Atmospheric Environment (v.45, #1)

Toxic industrial chemical (TIC) source emissions modeling for pressurized liquefied gases by Rex Britter; Jeffrey Weil; Joseph Leung; Steven Hanna (1-25).
The objective of this article is to report current toxic industrial chemical (TIC) source emissions formulas appropriate for use in atmospheric comprehensive risk assessment models so as to represent state-of-the-art knowledge. The focus is on high-priority scenarios, including two-phase releases of pressurized liquefied gases such as chlorine from rail cars. The total mass released and the release duration are major parameters, as well as the velocity, thermodynamic state, and amount and droplet sizes of imbedded aerosols of the material at the exit of the rupture, which are required as inputs to the subsequent jet and dispersion modeling. Because of the many possible release scenarios that could develop, a suite of model equations has been described. These allow for gas, two-phase or liquid storage and release through ruptures of various types including sharp-edged and “pipe-like” ruptures. Model equations for jet depressurization and phase change due to flashing are available. Consideration of the importance of vessel response to a rupture is introduced. The breakup of the jet into fine droplets and their subsequent suspension and evaporation, or rainout is still a significant uncertainty in the overall modeling process. The recommended models are evaluated with data from various TIC field experiments, in particular recent experiments with pressurized liquefied gases. It is found that there is typically a factor of two error in models compared with research-grade observations of mass flow rates. However, biases are present in models’ estimates of the droplet size distributions resulting from flashing releases.
Keywords: Chlorine releases to atmosphere; Hazardous chemicals; Pressurized liquefied gas releases; Source emission models; Toxic industrial chemicals; Two-phase jets;

A series of experiments have been carried out in the York University smog chamber designed to study the products and pathways of the HO radical oxidation of β-pinene. Experiments on the oxidation of β-pinene and its most prominent oxidation product, pinaketone, by HO radicals with initial NO ranging from 0 to 2.5 ppm have been undertaken. An atmospheric pressure chemical ionization (API) mass spectrometer was operated for online, real-time identification and time profiling of the gas phase oxidation products. The formation of six organic nitrate products has been distinguished of which two have been assigned identifications, C10 dihydroxy nitrate (C10H17NO5) and nitrooxy-pinaketone (C9H13NO4). The real-time profiling and sensitivity to initial NO mixing ratio of each product has provided new insight into the β-pinene + HO radical oxidation mechanism. The distinguished products exhibited either no sensitivity or enhanced formations upon increasing the initial NO mixing ratio. The results also provide evidence supporting the formation of higher order organic nitrate products with formation pathways independent of pinaketone oxidation.
Keywords: β-pinene; Organic nitrates; HO oxidation; Mass spectrometry;

Evaluation of ozone generation and indoor organic compounds removal by air cleaners based on chamber tests by Kuo-Pin Yu; Grace Whei-May Lee; Ching-Pei Hsieh; Chi-Chi Lin (35-42).
Ozone can cause many health problems, including exacerbation of asthma, throat irritation, cough, chest ache, shortness of breath, and respiratory infections. Air cleaners are one of the sources of indoor ozone, and thus the evaluation of ozone generated by air cleaners is desired significant issue. Most evaluation methods proposed are based on chamber tests. However, the adsorption and desorption of ozone on the wall of test chamber and the deposition of ozone resulted from the surface reaction can influence the evaluation results. In this study, we developed a mass balance model that took the adsorption, desorption and deposition of ozone into consideration to evaluate the effective ozone emission rates of six selected air cleaners. The experiments were conducted in a stainless steel chamber with a volume of 11.3 m3 at 25 °C and 60% relative humidity. The adsorption, desorption and deposition rate constants of ozone obtained by fitting the model to the experimental data were ka  = 0.149 ± 0.052 m h−1, kd  = 0.013 ± 0.007 h−1, and kr  = 0.050 ± 0.020 h−1, respectively. The effective ozone emission rates of Air Cleaners No. 1, 2, and 3 ranged between 13,400–24,500 μg h−1, 7190–10,400 μg h−1, and 4880–6560 μg h−1, respectively, which were more stable than those of No.4, 5, and 6. The effective ozone emission rates of Air Cleaners No. 4, 5, and 6 increased with the time of operation which might be relevant to the decrease of ozone removal by the “aging” filter installed in these cleaners. The removal of toluene and formaldehyde by these six air cleaners were also evaluated and the clean air delivery rates (CADRs) of these two pollutants ranged from non-detectable to 0.42 ± 0.08 m3  h−1, and from non-detectable to 0.75 ± 0.07 m3  h−1, respectively. The CADRs showed an insignificant relationship with the effective ozone emission rates. Thus, the removal of toluene and formaldehyde might be resulted from the adsorption on the filters and the decomposition by the high-voltage electric discharge or the ionization that generated ozone.
Keywords: Ozone; Chamber test; Indoor, volatile organic compounds; Air cleaner;

Modeling the chemical evolution of nitrogen oxides near roadways by Yan Jason Wang; Allison DenBleyker; Elena McDonald-Buller; David Allen; K. Max Zhang (43-52).
The chemical evolution of nitrogen dioxide (NO2) and nitrogen monoxide (NO) in the vicinity of roadways is numerically investigated using a computational fluid dynamics model, CFD-VIT-RIT and a Gaussian-based model, CALINE4. CFD-VIT-RIT couples a standard kɛ turbulence model for turbulent mixing and the Finite-Rate model for chemical reactions. CALINE4 employs a discrete parcel method, assuming that chemical reactions are independent of the dilution process. The modeling results are compared to the field measurement data collected near two roadways in Austin, Texas, State Highway 71 (SH-71) and Farm to Market Road 973 (FM-973), under parallel and perpendicular wind conditions during the summer of 2007. In addition to ozone (O3), other oxidants and reactive species including hydroperoxyl radical (HO2), organic peroxyl radical (RO2), formaldehyde (HCHO) and acetaldehyde (CH3CHO) are considered in the transformation from NO to NO2. CFD-VIT-RIT is shown to be capable of predicting both NOx and NO2 profiles downwind. CALINE4 is able to capture the NOx profiles, but underpredicts NO2 concentrations under high wind velocity. Our study suggests that the initial NO2/NOx ratios have to be carefully selected based on traffic conditions in order to assess NO2 concentrations near roadways. The commonly assumed NO2/NOx ratio by volume of 5% may not be suitable for most roadways, especially those with a high fraction of heavy-duty truck traffic. In addition, high O3 concentrations and high traffic volumes would lead to the peak NO2 concentration occurring near roadways with elevated concentrations persistent over a long distance downwind.
Keywords: CFD-VIT-RIT; Nitrogen oxides; NO2/NOx ratio; Texas Roadway Study; CALINE4; Turbulence;

