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Atmospheric Environment (v.42, #31)

Editorial board (pp. i).

A Common Representative Intermediates (CRI) mechanism for VOC degradation. Part 1: Gas phase mechanism development by M.E. Jenkin; L.A. Watson; S.R. Utembe; D.E. Shallcross (pp. 7185-7195).
A reduced mechanism describing ozone formation from the tropospheric degradation of methane and 115 emitted non-methane hydrocarbons and oxygenated volatile organic compounds has been developed, using the Master Chemical Mechanism version 3.1 (MCM v3.1) as a reference benchmark. The Common Representative Intermediates mechanism version 2 (CRI v2) has been built up on a compound-by-compound basis, with the performance of its chemistry optimised for each compound in turn by comparison with that of MCM v3.1, using a series of five-day box model simulations. The resultant mechanism contains 1183 reactions of 434 chemical species, i.e., ca. 10% of the number of reactions and species to degrade the same set of VOCs in MCM v3.1. Similarly to CRI v1 (Jenkin et al., 2002a), a key assumption in the CRI v2 construction methodology is that the potential for ozone formation from a given volatile organic compound (VOC) is related to the number of reactive (i.e., CC and CH) bonds it contains. This index allows a series of generic intermediates to be defined, with each being used as a “common representative” for a large set of species possessing the same index, as formed in detailed mechanisms such as the MCM. The performance of CRI v2 is shown to compare well with that of MCM v3.1 for a wide range of ambient conditions, which consider variations in VOC/NO x emissions ratio over ranges of 32 and 400 for anthropogenic and biogenic VOCs, respectively, in box model simulations; and in simulations of the TORCH 2003 campaign in the southern UK using a photochemical trajectory model, which considers notable ranges in the relative and absolute emissions of NO x and VOCs, and in the relative contributions of anthropogenic and biogenic species to the VOC total. CRI v2 is a reduced mechanism of intermediate complexity, which is traceable to MCM v3.1, and which provides the basis for further systematic reduction. Two companion papers consider further reduction of CRI v2 through emissions lumping and development and assessment of an associated SOA module.

Keywords: Speciated VOC oxidation; Tropospheric chemistry; Degradation mechanisms; Mechanism reduction; Ozone modelling


A Common Representative Intermediates (CRI) mechanism for VOC degradation. Part 2: Gas phase mechanism reduction by L.A. Watson; D.E. Shallcross; S.R. Utembe; M.E. Jenkin (pp. 7196-7204).
The Common Representative Intermediates mechanism version 2 (CRI v2) is a reduced mechanism of intermediate complexity, traceable to the Master Chemical Mechanism version 3.1 (MCM v3.1), which couples with a detailed speciation of 112 emitted anthropogenic non-methane volatile organic compounds (VOCs). Systematic lumping techniques for the emitted anthropogenic VOC species have been used to reduce CRI v2, creating a series of five reduced variants, the performances of which have been evaluated against that of CRI v2 for a range of ambient conditions. For the initial reduction phases, minor emitted VOCs accounting for increasing proportions of the VOC mass emissions total, up to 20%, were redistributed into appropriate surrogates, and the redundant species and their associated chemistry were removed from the chemical mechanism. The surrogates were selected to maintain the chemical class of the redistributed VOCs within a number of VOC sub-categories, and aimed to preserve the ozone-forming ability of each category using the photochemical ozone creation potential (POCP) index as a criterion. This yielded three reduced mechanisms (CRI v2-R1, CRI v2-R2 and CRI v2-R3) and allowed respective reductions of up to 25% and 32% in the numbers of reactions and species, with no significant degradation in the overall performance of the mechanisms or in the relative contributions of the VOC sub-categories to ozone formation. More severe levels of reduction were also imposed, to limit the number of representative VOCs in each sub-catergory, with the choice of species taking account of their abundance in the detailed speciation, and the simplicity of the associated degradation mechanism. The POCP index was once again used as a guide to help optimise the overall ozone-forming ability of the VOC speciation. This yielded two further mechanisms (CRI v2-R4 and CRI v2-R5) with reductions of up to 53% and 55% in the numbers of reactions and species relative to CRI v2. These mechanisms display a degree of compromise in the ozone-forming ability of the VOC sub-categories, but retain a good level of overall performance. The most reduced variant (CRI v2-R5) uses 19 non-methane VOCs to represent the anthropogenic speciation, and is considered appropriate as a traceable reference mechanism for use in global chemistry-transport models.

