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Atmospheric Environment (v.45, #37)

Editorial board (pp. i).

Application of active optical sensors to probe the vertical structure of the urban boundary layer and assess anomalies in air quality model PM_2.5 forecasts by Chuen-Meei Gan; Yonghua Wu; B.L. Madhavan; Barry Gross; Fred Moshary (pp. 6613-6621).

In this paper, the simulations of the Weather Research and Forecast (WRF) and Community Multiscale Air Quality (CMAQ) Models applied to the New York City (NYC) area are assessed with the aid of vertical profiling and column integrated remote sensing measurements. First, we find that when turbulent mixing processes are dominant, the WRF-derived planetary boundary layer (PBL) height exhibits a strong linear correlation ( R > 0.85) with lidar-derived PBL height. In these comparisons, we estimate the PBL height from the lidar measurements using a Wavelet Covariance Transform (WCT) approach that is modified to better isolate the convective layer from the residual layer (RL). Furthermore, the WRF-Lidar PBL height comparisons are made using different PBL parameterization schemes, including the Asymmetric Convective Model-version2 (ACM2) and the Modified Blackadar (BLK) scheme (which are both runs using hindcast data), as well as the Mellor-Yamada-Janjic (MYJ) scheme run in forecast mode. Our findings show that the correlations for these runs are high (>0.8), but the hindcast runs exhibit smaller overall dispersion (≈0.1) than the forecast runs. We also apply continuous 24-hour/7-day vertical ceilometer measurements to assess WRF-CMAQ model forecasts of surface PM_2.5 (particulate matter has aerodynamic diameter <2.5 μm). Strong overestimations in the surface PM_2.5 mass that are observed in the summer prior to sunrise are particularly shown to be strongly connected to underestimations of the PBL height and less to enhanced emissions. This interpretation is consistent with observations that TEOM (Tapered Element Oscillating MicroBalance) PM_2.5 measurements are better correlated to path-integrated CMAQ PM_2.5 than the near-surface measurements during these periods.► Introduce a modified wavelet method that is able to accurate retrieve PBL height. ► Assessment of different WRF PBL Parameterization Schemes in urban environment. ► Addressing inherent biases in CMAQ forecasts of PM_2.5 with the use of ceilometer.

Keywords: Lidar; Wavelet covariance transform; Planetary boundary layer; Particulate matter; Air quality model; Aerosol; Ceilometer

PBDEs in the atmosphere over the Asian marginal seas, and the Indian and Atlantic oceans by Jun Li; Qilu Li; Rosalinda Gioia; Yanlin Zhang; Gan Zhang; Xiangdong Li; Baruch Spiro; Ravinder S. Bhatia; Kevin C. Jones (pp. 6622-6628).

Air samples were collected from Jan 16 to Mar 14, 2008 onboard the Oceanic II- The Scholar Ship which navigated an east–west transect from Shanghai to Cape Verde, and polybrominated diphenyl ethers (PBDEs) were analyzed in these samples. PBDE concentrations in the atmosphere over the open seas were influenced by proximity to source areas and land, and air mass origins. The concentrations of Σ₂₁PBDEs over the East and South China Seas, the Bay of Bengal and the Andaman Sea, the Indian Ocean, and the Atlantic Ocean were 10.8 ± 6.13, 3.22 ± 1.57, 5.12 ± 3.56, and 2.87 ± 1.81 pg m⁻³, respectively. BDE-47 and -99 were the dominant congeners in all the samples, suggesting that the widely used commercial penta-BDE products were the original sources. Over some parts of Atlantic and Indian Ocean, daytime concentrations of BDE-47 and BDE-99 were higher than the concentrations at night. The strong atmospheric variability does not always coincide with a diurnal cycle, but the variability in air concentrations in such remote areas of the ocean remains strong. No significant trends were found for each of PBDE congener with latitude.► Air samples were collected over the open seas from Shanghai to Cape Verde. ► PBDE concentrations were influenced by proximity to source areas. ► BDE-47 and -99 were dominant congeners in all samples. ► No significant trends were found for all PBDE congeners with latitude.

Keywords: South China Sea; Indian Ocean; Atlantic Ocean; PBDEs; POPs

How bias-correction can improve air quality forecasts over Portugal by C. Borrego; A. Monteiro; M.T. Pay; I. Ribeiro; A.I. Miranda; S. Basart; J.M. Baldasano (pp. 6629-6641).

Currently three air quality modelling systems operate routinely with high-resolution over mainland Portugal for forecasting purposes, namely MM5-CHIMERE, MM5-EURAD, and CALIOPE. They each operate daily using different horizontal resolutions (10 km × 10 km, 5 km × 5 km, and 4 km × 4 km, respectively), specific physical and chemical parameterizations, and their own emission pre-processors (with a common EMEP emission database source but different spatial disaggregation methodologies). The operational BSC-DREAM8b model is coupled offline within the aforementioned air quality systems to provide the Saharan dust contribution to particulate matter. Bias-correction studies have demonstrated the benefit of using past observational data to reduce systematic model forecast errors. The present contribution aims to evaluate the application of two bias-correction techniques, the multiplicative ratio and the Kalman filter, in order to improve air quality forecasts for Portugal. Both techniques are applied to the three modelling systems over the full year of 2010. Raw and unbiased model results for the main atmospheric pollutants (O₃, NO₂, SO₂, PM10, and PM2.5) are analysed and compared with data from 18 monitoring stations distributed within inland Portugal on an hourly basis. Statistical analysis shows that both bias-correction techniques improve the raw forecast skills (for all the modelling systems and pollutants). In the case of O₃ max-8 h, correlation coefficients improve by 19–45%, from 0.56–0.81 (raw models) to 0.78–0.86 (corrected models). PM2.5 also presents significant improvements, for example correlation coefficients increase by more than 50% (with both techniques), reaching values between 0.50 and 0.64. The corrected primary pollutants NO₂ and SO₂ demonstrate significant relative improvements compared to O₃, mostly because the original modelling system skills are lower for those species. Although the applied techniques have different mathematical formulations and complexity levels, there are comparable answers for all of the forecasting systems. Analysis performed over specific situations such as air quality episodes and cases of unvalidated or missing data reveals different behaviours of the bias-correction techniques under study. The results confirm the advantage of the application of bias-correction techniques for air quality forecasts. Both techniques can be applied routinely in operational forecast systems and they will be useful to provide accurate alerts about exceedances to the population.► We evaluate bias-correction techniques to improve air quality forecast of Portugal. ► Multiplicative ratio and Kalman filter approaches are evaluated and intercompared. ► We consider three air quality forecasting systems that operates daily over Portugal. ► We find that both bias-correction techniques improve the raw forecasts skills. ► The bias-correction techniques performed differently for specific situations.