Reactions of Cl atoms with 3-buten-1-ol, 3-methyl-3-buten-1-ol, 2-methyl-3-buten-1-ol and 4-penten-2-ol were investigated using relative technique with gas chromatograph coupled with flame ionization detection (GC-FID). At 298 ± 1 K and 1.01 × 105 Pa, the rate coefficients measured (in units of 10−10 cm3 molecule−1 s−1) were 3.63 ± 0.49, 4.13 ± 0.56, 3.51 ± 0.48, and 3.62 ± 0.49, respectively. The quoted errors included 2σ from the least-squares analysis and also 10% errors caused by the uncertainty of the reference rate coefficients. In addition, rate coefficients for reactions of the unsaturated alcohols with O3 were determined using absolute method. The values obtained have been presented, compared with those of their alkene structural homologues and discussed. Reactivity trends and atmospheric implications have also been discussed.
Keywords: Cl atoms; Ozone; Rate coefficient; Unsaturated alcohols;

PM2.5 water-soluble organic carbon (WSOC) was measured over 24-h periods with organic carbon and elemental carbon (OC and EC) at an urban site in Gwangju, Korea, during summer (1 June–22 August 2008) and winter (26 November 2008–27 February 2009). The average mass concentrations of OC and WSOC were 5.0 ± 2.9 μg C m−3 and 2.8 ± 1.6 μg C m−3 during summer, respectively, and 8.4 ± 4.6 μg C m−3 and 3.7 ± 2.5 μg C m−3 during winter, respectively. The WSOC/EC and WSOC/OC ratios were 1.74 ± 0.60 and 0.55 ± 0.10 in summer, and 1.30 ± 0.70 and 0.43 ± 0.11 in winter, respectively. According to the results of air mass backward trajectory analysis, high fractions of WSOC to OC in the study region, compared to those reported in many other urban sites, could be explained by the atmospheric transport of water-soluble organic species from upwind regions, i.e., large-scale Steel Works and national industrial complexes located in the southeastern and eastern directions of the sampling site and northeastern regions (Beijing, Shenyang, and Shanghai) of China in the summer, and the northeastern regions of China in the winter. The secondary OC concentrations, estimated using the EC-tracer method, accounted for 26.9 ± 19.1% (0.0–65.0%) and 24.3 ± 19.5% (0.0–73.5%) of the measured OC in summer and winter, respectively. Higher correlation between secondary OC and WSOC was found in the summer (R 2  = 0.78) than in the winter (R 2  = 0.34), reflecting a high fraction of secondary WSOC in the summer. The entire winter sampling period was separated into two periods, i.e., winter periods “A” (Nov 26 2008–Jan 8 2009) and “B” (Jan 19–Feb 27 2009), due to the existence of open burning activities around the sampling site. Highly enriched behaviors of potassium ion (K+) and WSOC concentrations during the winter “A” period are in accordance with the fact that open burning of wood and vegetation debris at a construction working place near the sampling site was occasionally observed. The moderate correlations between water- soluble K+ and WSOC concentrations suggest that some of the WSOC observed during summer and winter could be attributed to the impact of biomass burning.
Keywords: Carbonaceous aerosol; Organic carbon; Water-soluble organic carbon; Secondary organic aerosol; Atmospheric processing; Biomass burning;

This paper describes the Salt Lake Valley urban flux study that was designed to understand the role of vegetation and urbanization on CO2 and surface energy fluxes over surfaces typical of urbanized and pre-urbanized land cover in the semi-arid Salt Lake Valley. The eddy covariance technique was applied at two different sites with distinct land forms within an urbanizing mountain basin. One site was located in a suburban neighborhood with substantial mature vegetative cover (urban forest), prototypical of many residential neighborhoods in the valley, and the other site was in a pre-urban area. Results indicate that the suburban site was a net sink of CO2 during the midday period in the summer due to photosynthetic activity and was a source of CO2 during the evening and nighttime periods. The pre-urban site was a net source of CO2 with positive fluxes throughout the day. Even though the vegetation at the suburban site sequestered carbon dioxide during the daytime in the summer months, the daily net CO2 flux remained positive (i.e. a net source). In addition, the net CO2 emission at the suburban site was found to be three times greater in the fall than during summer. The vegetative cover around the suburban site also had a significant impact on the partitioning of the surface energy fluxes. During the summer months, the contribution of the latent heat flux was substantially higher at the suburban site, while the sensible heat flux was much larger at the pre-urban site. The general behavior of the energy and CO2 fluxes are consistent with typical climate modification due to urbanization in semi-arid climates (i.e. introduction of an urban forest), but quite different from changes reported in more mesic climates where highly vegetated regions are replaced with urban surfaces.
Keywords: Carbon dioxide fluxes; Eddy covariance; Semi-arid city; Surface energy budget; Urban forest;

Understanding and mitigating the challenge of bioaerosol emissions from urban community composting by L.J. Pankhurst; U. Akeel; C. Hewson; I. Maduka; P. Pham; J. Saragossi; J. Taylor; K.M. Lai (85-93).
Within the UK, local and regional government drives to reduce the quantity of waste being sent to landfill have led to an increase in small-scale composting schemes, instigated by local councils and not-for-profit organisations. The composting process relies upon the proliferation of microorganisms, leading to their emission into the ambient environment. In this investigative study, total bacteria and Aspergillus fumigatus emitted from a small-scale composting facility in central London were measured in different spatial and temporal dimensions. Bioaerosols did not disperse in concentrations significantly higher than those measured at ‘background’ locations, where maximum geometric mean was 55 × 102 Colony Forming Units (CFU) per m−3. Concentrations on-site and at the nearest potential receptor were comparable to those found at commercial facilities, reaching 25 × 104 and 29 × 103  CFU m−3 for total bacteria and A. fumigatus respectively. The room housing the facility was contaminated by moulds; likely to result from high relative humidity of the air (consistently above 80% during this study), building material, and the generation of organic dust. The complex diurnal meteorological variations of urban environments are likely to influence bioaerosol dispersal, and consequent exposure risk for sensitive receptors. Site planning tools including Geographical Information Systems (GIS) mapping with buffer zones around schools and hospitals, and use of computerised models for the design of rooms housing urban composting facilities are proposed as methods for reducing the risk of occupational and off-site receptor exposure.
Keywords: Bioaerosols; Urban environments; Composting; Aspergillus fumigatus; Public health;