Keywords: Speciated VOC oxidation; Tropospheric chemistry; Degradation mechanisms; Mechanism reduction; Ozone modelling; Emissions lumping


The relationship between physicochemical characterization and the potential toxicity of fine particulates (PM2.5) in Shanghai atmosphere by Lu Senlin; Yao Zhenkun; Chen Xiaohui; Wu Minghong; Sheng Guoying; Fu Jiamo; Daly Paul (pp. 7205-7214).
Fine particulate matter with aerodynamic diameter less than 2.5μm (PM2.5) was collected at urban and suburban sites in Shanghai from April 2005 to March 2006. Average mass concentrations of PM2.5 ranged from 43.5 to 149μgm−3 in the urban area and 21.7 to 159μgm−3 in suburban area. The mass levels of PM2.5 sampled at urban and suburban sites showed seasonal variation with much higher values in winter and spring, lower values in summer, and the lowest in autumn. The results of environmental scanning electron microscopy (ESEM) showed that Shanghai PM2.5 was consisted of soot aggregates, coal fly ashes, minerals, bio-particles and unidentified particles. Inductively coupled plasma atomic mission spectrum (ICP-AES) results showed total elements in Shanghai PM2.5 increased gradually from summer to winter and remained at a relatively high level in spring. There was a significant difference in the mass of elements in PM2.5 collected in urban and in suburban atmosphere. Enrichment factor (EF) analysis results demonstrated that K, Na, Ca, Mg, Al, Fe, Ba and Sr originated from natural sources, while As, Cu, Zn, Pb, Cd, Mn, Ni and Se were emitted from anthropogenic sources. The plasmid DNA assay showed that potential toxicity of Shanghai PM2.5 collected at urban and suburban sampling sites, and in different seasons, varied greatly. Toxicity of the Shanghai urban winter PM2.5 sample was much stronger compared to any of the other samples. Heavy metals in Shanghai PM2.5, including Cu, Zn, Pb, Cd, Cr, Mn, and Ni, might have synergic-effects on plasmid DNA damage.

Keywords: Shanghai PM; 2.5; Environmental scanning electron microscopy (ESEM); Inductively coupled plasma atomic mission spectrum (ICP-AES); Plasmid DNA assay; Toxicity


Development of a high-resolution (1km×1km, 1h) emission model for Spain: The High-Elective Resolution Modelling Emission System (HERMES) by José María Baldasano; Leonor Patricia Güereca; Eugeni López; Santiago Gassó; Pedro Jimenez-Guerrero (pp. 7215-7233).
This work presents the results of the development and application of the High-Elective Resolution Modelling Emission System (HERMES). HERMES generates the emissions for Spain needed for the application of high-resolution chemistry transport models, taking the year 2004 as reference with a temporal resolution of 1h and a spatial resolution of 1km2 considering both anthropogenic (power generation, industrial activities, on-road traffic, ports, airports, solvent use, domestic and commercial fossil fuel use) and biogenic sources (vegetation), using a bottom–up approach, up-to-date information and state-of-the-art methodologies for emission estimation. HERMES is capable of calculating emissions by sector-specific sources or by individual installations and stacks. The annual addition of hourly sectorial emissions leads to an estimation of total annual emissions as follows: NOx, 795kt; NMVOCs, 1025kt; CO, 1236kt; SO2, 1142kt and TSP, 180kt; which are distributed principally in the greater areas of the main cities, highways and large point sources. NOx, SO2 and PM2.5 highly correlate with the power generation by coal use, achieving higher emission levels during summertime due to the increase of electricity demand by cooling systems. NMVOCs show high correlation with temperature and solar radiation (mainly as a consequence of the important weight of biogenic emissions) causing the maximum emissions during the daylight hours of summer months. CO emissions are mostly influenced by the on-road traffic; consequently the higher emissions are attained in summer because of the increase of daily average traffic during holidays. The most significant total emission sources are on-road traffic (38%), combustion in power generation plants (33%), biogenic sources (12%) and combustion in manufacturing industries (9%). The inventory generated with HERMES emission model has been successfully integrated within the Spanish Ministry of the Environment's air quality forecasting system (Caliope project), being the emission core for the validation and assessment of air quality simulations in Spain.

