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Atmospheric Environment (v.40, #19)
Estimating emissions from fires in North America for air quality modeling by Christine Wiedinmyer; Brad Quayle; Chris Geron; Angie Belote; Don McKenzie; Xiaoyang Zhang; Susan O’Neill; Kristina Klos Wynne (pp. 3419-3432).
Fires contribute substantial emissions of trace gases and particles to the atmosphere. These emissions can impact air quality and even climate. We have developed a modeling framework to estimate the emissions from fires in North and parts of Central America (10–71°N and 55–175°W) by taking advantage of a combination of complementary satellite and ground-based data to refine estimates of fuel loadings. Various satellite drivers, including the MODIS Thermal Anomalies Product, the Global Land Cover Characteristics 2000 dataset, and the MODIS Vegetation Continuous Fields Product were used in conjunction with data mined from literature to determine fire location and timing, fuel loadings, and emission factors. Daily emissions of particulate matter and numerous trace gases from fires were estimated using this method for three years (2002–2004). Annual emission estimates differ by as much as a factor of 2 (CO emissions for North America ranged from 22.6 to 39.5Tgyr−1). Regional variations in emissions correspond to different fire seasons within the region. For example, the highest emissions from Central America and Mexico occur in the late spring whereas the highest emissions from the United States and Canada occur during the summer months. Comparisons of these results with other published estimates of CO emission estimates from fire show reasonable agreement, but substantial uncertainties remain in the estimation techniques. We suggest methods whereby future emissions models can reduce these uncertainties.
Keywords: Fires; Emissions; North America; Carbon monoxide; Particulate matter; Agricultural fires
Attribution of sulfate aerosols in Federal Class I areas of the western United States based on trajectory regression analysis by Jin Xu; Dave DuBois; Marc Pitchford; Mark Green; Vic Etyemezian (pp. 3433-3447).
Atmospheric aerosols can significantly reduce visibility and result in regional haze. The Clean Air Act amendments established a national visibility goal to remedy existing impairment and prevent future impairment in Federal Class I areas (national parks and wilderness areas designated by Congress), most of which are in the western United States. In order to identify the major source regions of the atmospheric aerosols in the Class I areas of the western United States, air mass backtrajectories were calculated for 84 western Class I areas every 3h at a starting height of 500m over the years 2000–2002 using the NOAA HYSPLIT v4.6 model. For each Class I area, multiple-linear regression between the Interagency Monitoring of Protected Visual Environments (IMPROVE) measured sulfate concentrations and the air mass residence times in the pre-defined potential source regions was conducted. Results suggest that shipping and other port emissions from along the Pacific Coast contributed significantly to atmospheric aerosol concentrations over large areas of the western United States.
Keywords: Haze; PM; 2.5; Ship emissions; California; Pacific Coast
Heterogeneous ozonation kinetics of polycyclic aromatic hydrocarbons on organic films by T.F. Kahan; N.-O.A. Kwamena; D.J. Donaldson (pp. 3448-3459).
The room temperature heterogeneous reaction rates of gas-phase ozone with naphthalene, anthracene, fluoranthene, phenanthrene, pyrene, and benzo[ a]pyrene were measured over a range of ozone concentrations from 3.5×1014 to 2.3×1016molec.cm−3. The polycyclic aromatic hydrocarbons (PAHs) were dissolved in organic mixtures composed of octanol or decanol along with proxies for compounds known to be present in “urban grime� films. In all cases, the reaction kinetics were well-described by the Langmuir–Hinshelwood mechanism, which suggests a surface reaction. The adsorption of PAHs to the air–organic interface was confirmed by an adsorption isotherm of anthracene. The presence of the additional organic compounds generally did not affect the reaction rates; however, unsaturated species such as oleic acid and squalene reduced the observed rates significantly.