PM10 concentrations were measured at Nellis Dunes Recreation Area (NDRA), Nevada, USA. NDRA is a desert area located 6 km northeast of the metropolitan area of Las Vegas. Three sources contribute to the dust at the site: local wind erosion, off-road vehicular activity and dust production in the city of Las Vegas. PM10 concentrations were measured during one complete year and stored as 20-min averages. Grain-size distribution was also determined from sediment collected in sediment traps. PM10 concentrations at NDRA are greater, and dust is finer in April–September as compared to October–March. Concentrations are also higher during the day than at night. The diurnal pattern of PM10 concentration at NDRA is characterized by a maximum in the early afternoon and a minimum in the morning. In all months except June–August, a secondary peak in concentration occurs around midnight. The higher concentrations during the day hours are not explained by local wind erosion, by meteorological parameters such as wind speed, wind direction, atmospheric stability or ventilation, or by the supply of dust from the Las Vegas metropolis. The diurnal pattern of PM10 concentration in NDRA also differs from that observed at other rural sites in the Las Vegas Valley and in the city itself. The aberrations in the PM10 pattern at NDRA are caused by intense off-road vehicular driving in this area. Although dust from NDRA is blowing towards Las Vegas from late autumn to early spring and also during most of the nights, no quantitative data is currently available to determine the impact NDRA-emitted dust may have on the PM10 concentrations in the city.
Keywords: PM10; Dust; Dust concentration; Diurnal patterns; Seasonal patterns; Las Vegas;

Chemkar PM10: An extensive look at the local differences in chemical composition of PM10 in Flanders, Belgium by Jordy Vercauteren; Christina Matheeussen; Eric Wauters; Edward Roekens; René van Grieken; Agnieszka Krata; Yaroslava Makarovska; Willy Maenhaut; Xuguang Chi; Benny Geypens (108-116).
The results of Chemkar PM10, the first large scale chemical characterisation project of PM10 in Flanders are presented. Between September 2006 and September 2007 a total of 365 PM10 samples were collected by sampling every sixth day at six different sites in Flanders (Belgium) varying in character from urban background to rural. Samples were analysed for a series of elements, elemental and organic carbon, 13C/12C- and 15N/14N-isotopic ratios, and water-soluble ions. At three sites extra sampling was carried out to determine PAHs by means of a novel technique that uses sorption tubes consisting of polydimethylsiloxane (PDMS) foam, PDMS particles and a TENAX TA bed. Results showed that the most important fractions were secondary inorganic ions (nitrate, sulphate and ammonium): 41% (12.6 μg m−3), organic matter: 20% (6.1 μg m−3), crustal matter: 14% (4.3 μg m−3), sea salt: 8% (2.4 μg m−3) and elemental carbon: 4% (1.2 μg m−3). Although the general composition profile was rather similar for the six sites, substantial differences could be observed for some main components and for several trace metals such as chromium, copper, zinc, arsenic and lead. Although the average sum of the “PAH 16” was quite variable between the three sites (between 132 and 248 ng m−3) the average sum of the “PAH 7” was between 7 and 9 ng m−3 for the three sites. The largest relative differences between sites were found for elemental carbon and crustal matter, thereby indicating that there is some potential for local measures to reduce the concentrations of particulate matter by a few μg m−3. Both for carbon and nitrogen isotopic ratios significant differences in time were observed. Isotopic differences in location could only be detected for carbon.
Keywords: PM10; EC/OC; Secondary inorganic aerosol (SIA); Elemental analysis; Isotopic ratios; PAHs;

The levels of ultrafine particles (UFPs) and their size distributions on a highway electronic toll collection (ETC) lane were measured from October 30 to November 1 and November 5 to November 6, 2008. The hourly UFP levels measured at the highway ETC lane were 1.3 × 104–1.9 × 105 particles cm−3 (mean = 9.4 × 104 particles cm−3). Compared with urban UFP levels, average UFP levels at the highway ETC lane were about 5–10 times higher than those previously measured in urban areas, indicating that a considerable amount of UFPs were exhausted from vehicles. At the highway ETC lane, the average UFP number size distribution had a dominant mode at about 10 nm and a minor mode at about 33 nm. Measurement results indicate that nucleation mode particles remained at relatively high levels compared to Aitken mode and accumulation mode particles at the highway ETC lane. This study identifies the impacts of traffic volumes and wind speeds on ambient UFP levels. Measurement results show that the elevated UFP levels resulting from traffic volume decreased exponentially as wind speed increased on the highway when wind speed was <2.0 m s−1. However, the elevated UFP levels resulting from traffic volume increased slightly when wind speed was >2.0 m s−1 due to local turbulent mixing causes UFPs at high wind speeds. According to measurement results, high levels of UFP were observed at low wind speeds and under high traffic volumes.
Keywords: Ultrafine particle; Number concentration; Size distribution; Traffic volume; Wind speed;

