Air Mass Concentration Research Articles

The effect of mixed layer across air mass trajectory pathways on PM2.5 constituent levels: The case of a major urban center in the Eastern Mediterranean

Αn advanced three dimensional (3D) version of air mass Concentration Weighted Trajectory (CWT) model was applied, coupled with Mixed Layer Depth (MLD) estimations across the trajectory pathways. Three years daily PM2.5 composition measurements from an urban background site in Athens (Greece) were incorporated in the 3D-CWT model, to identify the atmospheric circulation patterns affecting PM2.5 constituent levels during cold (October 16th to April 15th) and warm (April 16th to October 15th) periods. The recirculation of local air masses inside the Mixed Layer (ML) during the cold period, was associated with accumulation of all PM2.5 constituents emitted from combustion sources (EC, OC, SO42−, NO3−, NH4+ and K+), whilst regional contributions of the same species were mainly associated with Northern airflows above the ML through Balkan Peninsula. In the cold period, transport of sea spray (Cl−, Na+ and Mg2+) and dust (Ca2+), from the Mediterranean and the Sahara desert respectively, was detected mainly through the ML, whilst sea salt from the Black Sea and dust from Balkan Peninsula were also transferred with Northern airflows above the ML. Contrariwise, transport from the Balkans area especially above the ML enriched the levels of all constituents of anthropogenic origin during the warm period, whilst the pattern of Saharan dust advections was also vertically extended above the ML. Conclusively, the implemented 3D-CWT model revealed a more detailed description of PM2.5 transport pathways in Athens, in comparison with the classic CWT model, by including the effect of MLD across the air mass trajectories.

Job function as determinant of clinker exposure at workplaces during cement production.

In the cement production industry, exposure to airborne particulate matter is associated with a decline in lung function and increased airway symptoms. Exposure to clinker-the major constituent of cement and supposedly the cause of the observed adverse health effects-was determined recently in 15 cement production plants located in 8 different countries (Estonia, Greece, Italy, Norway, Sweden, Switzerland, Spain, Turkey). It was shown that the median clinker abundance in the thoracic fraction varied between approximately 20% and 70% for individual plants. The present study complements the previous work by investigating the significance of job function as a determinant of clinker exposure. The elemental composition (water and acid-soluble fractions separately) of 1,227 personal thoracic workplace samples was analyzed by positive matrix factorization (PMF) to determine the contribution of different sources to the composition of airborne particulate matter and to quantify the clinker content. Median thoracic mass air concentrations varied for individual job functions between 0.094 and 12 mg/m3 (estimated separately for different plants). The PMF 5-factor solution yielded median relative clinker abundances in the personal thoracic samples between 7.6% and 81% for individual job functions. Thoracic clinker air concentrations are highest for cleaning, production, and maintenance work, and lowest for administration and other work. Foremen and laboratory personnel show intermediate exposure levels. The plant was found to have a much higher contribution to the total variance of the thoracic clinker air concentrations than the job function. Thoracic clinker air concentrations (medians between 0.01 and 5.5 mg/m3) are strongly correlated with the thoracic mass air concentrations and to a lesser extent with the relative clinker abundance in an aerosol sample. Job function is an important predictor of exposure to clinker in the cement production industry. As clinker is suspected to be the causal agent for the observed adverse health effects among cement production workers, the clinker air concentration may be a better exposure metric than thoracic air mass concentration despite the strong correlation between the two. Reduction strategies should focus on the most exposed job categories cleaning, production, and maintenance work.

Retrieving ice-nucleating particle concentration and ice multiplication factors using active remote sensing validated by in situ observations

