Atmospheric Environment (v.40, #25)

Emissions of monoterpenes linalool and ocimene respond differently to environmental changes due to differences in physico-chemical characteristics by Steffen M. Noe; Paolo Ciccioli; Enzo Brancaleoni; Francesco Loreto; Ülo Niinemets (4649-4662).
We investigated the 13C-labeling kinetics of the emission of two major monoterpenes emitted by needles of Mediterranean conifer Pinus pinea L., monoterpene alcohol linalool and non-oxygenated monoterpene trans-β-ocimene. These data were further used to develop and parameterize a dynamics monoterpene emission model, predicting the emissions of monoterpenes with contrasting physico-chemical properties to environmental changes. All monoterpenes emitted were labeled by 13C in short pulse-labeling experiments. 13C-labeling experiments further indicated for these two monoterpenes comprising 77% of total emissions that a major part of the emissions of these two monoterpenes relied on recently synthesized carbon not on specific storage compartments within the resin ducts. However, labeling kinetics suggested existence of transient storage pools, located within the needle aqueous and lipid phases. For linalool, we found half-lives of 13 min for the aqueous phase storage and 3 h for the lipid phase while trans-β-ocimene exhibit an aqueous phase half-life of 2 and 15 min for the lipid phase, overall indicating that the transient storage due to limited monoterpene volatility can significantly alter the emission dynamics. The key physico-chemical characteristics determining the time constants of the transient storage pools were the Henry's law constant (liquid/gas phase partition coefficient) and the octanol/water (lipid/liquid) phase partition coefficient. As monoterpene Henry's law constants vary over four orders of magnitude and octanol/water partition coefficients over three orders of magnitude, the capacity for non-specific storage, and damping of the effects of rapidly changing environmental conditions is expected to strongly vary among different monoterpenes. Overall, our study suggests that non-specific storage due to limited volatility is a common phenomenon of common of plant-emitted compounds.
Keywords: 13C-labeling; Monoterpene emissions; Henry's law constant; Octanol/water partition coefficient; Dynamic model; Pinus pinea;

Comparison of CALPUFF and ISCST3 models for predicting downwind odor and source emission rates by Lingjuan Wang; David B. Parker; Calvin B. Parnell; Ronald E. Lacey; Bryan W. Shaw (4663-4669).
CALPUFF model and ISCST3 Gaussian dispersion models were evaluated for predicting downwind odor concentrations and back-calculating area source odor emission rates. The comparison between the predicted and field-sampled downwind concentrations indicates that the CALPUFF model could fairly well predict average downwind odor concentrations. However, ISCST3 tended to under predict downwind odor concentrations as compared to the measured concentrations. Both the CALPUFF and ISCST3 models failed to predict peak odor concentrations using the constant average emission rate. Odor emission rates obtained by back-calculating fluxes using CALPUFF and ISC models with the same field measurements of downwind odor concentrations are significantly different. It indicates that back-calculated emission rates are model specific. The modeled emission rates tended to be higher than flux chamber source sampling results. The flux chamber protocol may under-estimate odor emission rates.
Keywords: Odor modeling; CALPUFF; ISCST3; Odor emission rate; Odor flux;

The results from studies of the effects of several factors on the accurate measurement of particulate matter (PM) mass collected on ambient air monitoring filters are described. The main investigation quantifies the effect of humidity on the mass of blank filters of some commonly used materials in Europe, namely quartz fibre, glass fibre and PTFE-bonded glass fibre. Supplementary work investigates the effect of humidity on the mass of sampled PM, and effects of storage and transport are also reported.A number of fundamental problems associated with the weighing of filters are quantified and, for the materials and factors studied, we conclude that quartz filters are less well suited to high accuracy determinations of PM mass than glass fibre filters, while PTFE-bonded glass fibre filters are better than both. Though other factors also have an important role in the choice of filter material, we believe that the results form a useful addition to the limited amount of information available in this area.
Keywords: Particulate matter; Gravimetry; Filters; Air monitoring; Health;

