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Atmospheric Environment (v.45, #8)
Spatial and chemical patterns of size fractionated road dust collected in a megacitiy by Fabián Fujiwara; Raúl Jiménez Rebagliati; Laura Dawidowski; Darío Gómez; Griselda Polla; Victoria Pereyra; Patricia Smichowski (pp. 1497-1505).
A study was undertaken to investigate the content of 15 elements in size classified street dust. Samples were collected in the megacity of Buenos Aires during two months at 15 sites grouped in five zones with different urban characteristics and traffic profile. Samples were sieved in four fractions ( A<37μm, 37< B<50μm, 50< C<75μm and 75< D<100μm) before elemental analysis. X-ray powder diffraction (XRD) was selected to detect major components namely, minerals, silicate glass and gypsum. Individual mineral dust particle were analyzed by a scanning electron microscopy and energy dispersive X ray analysis (SEM-EDX) showing that sulphur tended to reside on the particles surface, while Al, Ca, Mg, K, Fe and Si belonged to the lattice. Major, minor and trace elements (Al, As, Ca, Cd, Cu, Fe, Mg, Mn, Mo, Ni, Pb, S, Sb, Sn, and Zn) content was quantified by inductively coupled plasma optical emission spectrometry (ICP OES) in the four particle size ranges. Geological elements, Fe (28–43mgg−1)>Al (13–40mgg−1)>>Ca (1.7–6.9mgg−1)>Mg (2.5–5.8mgg−1) together with S (0.2–1.7mgg−1) exhibited the highest concentrations and the lowest variability. The mean concentrations of anthropogenic elements ranged from 5.4 (Ni) to 1530 (Zn) μgg−1 and significant spatial variability was observed in the order: Cd>S>Sb>Sn>As>Ni>Mo. Cluster analysis allowed differentiating two groups, one composed by elements of both geological and anthropogenic origin (Cu, Fe, Ni and Sn) and another one composed by typical traffic related elements (Cd, Mn, Pb, S, Sb and Zn).Display Omitted► Multiple sources contribute to metal pollution in street dust. ► Traffic is the main anthropogenic input. ► Cd, S and Sb were exclusively associated with automotive wear. ► Mn, Pb and Zn resulted from the combination of both, wear and exhaust.
Keywords: Metals and metalloids; Road dust; Size fractionation; Traffic-related elements; Urban pollution
Particulate matter (PM) concentrations in underground and ground-level rail systems of the Los Angeles Metro by Winnie Kam; Kalam Cheung; Nancy Daher; Constantinos Sioutas (pp. 1506-1516).
Elevated concentrations of particulate matter (PM) have been found in a number of worldwide underground transit systems, with major implications regarding exposure of commuters to PM and its associated health effects. An extensive sampling campaign was conducted in May–August 2010 to measure PM concentrations in two lines of the Los Angeles Metro system – an underground subway line (Metro red line) and a ground-level light-rail line (Metro gold line). The campaign goals were to: 1) determine personal PM exposure of commuters of both lines, and 2) measure and compare PM concentrations at station platforms and inside the train. Considering that a commuter typically spent 75% of time inside the train and 25% of time waiting at a station, subway commuters were exposed on average to PM10 and PM2.5 concentrations that were 1.9 and 1.8 times greater than the light-rail commuters. The average PM10 concentrations for the subway line at station platforms and inside the train were 78.0 μg m−3 and 31.5 μg m−3, respectively; for the light-rail line, corresponding PM10 concentrations were 38.2 μg m−3 and 16.2 μg m−3. Regression analysis demonstrated that personal exposure concentrations for the light-rail line are strongly associated with ambient PM levels ( R2 = 0.61), while PM concentrations for the subway line are less influenced by ambient conditions ( R2 = 0.38) and have a relatively stable background level of about 21 μg m−3. Our findings suggest that local emissions (i.e., vehicular traffic, road dust) are the main source of airborne PM for the light-rail line. The subway line, on the other hand, has an additional source of PM, most likely generated from the daily operation of trains. Strong inter-correlation of PM10 between the train and station microenvironments shows that airborne PM at stations are the main source of PM inside the trains for both lines ( R2 = 0.91 and 0.81 for subway and light-rail line, respectively). In addition, PM2.5 and coarse PM (PM10-2.5) are also strongly correlated for the subway line ( R2 = 0.89) and the light-rail line ( R2 = 0.52–0.92), suggesting that PM2.5 and coarse PM originate from a common source. Finally, in comparison to worldwide subway systems, the L.A. Metro system is relatively ’clean’. Since the system is comparatively new (in operation since 1993), its ventilation system and braking technology are probably more efficient and more advanced than older subway systems.► Subway commuters are exposed to almost double the PM levels of light-rail commuters. ► PM levels for ground-level line are heavily influenced by local emissions; subway line is less influenced by ambient conditions and has a background level of about 21 μg m−3. ► Coarse and fine PM originate from a common source for both lines. ► L.A. Metro is relatively ‘clean’; compared to worldwide subway systems.