Exploratory study on the pyrolysis and PAH emissions of polylactic acid by Yi-Chi Chien; Chenju Liang; Shu-hua Yang (123-127).
The emission factors for 16 U.S. EPA priority polycyclic aromatic hydrocarbons (PAHs) from the polylactic acid (PLA) pyrolysis and the decomposition mechanism were investigated in this study. The fragments and gas compositions using on-line thermogravimetry-mass spectrometry (TG-MS) were determined. A temperature series of 7 fragments was analyzed in helium, and was found to include: m/z  = 16, which may represent methane; 28, which may be carbon monoxide; 44, which may be acetaldehyde; 56, which may be methylketene, 144, which may be oligomers of lactide. In addition, there are little amount of 100, and 200 which are oligomers of lactides observed in the pyrolysis of PLA. The pyrolysis of PLA is a non-radical, backbiting ester interchange reaction involving the OH chain ends. Depending on the size of the cyclic transition state, the product can be a lactide molecule, an oligomeric ring with more than two repeat units, methylketene, or acetaldehyde. Carbon monoxide and methane are contributions from the decomposition of acetaldehyde.Experimentally, not detected (n.d.)-40.47 μg of 16 PAH emissions were determined from per gram of PLA pyrolysis. The PAH profiles showed a predominance of naphthalene (58.9%), phenanthrene (12.5%), and fluoranthene (5.9%). The total PAH emissions for PLA pyrolysis is significantly lower than the values associated with PLA combustion. From the viewpoint of air pollution control, this result suggests that pyrolysis seems a better alternative than combustion for the disposal of waste PLA. Also, since pyrolysis is the first step for an incineration process, these results can provide important information on the control of PAHs formation for a commercialized incinerator.
Keywords: Polylactic acid (PLA); PAHs; Emission factor; TG-MS;

Investigating the influence of synoptic-scale meteorology on air quality using self-organizing maps and generalized additive modelling by John L. Pearce; Jason Beringer; Neville Nicholls; Rob J. Hyndman; Petteri Uotila; Nigel J. Tapper (128-136).
The influence of synoptic-scale circulations on air quality is an area of increasing interest to air quality management in regards to future climate change. This study presents an analysis where the range of expected synoptic-scale circulation patterns over the region of Melbourne, Australia are determined and linked to regional air quality. A self-organizing map (SOM) has been applied to daily mean sea level pressure (MSLP) reanalysis to obtain twenty large-scale synoptic patterns in the Australian region. A time series of the occurrence of the synoptic archetypes was then employed within the framework of a generalized additive model (GAM) to identify links between synoptic-scale circulation and observed changes air pollutant concentrations. The GAM estimated shifts in pollutant concentration under the occurrence of each synoptic type after controlling for long-term trends, seasonality, weekly emissions, spatial variation, and temporal persistence. Results found the overall explanatory power of the synoptic archetypes in the models to be rather modest with 5.1% of the day-to-day variation in O3, 4.7% in PM10, and 7.1% in NO2 being explained. This indicates that synoptic-scale circulation features are not the primary driver of day-to-day pollutant concentrations. Nonetheless, further analysis of the partial residual plots identified that despite a modest response at the aggregate level, individual synoptic categories had differential effects on air pollutants. In particular, NO2 and O3 were 20% higher than average when synoptic conditions resulted in a northeasterly gradient wind over the Melbourne area. For PM10 maximum increases of up to 20% occurred when a strong anticyclonic system was centered directly over the Melbourne area. In sum, the unified approach of SOM and GAM provided a complementary suite of tools capable of identifying the entire range synoptic circulation patterns over a particular region and quantifying how they influence local air quality.
Keywords: Air pollution; Generalized additive models; Self-organizing maps; Synoptic climatology;

The duration of PM10 concentration in a large metropolitan area by Giovanni Lonati; Stefano Cernuschi; Michele Giugliano (137-146).
Annual ambient PM10 concentration time series recorded between 1991 and 2006 at 13 monitoring stations located within the “critical area” of Milan (Italy), encompassing the city and its metropolitan area, are analysed for the temporal duration of concentration levels. Duration episodes occur when the measured concentration is continuously higher than fixed concentration thresholds. For 20 concentration thresholds, ranging from 10 μg m−3 up to 200 μg m−3 by a 10 μg m−3 step, the total time of exceedance, the number of events of exceedance and the duration of the events of exceedance are evaluated on annual basis. Simple, empirically-derived expressions, formulated in order to describe these features of the observed durations, are presented. Since these formulations are parameterized in terms of the annual average PM10 concentration, they can be used to assess expected exposure to high-concentration levels for future scenarios characterized by lower annual average concentrations. A case-study for Milan urban area is presented, assessing the occurrence of duration episodes at annual PM10 concentration at the compliance level of the PM10 air quality limits, currently not-attained.
Keywords: Air quality; Particulate matter; Urban area; Empirical modelling; Time structure; Exposure time; Milan;

Direct emissions of air pollutants from the cement industry in China were estimated by developing a technology-based methodology using information on the proportion of cement produced from different types of kilns and the emission standards for the Chinese cement industry. Historical emissions of sulfur dioxide (SO2), nitrogen oxides (NO X ), carbon monoxide (CO), particulate matter (PM) and carbon dioxide (CO2) were estimated for the years 1990–2008, and future emissions were projected up to 2020 based on current energy-related and emission control policies. Compared with the historical high (4.36 Tg of PM2.5, 7.16 Tg of PM10 and 10.44 Tg of TSP in 1997), PM emissions are predicted to drop substantially by 2020, despite the expected tripling of cement production. Certain other air pollutant emissions, such as CO and SO2, are also predicted to decrease with the progressive closure of shaft kilns. NO X emissions, however, could increase because of the promotion of precalciner kilns and the rapid increase of cement production. CO2 emissions from the cement industry account for approximately one eighth of China’s national CO2 emissions. Our analysis indicates that it is possible to reduce CO2 emissions from this industry by approximately 12.8% if advanced energy-related technologies are implemented. These technologies will bring co-benefits in reducing other air pollutants as well.
Keywords: Cement industry; Emission inventory; China; Technology-based methodology;

Acclimatory and direct responses of photosynthesis (A), stomatal (g s) and mesophyll (gm ) conductance, light (R L) and dark (R D) respiration, and isoprene emission, measured at different temperatures, were compared in one-year-old Populus×euramericana saplings grown at 25 °C, 35 °C, and in the saplings grown initially at 35 °C and then exposed for two weeks at 25 °C. Results show that A, g s and gm were significantly lower at 35 °C, than at the other growth temperatures. This resulted in a downward acclimation of these parameters over the range of measuring temperatures. Both R L and R D also showed a considerable downward acclimation. However, the respiration to photosynthesis ratio increased with high temperatures, for R L and R D were more responsive to increasing growth temperatures than A at all measuring temperatures. This type of acclimation would lead to a shift in the carbon balance between photosynthesis and respiration under changing climatic conditions. Isoprene emission was greatly affected by temperature treatments and showed a downward acclimation to higher temperatures. Respiration and isoprene emission rates were directly related, independently of growth and measuring temperatures. These findings may be likely relevant to predict the emissions of isoprenoid in globally changing environmental conditions.
Keywords: Carbon assimilation; Isoprene emission; Mesophyll conductance; Rising temperature; Stomatal conductance;