Origin and variability of particulate matter (PM10) mass concentrations over the Eastern Mediterranean by E. Gerasopoulos; G. Kouvarakis; P. Babasakalis; M. Vrekoussis; J.-P. Putaud; N. Mihalopoulos (4679-4690).
Five-year PM10 concentrations (2000–05) at Heraklion (urban), Crete, and concurrent measurements of TSP and PM10 (2001–02 and 2004–05, respectively) at Finokalia (background) have been used to discriminate between the various sources of PM over the area and investigate the factors that control their levels. PM10 concentrations at Heraklion (51±33 μg m−3) and Finokalia (28±30 μg m−3) lie within the range found for urban and background-rural sites in the Eastern Mediterranean, respectively. Special focus has been given to the influence of transported dust from N. Africa, which is found to be more frequent during spring and fall. The additional effect from local sources has been also calculated at Heraklion (about 20 μg m−3). The EU limit of 50 μg m−3 is exceeded at Heraklion, one in 4 days, during winter and spring (50% due to transported dust) and half of the days during summer and fall (pollution). At Finokalia exceedances are observed in winter and spring during one in 5 days, 80–100% of which are associated with dust events. The mass balance estimation for periods with no influence from dust shows that ions dominate the PM10 mass (40–60%) with dust and particulate carbonaceous matter (PCM) comprising the rest. During the identified dust outbreaks, the contribution of dust rises to 60–65%, while the contribution of ions declines to 30% and only 10% is PCM.
Keywords: Particulate matter (PM10); Chemical mass balance; Eastern Mediterranean;

Nitrogen and sulfur compounds in coastal Antarctic fine aerosol particles—an insight using non-destructive X-ray microanalytical methods by J. Osán; S. Török; B. Beckhoff; G. Ulm; H. Hwang; C.-U. Ro; C. Abete; R. Fuoco (4691-4702).
The capabilities of X-ray microanalytical methods, such as a near edge X-ray absorption fine structure (NEXAFS) investigation in conjunction with total reflection X-ray fluorescence (TXRF) analysis, as well as low-Z particle electron probe X-ray microanalysis (EPMA) to characterize fine Antarctic aerosol samples are demonstrated. Both techniques provided information on low-Z elements such as C, N and O. Size-segregated fine aerosol samples were collected at the Italian base at Terra Nova Bay (Antarctica) in February 2004. For comparative purposes, aerosol samples were also collected near the sea-shore in Alghero (Sardinia, Italy), in June 2004. The TXRF-NEXAFS measurements were carried out at the PGM monochromator beamline for undulator radiation in the PTB laboratory at the electron storage ring BESSY II. It was possible to quantify the molar ratio of ammonium and nitrate based on linear combinations of standard reference spectra of (NH4)2SO4 and NaNO3. Using TXRF-NEXAFS, the ammonium-to-nitrate ratio was determined in Antarctic fine aerosols collected from less than 2 m3 of air, i.e. considerably lower than the sampling volumes usually used for ion chromatography analyses (30 m3). This reduced sampling volume can enable the characterization of Antarctic aerosols to be done in higher temporal resolution. For Antarctic fine aerosols in the size range of 0.25–0.5 μm, nitrogen was observed to be present as almost entirely ammonium species. When the size of aerosol particles increases in the range of 0.25–2 μm, the content of ammonium decreases and yet the content of nitrate increases. An aerosol sample collected at Terra Nova Bay was investigated by the use of low-Z particle EPMA at a liquid nitrogen temperature in order to minimize beam damage of nitrogen-rich particles. Single-particle analytical results of 160 individual particles supported the TXRF-NEXAFS's observation that both ammonium-rich and nitrate-rich particles exist in the size range of 1–2 μm. Some particles were observed to contain both ammonium and nitrate species and yet pure ammonium nitrate particles were not encountered. The stoichiometry of the main chemical component of particles containing nitrogen and sulfur as major elements was found to be NH4HSO4.
Keywords: Antarctica; Aerosols; Non-destructive X-ray methods; TXRF; NEXAFS; Low-Z EPMA;