Keywords: Subway systems; Particulate matter; PM; 2.5; PM; 10; Coarse PM; Los Angeles Metro
Effect of water addition and the urease inhibitor NBPT on the abatement of ammonia emission from surface applied urea by Alberto Sanz-Cobena; Thomas Misselbrook; Vicci Camp; Antonio Vallejo (pp. 1517-1524).
Urea is considered the cheapest and most commonly used form of inorganic N fertiliser worldwide. However, it has been estimated that 5–30% of the urea N is lost as volatilised NH3. Implementation of NH3 mitigation strategies is crucial in order to reduce both the economic and environmental impact associated with NH3 losses from urea application. Urease activity inhibitors and water addition to the soil have been proposed by UNECE (i.e. Gothenburg Protocol) as means to reduce NH3 emission from fertiliser applications. In this study, two field experiments were carried out in order to test the effectiveness of water addition as NH3 mitigation technique from surface applied urea in comparison with the use of the urease inhibitor NBPT. A system of wind tunnels was used to measure NH3 fluxes. Contrasting irrigation strategies (or rainfall patterns), in terms of both rate and timing, were used in order to evaluate the amount of water necessary to achieve a significant NH3 mitigation. The addition of 7 and 14mm of water to the soil, immediately after urea spreading, reduced NH3 emission by 77 and 89%, respectively, similar to that achieved using NBPT (77–88% reduction). In contrast, a simulated 3mm rainfall, immediately after fertilising, significantly enhanced NH3 volatilisation (with an 8% increase in emission compared to urea application without water addition). These results demonstrate the potential of correct water management in abating NH3 volatilisation from urea applications to soil, giving a similar effect to that of the urease inhibitor NBPT under the experimental conditions presented here.► Effectiveness of water addition and the urease inhibitor NBPT, as NH3 mitigation techniques, was evaluated. ► A single watering was as effective as NBPT when mitigating NH3 from urea fertilising. ► Watering produced contrasting effects on NH3 emission depending on its rate and dose. ► These results add information to the sparse database on NH3 fluxes from urea fertilising. ► Although site-specific, these results provide supporting evidence for some UNECE NH3 mitigation strategies.
Keywords: Urea; Ammonia; Urease inhibitors; Wind tunnels; Rainfall
Theoretical study on the mechanism and kinetics of the reaction of 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47) with OH radicals by Haijie Cao; Maoxia He; Dandan Han; Yanhui Sun; Ju Xie (pp. 1525-1531).