Keywords: Air quality forecast; Modelling systems; Bias-correction; Multiplicative ratio; Kalman filter

Estimates of wood burning contribution to PM by the macro-tracer method using tailored emission factors by A. Piazzalunga; C. Belis; V. Bernardoni; O. Cazzuli; P. Fermo; G. Valli; R. Vecchi (pp. 6642-6649).

In this work, a methodology based on the macro-tracer approach was improved to obtain a more reliable estimate of the wood burning impact on PM10 and OC concentrations.Indeed, literature emission factors were weighed by the wood consumption data available for the investigated region and these tailored factors were used in the calculation. Moreover, an alternative approach using the chemical profile of the wood burning source obtained by the Positive Matrix Factorization was introduced. As far as we know, this is the first time that PMF-derived emission ratios instead of source emission factors are used in the macro-tracer method.A critical comparison of the results obtained by the two approaches was carried out. The results suggest that PMF-derived emission ratios can be a feasible alternative to the widely used wood smoke emission factors, which show a high variability.The proposed methodology was applied to a trial dataset of wintertime PM10 samples - characterised for anhydrosugars, organic, and elemental carbon – collected in the frame of a regional project. The results gave a preliminary estimate of the wood smoke contribution to PM10 and OC in different sites in Lombardy (Northern Italy).► Emission data tailored to wood consumption data available for the region. ► PMF source profile to obtain average real world emission ratios. ► Estimation of the wood burning contribution to PM10 and OC in a pollution hot-spot area.

Keywords: Levoglucosan; Wood burning; Emission factors; Source apportionment

A multi-compartment mass transfer model applied to building vapor intrusion by Brian L. Murphy; Wanyu R. Chan (pp. 6650-6657).

We develop a systematic approach to model steady-state advective and diffusive fluxes, as well as phase changes, between multi-media environmental compartments. The approach results in four simple rules for constructing mass transfer coefficients. Results are analogous to electrical circuit theory with resistors, including variable resistors or potentiometers, in parallel and series. This general approach lends itself particularly well to vapor intrusion calculations where there are multi-media compartments involving groundwater, soil, and air. In addition to showing that the model reduces to the well-known Johnson & Ettinger model in limiting cases, we illustrate its simplicity and ease of use with several examples: (1) an example of how multiple partition coefficients collapse into a single partition coefficient illustrated by a three-phase problem involving tar, water, and air, (2) determination of when the presence of a basement significantly lowers first floor exposures, and (3) addition of diffusion in the saturated zone to the model to investigate whether the resistance associated with this compartment can be neglected. We conclude that if the water table is truly steady, this resistance would be very significant. Therefore, a vapor intrusion model that neglects both water table fluctuations and diffusion in groundwater is ignoring important physical phenomena.► A new model for vapor intrusion (VI). ► Basements can reduce VI exposures. ► Diffusion in groundwater can limit VI.

Keywords: Johnson and Ettinger model; Air-flow; Advection; Diffusion; Groundwater contamination; Transport

On the surface air temperature variation in relation to chlorofluorocarbons over the Indian region by J.V. Revadekar; S.D. Patil (pp. 6658-6668).

Chlorofluorocarbons (CFCs) are among the greenhouse gases in the atmosphere that contribute to warming. Therefore, an attempt is made in the present study to examine the variation in the surface temperature in relation to CFCs over the Indian region during 1992–2007. Space-time distribution of correlation coefficients (CCs) between CFCs and monthly temperature show positive CCs except pre-monsoon months. From April onwards up to onset of monsoon over the country, CCs are negative. It clearly indicates that higher (lower) temperature values are associated with the lower (higher) values of CFCs in these months. This may be because of convection occurred over the country playing some role in association with CFC. Interannual variation of CFCs has contrasting behavior in the two epochs (1) 1992–1997 and (2) 1999–2007 where the CFCs increase and decrease respectively. It is seen that during increasing phase of CFCs, trends in temperature are also increasing except pre-monsoon months which show negative CCs. Trend magnitudes over the northern latitudes are higher. Though decreasing phase of CFCs show similar features, trend magnitude of temperature have substantially decreased. Regional analysis with temperature homogeneous regions, show positive CCs between CFCs and minimum temperature during most of the months. Analysis with regional maximum temperature shows negative trends starting from the month of May up to the month of July. Though further studies may be needed, the results observed in the present analysis show that the variation in surface air temperature indeed has a certain link with the changes in CFCs over Indian region.► We examine the temperature variation in relation to changes in CFCs over India. ► It show positive CCs with all-India CFCs except the pre-monsoon (MAM) months. ► Increase in all-India CFCs is seen from 1992 to 1997, afterward decreases continuously. ► During increasing phase of CFCs, temperature show increasing trends except MAM. ► During decreasing phase similar features seen but trend magnitudes decreased.

Keywords: Chlorofluorocarbons; Surface temperature; Convection; Interannual variability

Progress toward clean cloud water at Whiteface Mountain New York by James E. Dukett; Nenad Aleksic; Nathan Houck; Philip Snyder; Paul Casson; Michael Cantwell (pp. 6669-6673).

Fossil fuel combustion is the primary source of anthropogenic acidity in cloud water. Since 1994 there is a measurable decrease in hydrogen, sulfate, and nitrate ion concentrations in cloud water collected at Whiteface Mountain. In this paper we assess these changes from the point of view of progress toward clean air conditions.The cleanest clouds crossing Whiteface Mountain, those with the lowest total ion concentrations, are found to have pH values in the range 5.0–5.25. Furthermore, there is a linear relationship between pH, sulfate and nitrate ion concentrations in cloud water. With this in mind, we define clean cloud water values of sulfate, nitrate and hydrogen as mean concentrations observed in cloud water samples with pH in the range 5.0–5.25.We then compare mean annual values to clean air values to determine annual ratios. In 1994, ratios forSO42−,NO3− and H⁺ were respectively 26.9, 13.1 and 29.9 times above the clean air value. In 2009, theSO42−,NO3− and H⁺ corresponding ratios were 4.2, 2.7, and 4.8 times above the clean air value. In other words, comparison of the 1994 and 2009 results suggest reductions in anthropogenic concentrations ofSO42−,NO3− and H⁺, by 84%, 79% and 84% respectively.To verify our approach, we have calculated corresponding changes in the aerosolSO42− ratio, with clean air concentrations equal to the natural background aerosolSO42− value used for the Regional Haze Rule. These results compared favorably to our cloud waterSO42− ratio.► Identification of cleanest clouds passing over Whiteface Mountain New York. ► We examine cloud water values since 1994 and compare to emission reductions. ► SO₄ analyses compares favorably to the background value used for Regional Haze Rule. ► We show acidity improvements from policy decisions but there is more work to do.