Comparison of voltammetry and inductively coupled plasma-mass spectrometry for the determination of heavy metals in PM10 airborne particulate matter by Daniela Buzica; Michel Gerboles; Annette Borowiak; Pier Trincherini; Rosanna Passarella; Valerio Pedroni (4703-4710).
The potential of the voltammetry method was examined for the determination of heavy metals in ambient air particulate matter (PM10) on quartz filter. Cd, Pb, Cu, Zn, As were determined by anodic stripping voltammetry while adsorptive stripping voltammetry was used for the analysis of Ni. The method detection limit of these metals were 9.3, 0.1, 0.8, 0.3, 0.4, 0.1 ng m−3 for Zn, Cd, Pb, Cu, Ni and As, respectively. In addition, the analysis of a Certified Reference Material NIST 1648, yielded recoveries between 92% and 103%. Consequently, both the detection limit and recovery of the voltammetric method satisfy the requirements of the European Standard for the analyses of heavy metals in PM10 (EN 14902). A comparison of the inductively coupled plasma-mass spectrometry (ICP-MS) and voltammetry method on the NIST 1648 and PM10 filters showed the differences between them remained well within the level of uncertainty on the NIST 1648 requested by European Directives for heavy metals (25% for Pb and 40% for As, Cd and Ni, respectively). In addition to its compliance with legislations, the voltammetry method benefits from low investment cost and the potential of complete automation. As such, one may expect voltammetry to provide a reliable alternative to the European laboratories in charge of ambient air monitoring at the time when the European Directives require to measure heavy metals in PM10 on a regularly basis.
Keywords: Voltammetry; PM10; Heavy metals; ICP-MS;

Temporal trends and weekend–weekday differences in benzene and 1,3-butadiene concentrations were investigated at a number of sites in the Houston, Texas area using monitoring data collected by the Texas Commission on Environmental Quality (TCEQ). The dataset included two networks, the Community Air Toxics Monitoring Network (CATMN), which has 24-h measurements every six days, and the Photochemical Assessment Monitoring System (PAMS), which includes hourly measurements. The period for data analysis was 1997–2004. The CATMN network had the larger number of stations. Over this time period, the network average benzene concentration at the CATMN stations was 0.93 ppb with individual stations ranging within a factor of about two of this network average. The network average 1,3-butadiene concentration was 0.57 ppb with most individual stations ranging within a factor of about six of this network average. These ranges suggest more spatial variability for 1,3-butadiene concentrations compared to benzene concentrations. Variations in meteorology can influence benzene and 1,3-butadiene concentrations making it difficult to examine the true concentration trends. Therefore, a generalized additive model (GAM) was used in a time-series analysis to adjust the benzene and 1,3-butadiene concentrations for variations caused by daily differences in meteorology. The analysis revealed very little difference in the weekend–weekday concentrations, except for a block of time during the morning rush hour where weekday concentrations were slightly higher. The GAM analysis showed that there was a significant decrease in the benzene and 1,3-butadiene concentrations throughout the trend period of 1997–2004. The average annual percent decrease across the sites was 1.7% for benzene for a meteorologically adjusted model (MA model) and 3.2% for a model without meteorological adjustment (raw trend or RT model). For 1,3-butadiene, there was a 3.7% annual decrease for MA model and 5.1% annual decrease for the RT model. For the five stations with data for each of the 8-year period, the mean overall benzene reduction over the 8-year trend period was 20% for the MA models and 29% for the RT models. For 1,3-butadiene, the reduction was 30% for the MA models and 35% for the RT models.
Keywords: Benezene; Temporal trends; Houston;