The mechanism and kinetic properties of OH-initiated gas-phase reaction of 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47) have been studied at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31G(d) level of theory. Two types of reactions including hydroxyl addition and hydrogen abstraction have been considered. The calculation results indicate that addition reactions except for the bromo-substituted addition reaction have lower energy barriers than hydrogen abstraction reactions. Hydroxyl radical is most likely to be added to non-substituted C atoms (C(3), C(5), and C(6) atoms). Moreover, for all the reactions with OH radical, the bromo-substituted C atoms encountered the highest barrier compared to that of the rest C atoms. The rate constants and product branching ratios of each pathway have been deduced over a wide range of 200–1000K using canonical variational transition state (CVT) theory with small curvature tunneling (SCT) contribution. This study can be regarded as an attempt to investigate the OH-initiated photochemical reaction mechanism of polybrominated diphenyl ethers (PBDEs).► In this study, the reaction mechanism and the rate constants for the reaction of OH radicals with BDE-47 have been investigated deeply by using quantum chemical method. This method can accurately calculate the reaction energy barrier, the enthalpies of formation and the rate constants. By using these data, the detailed potential energy surface and completed reaction mechanism have been proposed. ► The results show that addition reaction is predominant than abstraction reaction. For addition reaction, Br atoms may block the OH radical adding to adjacent C atoms. The ortho-Br atom leads to higher barrier reaction of OH with ipso-C rather than with non-substituted C atoms. In addition, C(5) atom excel in reaction with OH radical when consider addition reaction and abstraction reaction separately. ► This work could be expected to be a supplement of experimental study and an attempt to theoretical investigation of the OH-initiated photochemical reaction mechanism of PBDEs.
Keywords: BDE-47; OH radicals; Reaction mechanism; Rate constants; Theoretical study
Multiyear analysis of Terra/Aqua MODIS aerosol optical depth and ground observations over tropical urban region of Hyderabad, India by Shailesh Kumar Kharol; K.V.S. Badarinath; Anu Rani Sharma; D.G. Kaskaoutis; H.D. Kambezidis (pp. 1532-1542).
Remote sensing of global aerosols has constituted a great scientific interest in a variety of applications related to global warming and climate change. The present study uses Level 2 (10 × 10 km) and Level 3 (1° × 1°) Terra/Aqua MODIS (C005) derived aerosol optical depths at 550 nm (AOD550) and compares them with ground-based (MICROTOPS-II, MT) sun photometer measured AOD550 in the period 2002–2008 over Hyderabad, India. The correlation coefficient ( R2) between Level 3 Terra/Aqua MODIS and MT AOD550 in all seasons ranges from 0.30 to 0.46. Even lower correlations revealed when the Level 2 MODIS data are used ( R2 = 0.16–0.30). The Level 3 MODIS AOD550 underestimates significantly the MT AOD550, while the Level 2 AOD550 values are much larger than those of Level 3. The comparison of the Terra/Aqua MODIS AOD550 at regional scale, and especially over urban/industrial areas with significant aerosol diurnal variation, constitutes a real challenge and may reveal the ability of the two sensors to capture the temporal variation of the aerosol loading within a time interval of ∼3 h. The results show relatively good correlation ( R2 ∼ 0.6–0.7) regarding the Level 3 dataset; however, the Level 2 data showed large scatter and very poor correlations. On the other hand, the mean seasonal AOD550 values are similar, while Terra AOD550 is higher than that obtained from Aqua. Both satellite and ground-based measurements show remarkable increasing trends in AOD over Hyderabad, which are attributed to the extension of the urbanized area, the growing of population, motor vehicles and local emissions.► A pronounced increasing trend in AOD550 is observed during the last 6 years. ► Terra/Aqua MODIS Level-3 datasets underestimated MICROTOPS-II AOD550 values. ► The highest frequency of MICROTOPS-II AOD550 to be observed at 0.4 and 0.5. ► Terra/Aqua MODIS AOD550 data demonstrated a good agreement over Hyderabad. ► Biomass burning and dust events lead to stronger diurnal AOD variation.
Keywords: Aerosol optical depth; MODIS; Sun photometer; Hyderabad; India
Methyl bromide and methyl chloride fluxes from temperate forest litter by Emanuel Blei; Mathew R. Heal (pp. 1543-1547).
