 2.5 and 4.7 g m−2  d−1 and on average represented 38% of fed nitrogen. Aerosol NH4 + fluxes were negligible compared with NH3 emissions. An REA system designed around the high-capacity speciation cartridges can be used to measure NH3 fluxes from cattle feedlots and other strong sources. The system could be adapted to measure fluxes of other gases and aerosols.
Keywords: Animal feeding operation; NH3 emission; Aerosol fluxes; Denuder; REA;

A receptor model of positive matrix factorization (PMF) was used to identify the emission sources of fine and coarse particulates in Bandung, a city located at about 150 km south-east of Jakarta. Total of 367 samples were collected at urban mixed site, Tegalega area, in Bandung City during wet and dry season in the period of 2001–2007. The samples of fine and coarse particulate matter were collected simultaneously using dichotomous samplers and mini-volume samplers. The Samples from dichotomous Samplers were analyzed for black carbon and elements while samples from mini-volume samplers were analyzed for ions. The species analyzed in this study were Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Pb, Cl, NO3 , SO4 2−, and NH4 +. The data were then analyzed using PMF to determine the source factors. Different numbers of source factors were found during dry and wet season. During dry season, the main source factors for fine particles were secondary aerosol (NH4)2SO4, electroplating industry, vehicle emission, and biomass burning, while for coarse particles, the dominant source factors were electroplating industry, followed by aged sea salt, volcanic dust, soil dust, and lime dust. During the wet season, the main source factors for fine particulate matter were vehicle emission and secondary aerosol. Other sources detected were biomass burning, lime dust, soil and volcanic dust. While for coarse particulate matter, the main source factors were sulphate-rich industry, followed by lime dust, soil dust, industrial emission and construction dust.
Keywords: Receptor model; PMF; Source profiles; Fine particles; Coarse particles;

Source characterization of ozone precursors by complementary approaches of vehicular indicator and principal component analysis by Chih-Chung Chang; Jia-Lin Wang; Shih-Chun Candice Lung; Shaw-Chen Liu; Chein-Jung Shiu (1771-1778).
Measurements of speciated non-methane hydrocarbons (NMHCs) were conducted in an ozone non-attainment metropolis with pronounced industrial emissions in addition to traffic ones. Highly variable and complex natures of industrial sources make their composition profiles difficult to determine. In the circumstances of no reliable source profiles, two simple complementary approaches were attempted to characterize sources of NMHCs. First, a robust vehicular indicator, 3-methylpentane (3MC5A), which is an intrinsic component of gasoline, was used to estimate contributions of traffic versus non-traffic sources for major NMHCs with high ozone-forming potentials (OFPs), such as ethene, toluene, xylene, isoprene, etc. Second, the method of principal component analysis (PCA) was employed to further discern non-traffic emissions into various source groups. A total of 454 ambient samples were sampled in the urban-industrial complex metropolis (Kaohsiung, Taiwan) to build up a large dataset to be tested by the two complementary approaches. It was found that four types of emissions, i.e., traffic, household fuel leakage, industrial, and biogenic, were responsible for the observed ambient NMHCs. The industrial contribution was significant for ethene and toluene (with 48–67% and 33–62%, respectively), whereas xylene was found to be mainly vehicular. In addition, isoprene revealed its biogenic nature. OFPs arising from vehicular, industrial and biogenic contributions could be further assessed for the purpose of emission control of NMHCs in the ozone non-attainment area.
Keywords: Vehicular tracer; Principle component analysis; NMHC; VOCs; Industrial emissions;

The distribution of historical ozone levels for a region is tabulated as a function of its prevailing synoptic and mesoscale influences. Meteorological patterns are determined sequentially from extended records of hourly surface wind measurements sampling relevant low-level flows. A visualization method is presented to readily indicate the likelihoods for exceedances to occur under a variety of meteorological conditions. The study domain is San Joaquin Valley (SJV) of California, which is divided into three subregions (North, Central, and South). Each day from May–October of 1996–2004 is labeled using synoptic (single-day) and mesoscale (intra-day) patterns. Emissions levels are assumed roughly constant for this period following the introduction of reformulated gasoline to California. Synoptic motions largely control the regional SJV ozone pollution potential; the same single-day patterns are identified for all three SJV subregions. Additionally, a unique mesoscale flow feature is identified in each subregion that strongly affects its ozone levels: flows through minor Coast Range gaps for N-SJV, the Fresno Eddy for C-SJV, and flows through Mojave Pass for S-SJV. The strength of each mesoscale feature is characterized using 1-h surface u or v wind components that explain local ozone pollution potentials.
Keywords: Synoptic and mesoscale ozone climatology; Central Valley; Low-level jet; Mountain drainage (katabatic) winds; Transport and dispersion patterns;

Secondary organic aerosol formation from cyclohexene ozonolysis in the presence of water vapor and dissolved salts by Bethany Warren; Quentin G.J. Malloy; Lindsay D. Yee; David R. Cocker (1789-1795).
A series of 90 experiments were conducted in the UC Riverside/CE-CERT environmental chamber to evaluate the impact of water vapor and dissolved salts on secondary organic aerosol formation for cyclohexene ozonolysis. Water vapor (low – 30 ± 2% RH, medium – 46 ± 2% RH, high – 63 ± 2% RH) was found to directly participate in the atmospheric chemistry altering the composition of the condensing species, thus increasing total organic aerosol formation by ∼22% as compared to the system under dry (<0.1% RH) conditions. Hygroscopicity measurements also indicate that the organic aerosol composition is altered in the presence of gaseous water. These results are consistent with water vapor reacting with the crigee intermediate in the gas phase resulting in increased aldehyde formation. The addition of dissolved salts ((NH4)2SO4, NH4HSO4, CaCl2, NaCl) had minimal effect; only the (NH4)2SO4 and NaCl were found to significantly impact the system with ∼10% increase in total organic aerosol formation. These results indicate that the organics may be partitioning to an outer organic shell as opposed to into the aqueous salt. Hygroscopicity measurements indicate that the addition of salts does not alter the aerosol composition for the dry or water vapor system.
Keywords: Secondary organic aerosol (SOA); Water vapor; Humidity; Aqueous salts; Cyclohexene; Hygroscopicity;