Characteristics of gaseous HNO2, HNO3, NH3 and particulate ammonium nitrate in an urban city of Central Taiwan by Yu-Chi Lin; Man-Ting Cheng; Wei-Yu Ting; Chiun-Rong Yeh (4725-4733).
Simultaneous measurements of ambient gaseous species HNO2, HNO3, NH3 and particulate NO3 and NH4 + were carried out during 2002 in the city of Taichung, Taiwan. An annular denuder system (ADS) was used for the measurements. The annual mean concentrations of HNO2, HNO3, NH3, NO3 and NH4 + were 2.9, 1.9, 8.5, 6.0 and 4.6 μg m−3, respectively. Daily and seasonal patterns were observed. The concentration of HNO2 was found to be lower during the summer, whereas HNO3 and NH3 displayed higher concentrations. On the other hand, particulate NO3 exhibited significant seasonal variation with lower levels observed in autumn and summer. The average nitrogen conversion ratios (Fn) in the spring and summer were 21%, approximately 1.5 factor higher than those in the autumn and winter. Moreover, the photochemical reaction played an important role for the oxidation of NO2 to nitrate since Fn was well correlated with O3 during daytime in all seasons. During nighttime, Fn correlated well with relative humidity. These results suggest that the factors affecting nitrogen conversion ratio are different during daytime and nighttime. The present findings are compared with similar measurements worldwide, and the prevailing mechanisms are discussed.
Keywords: Acidic gases; Ammonium nitrate; Nitrogen conversion ratio; Annular denuder system; Daytime; Nighttime;

High winds that blow sand from the desert regions of central Asia to points east are commonly known as Asian dust storms (ADS). In this paper we study the impact of an ADS on the PM2.5 aerosol extant in Tainan, a city in southern Taiwan. PM2.5 aerosol was collected at an urban and a coastal site in Tainan before the ADS (4–12 January 2001), during the ADS (13–16 January 2001), and the following summer (3–12 June 2001). Total PM2.5 mass was highest at both sites during the ADS despite already moderately high levels of PM2.5 beforehand, demonstrating that the ADS brought with it a significant amount of PM2.5 mass. The mass percentage of Ca2+ in PM2.5 increased noticeably during the ADS and there was a higher non-sea-salt SO4 2−/elemental carbon ratio. This latter change was due to a heightened level of non-sea-salt SO4 2−, which has a serious impact on air quality in southern Taiwan, and was likely sourced from sulfur integrated into the ADS aerosol as it passed major cities and industrial districts in China. The percentage water content in PM2.5 was at its lowest during the ADS. This was despite high levels of hygroscopic sulfate in the ADS aerosol and indicates that sulfate in the ADS may combine with Ca2+ to form CaSO4, a major component of ADS dust and one that does not have strong hygroscopic characteristics. Water content was at its highest in summer when winds arrive in Taiwan with elevated sea salt concentrations, having spent several days traversing the South China Sea. Non-ADS urban site aerosols were weakly acidic while coastal site aerosols were weakly alkaline. Urban site acidity was always higher than equivalent to coastal site acidity, due to locally produced acidic aerosols. Acidity peaked during the ADS, however, as a result of additional acidic aerosols transported by the ADS from urban and industrial regions in China.
Keywords: Asian dust storms; Long-range transport; Chemical compositions; Aerosol acidity; Water content;

In this study, the chemical characteristics of winter aerosol at four sites in southern Taiwan were determined and the Gaussian Trajectory transfer coefficient model (GTx) was then used to identify the major air pollutant sources affecting the study sites. Aerosols were found to be acidic at all four sites. The most important constituents of the particulate matter (PM) by mass were SO4 2−, organic carbon (OC), NO3 , elemental carbon (EC) and NH4 +, with SO4 2−, NO3 , and NH4 + together constituting 86.0–87.9% of the total PM2.5 soluble inorganic salts and 68.9–78.3% of the total PM2.5–10 soluble inorganic salts, showing that secondary photochemical solution components such as these were the major contributors to the aerosol water-soluble ions. The coastal site, Linyuan (LY), had the highest PM mass percentage of sea salts, higher in the coarse fraction, and higher sea salts during daytime than during nighttime, indicating that the prevailing daytime sea breeze brought with it more sea-salt aerosol. Other than sea salts, crustal matter, and EC in PM2.5 at Jenwu (JW) and in PM2.5–10 at LY, all aerosol components were higher during nighttime, due to relatively low nighttime mixing heights limiting vertical and horizontal dispersion. At JW, a site with heavy traffic loadings, the OC/EC ratio in the nighttime fine and coarse fractions of approximately 2.2 was higher than during daytime, indicating that in addition to primary organic aerosol (POA), secondary organic aerosol (SOA) also contributed to the nighttime PM2.5. This was also true of the nighttime coarse fraction at LY. The GTx produced correlation coefficients (r) for simulated and observed daily concentrations of PM10 at the four sites (receptors) in the range 0.45–0.59 and biases from −6% to −20%. Source apportionment indicated that point sources were the largest PM10 source at JW, LY and Daliao (DL), while at Meinung (MN), a suburban site with less local PM10, SO x and NO x emissions, upwind boundary concentration was the major PM10 source, followed by point sources and top boundary concentration.
Keywords: PM2.5; PM2.5–10; Spatial variations; Chemical composition; Source–receptor relationship;