Methyl halide fluxes were measured from fine (nonwoody) litter samples at a temperate deciduous forest site in Scotland on 16 occasions over more than a year and at a coniferous forest site. The resulting mean (±1 sd) CH3Br and CH3Cl fluxes were 4.1 ± 3.7 ng kg−1 h−1 and 0.98 ± 0.62 μg kg−1 h−1, respectively, for dry mass leaf litter and 5.7 ± 6.3 ng kg−1 h−1 and 0.47 ± 0.14 μg kg−1 h−1 for dry mass needle litter. Temporal variations of net fluxes from leaf litter were significantly greater than spatial variations suggesting seasonality in the fluxes. The mean CH3Cl/CH3Br mass ratio of fluxes was ∼200 (to 1 sig. fig.), an order of magnitude larger than the ratio of their estimated global turnovers. Temperate forest litter may be a moderate net source of CH3Cl globally but a negligible source of CH3Br. These statements refer to the nonwoody litter component only.► Methyl halide fluxes were measured from forest non-woody litter samples in Scotland. ► At a single site, temporal variations in fluxes were significantly greater than spatial variations. ► Findings indicate temperate forest litter may be moderate source for CH3Cl globally but negligible for CH3Br.
Keywords: Methyl halides; Leaf litter; Temperate; Forest
An old-growth subtropical Asian evergreen forest as a large carbon sink by Zheng-Hong Tan; Yi-Ping Zhang; Douglas Schaefer; Gui-Rui Yu; Naishen Liang; Qing-Hai Song (pp. 1548-1554).
Old-growth forests are primarily found in mountain ranges that are less favorable or accessible for land use. Consequently, there are fewer scientific studies on old-growth forests. The eddy covariance method has been widely used as an alternative approach to studying an ecosystem’s carbon balance, but only a few eddy flux sites are located in old-growth forest. This fact will hinder our ability to test hypotheses such as whether or not old-growth forests are carbon neutral. The eddy covariance approach was used to examine the carbon balance of a 300-year-old subtropical evergreen broadleaved forest that is located in the center of the largest subtropical land area in the world. The post-QA/QC (quality assurance and control) eddy covariance based NEP was ∼ 9tC ha−1 yr−1, which suggested that this forest acts as a large carbon sink. The inventory data within the footprint of the eddy flux show that ∼6tC ha−1 yr−1 was contributed by biomass and necromass. The large-and-old trees sequestered carbon. Approximately 60% of the biomass increment is contributed by the growth of large trees (DBH>60cm). The high-altitude-induced low temperature and the high diffusion-irradiation ratio caused by cloudiness were suggested as two reasons for the large carbon sink in the forest we studied. To analyze the complex structure and terrain of this old-growth forest, this study suggested that biometric measurements carried out simultaneously with eddy flux measurements were necessary.► The post-QA/QC eddy covariance based carbon flux data indicates that a 300-year-old subtropical evergreen broadleaved forest acts as a large carbon sink of ∼ 9tC ha−1 yr−1 during our investigation interval. ► Inventories within the eddy flux footprint support the eddy flux results and indicate that ∼6Mg C ha−1 yr−1 can be attributed to increases in plant biomass and necromass. ► The larger trees continue to strongly sequester carbon in the studied forest, with about 60% of biomass increment in trees>60cm. ► We suggest that low temperature and cloud-related high diffuse to direct radiation ratios may account for the large carbon sink in this. ► In complex terrain and forest structure, biometric measurements simultaneous with eddy flux appear to be necessary.
Keywords: Eddy covariance; Biometric method; Old-growth; Management
Dual-excitation-wavelength fluorescence spectra and elastic scattering for differentiation of single airborne pollen and fungal particles by Yong-Le Pan; Steven C. Hill; Ronald G. Pinnick; James M. House; Richard C. Flagan; Richard K. Chang (pp. 1555-1563).