Dependence of daily peak O3 concentrations near Houston, Texas on environmental factors: Wind speed, temperature, and boundary-layer depth by Robert M. Banta; Christoph J. Senff; Raul J. Alvarez; Andrew O. Langford; David D. Parrish; Michael K. Trainer; Lisa S. Darby; R. Michael Hardesty; Bryan Lambeth; J. Andrew Neuman; Wayne M. Angevine; John Nielsen-Gammon; Scott P. Sandberg; Allen B. White (162-173).
Airborne and surface measurements of ozone (O3) during the Texas Air Quality Study campaigns in 2000 and 2006 (TexAQS 2000 and TexAQS 2006) were used to investigate the relationship between maximum daily O3 and the vector-averaged wind speed <U>, calculated from radar wind profiler data, in the lower atmospheric boundary layer (BL). Both the maximum daily O3 and the peak “add-on” O3 contribution (calculated as the maximum minus the background values) from the Houston area showed a strong correlation (r∼0.7–0.9) with both the reciprocal of this wind speed <U>−1, and the wind speed <U> itself. Data from airborne platforms produced higher correlations in general than surface-measured values. Except for special cases where O3 was measured close to source activity in a location where the BL depth h was suppressed, peak daily ozone concentrations were not strongly correlated with h, and attempts to include 1/h dependence with <U>−1 degraded the correlations—indicating that in general, h was not a strong predictor for maximum daily O3. Inclusion of daily maximum temperature in the regression analysis also failed to improve the correlations significantly. The high correlations for wind speed thus showed that <U> was the meteorological variable most strongly associated with peak daily O3 concentrations. The best-fit regression line of peak daily O3 vs. <U> for the 2000 data lay above the line for 2006 for wind speeds less than 5 m s−1, the difference increasing as the wind speeds weakened. This six-year decrease in O3 concentrations for the weakest-wind, most polluted days suggests that control strategies implemented between 2000 and 2006 may be producing beneficial effects, especially on the most polluted days.
Keywords: Ozone; Air pollution; Sea breeze; Houston, Texas; Lidar; Differential-absorption lidar; DIAL;

Tropospheric ozone variability over the Iberian Peninsula by Pavan S. Kulkarni; D. Bortoli; R. Salgado; M. Antón; M.J. Costa; A.M. Silva (174-182).
To study tropospheric ozone variability over the Iberian Peninsula (IP), NASA Langley TOR data have been analyzed for the 1979–2005 period. The maximum tropospheric ozone concentration over the entire IP was found in June (∼41 DU) and a minimum in December (∼29 DU). However the maximum tropospheric ozone concentration was found over West Atlantic Coast (WAC) (∼44 DU), followed by Mediterranean Coast (MC) (∼42 DU), North Atlantic Coast (NAC) (∼41 DU), Central Iberian Peninsula (CIP) (∼40 DU) and Pyrenees Mountain Range (PMR) (∼39 DU) during June-July. The high concentration of tropospheric ozone in July over the Atlantic Ocean near IP is due to the presence of Azores anticyclone and related photochemistry and dynamics, and affects the observed higher tropospheric ozone concentration over WAC zone. Strong seasonal cycle in tropospheric ozone concentration has been observed with large variation over NAC (∼49%), followed by WAC (∼48%) and MC (∼41%) compared to CIP and PMR (∼38%) zones. When the data are compared over the IP for the two periods (1979–1993 and 1997–2005), a systematic increase in the number of months with higher tropospheric ozone concentration has been observed during the second period with respect to the first. These increases are almost 8% to 24% over NAC, 6% to 17% over WAC, 5% to 24% over CIP, 6% to 23% over MC and 13% to 18% over PMR, zones. It has been observed that topography, climatology and population density distribution plays a crucial role in the variability of tropospheric ozone concentration over the IP.
Keywords: Iberian Peninsula; Tropospheric ozone residual (TOR); Topography; Climatology;

Dissolved gaseous mercury (DGM, largely Hg(0)) in coastal seawater and gaseous elemental mercury (GEM or Hg(0)) in the atmosphere were simultaneously measured on the coast of the Yellow Sea, China in four different seasons (2008–09). Mean concentrations (±SD) of DGM and GEM over the study period were 34.0 ± 26.1 pg L−1 and 2.55 ± 0.98 ng m−3, respectively. DGM concentrations and the degree of DGM saturation (S a) exhibited distinct seasonal variation with the order of summer (DGM: 69.0 ± 23.3 pg L−1, S a: 11.00 ± 5.92) > fall (27.0 ± 16.4 pg L−1, 3.50 ± 2.60) > spring (23.0 ± 8.7 pg L−1, 2.00 ± 0.98) > winter (16.0 ± 6.0 pg L−1, 0.96 ± 0.39). Under typical meteorological condition with low wind speed and intensive solar radiation in warm seasons, DGM usually exhibited the clear diurnal variation with elevated levels around noon and low levels in morning and afternoon. The diurnal and seasonal variation of DGM indicated the importance of photochemical DGM formation in the seawater. A consistent low DGM levels in high wind speed condition suggested that the biological activity probably influenced the DGM formation. There was no significant correlation between DGM and total mercury (THg), reactive mercury (RHg), dissolved organic carbon (DOC) in the seawater, indicating that THg/RHg and DOC might be not the controlling factors for the DGM formation in our study region. Based on the data of DGM and GEM and a two-layer gas exchange model, Hg(0) fluxes (in the unit of ng m−2  h−1) at air–sea interface were 0.51 ± 1.29 over the entire study period with 0.89 ± 1.84 in fall, 0.88 ± 1.38 in summer, 0.32 ± 0.71 in spring, and −0.06 ± 0.64, a slightly net Hg(0) deposition rate, in winter, respectively.
Keywords: Dissolved gaseous mercury; Air–sea mercury flux; Total and reactive mercury; Yellow Sea; China;

