Annular Denuder Research Articles

Causes of the elevated nitrate aerosol levels during episodic days in Taichung urban area, Taiwan

The purpose of this study is to explore the possible reasons accounting for elevated nitrate aerosol levels during high particulate days (HPD) in Taichung urban area of central Taiwan. To achieve this goal, simultaneous measurements of particulate and gaseous pollutants were carried out from September 2004 to April 2005 using an annular denuder system (ADS). The formation rate of NO 2 to nitrate aerosol, calculated using the relevant chemical reactions, was employed to interpret enhanced nitrate aerosol concentrations during HPD. The observations showed that nitrate concentration during HPD was 14 times higher than that during low particulate days (LPD). The average formation rate during HPD was 4.0% h −1, which was 3.1 times higher than that during LPD. The quantitative analysis showed that the formation rate was mainly influenced by temperature and relative humidity. Lower temperature and higher relative humidity led much nitrate aerosol formation in HPD. Moreover, the residence time analysis of air masses staying over the studied area showed that the slow-motion air retained high nitrate concentrations due to more nitrate aerosol converted from the precursors in NOx-rich areas.

Field inter-comparison of eleven atmospheric ammonia measurement techniques

Abstract. Eleven instruments for the measurement of ambient concentrations of atmospheric ammonia gas (NH3), based on eight different measurement methods were inter-compared above an intensively managed agricultural field in late summer 2008 in Southern Scotland. To test the instruments over a wide range of concentrations, the field was fertilised with urea midway through the experiment, leading to an increase in the average concentration from 10 to 100 ppbv. The instruments deployed included three wet-chemistry systems, one with offline analysis (annular rotating batch denuder, RBD) and two with online-analysis (Annular Denuder sampling with online Analysis, AMANDA; AiRRmonia), two Quantum Cascade Laser Absorption Spectrometers (a large-cell dual system; DUAL-QCLAS, and a compact system; c-QCLAS), two photo-acoustic spectrometers (WaSul-Flux; Nitrolux-100), a Cavity Ring Down Spectrosmeter (CRDS), a Chemical Ionisation Mass Spectrometer (CIMS), an ion mobility spectrometer (IMS) and an Open-Path Fourier Transform Infra-Red (OP-FTIR) Spectrometer. The instruments were compared with each other and with the average concentration of all instruments. An overall good agreement of hourly average concentrations between the instruments (R2>0.84), was observed for NH3 concentrations at the field of up to 120 ppbv with the slopes against the average ranging from 0.67 (DUAL-QCLAS) to 1.13 (AiRRmonia) with intercepts of −0.74 ppbv (RBD) to +2.69 ppbv (CIMS). More variability was found for performance for lower concentrations (<10 ppbv). Here the main factors affecting measurement precision are (a) the inlet design, (b) the state of inlet filters (where applicable), and (c) the quality of gas-phase standards (where applicable). By reference to the fast (1 Hz) instruments deployed during the study, it was possible to characterize the response times of the slower instruments.

Characteristics of atmospheric nitrogen and sulfur containing compounds in an inland suburban-forested site in northern Kyushu, western Japan