Keywords: Heterogeneous chemistry; Kinetics; Ozone; Polycyclic aromatic hydrocarbons; Urban films; Air quality
Secondary limonene endo-ozonide: A major product from gas-phase ozonolysis ofR-(+)-limonene at ambient temperature by A.W. Nørgaard; J.K. Nøjgaard; K. Larsen; S. Sporring; C.K. Wilkins; P.A. Clausen; P. Wolkoff (pp. 3460-3466).
A 16s old gas-phase ambient temperature and 1% relative humidity reaction mixture of ozone and R-limonene (ca. 1:10) was sampled on XAD-2 resin followed by pressurized liquid extraction with dichloromethane at ambient temperature. Low temperature on-column injection and gas chromatography (GC) revealed equal amounts of diastereomeric secondary endo-limonene ozonides, in addition to 4-acetyl-1-methyl-cyclohexene (AMCH), 3-isopropyl-6-oxo-heptanal (IPOH), and endo-limonene mono-epoxides. The secondary endo-limonene ozonides began to decrease at extraction temperature above150∘C and were absent at200∘C. Their formation was unaffected by an increase of the relative humidity to 15%. The identification of the secondary limonene ozonides was confirmed by (1) unique consecutive losses of OH andH2O2, respectively, from the protonated quasi-molecular ion in GC-chemical ionization mass spectrometry mode (isobutane), in addition to high resolution mass determination of [M-OH] and [M-H2O2] ions in EI mode; (2) comparison of mass spectral data to that of synthesized secondary endo-limonene ozonides; and (3) oxidation of dimethyl sulfide to dimethyl sulfoxide and subsequent increase of IPOH.
Keywords: Endo-limonene ozonide; Gas-phase ozonolysis; Limonene; Pressurized liquid extraction
A microscopic and chemical study of airborne coarse particles with particular reference to sea salt in chile at 30°s by M. Fiebig-Wittmaack; E. Schultz; Cordova A.M. Córdova; C. Pizarro (pp. 3467-3478).
Along a transect ranging from the Pacific to the summit of Cerro Tololo at 2200m above sea level (a.s.l.) in Chile at 30°S, coarse particle concentration was measured at three sites in a one-year study from December 2002 to 2003. The climate of this area is characterised by semi-arid conditions. Intensive thermally induced valley winds occurring particularly in summer, possibly transporting polluted air masses form the coastal area into the mountain region. This may question the background characteristics of Cerro Tololo as suitable site in Chile for a monitoring station of the Global Atmospheric Watch (GAW) program. Particle sampling by a passive sampling technique was employed to analyse composition of particles, find out effective sources and trace possible transport of suspended particles in this area. Temporal resolution of sampling was one week. Composition and size distribution of weekly deposition samples were determined by microscopic single particle analysis and bulk ionchromatographic analysis. Coarse particle concentration decreases differently along the transect as a function of occurring sources and depending on reactivity of components. The percentage of a black particle component remains at the same level of about 4% at all the three sites, confirming biomass burning as a wide-spread pollution. The percentage of sea salt, by contrast, amounts on average about 50% of total coarse particle concentration at the coastal area, quickly decreasing to about 10% along the transect due to losses by particle deposition and chemical reaction during transport. Ammonium shows a different behaviour, characterised by enhanced values at the central part of the transect, due to emissions from agricultural activities in this area. A shift in size distribution between the different sites is explained not only by gravitational fractionation but also by chemical conversion during transport. As a result, it is concluded that an impact of contaminated air at Cerro Tololo cannot be ruled out at a low level particularly in summer. However, the amount, composition and size distribution of the coarse fraction rather confirms the pristine area characteristics of Cerro Tololo and its background conditions.
Keywords: Coarse particles; Sea salt; Passive sampling; Microscopic analysis; Ionchromatography
A two-dimensional analytical model for the dispersion of air-pollutants in the atmosphere with a capping inversion by Maithili Sharan; Manish Modani (pp. 3479-3489).