Abstract. Understanding the evolution of the ice phase within mixed-phase clouds (MPCs) is necessary to reduce uncertainties related to the cloud radiative feedback in climate projections and precipitation initiation. Both primary ice formation via ice-nucleating particles (INPs) and secondary ice production (SIP) within MPCs are unconstrained, not least because of the lack of atmospheric observations. In the past decades, advanced remote sensing methods have emerged which provide high-resolution data of aerosol and cloud properties and could be key in understanding microphysical processes on a global scale. In this study, we retrieved INP concentrations and ice multiplication factors (IMFs) in wintertime orographic clouds using active remote sensing and in situ observations obtained during the RACLETS campaign in the Swiss Alps. INP concentrations in air masses dominated by Saharan dust and continental aerosol were retrieved from a polarization Raman lidar and validated with aerosol and INP in situ observations on a mountaintop. A calibration factor of 0.0204 for the global INP parameterization by DeMott et al. (2010) is derived by comparing in situ aerosol and INP measurements, improving the INP concentration retrieval for continental aerosols. Based on combined lidar and radar measurements, the ice crystal number concentration and ice water content were retrieved and validated with balloon-borne in situ observations, which agreed with the balloon-borne in situ observations within an order of magnitude. For seven cloud cases the ice multiplication factors (IMFs), defined as the quotient of the ice crystal number concentration to the INP concentration, were calculated. The median IMF was around 80, and SIP was active (defined as IMFs > 1) nearly 85 % of the time. SIP was found to be active at all observed temperatures (−30 to −5 ∘C), with the highest IMFs between −20 and −5 ∘C. The introduced methodology could be extended to larger datasets to better understand the impact of SIP not only over the Alps but also at other locations and for other cloud types.

Evaluation of the anthropogenic black carbon emissions and deposition on Norway spruce and silver birch foliage in the Baltic region

This study investigates potential influence of urban trees on black carbon (BC) removal by Norway spruce and silver birch along with the BC formation, mass concentration in air, and source apportionment. The main sources of BC in urban areas are transport, household and industry. BC concentrations monitored in urban background station in Vilnius (Lithuania) showed that biomass burning was a significant contributor to BC emissions even during warm period of the year. Therefore, BC emission levels were determined for the most common biomass fuels (mixed wood pellets, oak, ash, birch and spruce firewood) and two types of agro-biomass (triticale and rapeseed straw pellets) burned in modern and old heating systems. The highest emissions were obtained for biomass fuels especially birch firewood. BC aerosol particles produced by the condensation mechanism during the combustion processes were found in all samples taken from the leaf surface.The short-term effect of BC exposure on photosynthetic pigments (chlorophyll a and b; and carotenoids) in the foliage of one-year-old Norway spruce and silver birch seedlings was evaluated by the experiment carried out in the phytotron greenhouse. The seedlings showed different short-term responses to BC exposure. All treatments applied in the phytotron greenhouse resulted in lower chlorophyll content in spruce foliage compared to natural conditions but not differed for birch seedlings. However, the exposure of BC particles on the spruce and birch seedlings in the phytotron increased the content of photosynthetic pigments compared to the control seedlings in the phytotron.Overall, urban trees can help improve air quality by reducing BC levels through dry deposition on tree foliage, and needle-like trees are more efficient than broad-leaved trees in capturing BC.Nevertheless, a further study could assess the longer-term effects of BC particles on tree biochemical and chemical reactions.

Ultrafine Aerosol Particle Sizer Based on Piezoresistive Microcantilever Resonators with Integrated Air-Flow Channel.

To monitor airborne nano-sized particles (NPs), a single-chip differential mobility particle sizer (DMPS) based on resonant micro cantilevers in defined micro-fluidic channels (µFCs) is introduced. A size bin of the positive-charged fraction of particles herein is separated from the air stream by aligning their trajectories onto the cantilever under the action of a perpendicular electrostatic field of variable strength. We use previously described µFCs and piezoresistive micro cantilevers (PMCs) of 16 ng mass fabricated using micro electro mechanical system (MEMS) technology, which offer a limit of detection of captured particle mass of 0.26 pg and a minimum detectable particulate mass concentration in air of 0.75 µg/m3. Mobility sizing in 4 bins of a nebulized carbon aerosol NPs is demonstrated based on finite element modelling (FEM) combined with a-priori knowledge of particle charge state. Good agreement of better than 14% of mass concentration is observed in a chamber test for the novel MEMS-DMPS vs. a simultaneously operated standard fast mobility particle sizer (FMPS) as reference instrument. Refreshing of polluted cantilevers is feasible without de-mounting the sensor chip from its package by multiply purging them alternately in acetone steam and clean air.