To evaluate the effects of the regional pollutant emission and long-range transport from East Asia of nitrogen and sulfur pollutants on air quality at an inland suburban-forested site in northern Kyushu, western Japan, nitrogen and sulfur pollutants were characterized from May 2006 to April 2007 using an annular denuder system. The annual mean concentration of HNO 3 (2.16 μg m − 3 ) at the study site was comparable to concentrations reported in urban areas. The HNO 3 concentration had a diurnal variation, being higher in daytime and lower at night. The diurnal variation of wind direction suggests air pollutants emitted from the regional urban area were transported to the study site during the daytime and caused a higher HNO 3 concentration. The HNO 3 concentration was significantly higher in summer and spring than in winter. The annual mean concentrations of SO 2 and nss-SO 4 2− (6.52 and 7.70 μg m − 3 , respectively) were higher than concentrations determined in other urban areas and forested areas near urban areas in Japan and other countries. The SO 2 concentration was significantly higher in winter and spring than in summer. Backward trajectory analysis indicates the long-range transport from East Asia partly contributed to the higher concentrations of SO 2 in winter and spring. In contrast, there were no statistical differences in the nss-SO 4 2− concentrations among seasons, which could be explained by increased oxidation of SO 2 to SO 4 2− in summer. The value of sulfur conversion ratio ( F s) being higher throughout the year at the study site (52.6%) than values determined in urban sites and there being no diurnal variation of F s indicates the long-range transport of nss-SO 4 2− not only from East Asia but also from other areas including Japan. The equivalent ratio of NH 4 + and nss-SO 4 2− at the study site (0.96 ± 0.22) indicates that acidic sulfate is neutralized by NH 3, existing mainly as (NH 4) 2SO 4 in fine particles. On the other hand, NH 4NO 3 had scarcely formed at the study site, unlike the case for urban areas. Ca 2+ and Na + are suggested to be the counter ions of NO 3 − in coarse particles, which is similar to the situation for the sites where the concentration of NH 3 is insufficient for NH 4NO 3 to form.

Gas/particle partitioning of low-molecular-weight dicarboxylic acids at a suburban site in Saitama, Japan

Abstract Low-molecular-weight dicarboxylic acids (diacids) exhibit semivolatile behavior in the atmosphere, but their partitioning between the gaseous and particulate phases is still unclear. An annular denuder–filter pack system with a cyclone PM2.5 was employed to investigate the gaseous and particulate phase concentrations of diacids, with high collection efficiency of most target compounds. Saturated diacids, unsaturated diacids, ketocarboxylic acids, and dicarbonyls were determined in gaseous and particulate samples collected from a suburban site in Japan, during 2007 summer, 2008 late-winter and early-winter. The concentrations of gaseous and particulate diacids in early-winter were lower than those in summer, but higher than those in late-winter. Individual diacid in gaseous phase showed a relatively good correlation with ambient oxidants, but a low correlation with NO gas (a primary pollutant). Particulate fraction to the total amount (FP) of individual acid was larger in winter than in summer, and also was larger at night than in the daytime. In the same sample, individual diacid and ketocarboxylic acid had higher particulate phase occurrence (FP > 56% in summer), whereas unsaturated diacid had higher gaseous phase occurrence (FP

A Measurement Method for Atmospheric Ammonia and Primary Amines Based on Aqueous Sampling, OPA Derivatization and HPLC Analysis

A method of precolumn derivatization HPLC with fluorescence detection has been developed for the measurement of ammonia, primary methylamine, ethylamine, propylamine, and butylamine in the atmosphere. Air samples were collected by two continuously wetted glass frit/coil samplers, one directly from ambient air for the sum of gaseous and aerosol species, and the other after an acid-coated annular denuder for the aerosol species. The collection efficiency for all analytes was found to be > or = 99% at a sampling gas flow rate of 2 L min(-1) and a scrubbing water flow rate of 0.24 mL min(-1). The collected ammonia and primary amines were derivatized with o-phthalaldehyde (OPA) and n-acetyl-cysteine (NAC) reagents in an in-line derivatization coil to form highly fluorescent sulfonatoisoindole derivatives. Detailed kinetic study showed that derivatization reactions were fast but the derivatives were not very stable. Derivatization conditions, such as reagent concentrations, derivatication medium pH, and derivatization time, were optimized to achieve maximum derivative yields for all the analytes. The derivatives were separated on a C-18 reverse-phase column using a gradient elution and detected by a fluorescence detector at an excitation wavelength of 330 nm and an emission wavelength of 471 nm. The respective lower detection limits for ammonia and for the four primary amines were 24 parts per trillion by volume (pptv) and < or = 3 pptv, with a sample time resolution of about 1 min and a sampling/ analysis time of 20 win per cycle. The analytical methodology has been applied in the field measurements; results from two case studies are presented.