Fluorescence spectra of aerosolized pollen (12 species or subspecies) and fungal (4 species) samples measured using a Dual-excitation-wavelength Particle Fluorescence Spectrometer (DPFS) are reported. The DPFS records two fluorescence spectra and two elastic scattering intensities from single airborne particles as they flow through an optical cell. Each particle is illuminated sequentially, first with a pulse from a 263-nm wavelength laser, followed by a second pulse from a 351-nm laser. The two dispersed fluorescence spectra (from 280nm–700nm) and elastic scattering intensities are measured by a single 32-anode photomultiplier tube. Principal component analysis (PCA) of the spectra is used to examine differences in the spectra. Plots of several principal components show that samples of pollens and fungal materials can largely be differentiated. These preliminary results suggest that fluorescence spectra and elastic scattering may be useful for real-time discrimination among a variety of airborne pollens, fungal materials, and other airborne particles.► Dual-excitation-wavelength Fluorescence Spectra for single pollen and fungal. ► Two fluorescence spectra and elastic scattering excited by 263 and 351-nm laser. ► Principal component analysis shows good real-time classification.
Keywords: Real-time classification; Pollen; Fungal; Two-excitation-wavelength; Fluorescence spectra; Elastic scattering
CO2 sources and sinks in urban and suburban areas of a northern mid-latitude city by Onil Bergeron; Ian B. Strachan (pp. 1564-1573).
Urban environments can modify the local climate and are net CO2 emitters, both of which can affect the life of an increasing proportion of the world’s population that lives in and around cities. Observational information on the seasonal and diurnal variations of CO2 fluxes(FCO2) as well as on the contribution from the different CO2 sources and sinks is needed at fine spatial resolution to help develop and validate weather prediction and atmospheric dispersion models. This study reports onFCO2 measured using the eddy covariance technique for a two-year period over a suburban and an urban residential area as well as a reference agricultural site located in the Montreal region, which experiences cold winters and warm summers. The seasonal and diurnal variability ofFCO2 and its response to incoming light and to air temperature was analysed. Typical weekday and weekend vehicular traffic CO2 emissions (EVT) were estimated from inventory data for both residential sites. The urban site was a net source of CO2 throughout the entire measurement period on the order of 200 t CO2 ha−1 year−1. The suburban site was a winter source and a summer daytime sink of CO2 resulting in a net source of 50 t CO2 ha−1 y−1. Lower emissions at the suburban site are attributed to the large biological uptake in summer and to its low anthropogenic emissions. Higher emissions at the urban site are partly associated with its greater population and building density, promoting higher emissions from vehicular traffic and heating fuel combustion. The cold climate induced increased heating fuel combustion as compared to cities under a warmer climate.► CO2 fluxes were measured for a two-year period over agricultural, suburban and urban sites. ► Summer CO2 fluxes depended primarily on the biological component at the suburban site. ► CO2 emissions at the urban site were dominated by human activity all year round. ► The suburban and urban sites were net CO2 sources of about 50 and 200 t CO2 ha−1 year−1.
Keywords: Urban climate; CO; 2; flux; Vehicular traffic emissions; Vegetation; Montreal; Canada; Eddy covariance
Toxicological characterization of diesel engine emissions using biodiesel and a closed soot filter by Ingeborg M. Kooter; Marcel A.T.M. van Vugt; Aleksandra D. Jedynska; Peter C. Tromp; Marc M.G. Houtzager; Ruud P. Verbeek; Gerrit Kadijk; Mariska Mulderij; Cyrille A.M. Krul (pp. 1574-1580).
This study was designed to determine the toxicity (oxidative stress, cytotoxicity, genotoxicity) in extracts of combustion aerosols. A typical Euro III heavy truck engine was tested over the European Transient Cycle with three different fuels: conventional diesel EN590, biodiesel EN14214 as B100 and blends with conventional diesel (B5, B10, and B20) and pure plant oil DIN51605 (PPO). In addition application of a (wall flow) diesel particulate filter (DPF) with conventional diesel EN590 was tested. The use of B100 or PPO as a fuel or the DPF reduced particulate matter (PM) mass and numbers over 80%. Similarly, significant reduction in the emission of chemical constituents (EC 90%, (oxy)-PAH 70%) were achieved. No significant changes in nitro-PAH were observed. The use of B100 or PPO led to a NOx increase of about 30%, and no increase for DPF application. The effects of B100, PPO and the DPF on the biological test results vary strongly from positive to negative depending on the biological end point. The oxidative potential, measured via the DTT assay, of the B100 and PPO or DPF emissions is reduced by 95%. The cytotoxicity is increased for B100 by 200%. The measured mutagenicity, using the Ames assay test with TA98 and YG1024 strains of Salmonella typhimurium indicate a dose response for the nitroarene sensitive YG1024 strain for B100 and PPO (fold induction: 1.6). In summary B100 and PPO have good potential for the use as a second generation biofuel resulting in lower PM mass, similar to application of a DPF, but caution should be made due to potential increased toxicity. Besides regulation via mass, the biological reactivity of exhaust emissions of new (bio)fuels and application of new technologies, needs attention. The different responses of different biological tests as well as differences in results between test laboratories underline the need for harmonization of test methods and international cooperation.► The use of B100 or PPO fuels reduces PM mass and numbers over 80%. ► The effects of B100 and PPO on the biological test results vary from positive to negative. ► The biological reactivity of exhaust emissions of new (bio)fuels needs attention.