Vapor condensation with low air mass fraction inside water seal branch tube under free convection

The pressure vessel has used a newly designed water seal structure, and the sealed water is from condensation at low hydrogen concentration. To get the condensation capacity of the water seal branch tube under the pressure vessel normal operation, the experimental loop named WASETEL was constructed, which is aimed at studying the heat transfer during the process of air-steam mixture condensation inside the inclined branch tube at the condition of low air mass fraction. The inner tube is diameter 0.134 m with length 0.68 m which is connected with diameter 1.4 m, high 2.5 m pressure vessel. A canon camera was set to record the images and videos of the condensate height through glass tube in communicating vessel liquidometer. The experiment was conducted under the pressure ranged from 0.2 to 0.6 MPa, air mass concentration ranged from 0.49 to 6.42% and wall subcooling ranged from 11 to 40 K. The test showed HTC (heat transfer coefficient) would sharply deteriorate with the small air fraction, compared with pure steam condensation, about 0.49% mass fraction of the air will reduce heat transfer coefficient by 70–80%. When air concentration is relatively small, those widely used relations can not predict the condensation well, therefore, a new heat transfer empirical correlation with air mass fraction, pressure and subcooling is proposed, covered all the experimental data within the error band ±13%.

Optical determination of black carbon mass concentrations in snow samples: A new analytical method

Black carbon (BC) aerosols in the atmosphere strongly affect direct radiative forcing and climate, not only while suspended in the atmosphere but also after deposition onto high albedo surfaces. Snow surfaces are especially sensitive to BC deposition, because of their high surface albedo and additional positive feedbacks further enhance faster snowpack melting caused by BC deposition, resulting in modifications in water resources and recession of glaciers. For the analysis of BC deposition on snow, a precise quantification of BC mass is needed. Instead, optical methods have the potential of quantifying only BC, based on its characteristic spectral absorption. Commercial optical transmissometers commonly use quartz filters to filter BC and measure its optical attenuation. They are calibrated for the determination of BC mass concentrations in air, but not adapted or calibrated for their determination in water or snowmelt samples. Additionally, they are generally calibrated using BC-simulating materials that are not representative of ambient BC particles.Here, a new analytical method is demonstrated for the quantitative determination of BC mass concentration in snow samples that considers filtering of melted snow with polycarbonate filters in a new device, and optical filter attenuation BC mass concentration measurement (880 nm). The attenuation can be obtained with any optical equipment that can measure the 880-nm attenuation of filters impacted with BC/snow impurities.This method has been calibrated using real diesel vehicle exhaust soot with well-known optical properties as reference material, yielding a multipoint calibration curve for common BC concentration levels in snow. The limits of detection (0.011 mg of BC), quantification (0.036 mg of BC) and reproducibility (96.39%) of this new analytical method have been determined. Real surface snow samples collected at different locations in “Los Andes” mountains of Chile were measured with this method given a BC concentrations ranged from 151 to 5987 μg kg−1.

Transport Pathways and Potential Sources of PM2.5 During the Winter in Zhengzhou

In this study, meteorological and air mass concentration data of Zhengzhou from December 2017 to February 2018 (winter) were used to quantify the influence of meteorological factors on the PM. The Hybrid Single-Particle Lagrangian Integrated Trajectory model was used to analyze the 48-hour backward trajectories and the cluster method was applied to classify the airflow backward trajectory. Moreover, the potential source contribution function and concentration-weighted trajectory analysis were applied to evaluate the transport pathways and sources of PM2.5 in Zhengzhou. The results show that the heavy pollution in Zhengzhou during winter is mainly due to the low wind speed, high relative humidity, and low precipitation. The cluster analysis revealed that up to 60% of the back trajectories came from the northwest and 25.56% of the back trajectories came from the Beijing-Tianjin area. The airflow trajectories from the south and east account for 7.5% and 6.1% with higher PM2.5 concentrations. The main potential sources of PM2.5 in Zhengzhou during winter are located in Beijing-Tianjin-Hebei air pollution transmission channel cities including Jiaozuo, Kaifeng, Xinxiang, Hebi, Puyang, Anyang, Handan, and Xingtai. The adjacent provinces, including Shanxi, Hubei, and Anhui, also have great influence on the PM2.5 in Zhengzhou.