The potential impact on the environment of alternative vehicle/fuel systems needs to be evaluated, especially with respect to human health effects resulting from air pollution. We used the G reenhouse gases, R egulated E missions, and E nergy use in T ransportation (GREET) model to examine the well-to-wheels (WTW) emissions of five criteria pollutants (VOCs, NO x , PM10, PM2.5, and CO) for nine vehicle/fuel systems: (1) conventional gasoline vehicles; (2) conventional diesel vehicles; (3) ethanol (E85) flexible-fuel vehicles (FFVs) fueled with corn-based ethanol; (4) E85 FFVs fueled with switchgrass-based ethanol; (5) gasoline hybrid vehicles (HEVs); (6) diesel HEVs; (7) electric vehicles (EVs) charged using the average U.S. generation mix; (8) EVs charged using the California generation mix; and (9) hydrogen fuel cell vehicles (FCVs). Pollutant emissions were separated into total and urban emissions to differentiate the locations of emissions, and emissions were presented by sources. The results show that WTW emissions of the vehicle/fuel systems differ significantly, in terms of not only the amounts but also with respect to locations and sources, both of which are important in evaluating alternative vehicle/fuel systems. E85 FFVs increase total emissions but reduce urban emissions by up to 30% because the majority of emissions are released from farming equipment, fertilizer manufacture, and ethanol plants, all of which are located in rural areas. HEVs reduce both total and urban emissions because of the improved fuel economy and lower emissions. While EVs significantly reduce total emissions of VOCs and CO by more than 90%, they increase total emissions of PM10 and PM2.5 by 35–325%. However, EVs can reduce urban PM emissions by more than 40%. FCVs reduce VOCs, CO, and NO x emissions, but they increase both total and urban PM emissions because of the high process emissions that occur during hydrogen production. This study emphasizes the importance of specifying a thorough life-cycle emissions inventory that can account for both the locations and sources of the emissions to assist in achieving a fair comparison of alternative vehicle/fuel options in terms of their environmental impacts.
Keywords: Well-to-wheels; Criteria pollutants; Alternative fuels; Total emissions; Urban emissions;

Source-to-receptor pathways of anthropogenic PM2.5 in Detroit, Michigan: Comparison of two inhalation exposure studies by Masako Morishita; Gerald J. Keeler; Jacob D. McDonald; James G. Wagner; Li-Hao Young; Satoshi Utsunomiya; Rodney C. Ewing; Jack R. Harkema (1805-1813).
Recent studies have attributed toxic effects of ambient fine particulate matter (aerodynamic diameter ≤ 2.5 μm; PM2.5) to physical and/or chemical properties rather than total mass. However, identifying specific components or sources of a complex mixture of ambient PM2.5 that are responsible for adverse health effects is still challenging. In order to improve our understanding of source-to-receptor pathways for ambient PM2.5 (links between sources of ambient PM2.5 and measures of biologically relevant dose), integrated inhalation toxicology studies using animal models and concentrated air particles (CAPs) were completed in southwest Detroit, a community where the pediatric asthma rate is more than twice the national average. Ambient PM2.5 was concentrated with a Harvard fine particle concentrator housed in AirCARE1, a mobile air research laboratory which facilitates inhalation exposure studies in real-world settings. Detailed characterizations of ambient PM2.5 and CAPs, identification of major emission sources of PM2.5, and quantification of trace elements in the lung tissues of laboratory rats that were exposed to CAPs for two distinct 3-day exposure periods were completed.This paper describes the physical/chemical properties and sources of PM2.5, pulmonary metal concentrations and meteorology from two different 3-day exposure periods—both conducted at the southwest Detroit location in July 2003—which resulted in disparate biological effects. More specifically, during one of the exposure periods, ambient PM2.5-derived trace metals were recovered from lung tissues of CAPs-exposed animals, and these metals were linked to local combustion point sources in southwest Detroit via receptor modeling and meteorology; whereas in the other exposure period, no such trace metals were observed. By comparing these two disparate results, this investigation was able to define possible links between PM2.5 emitted from refineries and incinerators and biologically relevant dose, which in turn may be associated with observed health effects.
Keywords: PM2.5; Detroit; Trace metals; Concentrated air particles (CAPs); Inhalation exposure; Receptor modeling; Asthma;

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.
Keywords: Secondary organic aerosol; Glyoxal; Methylglyoxal; Organic carbon; WSOC; ICARTT;

Passive sampling devices are popular in applications which do not require the monitoring of hourly concentrations. Nitrogen oxides are often collected using filters coated with 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). The filter extract can then be analyzed using flow injection analysis ion chromatography fitted with a copper/cadmium reduction column or UV–vis spectroscopy. When the latter is used to measure low concentrations of nitrogen oxides, absorbance by PTIO at the analytical wavelength of 545 nm contributes significantly. PTIO concentration on the filter also shows variation with filter storage and exposure time not accounted for in a single point blank subtraction at the analytical wavelength. A method is presented that uses a scaling factor to account for variations in concentration of PTIO on the field blank and provides a more accurate method for determining and correcting for the PTIO contribution to absorption when measuring ambient nitrogen oxide concentrations.
Keywords: Passive samplers; NO x ; PTIO; UV–vis;