In the recent years the effect of urbanization on local convections and lightning has been studied very extensively. Here we have analyzed the last 8 years (from 2001 to 2008) data of total lightning, Aerosol Optical Depth (AOD) and rainfall over two inland and two coastal metropolitan cities of India, to study the effect of urbanization on lightning. The lightning and rainfall data are taken from TRMM satellite and AOD data is taken from Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra (EOS AM) and Aqua (EOS PM) satellites. Our analysis shows that both the inland cities show considerable enhancement, where as both the coastal cities do not show enhancement in lightning, in the last 8 years. The results show that, over a inland city, where aerosol concentration is not increased appreciably in last few years the enhancement in convective activity and lightning is controlled by thermodynamic effect, where as, where aerosol concentration show increasing trend, aerosols play major roll in enhancement in lightning activity. It has been also found that over a city where aerosol concentration show increasing trend, lightning show a sharp increase due to combined positive effect of thermodynamics and aerosols, however rainfall show only small increase because of negative effect of aerosols on rainfall. The analysis of lightning, aerosols and rainfall over coastal cities do not show any increasing trend in rainfall and lightning activity which suggest that during premonsoon period all these parameters are controlled by large scale processes and therefore heat island effect or aerosol effect are not observed in both the coastal cities.
Keywords: Lightning over metropolitan cities of India;

Modeling the effects of a speed limit reduction on traffic-related elemental carbon (EC) concentrations and population exposure to EC by W. Lefebvre; F. Fierens; E. Trimpeneers; S. Janssen; K. Van de Vel; F. Deutsch; P. Viaene; J. Vankerkom; G. Dumont; C. Vanpoucke; C. Mensink; W. Peelaerts; J. Vliegen (197-207).
Despite the scarce effect of speed limit reduction measures on total mass PM10 and PM2.5 concentrations, it is shown that the effect on the probably more hazardous component elemental carbon (EC) is more important which means that, from the viewpoint of health benefit, speed reductions during smog episodes may well be justified. Especially in the very dense highway network in Flanders with a 60% share of diesel cars (the highest in Europe) a speed limit reduction from 120 to 90 km/h during winter smog episodes on selected sections of Flemish highways leads to a significant decrease of the EC concentrations near those highways. Key findings are that the decrease in EC depends on the distance from the highways. In the direct vicinity of the highways, a decrease compared to the base-line scenario where no speed limit changes were implemented of up to 30% of the EC concentrations is modeled. Within a distance of 1500 m of the concerned highway sections there is an average decrease in EC of 0.18 μg m−3 affecting about 1 million people living in these areas. When the speed limit reduction measure is in force, the EC exposure of about 300,000 people decreases by at least 5% and 7500 people experience a decrease of 15% or more.
Keywords: Air quality; Elemental carbon; Traffic; Speed reduction; Flanders;

Measurement of carbon dioxide fluxes in a free-air carbon dioxide enrichment experiment using the closed flux chamber technique by Merete Bang Selsted; Per Ambus; Anders Michelsen; Leon van der Linden; Klaus Steenberg Larsen; Kim Pilegaard; Teis N. Mikkelsen; Claus Beier (208-214).
Carbon dioxide (CO2) fluxes, composing net ecosystem exchange (NEE), ecosystem respiration (ER), and soil respiration (SR) were measured in a temperate heathland exposed to elevated CO2 by the FACE (free-air carbon enrichment) technique, raising the atmospheric CO2 concentration from c. 380 μmol mol−1 to 510 μmol mol−1. All CO2 fluxes were measured by the static chamber methodology. Although the FACE technique enriches the atmosphere with CO2 to a fixed level, the above ground CO2 concentrations may nevertheless locally vary strongly (from about ambient to ∼1000 μmol mol−1). Deployment of static chambers to FACE experiments should therefore be performed with great care in order to ensure reproducible conditions with respect to chamber headspace CO2 concentration. We demonstrate that that the fluxes measured by closed chambers relate linearly to the initial headspace CO2 concentration. When changing the initial headspace CO2 concentration from 380 to 510 μmol mol−1 the net CO2 assimilation expressed by NEE increased instantaneously 1.51 times in control plots and 1.71 times in FACE plots. By contrast, ER in control plots decreased, being 0.87 times that measured at the low CO2 concentration, and the flux also decreased in FACE plots, to 0.79 times that at low concentration. Similar SR in control plots was decreased 0.94 times in control plots and 0.88 times in FACE plots. We found that a useful method to achieve stable and reproducible chamber headspace and soil CO2 concentration prior to commencement of flux measurements was to turn off the FACE system at least 10 min in advance. Within 10 min a new equilibrium was established between the soil and atmosphere, apparently due to CO2 degassing from the top soil. The observed increase in SR in response to increased CO2 persisted for up to 18 h during which measurements should be performed. Soil CO2 concentrations were increased by up to 500 μmol mol−1 by the FACE treatment, substantially more than the 130 μmol mol−1 enrichment achieved in the atmosphere suggesting that the increased SR flux was caused by increased belowground respiration.
Keywords: FACE; CO2; Net ecosystem exchange; Ecosystem respiration; Soil respiration;

14C-Based source assessment of soot aerosols in Stockholm and the Swedish EMEP-Aspvreten regional background site by August Andersson; Rebecca J. Sheesley; Martin Kruså; Christer Johansson; Örjan Gustafsson (215-222).
Combustion-derived soot or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In order to propose effective mitigation strategies for BC emissions it is of importance to investigate geographical distributions and seasonal variations of BC emission sources. Here, a radiocarbon methodology is used to distinguish between fossil fuel and biomass burning sources of soot carbon (SC). SC is isolated for subsequent off-line 14C quantification with the chemothermal oxidation method at 375 °C (CTO-375 method), which reflects a recalcitrant portion of the BC continuum known to minimize inadvertent inclusion of any non-pyrogenic organic matter. Monitored wind directions largely excluded impact from the Stockholm metropolitan region at the EMEP-Aspvreten rural station 70 km to the south-west. Nevertheless, the Stockholm city and the rural stations yielded similar relative source contributions with fraction biomass (f biomass) for fall and winter periods in the range of one-third to half. Large temporal variations in 14C-based source apportionment was noted for both the 6 week fall and the 4 month winter observations. The f biomass appeared to be related to the SC concentration suggesting that periods of elevated BC levels may be caused by increased wood fuel combustion. These results for the largest metropolitan area in Scandinavia combine with other recent 14C-based studies of combustion-derived aerosol fractions to suggest that biofuel combustion is contributing a large portion of the BC load to the northern European atmosphere.
Keywords: Radiocarbon; Black carbon; Soot; Aerosols; Source apportionment;