Genotoxic effects of daily personal exposure to particle mass and number concentrations on buccal cells

The aim of this study is to assess personal exposure to Particle Number Concentrations (PNC) in four size ranges between 0.3 and 10 μm, and particulate matter (PM1; PM2.5; PM4; PM10) in order to evaluate possible genotoxic effects through a comet assay in buccal cells. A convenience cohort of 30 individuals from a Brazilian medium-sized city was selected. These individuals aged between 20 and 61 and worked in typical job categories (i.e., administrative, commerce, education, general services and transport). They were recruited to perform personal exposure measurements during their typical daily routine activities, totaling 240 h of sampling. The 8-h average mass concentrations in air for volunteers ranged from 2.4 to 31.8 μg m−3 for PM1, 4.2–45.1 μg m−3 for PM2.5, 7.9–66.1 μg m−3 for PM4 and from 23.1 to 131.7 μg m−3 for PM10. The highest PNC variation was found for 0.3–0.5 range, between 14 and 181 particles cm−3, 1 to 14 particles cm−3 for the 0.5–1.0 range, 0.2 to 2 particles cm−3 for the 1.0–2.5 range, and 0.06 to 0.7 particles cm−3 for the 2.5–10 range. Volunteers in the ‘education’ category experienced the lowest inhaled dose of PM2.5, as opposed to those involved in ‘commercial‘ activities with the highest doses for PM10 (1.63 μg kg−1 h−1) and PM2.5 (0.61 μg kg−1 h−1). The predominant cause for these high doses was associated with the proximity of the workplace to the street and vehicle traffic. The comet assay performed in buccal cells indicated that the volunteers in ‘commerce’ category experienced the highest damage to their DeoxyriboNucleic Acid (DNA) compared with the control category (i.e. ‘education’). These results indicate the variability in personal exposure of the volunteers in different groups, and the potential damage to DNA was much higher for those spending time in close proximity to the vehicle sources (e.g. commercial services) leading to exposure to a higher fraction of fine particles. This study builds understanding on the exposure of people in different job categories, and provide policy makers with useful information to tackle this neglected issue.

Heavy pollution episodes, transport pathways and potential sources of PM2.5 during the winter of 2013 in Chengdu (China).

Air mass concentration data from 8 environmental quality monitoring sites and meteorological data of Chengdu from 1 December 2013 to 28 February 2014 were used in this study. Chengdu suffered five continuous heavy pollutions during this winter due to the basin terrain and the meteorological conditions of low wind speed, low precipitation and high relative humidity. Analysing the hourly resolution time series of pollutants' concentrations, variation of PM2.5 in the urban area followed a growing "saw-tooth cycle" pattern during the heavy pollution, with a daily cycle of bimodal distribution. The massive letting-off of fireworks within a short period of time on the Eve of the Lunar New Year under the unfavourable diffusion conditions resulted in an extreme pollution event. The sharply rising Longmen-Qionglai Mountains to the west of the Sichuan Basin not only acted as a huge barrier to block the air mass from the east but also favoured the formation of a local circulation. The cluster analysis of back trajectories revealed that up to 77% of them came from the inner part of the Basin. Combining the concentration data of PM2.5 with air mass back trajectories, a potential source contribution function (PSCF) model and a concentration-weighted trajectory (CWT) method were used to evaluate the transport pathways and sources over PM2.5 of Chengdu, revealing that the main potential sources of PM2.5 were located in southeast cities and the western margin of the Sichuan Basin. The result provided advice for the government to take measures in improving air quality.

Impact of Marine-atmospheric Process on Aerosol Number Size Distribution in the South China Sea