A two-dimensional steady-state mathematical model has been developed for the pollutant released from an elevated source in an inversion layer by parameterizing vertical eddy diffusion coefficient as a generalized functional form of downwind distance from the source and wind speed as power-law function of the height above the ground. A closed form analytical solution of the resulting partial differential equation with the physically relevant boundary conditions is obtained. The developed model is validated with the data sets obtained at the Northern part of Copenhagen and from the EPRI (Electric Power Research Institute) field experiment conducted at Kincaid in unstable conditions. In stable conditions, the performance of the present model is analyzed with the data set obtained at the Hanford diffusion grid. The present model is performing better to Gaussian model in case of Copenhagen and gives comparable prediction for EPRI data set. For the Hanford data set in stable conditions, present model gives under predicting trend. A slight variation (upto 1°) in the value ofσ φ observed in Hanford diffusion experiment, the performance of the present model improves significantly. The proposed model can also be used for computing the concentration distribution of a pollutant released from an infinite line source perpendicular to the direction of the mean wind.
Keywords: Mathematical model; Near-source dispersion; Crosswind-integrated concentration; Power-law; Eddy diffusivity; Eigen-function expansion; Validation
Systems approach to evaluating sensor characteristics for real-time monitoring of high-risk indoor contaminant releases by Priya Sreedharan; Michael D. Sohn; Ashok J. Gadgil; William W. Nazaroff (pp. 3490-3502).
Rapid detection of toxic agents in the indoor environment is essential for protecting building occupants from accidental or intentional releases. While there is much research dedicated to designing sensors to detect airborne toxic contaminants, little research has addressed how to incorporate such sensors into a monitoring system designed to protect building occupants. To design sensor systems, one must quantify design tradeoffs, such as response time and accuracy, and select values to optimize the performance of an overall system. We illustrate the importance of a systems approach for properly evaluating such tradeoffs, using data from tracer gas experiments conducted in a three-floor building at the Dugway Proving Grounds, Utah. We explore how well a Bayesian interpretation approach can characterize an indoor release using threshold sensor data. We use this approach to assess the effects of various sensor characteristics, such as response time, threshold level, and accuracy, on overall system performance. The system performance is evaluated in terms of the time needed to characterize the release (location, amount released, and duration). We demonstrate that a systems perspective enables selecting sensor characteristics that optimize the system as a whole.
Keywords: Sensor system; Chemical sensor; Inverse modeling; Bayes Monte Carlo; Buildings
Investigation of air–water exchange of formaldehyde using the water surface sampler: Flux enhancement due to chemical reaction by Remzi Seyfioglu; Mustafa Odabasi (pp. 3503-3512).
Laboratory (n=30) and field (n=89) experiments were conducted using the water surface sampler (WSS) to investigate the air–water exchange of formaldehyde (HCHO). Average gas-phase overall mass transfer coefficients ( Kg) calculated using concurrently measured gas-phase fluxes and air concentrations were 0.58±0.21 and 0.25±0.12cms−1 for laboratory and field experiments, respectively. Kg values were compared to the predictions of two different models, one previously developed based on experiments performed with the WSS (considering no enhancement, Model I) and, one previously published by others (accounting the enhancement due to chemical reaction, Model II). The predictions of Model I (0.17±0.07cms−1) significantly underestimated the laboratory determined Kg while the predictions of Model II (0.58±0.17cms−1) were in excellent agreement with those measured. Under the laboratory conditions, the flux enhancement of HCHO mass transfer due to chemical reaction ranged between 2.8 and 4.1 times (average±SD, 3.6±0.4).For field studies, the average measured Kg was significantly lower than the average predictions of Model I (0.44cms−1) and the Model II (0.90cms−1). It was shown that the difference between the modeled and experimental Kg values was due to the propagated effect of interfering factors with the measured gas-phase flux (i.e., decreased deposition due to non-zero water concentration, sulfite/bisulfite interference, and losses due to chemical degradation or transformation).The results of this study indicated that the formaldehyde transfer into the surface waters is significantly enhanced due to chemical reaction and air–water exchange may be an important removal mechanism for atmospheric HCHO. The results also suggest that transformation and degradation of aqueous HCHO may be significant under field conditions.