Keywords: Biodiesel; Diesel particulates filter; Engine emission; Mutagenicity; Oxidative stress
Seasonal variation of carbonaceous and ionic components in ultrafine and fine particles in an urban area of Japan by Kyung Hwan Kim; Kazuhiko Sekiguchi; Masami Furuuchi; Kazuhiko Sakamoto (pp. 1581-1590).
The carbonaceous and ionic components of atmospheric ultrafine particles (UFPs; Dp<0.1μm) and fine particles (FPs; Dp<2.5μm) were measured four times during one year in Saitama City, Japan, in order to observe the seasonal variation of chemical components, to characterize the chemical components for the two particle sizes, and to estimate the possible emission sources qualitatively. Generally, the carbonaceous and ionic components in UFPs and FPs tended to increase from summer to winter. Over the year, approximately 63∼67% of the total carbon (TC) consisted of organic carbon (OC) in FPs, whereas 80∼88% of TC consisted of OC in UFPs. Char-elemental carbon (EC) and soot-EC constituted equal proportions of the total EC in UFPs, while soot-EC accounted for only a small amount of the total EC in FPs, indicating that char-EC and soot-EC were mainly present in relatively larger particles and much smaller particles, respectively. The water-soluble OC concentration tended to decrease from summer to winter, indicating that secondary organic aerosol formation dominated the OC fractions during the summer sampling period. The transport of atmospheric particulate matter from cities to the north of the sampling site is one reason for the high levels of carbonaceous components in FPs for the fall and winter samples. On the other hand, Tokyo and other industrial cities near the ocean are responsible for the highest soot-EC concentrations found in the summer FP samples.► Char-elemental carbon (EC) and soot-EC constituted similar proportions of the total EC in ultrafine particles. ► Chemical species relationship between ultrafine (UFPs; Dp<0.1μm) and fine particles (FPs; Dp<2.5μm). ► Simultaneous sampling campaign for UFPs and FPs collection. ► Possibility of water soluble organic carbon emission from motor vehicles.
Keywords: Ultrafine particles; Char-EC; Soot-EC; Seasonal variation; Carbonaceous aerosol
Build-up and decay of two ozone episodes through northern Iberia and southern France – An inter-regional transport analysis by V. Valdenebro; G. Gangoiti; A. Albizuri; L. Alonso; M. Navazo; J.A. García; J. Iza; M.M. Millán (pp. 1591-1603).
Further analysis of the previously-reported relationship between blocking anticyclones over the British Isles and severe ozone episodes in the Basque Country (BC) has shown that an even wider area is affected by these situations. Two episodes have been studied. The analysis of ozone data from approximately 60 AirBase stations throughout the area showed that they were among the most severe episodes of ozone exceedances in all northern Iberia and south-western France. Concentrations have been found to be related to inter-regional transport in southern Europe, and the temporal length of the whole process (development and decay) has been found to range from 7 to 10 days. A temporal delay in the recording of maximum concentrations within the region has been observed and explained for the first time. A new pathway for the export of European pollutants towards the Atlantic Ocean has also been documented, along with the export of pollutants from the eastern Cantabrian Coast (CC) to Africa at the beginning of the episodes. A huge eastward transport of pollutants across the CC towards southern France, and along the Ebro Valley towards the Mediterranean Sea, has been documented during the dissipation phase, but may not be definitive.► Blocking anticyclones are behind ozone episodes in a wide region of Southern Europe. ► The build-up and complete decay of these episodes can take from 7 to 10 days. ► Ozone concentrations throughout the area present a predictable behaviour. ► These concentrations are related with internal and inter-regional transport. ► A link between the local-to-intercontinental scales is shown in the episodes.