The shipboard measurements of aerosol number concentration from August 28th to October 13th, 2012 were conducted to analyze the characteristics of temporal-spatial distribution and number size distribution of marine aerosol in the South China Sea. The impact of meteorological condition on the marine aerosol was also analyzed in this paper. The result showed that the temporal-spatial distribution and number size distribution of marine aerosol were influenced by the backward trajectory of the air masses and the time they spent over the sea, and the meteorological conditions in the local sea area such as wind speed, wind direction, temperature, relative humidity and cloud cover. In terms of temporal-spatial distribution of marine aerosol in the South China Sea, the aerosol in the sea areas under the influence of continental air mass concentration showed much higher concentration than that in the clean maritime air mass (2300 cm-3 vs. 1200 cm-3). During the ship observation, three kinds of number size distribution of marine aerosol were found and classified:polluted type, marine type 1 and marine type 2 (clean). All the distributions had a similar sub-micron mode and a similar coarse mode. The marine type 2 (clean) had the same distribution shape as polluted type except that the value of concentration was much lower. The sub-micron peak of marine type 1 appeared near 0.08 μm and its concentration was significantly higher than that of marine type 2 (clean). Non-precipitating clouds as well as abundant moisture contributed to the growth of ultrafine particles to the size of accumulation mode aerosol (0.05-0.12 μm). Number concentration of particles in this range showed weak positive correlation with wind speed since wind can enhance the efficiency of sea-air exchange and accelerate the release of gas precursors of sulfate aerosol to the atmosphere. The concentration of coarse particles ranging from 0.5-6 μm in diameter strongly depended on the wind speed, and the correlation coefficient reached a value of 0.7.

Regional atmospheric Cr(VI) pollution from the Bushveld Complex, South Africa

Hexavalent chromium, Cr(VI), is a proven human carcinogen. Of interest in this paper was the regional atmospheric pollution of Cr(VI) from the ferrochromium and related industries located in the western Bushveld Complex (wBC) of South Africa. A significant fraction of the world's ferrochromium and platinum group metals is produced in this region. Particulate matter (PM), in two size fractions, i.e. PM2.5 (≤2.5 μm) and PM2.5−10 (2.5–10 μm), was sampled for a full calendar year at a regional background site, which is situated downwind of the wBC on the dominant anti-cyclonic recirculation route of air mass over the South African interior. Results indicated that Cr(VI) concentrations in air masses that had passed over the regional background were below the detection limit of the analytical technique applied, but that Cr(VI) in air masses that had passed over the wBC were elevated and had a median concentration of 4.6 ng/m3. The majority of Cr(VI) was found to be in the finer size fraction (PM2.5), which could be explained by the nature of Cr(VI)-containing PM being emitted by the sources in the wBC and the atmospheric lifetimes of different PM size fractions. The results further indicated that it is possible that not only pyrometallurgical sources in the wBC, but also other combustion sources outside the wBC contributed to the observed atmospheric Cr(VI) concentrations.

Process analysis of characteristics of the boundary layer during a heavy haze pollution episode in an inland megacity, China

Ground observation data from 8 meteorological stations in Xi'an, air mass concentration data from 13 environmental quality monitoring sites in Xi'an, as well as radiosonde observation and wind profile radar data, were used in this study. Thereby, the process, causes and boundary layer meteorological characteristics of a heavy haze episode occurring from 16 to 25 December 2013 in Xi'an were analyzed. Principal component analysis showed that this haze pollution was mainly caused by the high-intensity emission and formation of gaseous pollutants (NO2, CO and SO2) and atmospheric particles (PM2.5 (fine particles) and PM10 (respirable suspended particle). The second cause was the relative humidity and continuous low temperature. The third cause was the allocation of the surface pressure field. The presence of a near-surface temperature inversion at the boundary layer formed favorable stratification conditions for the formation and maintenance of heavy haze pollution. The persistent thick haze layer weakened the solar radiation. Meanwhile, a warming effect in the urban canopy layer and in the transition zone from the urban friction sublayer to the urban canopy was indicated. All these conditions facilitated the maintenance and reinforcement of temperature inversion. The stable atmospheric stratification finally acted on the wind field in the boundary layer, and further weakened the exchange capacity of vertical turbulence. The superposition of a wind field with the horizontal gentle wind induced the typical air stagnation and finally caused the deterioration of air quality during this haze event.