Keywords: Dry deposition; Formaldehyde; Air–water exchange; Mass transfer coefficient; Flux enhancement
Ozone variations through vehicle emissions reductions based on air quality monitoring data in Taipei City, Taiwan, from 1994 to 2003 by S.-C. Shuenn-Chin Chang; C.-T. Chung-Te Lee (pp. 3513-3526).
The ozone (O3) ambient air quality is evaluated using two indices in Taiwan: the daily maximum O3 concentration (O3,max) greater than 120ppb and the daily 8-h O3 moving average (O3,8h) greater than 60ppb. Results of air quality monitoring data from 1994 to 2003 in Taipei City indicate that the 99th percentile O3,max was reduced, but those below the 90th percentile O3,max obviously increased and days with O3,8h greater than 60ppb were doubled after the reduction of O3 precursor emissions. Because of Taipei's unique vehicle emissions pattern in having more motorcycles than cars, Sunday, as compared to weekdays, has more reductions of non-methane hydrocarbons (NMHCs) than NO X. This results in Sunday O3,max being lower than weekday O3,max average for those days with O3,max exceeding 80ppb. On the contrary, if O3,max is lower than 60ppb, Sunday O3,max is relatively higher than weekday O3,max average, due to the reduced NO titration effect. In addition, our evaluations of O3 levels with respect to the ambient air quality standards show that the number of Sundays with O3,max greater than 120ppb is fewer than the number average of weekdays with O3,max exceeding 120ppb for every month. Concerning O3,8h, only in June, July, and August, when the meteorological conditions favor O3 production, does the reduction of Sunday vehicle exhaust reduce the number of days with O3,8h greater than 60ppb. However, in September and October, the reduction of Sunday vehicle exhaust will increase the number of days. The results presented in this paper indicate that the O3 pollution in Taipei City is VOC-limited. Thus, for a greater reduction in NMHCs, like the Sunday vehicle reduction in Taipei City, the upper percentile O3,max is reduced more and those below the moderately high percentile O3,max are increased less.
Keywords: Air quality monitoring; Ozone variation; Ozone precursor reduction; Ozone control strategy
What can size distribution of spheroidal carbonaceous particles reveal about their source? by Vukic Jasna Vukić; Jan Fott; Adam Petrusek; Sanda Radek Šanda (pp. 3527-3535).
Spheroidal carbonaceous particles (SCPs) are produced by fossil fuel burning and are good indicators of the extent of industrial pollution. The purpose of our study was to examine whether the size distribution of SCPs reflects well the distance from the particle source and the character of SCP atmospheric transport. We analysed the size distribution of SCPs in surface sediments of six water bodies in the Czech Republic, and in the vertical profile of a whole sediment core from one of the sites; all samples were collected in 1994–1995. The presence of more than 20% of particles with a diameter exceeding 40μm in the sediments indicated a local origin of SCPs, with the source within a few kilometres. The SCP size distribution in the surface sediments agreed in general with the location of SCP sources around the sites, with average SCP diameters over 30μm near the local source, 17–23μm in polluted areas not directly affected by local sources, and less than 12μm in a relatively clean region. However, results from the vertical profile of the whole core revealed that a change in the combustion regime of the main source may significantly affect the SCP size distribution as well. This suggests that the use of the SCP size distribution as the sole indicator of the distance from the particle source is limited. The presence of a relatively high proportion of particles over 40μm in diameter at all studied sites demonstrates that particle retention equipment was not sufficiently used in the early 1990s in the Czech Republic. Our results show that the value of the data obtained from SCP analyses can be enhanced by evaluation of the size distribution of the particles.