Chemical composition and photochemical formation of hydroxyl radicals in aqueous extracts of aerosol particles collected in Okinawa, Japan by Takemitsu Arakaki; Yukiko Kuroki; Kouichirou Okada; Yoshihide Nakama; Hirotsugu Ikota; Mika Kinjo; Tomihiko Higuchi; Masaya Uehara; Akira Tanahara (4764-4774).
We investigated the chemical composition and photochemical formation of hydroxyl (OH) radicals in the water-soluble fractions (WSF) of aerosol particles collected in Okinawa, Japan. Bulk aerosol samples were collected for 2–7 days at a time by a high-volume air sampler over a 3-month period. Major ions present in the WSF solutions were SO4 2−, Na+, and Cl. Sulfate ion concentrations were much higher when Yellow Sand events occurred. The mass-based Cl/Na+ ratio found in the WSF solutions averaged 49.7%, much lower than the ratio in seawater, indicating that chlorine was lost from the aerosol particles. A negative correlation (R=−0.67) was found between the Cl/Na+ ratio and the concentration of non-sea-salt–SO4 2−. We confirmed the photochemical formation of OH radicals in the study samples using illumination experiments at 313 nm. The apparent quantum yields of OH radical photoformation, based on the total absorbance at 313 nm, ranged from ND to 0.0017, with a mean±1 SD of 0.0010±0.0005. Hydroxyl radical photoformation rates from nitrate and nitrite photolyses, estimated based on nitrate and nitrite ion concentrations and our illumination conditions, averaged 32±24% and <10%, respectively, of the total formation rates. Hydroxyl radical photoformation rates were strongly correlated with total dissolved iron concentrations (R=0.88). A correlation also existed between OH radical photoformation rates and dissolved organic carbon concentrations (R=0.69).
Keywords: Hydroxyl radical; Bulk aerosols; Asia; Photochemistry; Okinawa;

Measurements of elements, sulphate and SO2 in Nuuk Greenland by Henrik Skov; Peter Wåhlin; Jesper Christensen; Niels Z. Heidam; Dorthe Petersen (4775-4781).
The Greenlandic population is known to be exposed to heavy metals and persistent organic compounds (POPs) depending on the fraction of their diet coming from sea animals. Long-range atmospheric transport of air pollution to western Greenland, possibly from Canada or USA and in episodes also from Eurasia, is suspected to be a main cause.At Lille Malene Mountain close to Nuuk, the capital of Greenland, continuous monitoring of heavy metals as well as SO2 and sulphate were carried out by a filter pack system. The results are presented and discussed in this article. Sources were identified by a receptor model (COPREM), and model calculations of the concentrations were performed with an Eulerian model (DEHM).The levels of particle bound heavy metals and sulphur were very low. Analysis of data by COPREM showed that sea spray and crustal dust were the dominant source of inorganic particulate mass and that anthropogenic sources contributed with less than 8% of the inorganic particle mass.The measured levels of SO x (sum of SO 4 2 - and SO2) and Pb in Nuuk were reproduced by DEHM. However, the very low measured values of SO x and Pb concentrations made it impossible to use them to improve and develop model performance of DEHM.
Keywords: Atmosphere; COPREM; DEHM; PIXE; Long-range transport; Sources; Elements;