Keywords: Clean air; Acid deposition; Adirondack mountains; Cloud water; Acidity; Emissions

Impact of assimilated observations on improving tropospheric ozone simulations by Palmira Messina; Massimo D’Isidoro; Alberto Maurizi; Federico Fierli (pp. 6674-6681).

The work aims to evaluate the improvement in the capability of regional models to reproduce the distribution of tropospheric pollutants, using the assimilation of surface chemical observations. In particular, the efficacy in correcting the biases of perturbed emission scenarios was analysed. The study was carried out using the Air Quality Model BOLCHEM coupled with a sequential Optimal Interpolation (OI) routine to perform ozone and nitrogen dioxide assimilation. The OI routine was chosen because it is computationally inexpensive. The work was performed using the Observing System Simulation Experiment (OSSE), which allowed the quantification of assimilation impact, through comparison with a reference state. Different sensitivity tests were carried out in order to identify how assimilation can correct perturbations on O₃, induced by NO_x emissions biased in both flux intensity and time. This simple assimilation approach provided a substantial improvement in surface O₃. It was found to be more effective to assimilate an O₃ precursor, like NO₂, than O₃ itself, and, in order to obtain a discernible impact on 24-h forecasts, it could be sufficient to assimilate observations when NO_x emissions are higher over a 12-h window. It was also found that temporally biased NO_x emissions only slightly perturb O₃.► Assimilating NO₂ can reduce the biases induced on O₃ forecasts by biased emissions. ► Positive effect remains up to 36–40 h after the end of the assimilation. ► It is more effective to assimilate O₃ precursors (like NO₂) than O₃ itself. ► Best result is obtained for assimilation during the photochemically active period. ► Temporally biased NO_x emissions slightly perturb the O₃ concentration.

Keywords: Tropospheric ozone; Data assimilation; Air quality modelling; Emission inventories

Potential impact of spatial patterns of future atmospheric warming on Asian dust emission by Nobumitsu Tsunematsu; Hiroaki Kuze; Tomonori Sato; Masamitsu Hayasaki; Feifei Cui; Akihiko Kondoh (pp. 6682-6695).

Spatial patterns of future atmospheric warming presented by climate model projections indicate that the temperatures of the lower troposphere will increase markedly at high latitudes in the Northern Hemisphere and also the upper troposphere at low-middle latitudes. In this study, potential impacts of the spatial patterns of future atmospheric warming on Asian dust emission were investigated by performing numerical experiments using a dynamical downscaling method. After three significant Asian dust outbreak events were reproduced as control runs, initial and boundary conditions of the control runs were updated by adding differences in atmospheric variables between the future climate (2091–2100) and the recent climate (1991–2000) to execute pseudo global warming runs. The results showed that the dust emission fluxes in the main Asian dust sources (MADSs), i.e., the Taklimakan and Gobi deserts, decrease markedly in the future climate condition. The future decreases in the dust emission fluxes are likely to be caused by a combination of the relatively large increases in sea level pressures (SLPs) in MADSs and the small SLP changes to the north of MADSs, which reduces the meridional SLP gradients between the two areas and consequently weakens cold air outbreaks. The large SLP increases in MADSs may be due to a northward shift of storm tracks and increased atmospheric stabilities caused by the large upper-tropospheric warming at low-middle latitudes. The small SLP changes to the north of MADSs corresponded to the large increases in surface air temperatures, which would be influenced by the large lower-tropospheric warming at high latitudes.► Dynamical downscaling of climate model projections into dust simulations by WRF model. ► Pseudo global warming experiments showed future decreases in Asian dust emission. ► Future decreases in meridional SLP gradients are likely to reduce dust emission.

Keywords: Asian dust emission; Future global warming; Dynamical downscaling; WRF model; Dust simulations

Temperature response of the submicron organic aerosol from temperate forests by W. Richard Leaitch; Anne Marie Macdonald; Peter C. Brickell; John Liggio; Steve J. Sjostedt; Alexander Vlasenko; Jan W. Bottenheim; Lin Huang; Shao-Meng Li; Peter S.K. Liu; Desiree Toom-Sauntry; Katherine A. Hayden; Sangeeta Sharma; Nicole C. Shantz; H. Allan Wiebe; Wendy Zhang; Jonathan P.D. Abbatt; Jay G. Slowik; Rachel Y.-W. Chang; Lynn M. Russell; Rachel E. Schwartz; Satoshi Takahama; John T. Jayne; Nga Lee Ng (pp. 6696-6704).

Observations from four periods (three late springs and one early summer) at temperate forest sites in western and eastern Canada offer the first estimation of how the concentrations of submicron forest organic aerosol mass (SFOM) from the oxidation of biogenic volatile organic compounds (BVOC) vary over the ambient temperature range of 7°C to 34°C. For the measurement conditions of clear skies, low oxides of nitrogen and within approximately one day of emissions, 50 estimates of SFOM concentrations show the concentrations increase exponentially with temperature. The model that is commonly used to define terpene emissions as a function of temperature is able to constrain the range of the SFOM values across the temperature range. The agreement of the observations and model is improved through the application of an increased yield of SFOM as the organic mass concentration increases with temperature that is based on results from chamber studies. The large range of SFOM concentrations at higher temperatures leaves open a number of questions, including the relative contributions of changing yield and of isoprene, that may be addressed by more ambient observations at higher temperatures.► First observations of the forest biogenic SOA versus temperature. ► SOA variations constrained with the model of terpene emissions versus temperature. ► Comparison improved assuming increased SOA yield with organic mass concentration.

Keywords: Biogenic organic aerosols; Biogenic volatile organic compounds; Temperature

Validation of the MIMOSA-AURORA-IFDM model chain for policy support: Modeling concentrations of elemental carbon in Flanders by Wouter Lefebvre; Jordy Vercauteren; Liesbeth Schrooten; Stijn Janssen; Bart Degraeuwe; Willy Maenhaut; Ina de Vlieger; Jean Vankerkom; Guido Cosemans; Clemens Mensink; Nele Veldeman; Felix Deutsch; Stijn Van Looy; Wim Peelaerts; Filip Lefebre (pp. 6705-6713).