Keywords: Fly ash particles; SCP; Lake sediment; Atmospheric transport; Historical reconstruction
Long-range aerosol transport from Europe to Istanbul, Turkey by T. Kindap; A. Unal; S.-H. Chen; Y. Hu; M.T. Odman; M. Karaca (pp. 3536-3547).
Northern and western parts of Turkey frequently experience air pollution episodes. Transport of air pollutants from Europe to these regions has not been studied sufficiently. This study aims to identify and analyze the contribution of long-range aerosol transport to air pollution in the city of Istanbul. Istanbul is the largest urban settlement in Northwestern Turkey, with more than 12 million inhabitants in the metropolitan area.The methodology developed for the study as well as the results obtained are presented here. Meteorological modeling provided the wind fields that were first used in a trajectory analysis and then, along with other meteorological data, input to an advanced air quality model. Backward trajectories suggested that when the prevailing wind direction is westerly or northwesterly, such as in the case of the episode studied here, a significant fraction of the pollutants emitted from Europe may be transported to and deposited in Turkey. An emission processing module was developed to prepare the emission inputs required by the air quality modeling system. The long-range aerosol transport simulations demonstrated and quantified the source/receptor relationships between Europe and Turkey. For the selected episode, it has been found through model simulations that the responses of Istanbul background PM10 levels to the emissions of individual European countries can range from 0.5 to 13%. The response of Istanbul background PM10 concentrations can be as much as 26% according to the sensitivity analysis results, when anthropogenic emissions throughout Europe are changed by 50%. This result suggests that trans-boundary sources may be responsible for as much as half of the background PM10 in Istanbul.
Keywords: Air pollution; Trans-boundary aerosol transport; Emission processing; PM10
A probabilistic model for acute bystander exposure and risk assessment for soil fumigants by Richard Reiss; John Griffin (pp. 3548-3560).
There is currently significant regulatory interest in estimating exposures and risks to bystanders following applications of soil fumigants. Soil fumigants are generally volatile and some of the fumigant mass will escape the field causing downwind exposures to resident populations. Regulatory agencies in the US are currently considering implementing buffer zones for many of the fumigants. These buffer zones would provide a restricted-entry zone around fumigant applications to mitigate potential exposures. This paper describes a probabilistic dispersion modeling application that has been developed to address this issue. The Probabilistic Exposure and Risk Model for FUMigants (PERFUM) employs the Gaussian dispersion algorithms developed by the US Environmental Protection Agency (US EPA). The model adapts EPA air dispersion algorithms to develop probabilistic estimates of acute exposures to bystanders following fumigant applications. The model considers the potential variability in exposures caused by differences in mass emission rates of the fumigants and the meteorological conditions following the application. The model is generalized to model exposures for fumigants with different exposure averaging times of concern to regulators (1–24h), varying field sizes (up to 40acres), and field dimensions. PERFUM also outputs the probabilistic exposures both based on the whole population surrounding the field and for the maximally exposed location only. The model is non-proprietary and publicly available.
Keywords: Fumigants; Dispersion modeling; Probabilistic risk assessment
Land use planning and surface heat island formation: A parcel-based radiation flux approach by Brian Stone; John M. Norman (pp. 3561-3573).
This article presents a study of residential parcel design and surface heat island formation in a major metropolitan region of the southeastern United States. Through the integration of high-resolution multispectral data (10m) with property tax records for over 100,000 single-family residential parcels in the Atlanta, Georgia, metropolitan region, the influence of the size and material composition of residential land use on an indicator of surface heat island formation is reported. In contrast to previous work on the urban heat island, this study derives a parcel-based indicator of surface warming to permit the impact of land use planning regulations governing the density and design of development on the excess surface flux of heat energy to be measured. The results of this study suggest that the contribution of individual land parcels to regional surface heat island formation could be reduced by approximately 40% through the adoption of specific land use planning policies, such as zoning and subdivision regulations, and with no modifications to the size or albedo of the residential structure.