Gas–Particle Distribution of PAHs in Wood Combustion Emission Determined with Annular Denuders, Filter, and Polyurethane Foam Adsorbent

Equipment consisting of annular denuders, a filter, and a polyurethane foam adsorbent was used for sampling 15 PAHs from the diluted emission from a heat-storing masonry heater. The denuder method was compared to the ISO 11338 method which was used for the sampling from hot and undiluted exhaust gas. The denuder method used with the exhaust dilution gave a realistic gas–particle distribution of PAHs in more atmospheric-like conditions compared to the sampling from undiluted exhaust gas where PAHs were almost totally in the gas phase. The results gained with the denuder method from the diluted exhaust are more relevant, e.g., from exposure and atmospheric processes point of view. The emissions from smoldering combustion conditions (SC) were compared with the emissions from normal combustion conditions (NC). The emission of each PAH was 7 to 14 times higher from SC than from NC, and the gas–particle distribution was shifted towards the particle phase due to increased condensation of PAHs. The PAHs could be divided into three groups based on their phase distributions. In the first group, PAHs existed mostly in the gas phase in both combustion cases; the vapor pressures of PAHs were lower than the saturation vapor pressures. In the second group, the gas phase was saturated and the concentration was almost the same in both combustion cases, whereas the particle phase concentration was higher in SC. In the third group, PAHs were mostly in the particle phase where the concentration was higher in SC.

Spatial variability of sulfur dioxide and sulfate over complex terrain in East Tennessee, USA

In 2004 and 2005, the East Tennessee Ozone Study (ETOS) enhanced its regional measurement program with annular denuder systems to quantify sulfur dioxide (SO 2) and PM 2.5 sulfate (SO 4 2−) at five sampling sites that were representative of the complex terrain and physiographic features of East Tennessee. Intersite spatial variability was more defined for SO 2 than for SO 4 2−, which showed a fairly uniform structure in both daytime and nighttime measurements. Pollution roses indicated that two sites may have been influenced by the proximity of SO 2 emission sources. The data suggest that SO 2 is affected by nearby sources in the study area while the sources of SO 4 2− are regionally distributed.

Assessing the Relationship between Air Mass Age and Summer Ozone Episodes Based on Photochemical Indices

Although pollutant sources are usually in urban and industrialized areas, poor air quality is frequently encountered in downwind rural areas. This study utilized a tethered balloon to measure the pollutant concentrations in a downwind side (Caotun) of the Taichung Basin during the summer of 2002. Furthermore, an annular denuder system (ADS) was used to measure PM2.5 and gaseous pollutant concentrations. Concentrations of 55 VOCs species were measured continuously by a network of photochemical assessment monitoring stations in central Taiwan. This study discusses the correlation between the ozone concentration and the routes of an air mass during ozone episodes. Backward trajectory, ratio of particulate matter and photochemical indices were used to examine the aging degree of an air mass. During ozone episodes, the trajectory distribution had a clear sea-land breeze mechanism with a relatively slow wind speed, and the air mass primarily entered through the western coastal industrial area. Analytical results demonstrate that daytime ozone concentrations accompany HNO3 concentrations by photochemical reactions and depend on the previous night’s HNO2 concentration. The sulfur and nitrogen conversion ratios, and the photochemical indices (ethylbenzene/m,p-xylene, n-pentane/t-2-pentene and NO2/NO) increased with the ozone concentration. The downwind photochemical indices were strongly correlated with ozone concentration and were higher than those upwind. These phenomena indicate that the air mass during ozone episodes belongs to the “more aged” category.