Influência do tamanho de flocos e da concentração de ar dissolvido na eficiência da flotação

RESUMO O presente artigo apresenta resultados de pesquisa que teve por objetivo a investigação da influência do tamanho de partículas floculadas na eficiência da clarificação de águas para abastecimento por flotação por ar dissolvido (FAD) com o emprego de método e equipamento para a aquisição e análise de imagens especialmente desenvolvidos para a caracterização da distribuição de tamanho de flocos e microbolhas de ar presentes no processo de flotação. Os ensaios foram realizados com água sintética (temperatura de 26,0±0,5oC; turbidez de 7,5±0,2 NTU; cor aparente de 38±1 uC; alcalinidade de 29,8±0,6 mgCaCO3.L-1; condutividade de 59,3±0,8 µS.cm-1; UV254nm de 0,128±0,004cm-1), a qual foi coagulada com a aplicação de 1,9 mg.L-1 de Al3+ (pH de 6,6±0,05; 22,5 mg.L-1alum). Os resultados alcançados demonstraram que: i) a distribuição de tamanho de partículas floculadas influenciou diretamente a clarificação por flotação da água em estudo, sendo que as melhores condições de floculação foram aquelas que conduziram à formação, em sua maioria, de partículas floculadas com diâmetro médio de Feret acima de 300 µm; ii) os menores valores residuais dos parâmetros analisados na água em estudo foram alcançados com o emprego da Condição 2 de floculação (T=17 min/G=60 s-1) associada a uma concentração em massa de ar (Cb) de 4,8 mg.L-1, entretanto, a FAD foi capaz de operar também com boa eficiência com a utilização de tempo de floculação (T) de 10 minutos; iii) o método e o equipamento desenvolvidos nesta pesquisa para aquisição e análise de imagens demonstraram constituir importantes ferramentas para a obtenção das distribuições de tamanho de flocos e microbolhas de ar.

Significant increase of aerosol number concentrations in air masses crossing a densely trafficked sea area

In this study, we evaluated 10 months data (September 2009 to June 2010) of atmospheric aerosol particle number size distribution at three atmospheric observation stations along the Baltic Sea coast: Vavihill (upwind, Sweden), Uto (upwind, Finland), and Preila (downwind, Lithuania). Differences in aerosol particle number size distributions between the upwind and downwind stations during situations of connected atmospheric flow, when the air passed each station, were used to assess the contribution of ship emissions to the aerosol number concentration (diameter interval 50-400 nm) in the Lithuanian background coastal environment. A clear increase in particle number concentration could be noticed, by a factor of 1.9 from Uto to Preila (the average total number concentration at Uto was 791 cm(-3)), and by a factor of 1.6 from Vavihill to Preila (the average total number concentration at Vavihill was 998 cm(-3)). The simultaneous measurements of absorption Angstrom exponents close to unity at Preila supported our conclusion that ship emissions in the Baltic Sea contributed to the increase in particle number concentration at Preila. (C) 2015 Institute of Oceanology of the Polish Academy of Sciences. (Less)

On the relationship between Arctic ice clouds and polluted air masses over the North Slope of Alaska in April 2008

Abstract. Recently, two types of ice clouds (TICs) properties have been characterized using the Indirect and Semi-Direct Aerosol Campaign (ISDAC) airborne measurements (Alaska, April 2008). TIC-2B were characterized by fewer (< 10 L−1) and larger (> 110 μm) ice crystals, and a larger ice supersaturation (> 15%) compared to TIC-1/2A. It has been hypothesized that emissions of SO2 may reduce the ice nucleating properties of ice nuclei (IN) through acidification, resulting in a smaller concentration of larger ice crystals and leading to precipitation (e.g., cloud regime TIC-2B). Here, the origin of air masses forming the ISDAC TIC-1/2A (1 April 2008) and TIC-2B (15 April 2008) is investigated using trajectory tools and satellite data. Results show that the synoptic conditions favor air masses transport from three potential SO2 emission sources into Alaska: eastern China and Siberia where anthropogenic and biomass burning emissions, respectively, are produced, and the volcanic region of the Kamchatka/Aleutians. Weather conditions allow the accumulation of pollutants from eastern China and Siberia over Alaska, most probably with the contribution of acidic volcanic aerosol during the TIC-2B period. Observation Monitoring Instrument (OMI) satellite observations reveal that SO2 concentrations in air masses forming the TIC-2B were larger than in air masses forming the TIC-1/2A. Airborne measurements show high acidity near the TIC-2B flight where humidity was low. These results support the hypothesis that acidic coating on IN could be at the origin of the formation of TIC-2B.