The ability of a complex model chain to simulate elemental carbon (EC) concentrations was examined. The results of the model chain were compared to EC concentration measurements made at several locations, every sixth day. Two measurement campaigns were taken into account, one in 2006–2007 and one in 2008–2009. The model results compare very well for both periods, with an R² of 0.74, a bias of 0.02 μg m⁻³ and a RMSE of 0.32 μg m⁻³. Sensitivity analyses to different meteorology inputs and changing emissions from year to year were performed. The differences between the two measurement periods were also investigated. It is shown that somewhat more than half of these differences is due to meteorology. However, emission changes also play an important role.► The ability of a model chain to simulate elemental carbon was examined. ► The model simulations were made at very high resolutions. ► The results of the model chain were compared to EC concentration measurements. ► The model results compare very well for both periods: R² = 0.74; Bias = 0.02 μg m⁻³. ► Sensitivity analyses to different meteorology inputs and changing emissions.

Keywords: Elemental carbon; Validation; Policy support; Flanders

Size distributions of trace elements associated with ambient particular matter in the affinity of a major highway in the New Jersey–New York metropolitan area by Fei Song; Yuan Gao (pp. 6714-6723).

To characterize the size distributions of trace elements associated with particulate matter in the areas heavily impacted by traffics, eleven sets of size-segregated aerosol samples were collected using a MOUDI sampler in winter and summer of 2007–2008 along the side of a highway in the northeast New Jersey near New York City. Selected trace metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Sc, V and Zn) in aerosol samples were determined by ICPMS. A bimodal mass size distribution with peaks at the size ranges of 0.32–0.56 μm and 3.2–5.6 μm was identified, and the general size distributions of the mass concentrations did not change significantly with seasons. Trace metals of potential anthropogenic origin, including Cd, Co, Fe, Ni, Pb, Sb and Zn, had higher concentrations and enrichment levels in winter, especially for fine particles. For trace metals of crustal origin, such as Al and Sc, their size distributions of enrichment factors showed significant seasonal variations, while no such variations were found for Cd, Co, Cr, Ni, Pb, Sb, V, and Zn. Two groups of size distributions in trace metal concentrations were identified using cluster analysis: (1) coarse particles (>1.0 μm) with accumulation of mainly crustal trace metals such as Al, Fe, Sc, and Mn; (2) fine particles (<1.0 μm) with accumulations of trace metals of anthropogenic origins such as Cd, Pb, Ni, V and Co. The size distributions of trace metal enrichment factors showed primarily monotonic decline patterns with overwhelmingly high peaks in the size range of 0.18–0.32 μm for most of the trace metals from pollution sources. Crustal elements including Cu (summer), Mn (summer) and Sc (winter), however, showed tilted normal distributions pattern with peaks at 1.0–1.8 μm. Three major types of sources for these metals were identified at this location: (1) brake wear and fuel combustion, (2) primary fuel combustion, and (3) tires abrasion and fuel combustion. The particulate trace metals in the study area are primarily characterized by either the mixed sources or the exhaust emissions source. Weather factors, in particular temperature, wind speed and precipitation, were found to significantly ( α = 0.05) influence the concentrations of trace metals and their size distributions.► Mass size bimodal distributions of PM at roadside. ► Size distributions of trace metals in aerosol in the ambient air. ► Major source of trace metals derived from highways.

Keywords: Size distributions; Trace metals; Urban air pollution; Traffic emission

Tropical cirrus cloud contamination in sun photometer data by Boon Ning Chew; James R. Campbell; Jeffrey S. Reid; David M. Giles; Ellsworth J. Welton; Santo V. Salinas; Soo Chin Liew (pp. 6724-6731).

Cirrus clouds are endemic to Southeast Asia and are a source of potential bias in regional passive aerosol remote sensing datasets. Here, performance of the cloud-screening algorithm for the ground-based Aerosol Robotic Network (AERONET) sun photometer data is evaluated for cirrus cloud contamination at Singapore (1.30° N, 103.77° E). Using twelve months of concurrent AERONET Level 1.5 and 2.0 cloud-screened aerosol optical depth (AOD) data, and collocated Level 1.0 Micro-Pulse Lidar Network (MPLNET) measurements, we investigate the baseline AOD bias due to cirrus cloud presence. Observations are considered for a primary sample of all data and a secondary sample where AERONET data are restricted to a zenith viewing angle ≤ 45°. Cirrus clouds are present in zenith-viewing MPL profiles for 34% and 23% of these samples respectively. Based on approximations of cirrus cloud optical properties necessary to estimate cloud optical depth from the single-channel lidar signal, and assuming partial forward scattering of diffuse light by cirrus clouds into the sun photometer’s field of view, we estimate a range in AOD bias due to unscreened cloud presence of 0.034 to 0.060 and 0.031 to 0.055 ± 0.01 for the primary and secondary sample respectively. From the analysis of AERONET AOD for the angle-limited subset alone, we also derive a positive AOD bias of 0.034, which is comparable to the lower bounds for the estimated cloud bias reported for our datasets. These findings, which we attribute to the prevalence of cirrus clouds present from regional convection, are higher than previous reports of global AOD bias in the Moderate Resolution Infrared Spectroradiometer (MODIS) satellite-borne measurements due to residual cirrus cloud presence.► Compare observations from NASA AERONET sun photometer and MPLNET lidar in Singapore. ► Identify cirrus clouds & quantify the resultant bias in aerosol optical depth (AOD). ► AOD bias of 0.034 is observed and is double the MODIS AOD bias due to cirrus clouds. ► Cirrus cloud contamination has implications for remote sensing in Southeast Asia. ► Physical and optical properties of such cirrus clouds are discussed.

Keywords: AERONET; Aerosol particles; Cirrus clouds; Lidar; MPLNET; Southeast Asia; Sun photometer

Atmospheric polycyclic aromatic hydrocarbons (PAHs) from post-harvest biomass burning emissions in the Indo-Gangetic Plain: Isomer ratios and temporal trends by Prashant Rajput; M.M. Sarin; R. Rengarajan; Darshan Singh (pp. 6732-6740).