Evaluation of Multichannel Annular Denuders for a Newly Developed Ultrafine Particle Sampling System

Laboratory studies evaluated the gas collection efficiencies and particle transmission efficiencies of 1-, 3-, 5-, and 8-channel denuders under simulated atmospheric conditions with the goal of combining an annular denuder–filter pack (AD-FP) system with a newly developed inertial classification. The multichannel denuders having large surface areas were considered for this AD-FP system since the inertial classification system operates at a flow rate of 40 L/min. Gas collection efficiency was measured with phosphorous acid–coated denuders targeted on ammonia gas. Particle transmission efficiency was measured for ammonium sulfate particles. The denuder-coating procedure and the method for extracting the multichannel denuders are described in detail. Gas collection efficiencies for the 1-, 3-, 5-, and 8-channel denuders were 96.3, 98.6, 98.2, and 98.3% (1-ch < 5-ch, 8-ch, and 3-ch), respectively. The extraction efficiency was greater than 96% for all but the 8-channel denuder (92%). The particle transmission efficiencies for the 1-, 3-, 5-, and 8-channel denuders at 40 L/min were 97.3, 97.4, 94.7, and 93.4% (8-ch < 5-ch < 1-ch and 3-ch), respectively. These results indicate that a 1- or 3-channel denuder can be effectively used in this AD-FP system at a flow rate of 40 L/min.

Experimental testing of an annular denuder and filter system to measure gas–particle partitioning of semivolatile bifunctional carbonyls in the atmosphere

An annular denuder and filter-pack system was tested in combination with the use of the in-tube and on-fiber O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA)-derivatization technique to simultaneously sample and measure gaseous and particulate concentrations of semivolatile bifunctional carbonyl compounds in the atmosphere. Ozone was denuded from the sampling air to avoid oxidation and PFBHA was used as the sorbent by coating the sampling denuders and impregnating the filters. The collection efficiency of the system was evaluated under different conditions in photochemical smog chamber experiments and in field samplings of urban and suburban atmospheres. The effects of concentration level, temperature, and humidity on the collection efficiency were assessed. The system showed average collection efficiencies in one denuder from 81% for pyruvic acid and 82% for glyoxylic acid to 87% for hydroxyacetone and dihydroxyacetone. The capacity of the filters to collect the gaseous fraction that cannot be collected in the denuders was also evaluated, and the system allows a correction for this artifact. The application of this method to chamber experiments and field samplings offers an easy-to-apply technique with good results that can be used to evaluate the partition mechanisms of these compounds in the atmosphere.

미세입자(PM2.5)의 질산염 (NO3-) 휘발 특성 분석 -서울시 4개 측정지역을 중심으로-

The purpose of this study is to understand the impact that temperature and relative humidity have on the volatilization loss of particulate nitrate <TEX>$(NO_3^-)$</TEX> from Teflon filters during measurements of ambient fine particles <TEX>$(PM_{2.5})$</TEX>. Fine particles <TEX>$(d_p</TEX><TEX><</TEX><TEX>2.5{\mu}m)$</TEX> were measured using an annular denuder system (ADS) at four representive areas in Seoul. The measurements were made during 28 different days at 24-hr sampling intervals from February 14 to October 15, 1997. In this study, nitrate losses. calculated by the ratio of nitrate on the nylon filter to their sum in both Teflon and nylon titters, varied seasonally in the following order: summer (45.5%) > spring (23.8%) > fall (20.6%) > winter (19.7%). The results showed strong correlations with temperature, but we did not observe any significant effects of relative humidity. However, we observed that both temperature and relative humidity influenced the ambient gas/particle nitrate ratio in a different case study using a denuder.

Investigation of the positive artifact formation during sampling semi-volatile aerosol using wet denuders