Keywords: Urban heat island effect; Climate change; Land use; Urban planning; Remote sensing; Surface heat island; Thermal infrared
Climate-relevant properties of primary particulate emissions from oil and natural gas combustion by Tami C. Bond; Birgit Wehner; Antje Plewka; Alfred Wiedensohler; Jost Heintzenberg; Robert J. Charlson (pp. 3574-3587).
We report emissions of mass, light absorption, particle number, chemical composition and size-resolved organic species from an industrial boiler that burned natural gas and residual oil. Organic compounds detected from oil combustion are mainly alkanes; it is not a major source of identifiable polyaromatic hydrocarbons. Elemental carbon (EC) and organic carbon (OC) make up approximately 38% and 15% of the particles from oil burning, respectively. Mass emissions from natural gas were below detection limits. A number peak of ultrafine aerosol (diameters lower than 10nm) was always associated with oil burning. Burning at full power produced the greatest number of particles in the accumulation mode. Natural gas also produced fine particles, but at a much lower rate. The emission rate of light-absorbing particles from this relatively new boiler is lower than that in current emission inventories. However, real-time measurements show a large contribution to emitted light absorption from boiler warm-up and transients, even those with very short durations. The measured absorption is best explained with a constant absorption cross-section for EC, rather than predictions based on size distribution or mixed aerosol; this finding is consistent with EC in fractal-aggregate form. We compare the emissions with those of a lignite stoker, which this boiler replaced during environmental cleanup in the mid-1990s. Emissions of mass, light absorption and particles are lowest from natural gas, but the oil boiler is also a substantial improvement: emissions of particulate matter are 100 times lower, and emitted absorption is three times lower. However, the oil-burning emissions have a greater net warming effect per mass than those of the lignite plant.
Keywords: Particle size distributions; Light absorption; Elemental carbon; Organic speciation; Technology change
Vapor pressure prediction for alkenoic and aromatic organic compounds by a UNIFAC-based group contribution method by William E. Asher; James F. Pankow (pp. 3588-3600).
A UNIFAC-based group contribution method is developed for predicting liquid vapor pressure(pLo) values of organic compounds, including molecules containing CC bonds. The method is an extension of UNIFAC-pLo.1 as developed by Asher et al. [2002. Estimating the vapor pressures of multi-functional oxygen-containing organic compounds using group contribution methods, Atmospheric Environment 36, 1483–1498] in which CO is the only type of sp2-bonded carbon considered. The current work is important due to the widespread interest in the physical behavior of organic compounds with sp2 carbon–carbon bonds, e.g., alkenes and aromatics. In the context of particulate matter (PM) formation in the atmosphere, condensable molecules of interest that contain sp2 bonds include initial oxidation products such as 4-oxo-but-2-enoic acid and 2,6-dihydroxybenzoic acid. UNIFAC-pLo.2 as developed here was based on experimentally determined, temperature-dependentpLo data for 39 alkene compounds, 26 aromatic compounds, and 81 saturated compounds. In order to check the method, an independent set of 22 alkene and 40 aromatic compounds with known volatilities was assembled. Vapor pressures for these compounds were estimated using UNIFAC-pLo.2 and the results compared to known values. The UNIFAC-pLo.2 method was found to predict vapor pressure within a factor of 1.8 and this accuracy was equal across the volatility range of the basis set (3×10−10 – 3×10−1atm). The SPARC method [Hilal, S.H., Carreira, L.A., Karickhoff, S.W., 1994. Estimation of chemical reactivity parameters and physical properties of organic molecules using SPARC. In: Murray, P.P.A.J.S. (Ed.), Quantitative Treatments of Solute/Solvent Interactions. Elsevier, Amsterdam] was also used to estimatepLo for the 22 alkene and 40 aromatic compounds in the test set. Comparing the results of SPARC with UNIFAC-pLo.2 shows that the UNIFAC-pLo.2 method was on average 50% more accurate than the SPARC. The combined basis and test sets totaled 81 saturated, 61 alkene, and 66 aromatic compounds which were then used to generate an overall set of UNIFAC-pLo.2 method coefficients.