Atmospheric concentrations of particulate polycyclic aromatic hydrocarbons (PAHs) and their isomer ratios have been studied for two distinct biomass burning emissions (post-harvest burning of paddy-residue in Oct–Nov and wheat-residue burning during April–May) in the Indo-Gangetic Plain (IGP). The mass concentrations of PM_2.5 (Av: 246 μg m⁻³), OC (92 μg m⁻³), EC (7 μg m⁻³) and ΣPAHs (40 ng m⁻³) are significantly higher from the paddy-residue burning. In contrast, for wheat-residue burning emissions, concentrations of PM_2.5 (53 μg m⁻³), OC (15 μg m⁻³), EC (4 μg m⁻³) and ΣPAHs (7 ng m⁻³) are about 4–5 times lower. The large temporal variability in the concentrations of particulate species and OC/EC ratio (range: 1.9–25.7) is attributed to differences in the two biomass burning emissions and their relative source strength. The mass fraction of EC (Av: 3.1%), associated with the poor combustion efficiency of moist paddy-residue, is significantly lower than that from the wheat-residue burning (EC/PM_2.5 = 7.6%) during dry weather conditions. Furthermore, OC mass fractions from paddy- and wheat-residue burning emissions are 37% and 28% respectively; whereas ΣPAHs/EC ratios are significantly different, 5.7 and 1.6 mg g⁻¹, from the two emission sources. The particulate concentrations of 5- and 6-ring isomers (normalized to EC) from paddy-residue burning are about 3–5 times higher than those from the wheat-residue burning emissions. The cross plots of PAHs show distinct differences in isomer ratios from agricultural-waste burning emissions vis-à-vis fossil-fuel combustion.► A comprehensive data set on PAHs isomer ratios for open agricultural-waste burning. ► Heterogeneous reactivity of PAHs decreases their mass fraction in ambient aerosols. ► PAHs isomer ratios for agricultural-waste burning are distinct from fossil-fuel.

Keywords: Agricultural-waste burning; Rice-straw; Wheat-straw; PM; _2.5; PAHs; Indo-Gangetic Plain

Carboxylic acids in PM_2.5 over Pinus morrisonicola forest and related photoreaction mechanisms identified via Raman spectroscopy by Su-Ching Kuo; Ying I. Tsai; Cheng-Hsien Tsai; Li-Ying Hsieh (pp. 6741-6750).

The PM_2.5 aerosol from within an area of Pinus morrisonicola Hayata in Taiwan was collected and analyzed for its low molecular weight carboxylic acid (LMWCAs) content. Oxalic acid was the major LMWCA in the aerosol, followed by acetic, tartaric and maleic acids. This differs significantly from the LMWCA composition of PM_2.5 aerosol reported for a southern Taiwan suburban region (oxalic > succinic > malonic) [Atmospheric Environment 42, 6836–6850 (2008)]. P. morrisonicola Hayata emits oxalic, malic and formic acids and yet there was an abundance of maleic and tartaric acids in the PM_2.5 forest aerosol, indicating that tartaric acid is derived from the transformation of other P. morrisonicola Hayata emissions. Raman spectroscopy was applied and 28 species of LMWCAs and inorganic species were identified. The photochemical mechanisms of maleic and tartaric acids were studied and it was found that the abundant tartaric acid in forest aerosol is most probably the photochemical product from reactions of maleic acid. Furthermore, tartaric acid is photochemically transformed into formic acid and ultimately into CO₂.► Pinus morrisonicola Hayata in Taiwan emits abundant oxalic acid. ► Raman spectroscopy was applied to identify low molecular weight carboxylic acid species. ► The abundant tartaric acid in forest aerosol is most probably the photochemical product from reactions of maleic acid.

Keywords: Carboxylic acids; Coniferous forest; Raman spectroscopy; Photooxidation; Maleic acid; Tartaric acid

Performance evaluation of modified Semi-continuous Elements in Aerosol Sampler-III by Joseph Patrick Pancras; Matthew S. Landis (pp. 6751-6759).

A field study was conducted to evaluate the performance of a Semi-continuous Elements in Aerosol Sampler-III (SEAS-III), designed to collect ambient PM_2.5 aerosol samples at a time resolution of 30min for elemental concentration measurements. Two identical but modified SEAS-III samplers were operated for four continuous weeks in Dearborn, MI, during July–August 2007. A total of 2308 samples were collected from the two samplers. Sampling completeness from the primary and duplicate samplers was 90% and 84%, respectively. All of the collected samples were analyzed for dilute acid-extractable trace metal concentrations using HR-ICPMS.A total of 878 collection time-matched sample pairs were available to evaluate whole-system uncertainty from collocated concentration measurements. The collocated precision for the 27 studied elements (Al, As, Ba, Ca, Cd, Ce, Cs, Cu, Fe, Ge, K, La, Mg, Mn, Mo, Na, P, Pb, Rb, S, Sb, Se, Sn, Sr, Ti, V, and Zn) varied between 9% and 40%. Twenty elements showed precision better than 25%. Uncertainty estimates from propagation of errors compared well with the whole-system uncertainty values for all minor aerosol elements studied. SEAS-III measurements of As, Cd, Ge, K, La, Mn, Mo, Na, Rb, Se, Sb, Sr, Ti, V, and Zn correlated well ( r>0.8) with a FRM equivalent PM_2.5 integrated filter sampling method. Based on these measurements, collection efficiency of SEAS-III was estimated to be 87±16%. Solubility of particles in the collection medium (water) was identified as a possible reason for low recovery of Al, Fe, Pb, Sb, and Sn.► SEAS-III offers trace element concentrations at sub-hourly resolution. ► Two modified SEAS-III were collocated and results compared against FRM data. ► Most elements in primary particle emissions compared well. ► Precision and accuracy of elements from SEAS-III are reported for the first time. ► Collection efficiency of SEAS-III was estimated to be 87±16%.

Keywords: Collocated precision; Highly time-resolved trace elements; PM; _2.5; SEAS-III; HR-ICPMS

Effects of animal activity and air temperature on methane and ammonia emissions from a naturally ventilated building for dairy cows by N.M. Ngwabie; K.-H. Jeppsson; G. Gustafsson; S. Nimmermark (pp. 6760-6768).