Aerosol Metrology Supporting Air Quality Monitoring in the United Kingdom and Europe

Regulatory measurements of particle mass concentration in air, such as PM10 and PM2.5, have been required in Europe for many years, but have been problematic as issues affecting the comparability of measurements, even when made by the reference method, have become apparent. The importance of airborne particulate matter for human health, and the complexity of the atmospheric processes affecting it, have led to many other parameters, such as particle number concentration, size distribution and composition being monitored, in some cases also as a regulatory requirement. Generally the metrological aspects have been covered by the monitoring network operators, with little involvement from National Metrology Institutes (NMIs). The United Kingdom (UK) National Physical Laboratory is unusual in being an NMI that also operates air quality networks on behalf of the government, directly involved in the full range of activities from fundamental metrology, standardisation of methods, and field operation. More recently, some of the measurement issues have started to be addressed by a group of NMIs within the European Metrology Research Programme. This paper outlines some of the key metrological problems in this area, and the current position in dealing with them from a UK and European perspective.

Atmospheric concentrations and potential sources of PCBs, PBDEs, and pesticides to Acadia National Park

This study assessed concentrations and investigated potential source regions for PCBs, PBDEs, and organochlorine pesticides in Acadia National Park, Maine, USA. Back-trajectories and potential source contribution function (PSCF) values were used to map potential source areas for total-PCBs, BDE-47, and 10 organochlorine pesticides. The constructed PSCF maps showed that ANP receives high pollutant concentrations in air masses that travel along four main pathways: (1) from the SW along the eastern Atlantic seaboard, (2) from the WSW over St. Louis, and Columbus regions, (3) from the west over Chicago, and Toronto regions, and (4) from WNW to NNW over the Great Lakes, and Quebec regions. Transport of all studied pollutants were equally distributed between the first three pathways, with only minor contributions from the last pathway. This study concludes that the high-pollutant concentrations arriving at ANP do not exclusively originate from the major urban centers along the eastern Atlantic seaboard.

Dust-induced shading on photovoltaic modules

The effect of dust on photovoltaic modules is investigated with respect to concentration and spectral transmittance. Samples were collected in the form of raw dust as well as accumulated dust on exposed sheets of glass at different tilt angles. Spectral transmittance of the samples was determined. Transmittance variation between top, middle and bottom was identified for samples collected at different inclinations, where the worst case was seen at a tilt angle of 30o with a non-uniformity of 4.4% in comparison with 0.2% for the 90° tilt. The measured data showed a decrease in transmittance at wavelengths <570 nm. Integrating this with measured spectral responses of different technologies demonstrates that wide band-gap thin-film technologies are affected more than, for example crystalline silicon technologies. The worst case is amorphous silicon, where a 33% reduction in photocurrent is predicted for a dust concentration of 4.25 mg/cm2. Similarly, crystalline silicon and CIGS technologies are predicted to be less affected, with 28.6% and 28.5% reductions in photocurrent, respectively. The same procedure was repeated with varying Air Mass (AM), tilt angle and dust concentration values to produce a soiling ratio table for different technologies under different AM, tilt angle and dust concentration values. Copyright © 2012 John Wiley & Sons, Ltd.

Accurate calibration of mercury vapour measurements

Almost all measurements of mercury vapour, for example those to determine mass concentration in air, are currently ultimately traceable to the vapour pressure of mercury, usually via a bell-jar calibration apparatus. This allows a saturated concentration of mercury vapour in air to develop in a confined space in equilibrium with ambient conditions, from which a known mass of mercury can be removed for calibration purposes. Setting aside the uncertainty in the vapour pressure of mercury at a given temperature, the accuracy of vapour phase mercury determinations depends critically on fully understanding the operation and sensitivities of the mercury bell-jar apparatus. This paper discusses the thermodynamic and kinetic considerations that must be taken into account when using the bell-jar apparatus, provides the theoretical basis for understanding the operation of the bell-jar, and presents experimental data demonstrating the systematic biases which may be obtained if the bell-jar is used incorrectly. These biases depend on the temperature difference between the mercury vapour in the bell-jar and the syringe used to remove the mercury vapour from the bell-jar, but they may be well in excess of 10% under some operating conditions. The results from this study have been used to propose best practice solutions for mercury vapour calibrations using the bell-jar.