Modeling the fate of atmospheric reduced nitrogen during the Rocky Mountain Atmospheric Nitrogen and Sulfur Study (RoMANS): Performance evaluation and diagnosis using integrated processes rate analysis by Marco A. Rodriguez; Michael G. Barna; Kristi A. Gebhart; Jennifer L. Hand; Zachariah E. Adelman; Bret A. Schichtel; Jeffrey L. Collett; William C. Malm (223-234).
Excess wet and dry deposition of nitrogen-containing compounds is a concern at a number of national parks. The Rocky Mountain Atmospheric Nitrogen and Sulfur Study (RoMANS) was conducted during the spring and summer of 2006 to identify the overall mix of ambient and deposited sulfur and nitrogen at Rocky Mountain National Park (RMNP), in north-central Colorado. The Comprehensive Air Quality Model with extensions (CAMx) was used to simulate the fate of gaseous and particulate species subjected to multiple chemical and physical processes during RoMANS. This study presents an operational evaluation with a special emphasis on the model performance of reduced nitrogen species. The evaluation showed large negative biases and errors at RMNP and the entire domain for ammonia; therefore the model was considered inadequate for future source apportionment applications. The CAMx Integrated Processes Rate (IPR) analysis tool was used to elucidate the potential causes behind the poor model performance. IPR served as a tool to diagnose the relative contributions of individual physical and chemical processes to the final concentrations of reduced nitrogen species. The IPR analysis revealed that dry deposition is the largest sink of ammonia in the model, with some cells losing almost 100% of the available mass. Closer examination of the ammonia dry deposition velocities in CAMx found that they were up to a factor of 10 larger than those reported in the literature. A series of sensitivity simulations were then performed by changing the original deposition velocities with a simple multiplicative scaling factor. These simulations showed that even when the dry deposition values were altered to reduce their influence, the model was still unable to replicate the observed time series; i.e., it fixed the average bias, but it did not improve the precision.
Keywords: Ammonia; Reduced nitrogen; CAMx; Process analysis; RoMANS; Rocky Mountain National Park;

Reduction of CB05 mechanism according to the CSP method by M.A. Mora-Ramirez; R.M. Velasco (235-243).
In this work we are interested in the research and development of a useful tool to reduce the complexity of chemical mechanisms used in miscellaneous air quality models. We present a study of two methods to classify between species reacting at fast or slow rates. The first method is based on lifetimes of species and the second one is the so called Computational Singular Perturbation (CSP) technique. Both methods provide us with a criterion which allows some simplification of the chemical mechanism. In particular, we will take the core of the Carbon Bond mechanism (CB05) under the conditions in Mexico City. This means that we will introduce the adequate temperature profile and the photolytic contributions in the rates of reaction, in both the lifetime and the CSP method. We compare the corresponding criteria paying special attention to the results coming from the CSP method. Finally, our results show that the CSP method is a robust criterion to select the stationary species through the Integrated Pointers.
Keywords: Singular computational perturbation method; CB05; Reduced mechanisms; Chemical kinetics;

Identification of chemistry-dependent artifacts on gravimetric PM fine readings at the T1 site during the MILAGRO field campaign by M. Moya; S. Madronich; A. Retama; R. Weber; K. Baumann; A. Nenes; M. Castillejos; C. Ponce de León (244-252).
As part of the MIRAGE (MILAGRO) study conducted 7–30 March 2006 in Mexico City and its Metropolitan Area (MCMA), fine particulate matter (PM2.5) was collected using two Tapered Element Oscillating Microbalance (TEOM) systems, and a Partisol instrument at the T1 super-site (Tecamac, State of Mexico). Inorganic analysis was performed on filter-based (PM1, PM2.5-URG) measurements also collected at this site. Measurements from the gravimetric (TEOMs, Partisol) and URG systems were inter-compared with chemical speciation measurements using a Particle Into Liquid Sampler (PILS) and Thermal Optical methods.Mass and chemical balances applied over the first part of the study (11–22 March) showed that a TEOM using a device (SES) which reduces particle-bound water and retains a fraction of semi-volatile compounds (SVM) gives readings ∼30% larger than a conventional TEOM. In the second part of the study (26–30 March), the loss of SVM during TEOM-heated filter collection (both systems) represented a significant fraction of PM2.5 mass due to changes in particle composition. Overall, when nonvolatile nitrate dominated (i.e., when associated with crustal species and not NH4 +) and/or sulfate dominates (SO4 2−/NO3 molar ratio is >1), PM2.5 mass readings are in agreement with those reported for the T1 site if TEOM is using a SES device. However, when volatile nitrate dominates (i.e., NH4NO3) or SO4 2−/NO3 molar ratio is <1, a larger fraction is lost from both TEOMs (with or without the SES device). Under the latter regime, uncertainties are large and gravimetric losses may reach 30%–50%. The gravimetric PARTISOL instrument recorded lower readings under all of the aforementioned conditions with differences versus TEOMs decreasing with increasing RH. These findings call for a careful characterization of such volatilization biases to improve current PM (PM10, PM2.5) measurements/networks, especially in alkaline-rich environments that can favor such biases.With regards to PM1 and PM2.5 filter-based measurements, findings are: 1) crustal-related elements are important features in the PM2.5–1 size fraction; 2) a factor of ∼2 overestimation of SO4 2− concentrations is recorded on substrates during PM collection and 3) main elements of a typical urban aerosol size distribution are concentrated in the 1 μm (versus 2.5 μm) size fraction.
Keywords: MILAGRO; Mexico City; Particulate matter; Air pollution;