Keywords: Emission inventories; Anthropogenic emissions; Biogenic emissions; Models; High-resolution modelling


Observations on persistent organic pollutants in indoor and outdoor air using passive polyurethane foam samplers by Pernilla Bohlin; Kevin C. Jones; Horacio Tovalin; Bo Strandberg (pp. 7234-7241).
Air quality data of persistent organic pollutants (POPs) indoors and outdoors are sparse or lacking in several parts of the world, often hampered by the cost and inconvenience of active sampling techniques. Cheap and easy passive air sampling techniques are therefore helpful for reconnaissance surveys. As a part of the Megacity Initiative: Local and Global Research Observations (MILAGRO) project in Mexico City Metropolitan Area in 2006, a range of POPs (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs)) were analyzed in polyurethane foam (PUF) disks used as passive samplers in indoor and outdoor air. Results were compared to those from samplers deployed simultaneously in Gothenburg (Sweden) and Lancaster (United Kingdom). Using sampling rates suggested in the literature, the sums of 13 PAHs in the different sites were estimated to be 6.1–180ngm−3, with phenanthrene as the predominant compound. Indoor PAH levels tended to be higher in Gothenburg and outdoor levels higher in Mexico City. The sum of PCBs ranged 59–2100ngm−3, and seemed to be highest indoors in Gothenburg and Lancaster. PBDE levels (sum of seven) ranged 0.68–620ngm−3, with the highest levels found in some indoor locations. OCPs (i.e. DDTs, HCHs, and chlordanes) were widely dispersed both outdoors and indoors at all three studied areas. In Gothenburg all POPs tended to be higher indoors than outdoors, while indoor and outdoor levels in Mexico City were similar. This could be due to the influence of indoor and outdoor sources, air exchange rates, and lifestyle factors. The study demonstrates how passive samplers can provide quick and cheap reconnaissance data simultaneously at many locations which can shed light on sources and other factors influencing POP levels in air, especially for the gaseous fractions.

Keywords: PUF; POP; Passive; Indoor; Outdoor


Levels of PM10 and PM2.5 in Taipei Rapid Transit System by Yu-Hsiang Cheng; Yi-Lun Lin; Chia-Chen Liu (pp. 7242-7249).
The PM10 and PM2.5 levels have been measured inside trains on four routes and on platforms at five stations in the Taipei Rapid Transit System using TSI Model 8520 DustTrak monitors. In this study, the TSI DustTrak was calibrated with a Met One E-BAM sampler within the metro station. Experimental results suggest that the TSI DustTrak overestimated PM10 and PM2.5 levels by about 2.0 and 2.2 times, respectively, compared with those measured by the Met One E-BAM sampler. Measurement results show that average PM10 levels inside trains and on station platforms were 10–97μgm−3 and 11–137μgm−3, respectively, and average PM2.5 levels were 8–68μgm−3 and 7–100μgm−3, respectively. Moreover, experimental results demonstrate that PM levels inside trains and on platforms were lower than those measured for other subway systems worldwide. Additionally, the PM10 and PM2.5 levels measured by ambient air-quality monitoring stations near selected metro stations correspond to PM levels in the urban atmospheric environment in Taipei. Statistical results demonstrate that average PM10 and PM2.5 levels in metro stations were about 0.65–1.53 times and 0.89–1.75 times, respectively, those for urban ambient air. The PM levels inside stations and outdoors are positively correlated, indicating that PM levels in the metro system are influenced significantly by outdoor ambient PM levels.

Keywords: PM; 10; PM; 2.5; Taipei Rapid Transit System; TSI DustTrak; Met One E-BAM


Multi-model ensemble analysis of the ETEX-2 experiment by S. Potempski; S. Galmarini; R. Addis; P. Astrup; S. Bader; R. Bellasio; R. Bianconi; F. Bonnardot; R. Buckley; R. D'Amours; A. van Dijk; G. Geertsema; A. Jones; P. Kaufmann; U. Pechinger; C. Persson; E. Polreich; M. Prodanova; L. Robertson; J. Sørensen; D. Syrakov (pp. 7250-7265).
In this paper we investigate the results of multi-model simulations performed on the ETEX-2 experiment by the ENSEMBLE modelling community. New sets of results were created by taking different percentiles of the distribution of the models' predicted values. Both single models and the new constructed sets of results have been compared with the observed data. While a similar comparison for the ETEX-1 case indicated the median model was superior to any single model, for the ETEX-2 case, the situation is more difficult due to complex meteorological conditions, and no absolute and clear conclusions can be obtained. However, for emergency response purposes the median model still can be considered the most viable option also for complicated meteorological situation such is the ETEX-2 experiment.