Keywords: Vapor pressure estimation; UNIFAC; Atmospheric VOCs; Secondary organic aerosol; Organic particulate matter
Hydrocarbon emissions from a modern commercial airliner by Bruce E. Anderson; Gao Chen; Donald R. Blake (pp. 3601-3612).
We report selected carbon species emission indices (EIs) for a Rolls Royce RB211-535-E4 turbofan engine that were acquired during the NASA EXperiment to Characterize Aircraft Volatile Aerosol and Trace-species Emissions (EXCAVATE). Conducted during winter 2002, the mission focused upon characterizing the exhaust constituents of the NASA Boeing 757 aircraft during ground-based operation. Carbon species concentrations were determined by chromatographic analyses of whole air samples collected 10m behind the engine exit plane as engine power was varied from ground idle to about 60% of maximum rated thrust. Ambient air samples were also collected and analyzed to facilitate correction of calculated EIs for background concentrations. Results are consistent with previous observations and indicate that, on a relative basis, turbine engines emit considerable amounts of light hydrocarbon species at idle, but significantly lesser amounts at higher engine powers.
Keywords: Aircraft emission; Hydrocarbon emission indices; Turbine engine
Monoterpene source emissions from Chamonix in the Alpine Valleys by A. Rouviere Aurélie Rouvière; Guillaume Brulfert; Patrick Baussand; Jean-Pierre Chollet (pp. 3613-3620).
Measurements of volatile organic compounds (VOCs) and in particular biogenic VOCs were taken near Chamonix, in the alpine valleys within the framework of the POVA program (Alpine Valley Pollution). The general topics of the program were the comparative studies of air quality in the Chamonix and Maurienne valleys (France) and the modelling of atmospheric chemistry. The main objective is to characterize the pollution sources and study the relationship between atmospheric dynamics and pollution events. To do this, it was necessary to take into account all quantifiable and localizable sources. Measurements of VOCs showed an abnormally high quantity of monoterpene concentrations (around 10% in mass of the total VOC concentrations). Isoprene and monoterpenes produced mainly by vegetation are among the most abundant natural VOCs, but these measurements were carried out in winter and during this season biogenic emissions are weak. The aim of this present work is to determine and understand this phenomenon. Domestic heating, generally not taken into account in studies of outdoor air, had a considerable impact on terpene concentrations in the valley.
Keywords: Monoterpenes; Heating; Modelling; Wood combustion; Alpine valley
Ten years of light hydrocarbons (C2–C6) concentration measurements in background air in Finland by Hannele Hakola; Hellen Heidi Hellén; Tuomas Laurila (pp. 3621-3630).
Light hydrocarbons (C2–C6) have been measured at two background stations, Utö (EMEP station) and Pallas (GAW station), in Finland since 1994. Utö is a small, rocky island in the Baltic Sea southwest of the mainland and Pallas is located in Lapland. Canister samples were taken twice a week and analyzed in a laboratory using gas chromatography.Maximum concentrations are observed in winter due to the very limited amount of daylight and hence of hydroxyl radicals. During spring the concentrations start declining as more light becomes available, and for most of the compounds minimum concentrations are measured during summer. Concentrations are lower at Pallas than on Utö, indicating more aged air there. Only isoprene, ethene and propene have higher concentrations at Pallas, due to natural emissions. Higher concentrations are measured in air masses coming from Central Europe and Russia, whereas air masses coming from the North Sea and the Arctic are cleaner. During the ten years of measurements, the concentrations of ethyne, pentanes and hexanes have decreased by about 10–40%, although only few of these trends are significant. However, the compounds with long lifetimes (ethane and propane) show an increasing trend especially at Pallas. Butane concentrations are also increasing at Pallas. This can indicate an increase of the VOC emissions in areas more distant than Europe.
Keywords: Long-term trends; Voc emissions; EMEP; Ozone precursors; Gaw