Knowledge of how different factors affect gas emissions from animal buildings can be useful for emission prediction purposes and for the improvement of emission abatement techniques. In this study, the effects of dairy cow activity and indoor air temperature on gas emissions were examined. The concentrations of CH₄, NH₃, CO₂ and N₂O inside and outside a dairy cow building were measured continuously between February and May together with animal activity and air temperature. The building was naturally ventilated and had a solid concrete floor which sloped towards a central urine gutter. Manure was scraped from the floor once every hour in the daytime and once every second hour at night into a partly covered indoor pit which was emptied daily at 6 a.m. and at 5 p.m. Gas emissions were calculated from the measured gas concentrations and ventilation rates estimated by the CO₂ balance method. The animal activity and emission rates of CH₄ and NH₃ showed significant diurnal variations with two peaks which were probably related to the feeding routine. On an average day, CH₄ emissions ranged from 7 to 15 g LU⁻¹ h⁻¹ and NH₃ emissions ranged from 0.4 to 1.5 g LU⁻¹ h⁻¹ (1 LU = 500 kg animal weight). Mean emissions of CH₄ and NH₃ were 10.8 g LU⁻¹ h⁻¹ and 0.81 g LU⁻¹ h⁻¹, respectively. The NH₃ emissions were comparable to emissions from tied stall buildings and represented a 4% loss in manure nitrogen. At moderate levels, temperature seems to affect the behaviour of dairy cows and in this study where the daily indoor air temperature ranged from about 5 up to about 20 °C, the daily activity of the cows decreased with increasing indoor air temperature ( r = −0.78). Results suggest that enteric fermentation is the main source of CH₄ emissions from systems of the type in this study, while NH₃ is mainly emitted from the manure. Daily CH₄ emissions increased significantly with the activity of the cows ( r = 0.61) while daily NH₃ emissions increased significantly with the indoor air temperatures ( r = 0.66). Daily CH₄ emissions were negatively correlated to the indoor air temperature ( r = −0.84). This suggests that increased daily indoor air temperatures due to seasonal changes may bring about decreased animal activity which may decrease the release of CH₄ from dairy cows. Finally, changes in daily NH₃ emissions were influenced more by the indoor air temperature than by the activity of the cows.► Effect of air temperature and cow activity was analysed. ► Effects of temperature and cow activity on CH₄ and NH₃ emissions were studied. ► Daily cow activity decreased with increasing daily indoor air temperatures. ► Daily CH₄ emissions were influenced more by animal activity than by air temperature. ► Daily NH₃ emissions were influenced more by air temperature than by animal activity.

Keywords: Dairy cows; Animal activity; Temperature; Ammonia; Methane; Manure removal

Improved estimate of the policy-relevant background ozone in the United States using the GEOS-Chem global model with 1/2° × 2/3° horizontal resolution over North America by Lin Zhang; Daniel J. Jacob; Nicole V. Downey; Dana A. Wood; Doug Blewitt; Claire C. Carouge; Aaron van Donkelaar; Dylan B.A. Jones; Lee T. Murray; Yuxuan Wang (pp. 6769-6776).

The policy-relevant background (PRB) ozone is defined by the US Environmental Protection Agency (EPA) as the surface ozone concentration that would be present over the US in the absence of North American anthropogenic emissions. It is intended to provide a baseline for risk and exposure assessments used in setting the National Ambient Air Quality Standard (NAAQS). We present here three-year statistics (2006–2008) of PRB ozone over the US calculated using the GEOS-Chem global 3-D model of atmospheric composition with 1/2° × 2/3° horizontal resolution over North America and adjacent oceans (2° × 2.5° for the rest of the world). We also provide estimates of the US background (no anthropogenic US emissions) and natural background (no anthropogenic emissions worldwide and pre-industrial methane). Our work improves on previous GEOS-Chem PRB estimates through the use of higher model resolution, 3-year statistics, better representation of stratospheric influence, and updated emissions. PRB is particularly high in the intermountain West due to high elevation, arid terrain, and large-scale subsidence. We present for this region a detailed model evaluation showing that the model is successful in reproducing ozone exceedances up to 70 ppbv. However, the model cannot reproduce PRB-relevant exceptional events associated with wildfires or stratospheric intrusions. The mean PRB estimates for spring–summer are 27 ± 8 ppbv at low-altitude sites and 40 ± 7 ppbv at high-altitude sites. Differences between the PRB simulation and the natural simulation indicate a mean enhancement from intercontinental pollution and anthropogenic methane of 9 ppbv at low-altitude sites and 13 ppbv at high-altitude sites. The PRB is higher than average when ozone exceeds 60 ppbv, particularly in the intermountain West. Our PRB estimates are on average 4 ppbv higher than previous GEOS-Chem studies and we attribute this to higher lighting, increasing Asian emissions, and improved model resolution. Whereas previous studies found no occurrences of PRB exceeding 60 ppbv, we find here some occurrences in the intermountain West. The annual 4th-highest PRB values in the intermountain West are typically 50–60 ppbv, as compared to 35–45 ppbv in the East or on the West Coast. Such high PRB values in the intermountain West suggest that special consideration of this region may be needed if the ozone NAAQS is decreased to a value in the 60–70 ppbv range.► Improved estimates of PRB ozone in the US are presented. ► The model is evaluated in the intermountain West where PRB ozone is highest. ► PRB ozone is higher than average when ozone exceeds 60 ppbv. ► The annual 4th-highest PRB is 50–60 ppbv in the intermountain West. ► Our PRB estimates are 4 ppbv higher than previous studies.

Keywords: Ozone; Background ozone; Policy-relevant background; Air quality standard

Sources and variability of inhalable road dust particles in three European cities by F. Amato; M. Pandolfi; T. Moreno; M. Furger; J. Pey; A. Alastuey; N. Bukowiecki; A.S.H. Prevot; U. Baltensperger; X. Querol (pp. 6777-6787).

Despite their importance, current scientific knowledge on non-exhaust emissions by road traffic is scarce, severely hampering a reliable description of these particles in atmospheric dispersion models. Consequently, it is still very difficult to convincingly evaluate population exposure to traffic-related components in large cities, especially given the significant variation in traffic-related air pollution concentrations on a small scale (e.g. within 100–1000 m of a busy road). One factor contributing to this uncertainty is the lack of a reliable emission estimate for vehicular non-exhaust emissions. Emissions vary from location to location due to the impact of climate, road surface characteristics and traffic conditions, but the geographical coverage for which Emission Factors are available and the amount of knowledge regarding the variability within a city environment are very limited.The present study investigates the spatial and chemical properties of the strength of the emission source (road dust particles below 10 μm) in three contrasting European urban environments: two Spanish cities (Barcelona and Girona), and a Swiss city (Zürich). Loadings of road dust <10 μm from the 8 sites sampled in Zürich ranged from 0.2 to 1.3 mg m⁻², the lowest loadings of the study. The minimum loadings in Girona (Spain) were as high as the maximum in Zürich, with a range of 1.3–7.1 mg m⁻². By far the most polluted site in terms of road dust <10 μm mass loading is Barcelona (Spain), where a range of 3.7–23.1 mg m⁻² was recorded in the city center samples. Four main sources were found to drive the variability of road dust particles <10 μm: Mineral (road wear and urban dust generated mostly by construction emissions), Motor Exhaust, Brake wear and Tire wear. Road wear/Mineral is the dominating source in Spanish cities (∼60%), but represents only 30% of road dust loadings in Zürich where contributions are more equally distributed among the four main sources of road dust. Regardless of the city categories loadings of OC, EC, Fe, Cr, Mn, Cu, Zn, Mo, Sn, Sb, Cs, Ba, W, Pb and Bi (μg m⁻²) increase by a factor of 1.2–2.2, from streets with <15 kveh to streets with 15–40 kveh day⁻¹. At highly trafficked sites (>40 kveh day⁻¹) loadings were again increasing by a further factor of 2.6–10.1. Finally, agreement was found between the composition of sampled materials and the composition (available from literature) of PM10 material emitted by vehicles via resuspension (both in Zürich and Barcelona). This permitted to find a relationship, potentially able to calculate emission factors from known amount of deposited pollutants in those cities/environment where no real-world EFs are available from literature.► In this study we investigate loadings and sources of inhalable (<10 μm) road dust particles, in three European cities. ► Dry Mediterranean cities showed higher particles loadings with respect to a Central European city. ► The road wear/Mineral source was found to be dominant in Spanish cities. ► In the Swiss city contributions from different sources are similar. ► Loadings of OC, EC, Fe, Cr, Mn, Cu, Zn, Mo, Sn, Sb, Cs, Ba, W, Pb and Bi were found to increase with traffic intensity.