Keywords: Multi-model ensemble; Percentile models


Quantifying air pollution removal by green roofs in Chicago by Jun Yang; Qian Yu; Peng Gong (pp. 7266-7273).
The level of air pollution removal by green roofs in Chicago was quantified using a dry deposition model. The result showed that a total of 1675kg of air pollutants was removed by 19.8ha of green roofs in one year with O3 accounting for 52% of the total, NO2 (27%), PM10 (14%), and SO2 (7%). The highest level of air pollution removal occurred in May and the lowest in February. The annual removal per hectare of green roof was 85kgha−1yr−1. The amount of pollutants removed would increase to 2046.89metric tons if all rooftops in Chicago were covered with intensive green roofs. Although costly, the installation of green roofs could be justified in the long run if the environmental benefits were considered. The green roof can be used to supplement the use of urban trees in air pollution control, especially in situations where land and public funds are not readily available.

Keywords: Extensive green roofs; Intensive green roofs; Dry deposition; Cost


PM10 air quality variations in an urbanized and industrialized harbor by Juliette Rimetz-Planchon; Esperanza Perdrix; Sophie Sobanska; Claude Brémard (pp. 7274-7283).
In this paper we investigate the PM10 pollution episodes associated with meteorological situations in an urban and industrialized coastal site of the southern part of the North Sea, representative of a typical harbor for trade. In a first part, the spatio-temporal variability of PM10, SO2, NOx and O3 concentrations at the urban scale suggests that both regional air masses and local emissions affect harbor's pollution. In a second part, hierarchical clustering analysis (HCA) performed on meteorological data and PM10 concentrations reveals two main air quality (AQ) regimes. The first one is related to low PM10 levels, which occur under low-pressure conditions due to meteorological conditions favoring a good dispersion of pollutants. The second one is characterized by higher PM10 concentrations appearing under high-pressure conditions. The highest polluted days are characterized by the highest temperatures and hardly any rain. These pollution episodes predominantly occur during sea breeze days, but also as the result of occasional industrial releases. The HCA proved to be an appropriate method to define AQ regimes and to identify meteorological conditions favoring or not PM pollution episodes in Dunkerque conurbation.

Keywords: Air quality regime; Sea breeze; North Sea; PM; 10; Hierarchical clustering analysis


Short-range forecast of atmospheric pollutants using non-linear prediction method by Valeriy N. Khokhlov; Alexander V. Glushkov; Nataliya S. Loboda; Yulia Y. Bunyakova (pp. 7284-7292).
In this paper chaotic behavior in the nitrogen dioxide and sulphurous anhydride concentration time series at two sites in Gdansk region is investigated. To reconstruct an attractor, the time delay and embedding dimension are needed. The former is determined by the methods of autocorrelation function and average mutual information, and the latter is calculated by means of correlation dimension method and algorithm of false nearest neighbors. It was shown that the low-dimensional chaos existed in the time series under investigation. The spectrum of Lyapunov exponents was reconstructed as well as both Kaplan–Yorke dimension and Kolmogorov entropy that inversely proportional to the predictability limit are calculated. Non-linear prediction method is used for the time series. It is shown that even though the simple procedure is used to construct the non-linear model, the results are quite satisfactory.

Keywords: Atmospheric pollutants; Chaos theory; Lyapunov exponents; Non-linear modelling