Atmospheric N- and S-fluxes to a spruce forest—Comparison of inferential modelling and the throughfall method by Frank Zimmermann; Kirsten Plessow; Ronald Queck; Christian Bernhofer; Jörg Matschullat (4782-4796).
The vertical transport of reactive nitrogen gases such as NH3 and HNO3, and of NH4 and NO3 particle fluxes, and the dry deposition of SO2 and sulphate particles was studied within the BMBF-project VERTIKO (Vertical Transport under Complex Natural Conditions). An inferential model, based on measurements of meteorological and air chemistry parameters and the throughfall method, using wet precipitation and throughfall measurements as input data for the canopy budget model, were used for dry deposition estimates. The deposition calculations were performed with the newly compiled SVAT model SPRUCEDEP. This model uses 0.5 h meteorological data, and ambient air concentration figures with a time resolution of 0.5 h (SO2, NO, NO2) and 2 weeks (HNO2, HNO3, NH3, particulate NO 3 - , SO 4 2 - , and NH 4 + ). Compensation points in the inferential model were assumed to be 0 ppbv for NH3 and 1.7 ppbv for NO x . Annual dry deposition rates were estimated for oxidised N-species (NO, NO2, HNO2, HNO3, pNO3) to amount to about 6.1 kg ha−1, for reduced N (NH3, pNH4) to 6.4 kg ha−1, and for S (SO2, pSO4) to 10.1 kg ha−1 for the years 2002–2004. The relative contribution of dry to total (dry+wet) deposition was 63% for sulphur, 61% for oxidised nitrogen, and 57% for reduced nitrogen. Total S-deposition and oxidised N-species showed good agreement with data from throughfall measurements and a canopy exchange model. For reduced N-species, the modelling approach yielded a considerably higher deposition in the vegetation period which could be explained by the inability of canopy throughfall measurements to account for stomatal uptake of NH3 and probably microbial utilisation. The good agreement of the two methods suggests that a combination of the two modelling approaches may be an alternative to cost-intensive micrometeorological measurements for the determination of dry deposition fluxes on weekly or biweekly basis and long-term monitoring of total deposition.
Keywords: Dry deposition; Inferential model; S-compounds; N-compounds; SVAT model; Throughfall; Canopy budget model;

Loss of fine particle ammonium from denuded nylon filters by Xiao-Ying Yu; Taehyoung Lee; Benjamin Ayres; Sonia M. Kreidenweis; William Malm; Jeffrey L. Collett (4797-4807).
Ammonium is an important constituent of fine particulate mass in the atmosphere, but can be difficult to quantify due to possible sampling artifacts. Losses of semivolatile species such as NH4NO3 can be particularly problematic. In order to evaluate ammonium losses from aerosol particles collected on filters, a series of field experiments was conducted using denuded nylon and Teflon filters at Bondville, IL (February 2003), San Gorgonio, CA (April 2003 and July 2004), Grand Canyon NP, AZ (May, 2003), Brigantine, NJ (November 2003), and Great Smoky Mountains National Park (NP), TN (July–August 2004). Samples were collected over 24 h periods. Losses from denuded nylon filters ranged from 10% (monthly average) in Bondville, IL to 28% in San Gorgonio, CA in summer. Losses on individual sample days ranged from 1% to 65%. Losses tended to increase with increasing diurnal temperature and relative humidity changes and with the fraction of ambient total N(−III) (particulate NH4 ++gaseous NH3) present as gaseous NH3. The amount of ammonium lost at most sites could be explained by the amount of NH4NO3 present in the sampled aerosol. Ammonium losses at Great Smoky Mountains NP, however, significantly exceeded the amount of NH4NO3 collected. Ammoniated organic salts are suggested as additional important contributors to observed ammonium loss at this location.
Keywords: Ammonium nitrate; Ammonia; PM2.5; Nylon filter; Teflon filter; Annular denuder; IMPROVE;