Keywords: Ozone; Mesoscale; Modelling; Wind profiler radar; Regional transportAbbreviations; BC; Basque Country; CC; Cantabrian Coast; HYPACT; Hybrid Particle and Concentration Transport; RAMS; Regional Atmospheric Modelling System; WPR; Wind Profiler Radar; WEA; Western European Atlantic; WM; Western Mediterranean; MBL; Marine Boundary Layer
Simulating secondary organic aerosol in a 3-D Lagrangian chemistry transport model using the reduced Common Representative Intermediates mechanism (CRI v2-R5) by S.R. Utembe; M.C. Cooke; A.T. Archibald; D.E. Shallcross; R.G. Derwent; M.E. Jenkin (pp. 1604-1614).
A secondary organic aerosol (SOA) code, coupled to the reduced Common Representative Intermediates chemical mechanism (CRI v2-R5), has been used in the global 3-D chemistry-transport model, STOCHEM, to simulate the global distribution of organic aerosol (OA) mass loadings. The SOA code represents the gas-to-aerosol partitioning of products formed over several generations of oxidation of a variety of organic precursors emitted from anthropogenic, biogenic and biomass burning sources. The model also includes emissions of primary organic aerosol (POA), based on the AeroCom inventory and the Global Fire Emissions database (GFED). The calculated burdens for POA, 0.89Tg, and SOA, 0.23Tg, are well within the range of values that have been reported in previous modelling studies. The calculated SOA annual in-situ production of 22.5Tgyr−1 also falls within the 8–110Tgyr−1 range calculated by other models, but is somewhat lower than observationally-constrained top-down estimates which have been reported recently. The oxidation of biogenic precursors is found to account for about 90% of the global SOA burden, and this makes a substantial contribution to the highest annual mean surface OA concentrations (up to 8μgm−3), which are simulated in tropical forested regions. Comparison of the simulated OA mass loadings with surface observations from a variety of locations indicate a good description of the OA distribution, but with an average underestimation of about a factor of 3. Sustained formation of SOA into the free troposphere is simulated, with important contributions from second and third-generation products of terpene oxidation in the upper troposphere. Comparison of the simulated OA mass loadings with vertical profiles from the ACE-Asia campaign indicates a very good description of the relative variation of OA with altitude, but with consistent underestimation of about a factor of 5. Although the absolute magnitude of the global source strength is underestimated, this consistency nonetheless provides support for an important role for multigenerational oxidation chemistry as a large source of SOA in the free troposphere, and lends credence to the necessity of representing condensable material formed over several generations of VOC oxidation in global chemistry-transport models.► Code traceable to Master Chemical Mechanism (MCM) used to simulate global SOA. ► Multigenerational chemistry simulates sustained formation of SOA into the free troposphere. ► Important contributions from 2nd and 3rd-generation terpene products in the upper troposphere. ► Condensable material formed over several generations should be represented in CTMs.
Keywords: Speciated VOC oxidation; Tropospheric chemistry; Degradation mechanisms; Multigenerational oxidation chemistry; Traceable mechanism reduction; SOA composition
Ozone long-range transport in the Balkans by Sotirios D. Glavas; Eleni Sazakli (pp. 1615-1626).