Atmospheric concentrations of organochlorine pesticides, polybrominated diphenyl ethers and polychloronaphthalenes in Nuuk, South-West Greenland by Rossana Bossi; Henrik Skov; Katrin Vorkamp; Jesper Christensen; Suresh C. Rastogi; Axel Egeløv; Dorthe Petersen (pp. 7293-7303).
Atmospheric concentrations of organochlorine pesticides (OCs), polybrominated diphenyl ethers (PBDEs) and polychloronaphthalenes (PCNs) were measured for the first time in Nuuk, Greenland in 2004 and 2005. The annual mean concentrations of the measured OCs were: α-HCH 20.2pgm−3, γ-HCH (lindane) 5.1pgm−3, endosulfan 4.8pgm−3 and dieldrin 1.9pgm−3. Concentrations of Σ-chlordanes, DDEs and heptachlor epoxide were generally similar and lower than those of α-HCH and γ-HCH. The concentrations of most chlorinated pesticides did not show any clear seasonal variation, with the exception of γ-HCH, which had maximum concentration in August in both years.The average annual mean for ΣPBDEs was 1.14±0.81pgm−3. The predominant congeners measured in Nuuk were BDE-47 and BDE-99 followed by BDE-100, -153 and -28, indicating the use of penta-BDE technical products as the main source. A clear seasonal variation of PBDE concentrations was observed with maximum concentrations occurring in the summer months.The ΣPCNs concentrations ranged between 0.062 and 0.258pgm−3 with an annual mean concentration of 0.161±0.004pgm−3. The PCNs profile was dominated by the tetra-PCNs (74% of the annual mean) and the penta-PCNs (18% of the annual mean). A seasonal trend for ΣPCNs was not observed.Atmospheric concentrations of the investigated compounds were correlated with temperature and anthropogenic CO in order to obtain information about their transport pattern. Positive correlations were found between CO and chlordanes, p, p′-DDE and trifluralin, while a negative correlation was found for γ-HCH. A significant correlation with temperature variations was found for dieldrin, heptachlor epoxide, α-HCH, γ-HCH, BDE-47, BDE-99 and tetra-PCNs, which indicates that re-emission of these compounds from previously contaminated surfaces as an important factor for the observed variations in concentrations.

Keywords: Greenland; Atmosphere; Chlorinated and brominated persistent organic pollutants


Application of aerosol speciation data as an in situ dust proxy for validation of the Dust Regional Atmospheric Model (DREAM) by Patrick Shaw (pp. 7304-7309).
The Dust REgional Atmospheric Model (DREAM) predicts concentrations of mineral dust aerosols in time and space, but validation is challenging with current in situ particulate matter (PM) concentration measurements. Measured levels of ambient PM often contain anthropogenic components as well as windblown mineral dust. In this study, two approaches to model validation were performed with data from preexisting air quality monitoring networks: using hourly concentrations of total PM with aerodynamic diameter less than 2.5μm (PM2.5); and using a daily averaged speciation-derived soil component. Validation analyses were performed for point locations within the cities of El Paso (TX), Austin (TX), Phoenix (AZ), Salt Lake City (UT) and Bakersfield (CA) for most of 2006. Hourly modeled PM2.5 did not validate at all with hourly observations among the sites (combined R<0.00, N=24,302 hourly values). Aerosol chemical speciation data distinguished between mineral (soil) dust from anthropogenic ambient PM. As expected, statistically significant improvements in correlation among all stations (combined R=0.16, N=343 daily values) were found when the soil component alone was used to validate DREAM. The validation biases that result from anthropogenic aerosols were also reduced using the soil component. This is seen in the reduction of the root mean square error between hourly in situ versus hourly modeled (RMSEhourly=18.6μg m−3) and 24-h in situ speciation values versus daily averaged observed (RMSEsoil=12.0μg m−3). However, the lack of a total reduction in RMSE indicates there is still room for improvement in the model. While the soil component is the theoretical proxy of choice for a dust transport model, the current sparse and infrequent sampling is not ideal for routine hourly air quality forecast validation.

Keywords: Dust model validation; Aerosol speciation; Particulate matter pollution; PM; 2.5; measurements


Chemical characterization of ambient particulate matter near the World Trade Center: Source apportionment using organic and inorganic source markers by David A. Olson; Gary A. Norris (pp. 7310-7315).
Concentrations of alkanes (C20–C35), 14 polycyclic aromatic hydrocarbons (PAHs) and PAH ketones, and three hopanes are reported from four locations near the World Trade Center (WTC) (three of the locations within 300m of the debris pile). The highest concentrations of individual PAHs across the four locations were for fluoranthene (10.3ng/m3 at site W), pyrene (8.7ng/m3 at site W), and chrysene (6.2ng/m3 at site W). The EPA Unmix Version 6.0 receptor model was used to estimate the impact of WTC fires and recovery efforts on ambient PM2.5 concentrations. Five factors were identified: open burning of building debris, smoldering fires from building debris, a mixed recovery source, a sulfate/debris removal source, and motor vehicle exhaust.

Keywords: World Trade Center; Receptor modeling; Source apportionment; Building fire
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