Keywords: PM10; Traffic; Non-exhaust; Source apportionment; PM10; Mineralogy; Emissions; PMF

MBAS (Methylene Blue Active Substances) and LAS (Linear Alkylbenzene Sulphonates) in Mediterranean coastal aerosols: Sources and transport processes by S. Becagli; C. Ghedini; S. Peeters; A. Rottiers; R. Traversi; R. Udisti; M. Chiari; A. Jalba; S. Despiau; U. Dayan; A. Temara (pp. 6788-6801).

Methylene Blue Active Substances (MBAS) and Linear Alkylbenzene Sulphonates (LAS) concentrations, together with organic carbon and ions were measured in atmospheric coastal aerosols in the NW Mediterranean Basin. Previous studies have suggested that the presence of surfactants in coastal aerosols may result in vegetation damage without specifically detecting or quantifying these surfactants. Coastal aerosols were collected at a remote site (Porquerolles Island-Var, France) and at a more anthropised site (San Rossore National Park-Tuscany, Italy). The chemical data were interpreted according to a comprehensive local meteorological analysis aiming to decipher the airborne source and transport processes of these classes of compounds.The LAS concentration (anthropogenic surfactants) was measured in the samples using LC-MS/MS, a specific analytical method. The values were compared with the MBAS concentration, determined by a non-specific analytical method. At Porquerolles, the MBAS concentration (103 ± 93 ng m⁻³) in the summer samples was significantly higher than in the winter samples. In contrast, LAS concentrations were rarely greater than in the blank filters. At San Rossore, the mean annual MBAS concentration (887 ± 473 ng m⁻³ in PM10) contributed about 10% to the total atmospheric particulate organic matter. LAS mean concentration in these same aerosol samples was 11.5 ± 10.5 ng m⁻³. A similar MBAS (529 ± 454 ng m⁻³) – LAS (7.1 ± 4.1 ng m⁻³ LAS) ratio of ∼75 was measured in the fine (PM2.5) aerosol fraction. No linear correlation was found between MBAS and LAS concentrations.At San Rossore site the variation of LAS concentrations was studied on a daily basis over a year. The LAS concentrations in the coarse fraction (PM10–2.5) were higher during strong sea storm conditions, characterized by strong air flow coming from the sea sector. These events, occurring with more intensity in winter, promoted the formation of primary marine aerosols containing LAS from the sea surface microlayer. In contrast to LAS, MBAS concentrations in the coarse fraction peaked in summer. Therefore, different sources are suggested for the two classes of compounds. In summer, increased MBAS concentration could be an indicator of phytoplanktonic blows enriching the sea surface microlayer with biogenic surfactants. In winter, some spikes in MBAS concentrations in the coarse fraction could be related to LAS concentrations and sea storm events. Moreover, in the fine fraction MBAS have a large concentration maxima in winter, corresponding to air masses coming from polluted continental areas. It is concluded that MBAS concentration in the fine or the coarse fraction is not an appropriate surrogate measurement of LAS concentration in aerosols because of the significant contribution from other sources to the MBAS concentration.► Determination of MBAS and LAS in Mediterranean coastal aerosols. ► The LAS/MBAS ratio is 0.02–0.03. ► MBAS contribute for about 10% to the organic compounds of the atmospheric aerosol. ► MBAS and LAS in aerosol are positioned in a comprehensive meteorological analysis. ► MBAS and LAS have different source and transport processes.

Keywords: Surfactants; LAS; MBAS; PM10; PM2.5; Mediterranean coastal sites

Spatio-temporal variation trends of satellite-based aerosol optical depth in China during 1980–2008 by Jian-Ping Guo; Xiao-Ye Zhang; Ye-Rong Wu; Yangzong Zhaxi; Hui-Zheng Che; Ba La; Wei Wang; Xiao-Wen Li (pp. 6802-6811).

This paper analyzes TOMS AOD at 500 nm (1980–2001), along with MODIS data (2000–2008) at 550 nm to investigate variations at one-degree grid over eight typical regions in China and the trends in AODs, temporally and spatially. In contrast to recently reported global decrease in AOD over global ocean beginning around 1990, we find there virtually exists no apparent AOD transition in China for that: firstly no notable upward tendencies in AOD during 1980–1992 for the relative low value (+0.001/decade), then during 1996–2001 a discernible ascending tendency with larger magnitude at 0.01/decade, and finally, since 2000, a weak upward trend with +0.004/decade. The large increases during 1996–2001 are presumably consequences of large increases in industrial activities and bear a strong resemblance to the long-term decreasing observations of incident solar radiation and cloud cover in China. Specifically, in late 1990’s, only in Taklimakan Desert a negative trend with a maximum magnitude of −0.04/decade is detected. However, over regions such as Jingjinji and Pearl River Delta influenced by industrial activities, positive tendencies at +0.01/decade are observed.Seasonal patterns in the AOD regional long-term trend are evident. AODs exhibit generally similar seasonality and the summer dominates higher AOD value than the autumn. In particular, during the period 1980–2001, all the eight regions except Taklimakan Desert witness the maximum aerosols in winter while there is not such seasonality during the period 2000–2008. Geographically, we also document spatial patterns of AOD variations over China. Results reveal that no apparent upward trends in AOD (about 15% per decade) are observed in 1980’s, while beginning 1990 till 2008, both data (TOMS and MODIS) are indicative of a significant AOD increase across China, especially in 1990’s it is indeed the case, roughly in accordance with the overall trends at regional scale.► We investigate the spatio-temporal trends in AOD in eight typical regions of China. ► Transition in overall AOD trend from downward to upward is observed beginning 1990. ► The spatial variation in AOD suggests no apparent upward trends in 1980’s. ► Since 1990, both TOMS and MODIS indicate a significant AOD increase across China.