Based on one year ground level ozone and NOx and six months' CO measurements, two major routes of long-range transported ozone were derived, route 1 from the north–northeast and route 2 from the west, both appearing locally as NE–E winds. During the cold and rainy periods low pressure systems over central Mediterranean in conjunction with highs over central-eastern Europe created strong NE–E winds at our site, route 1. In these periods ozone exhibited little diurnal variation with midday/night ratios 0.97–0.99, NOx less than 3 ppb, while temperature and relative humidity remained rather constant day and night. Less frequently, lows in the Mediterranean without highs over central-eastern Europe, also caused NE–E but weaker winds, which eventually had western origin, route 2. The midday/night ozone ratio was 1.08, and NOx was slightly larger. The stronger the NE–E winds the larger the ozone concentration and the smaller the NOx and CO. In the spring the frequency of lows in the Mediterranean decreased and in the summer stagnating highs prevailed. As a consequence the periods of long-range transport from the north decreased and midday/night ozone ratios varied from 1.2 to 1.3 due to the greater photochemical activity. Still in certain periods under strong northerlies diurnal ozone variation was also small and midday/night ratios dropped to 0.97–0.99. In the warm period air masses were originating mostly from W–NW and ozone and NOx had significant diurnal variation and higher mixing ratios. When transport from the north was indicated air mass back-trajectories were originating mostly in central-eastern Europe, while for transport from the west, back-trajectories were originating in western Mediterranean. Under transport conditions to Patras, ozone levels at Aliartos, 150 km east of Patras, an upwind EMEP site, on the trajectory path from the north, had diurnal ozone variation similar to Patras. In the cold months, ozone values observed at upwind EMEP stations in Bulgaria, Hungary, Slovakia, Poland, Lithuania and Malta were similar if not larger than those measured, under transport conditions, in Patras. In these periods the transported ozone concentration was larger than that due to local formation, whereas in the warm months locally formed ozone was larger. Because long-range transport ozone is very important for rural areas the ozone levels at the Greek EMEP sites were compared to those measured in Patras.► Ground level ozone measurements are used to determine periods of long-range ozone transport. ► Air mass back-trajectories indicate transport routes from central-east Europe and western Mediterranean. ► In winter, under transport conditions, ozone levels at upwind EMEP sites are equal or higher than in Patras. ► In winter, transported ozone concentrations are higher than those due to local conditions.
Keywords: NOx; Back-trajectories; Synoptic conditions; Central-east Europe; Central Mediterranean
Identification of ambient PM2.5 sources and analysis of pollution episodes in Detroit, Michigan using highly time-resolved measurements by Masako Morishita; Gerald J. Keeler; Ali S. Kamal; James G. Wagner; Jack R. Harkema; Annette C. Rohr (pp. 1627-1637).
Recent studies have indicated that the chemical composition of ambient PM2.5, or fine particulate matter (aerodynamic diameter <2.5μm), may be closely associated with the health effects induced by PM. Thus, identification of the sources of these components of PM2.5 is critical to understanding source-specific health risks posed by PM2.5. However, ambient PM measurements are typically 24-h average concentrations, masking the temporal variability of individual sources. These daily samples can limit our understanding of the associations between sources and observed heath effect parameters. In the present study, highly time-resolved sampling methods were utilized to characterize trace element concentrations and to obtain information on potential emission sources impacting a site in urban Detroit where a complex mixture of local point and mobile sources, as well as regional sources, is observed.Positive matrix factorization (PMF) was applied to 117 8-h PM2.5 filter samples from which six major factors were extracted including secondary aerosol, gasoline-powered vehicles, iron and steel manufacturing, diesel-powered vehicles, refining, and sludge incineration. In addition, PMF was applied to 268 30-min PM2.5 samples where six major source factors were identified including secondary aerosol, gasoline- and diesel-powered vehicles, iron and steel manufacturing, refining, sludge incineration, and cement/lime production.Contributions of various emission source factors and peak concentrations for each factor were characterized using detailed meteorology and, factor directionality analysis. Although some variations were observed between the 8-h integrated filter samples and the 30-min SEAS samples, the results from the two datasets are generally consistent, suggesting that 46% and 43% of ambient PM, respectively, is derived from local sources. These findings have advanced our understanding of temporal PM source-receptor relationships in a complex urban air shed.
Keywords: PM; 2.5; Detroit; Trace elements; Receptor modeling; Continuous monitoring