Ground and shipboard measurements of atmospheric gaseous elemental mercury over the Yellow Sea region during 2007–2008 by Duc Luong Nguyen; Jin Young Kim; Shang-Gyoo Shim; Xiao-Shan Zhang (253-260).
The first ever shipboard measurements of atmospheric gaseous elemental mercury (GEM) over the Yellow Sea were carried out. Ground measurements were also performed at background and urban sites surrounding the Yellow Sea during 2007–2008. The GEM mean concentrations obtained from ground measurements at Ningbo, Chengshantou, and Deokjeok, and from shipboard measurements for the routes of Incheon–Qingdao, Incheon–Weihai, and Incheon–Jeju were 3.79 ± 1.29, 2.07 ± 0.91, 1.79 ± 0.80, 1.82 ± 0.51, 2.03 ± 0.66, and 2.43 ± 0.59 ng m−3, respectively. Compared with the GEM background concentration in the northern hemisphere, the slightly higher GEM regional background concentration of 2.08 ± 0.85 ng m−3 over the Yellow Sea region, based on shipboard measurements and ground measurements at background sites, gave implications for the impact of anthropogenic mercury sources surrounding the Yellow Sea. Shipboard measurements over the Yellow Sea showed a decrease of mercury concentration compared with aircraft measurements during ACE-ASIA campaign in 2001, though it was still generally higher than those from other seas or oceans around the world. The contrasting patterns in seasonal and diurnal variations of GEM concentration between background and urban sites were apparent due to the influence of different sources; for example, natural sources, such as vegetative and foliar emissions in background area, and local anthropogenic sources, such as coal combustion in urban area. The significantly elevated GEM concentrations at Deokjeok, a Korean background site, during the spring of 2008 were attributed to the long-range transport from the southern part of Liaoning province, one of the heaviest mercury-polluted areas in China.
Keywords: GEM measurement; Long-range transport; East Asia; Background concentration; Seasonal variation; Yellow Sea;

Unsuitability of using the DNPH-coated solid sorbent cartridge for determination of airborne unsaturated carbonyls by Steven Sai Hang Ho; K.F. Ho; W.D. Liu; S.C. Lee; W.T. Dai; J.J. Cao; H.S.S. Ip (261-265).
Measurements of aldehydes and ketones are typically conducted by derivatization using sorbent cartridges coated with 2,4-dinitrophenylhydrazine (DNPH). The collected samples are eluted with acetonitrile and analyzed by high-pressure liquid chromatography coupled with an ultra-violet detector (HPLC/UV). This paper intends to examine artifacts about its suitability in identification of unsaturated carbonyls. Kinetic tests for acrolein, crotonaldehyde, methacrolein and methyl vinyl ketone (MVK) showed formations of carbonyl-DNP-hydrazone during sampling, which could further react with DNPH, resulting in undesired UV absorption products [e.g., carbonyl-DNP-hydrazone-DNPH (dimer) and 2(carbonyl-DNP-hydrazone)-DNPH (trimer)]. The dimerization and trimerization occurred for acrolein and MVK whereas only dimerization for crotonaldehyde and methacrolein. The polymerization products undoubtedly affect the integrity of the chromatogram, leading to misidentification and inaccurate quantification. Whether precautions taken during sampling and/or sample treatment could avoid or minimize this artifact has not been thoughtfully investigated. More often, such artifacts are usually overlooked by scientists when the data are reported.
Keywords: Unsaturated carbonyls; DNPH cartridge; HPLC; Acrolein; Crotonaldehyde; Methacrolein; Methyl vinyl ketone;

Endotoxins in urban air in Stockholm, Sweden by S. Nilsson; A.S. Merritt; T. Bellander (266-270).
Endotoxins, i.e. components originating from the outer membrane in the cell wall of Gram-negative bacteria, activate the human immune system, which may result in airway symptoms such as shortness of breath and airway inflammation. Endotoxins are present in the environment, both outdoors and indoors, and stay airborne for a long time. In order to investigate the levels of endotoxins in urban air and the influence of traffic and meteorological factors, particles (PM10 and PM2.5) were collected at five sites in Stockholm, Sweden on four occasions per site between May and September 2009. Endotoxins were extracted from the filters and analysis was conducted with the Limulus Amebocyte Lysate (LAL)-assay.Endotoxins were present in urban air in Stockholm, albeit in low levels, and were similar to levels found in urban areas outside Sweden. To our knowledge, this is the northernmost location where endotoxins have been measured. The endotoxin levels found in PM10 ranged from 0.020 to 0.107 EU m−3 with a geometric mean of 0.050 EU m−3 and the levels found in PM2.5 ranged from 0.005 to 0.064 EU m−3 with a geometric mean of 0.015 EU m−3. No obvious effects of traffic or meteorological factors on endotoxin levels were observed, although a moderate correlation could be seen with soot. The small number of sampling sites is however a shortcoming of the present study. In future studies, more sites and sampling during all seasons would be preferable in order to get a better picture of the influence of different sources on endotoxin levels.
Keywords: Endotoxin; Particulate matter; LAL;

Assessment of dioxin-like activity in ambient air particulate matter using recombinant yeast assays by Alba Olivares; Barend L. van Drooge; Pascual Pérez Ballesta; Joan O. Grimalt; Benjamin Piña (271-274).
Ectopic activation of the aryl hydrocarbon receptor (AhR), also known as dioxin-like activity, is a major component of the toxicity associated with polycyclic aromatic hydrocarbons (PAH). Filtration of ambient air particulate matter through PM10 filters followed by chemical determination of PAH concentrations and a yeast-based bioassay (RYA) were combined to evaluate and characterize dioxin-like activity in ambient air. Samples were collected in a semirural area of Northern Italy between September 2008 and February 2009. Total PAH contents ranged between 0.3 ng m−3 and 34 ng m−3 and were in correlation with seasonal variations of meteorological conditions and combustion processes. Dioxin-like activity values in air samples showed an excellent correlation (0.71 <  R 2  < 0.86) with the observed PAH concentrations and the predicted toxicity equivalents for PAH. This RYA-bioassay reported in the present study provides a simple and low-cost routine control for toxic PAH emissions, even at background air concentration levels.
Keywords: Polycyclic aromatic hydrocarbons; Air pollution; Aryl hydrocarbon receptor; Recombinant yeast assays; Combined determination of PAH composition and AhR activity;