Keywords: AOD; Trend; TOMS; MODIS

Application of the np+ mP modeling approach for simulating secondary organic particulate matter formation from α-pinene oxidation by Kelley C. Barsanti; James N. Smith; James F. Pankow (pp. 6812-6819).

Simulations of the levels of organic particulate matter (OPM) in chemical transport models typically proceed by a two-product (2p) model approach, in which up to two lumped products are assumed to represent the condensable oxidation products of each hydrocarbon precursor. With the 2p approach, as well as with more detailed semi-explicit approaches, significant underpredictions of OPM levels are not uncommon, particularly at low OPM mass loadings in the atmosphere and in chamber studies. Here the recently developed np+ mP OPM model approach was applied to evaluate OPM formation by α-pinene ozonolysis using: 1) product lumping based on carbon number and an estimate of molecular polarity, and 2) explicit inclusion of a low-volatility “polymeric” (P) compound. The np+ mP approach allows for consideration of more than two products of type p ( n > 2) per precursor, and consideration of further oxidation and/or reaction of those products to form m essentially non-volatile high molecular weight products of type P. Simulations were carried out for several different case types, namely 16p+0P, 8p+0P, 5p+0P, and 5p+1P in which one representative low-volatility compound was added. Predicted OPM levels were compared with levels predicted using alternative parameterizations (2p and volatility basis set) and with levels measured in chamber experiments conducted over a range of α-pinene oxidation conditions. The results from the 5p+1P case provided good agreement with available data from low, atmospherically-relevant mass loading experiments. Predicted O:C and H:C ratios also were compared with measured ratios, providing insight into differences and similarities between model compounds and the products they represent. The results will inform further development of OPM models, especially as regards oxidation product lumping and inclusion of low-volatility products.► Carbon number-polarity grid serves as an oxidation product lumping tool. ► Explicit inclusion of low-volatility accretion product improves OPM model parameterization. ► The np+ mP model approach guides development of OPM model parameterizations.

Keywords: SOA; PM; OPM; Alpha-pinene; Modeling; Carbon number-polarity grid

CVPS: An operator solving complex chemical and vertical processes simultaneously with sparse-matrix techniques by Jinyou Liang; Mark Z. Jacobson (pp. 6820-6827).

We present a locally, one-dimensional operator that couples complex Chemical and Vertical Physical processes with Sparse-matrix techniques (CVPS) for multi-dimensional regional photochemical transport models. The CVPS operator solves fundamental interaction between chemical reactions and vertical physical processes in the atmospheric boundary layer at each time step, and may be used to simulate chemicals sensitive to both vertical mixing and photochemistry at a time step. The CVPS operator is numerically stable and computationally efficient in atmospheric boundary layers over California. The computational advantage originates from sparse-matrix techniques and the low frequency for communicating feedbacks between CVPS and other local operators. Based on surface Ox (O₃+NO₂) simulations in the Southern California Air Quality Study domain (; ) on a dual quad-core Linux processor, the ratio of simulation/computer times may reach two for three-dimensional modeling using a classic horizontal advection solver and the CVPS operator.► We developed an operator (CVPS) for simulating surface oxidants more accurately. ► The CVPS solves chemical and physical processes in a column of air simultaneously. ► The CVPS is validated with focuses on transport and chemistry, respectively. ► A classic ozone episode is used to evaluate the CVPS for simulating surface oxidants. ► The CVPS is used to assess the success of clean air measures in reducing Ox over LA.

Keywords: Ozone; Atmospheric boundary layer; Air quality model; Complex operator; Computer simulation

Estimating the effect of on-road vehicle emission controls on future air quality in Paris, France by Yelva Roustan; Marie Pausader; Christian Seigneur (pp. 6828-6836).

For several years several vehicle emission control technologies have been developed and introduced to reduce the contribution of road traffic to air pollution. However, this contribution in the Île de France region, around Paris, France, has been estimated to still be significant. We present a modeling study of the effect of the future evolution of traffic emissions on air quality at the urban scale. The aim is to assess the respective contribution of the different processes involved in the nonlinear chemistry of photochemical air pollution (change in emissions and/or chemical behaviour) that explain the observed evolution of concentrations of traffic-related pollutants at monitoring urban background stations. The modeling results suggest that the reduction of NO_x emissions must be coupled with more stringent measures on NMVOC emissions than those currently planned in the transportation sector to avoid an increase of O₃ concentrations in some densely populated areas. The modeled NO₂ concentrations in Paris reach a maximum in 2010 due to an increase of the NO₂ emissions related to the evolution of the NO₂/NO_x ratio of the Diesel vehicle emissions. The reduction of PM emissions leads to a non-proportional decrease in PM concentrations, which results mostly from the decrease in Diesel particulate emissions.► Catalytic device of early Diesel particle filter leads to increase NO2 emissions. ► A joint decrease in NO_x and NMVOC emissions leads to compensating effect for O3. ► Emission control technology affects both primary and secondary particulate matter.

Keywords: Model; Vehicles; Nitrogen dioxide; Ozone; Particulate matter

Should moss samples used as biomonitors of atmospheric contamination be washed? by J.R. Aboal; A. Pérez-Llamazares; A. Carballeira; S. Giordano; J.A. Fernández (pp. 6837-6840).

When terrestrial mosses are used to monitor atmospheric contamination, the samples are usually analysed without first being washed, so that the contaminants deposited on the moss can be quantified. However, when the aim is to evaluate phyto-toxic effects and the risks associated with increased concentrations of contaminants, it is the bioconcentrated fraction that is of interest. In such cases, the samples are washed to remove deposited material adhering to the surface of the moss. In the present study, the efficacy of the washing step was evaluated, by electron microscopy and microanalysis, in samples exposed to different levels of contamination. The results obtained show that washing is not effective at removing particles deposited on the moss surface, so that an alternative cleaning method is required. Until such a method becomes available, use of the Sequential Elution Technique is recommended for precise determination of the bioconcentrated contaminants.► Advisable washing is not effective removing particles from the moss surface. ► Moss samples used as biomonitors of atmospheric contamination must not be washed. ► Alternative cleaning methods must be tested for determining bioconcentrated fraction.

Keywords: Biomonitoring; Particulate matter pollution; Bryophytes

Comment on Estimating historical landfill quantities to predict methane emissions (Lyons et al., 2010) by Phillip O’Brien; Frank McGovern; Bernard Hyde (pp. 6841-6842).

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Atmospheric Environment (v.45, #37)

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Atmospheric Environment (v.45, #37)