Wet denuders are used in several steam-based semi-continuous aerosol monitors to avoid gaseous absorption artifacts and pre-humidify the air stream, while simultaneously allowing measurements of water-soluble gaseous species. Unlike dry denuders, wet denuders saturate the sample air stream with water vapor, which can lead to re-partitioning of water-soluble volatile species to the aerosol phase, thereby causing a positive artifact in aerosol measurements. This paper investigates the magnitude of the positive artifact formation occurring in wet denuders using modeling techniques. Gaseous nitric acid was used as an example of volatile water-soluble gas in both flat and annular wet denuders. We have also verified the occurrence of the positive artifact in a flat wet denuder through a laboratory experiment. The model results indicate that the magnitude of the artifact is rather limited under typical conditions being less than 2.5% of ambient nitric acid concentration for the flat denuder and less than 0.6% for the annular denuder. The magnitude of the artifact increases with condensational sink of the aerosol (i.e. with the mean aerosol size and number concentration) and aerosol water solubility. While the artifact is relatively small in the absolute sense, it could be substantial for aerosol nitrate measurements, especially in ammonia limited conditions, when the concentration of the nitric acid is high and the concentration of nitrate is low. Therefore, we recommend that the artifact is assessed regularly by replacing the wet denuder with a dry denuder.

Concentrations and Formation Rates of Ambient Nitrous Acid in Taichung City, Taiwan

This paper investigates the concentrations and formation rates of ambient nitrous acid (HNO2) in the urban atmosphere. Simultaneous measurements of HNO2 and aerosol particles were carried out from July 2005 to January 2006 by using an annular denuder system (ADS). In addition, the formation rates of NOx to HNO2 were assessed by evaluating potential reactions. The HNO2 concentrations ranged from 0.1 to 15.3 μg m−3 with a mean value of 2.9 μg m−3. The lower levels of HNO2 found in the 10–14 and 14–18-h sampling intervals were due to photolytic reactions. Moreover, heterogeneous reactions of NO2 and H2O on the aerosol surface contributed to the numerous production pathways of HNO2 during nighttime, which was verified by experimental observations and theoretical evaluations. The formation rates of HNO2 ranged from 0.5–2.6 % h−1, while the highest values were found at nighttime. Finally, the factors affecting the formation rate were investigated using sensitivity analysis. The results showed that HNO2 was sign...

A Gaseous Nitric Acid Analyzer for the Remote Atmosphere Based on the Scrubber Difference/NO-Ozone Chemiluminescence Method

An in situ nitric acid analyzer has been designed for sensing in the remote atmosphere. Its operation is based on measuring the concentration difference between the total odd nitrogen species (NO(y)) and HNO(3)-scrubbed NO(y). NO(y) was measured by an NO-ozone chemiluminescent detector equipped with a molybdenum converter. A temperature-controlled annular denuder coated with NaCl was used as a scrubber of gaseous HNO(3). The current detection limit of the HNO(3) analyzer was estimated to be 158 and 71 pptv (parts per trillion by volume) with an integration time of 2 and 10 min (2sigma), respectively. The analyzer was calibrated using standard gaseous HNO(3) to verify its performance. The HNO(3) concentrations measured by the scrubber difference and the NO-ozone chemiluminescence methods (SDCL method) were in agreement with those obtained by the denuder method within the experimental uncertainties (more than +/-4%). We conducted limited field observations of NO(y) and HNO(3) in the remote atmosphere using the newly designed SDCL method at Cape Hedo, Okinawa, Japan.

Gaseous and aerosol pollutants during fog and clear episodes in South Asian urban atmosphere

We report the first measurements of acidic gases and ammonia (NH 3) during fog and clear episodes in Lahore, a highly polluted mega-city of South Asia, along with concentrations of PM 2.5 (particles of <2.5 μm aerodynamic diameter) and ions. An annular denuder system was used to measure acidic gases, NH 3, and PM 2.5 from December 2005 to February 2006 in Lahore, a mega-city in Pakistan. The denuders yielded average concentrations (μg m −3) as follows: ammonia, 50; nitrous acid, 19.6; sulfur dioxide, 19.4; hydrochloric acid, 1.16; nitric acid, 1.00; and oxalic acid, 0.6. The filters yielded average concentrations (μg m −3): PM 2.5, 209; sulfate, 19.2; nitrate, 18.9; chloride, 7.43; oxalate, 0.97; ammonium, 16.1; potassium, 3.49; calcium, 0.89; sodium, 0.76; and magnesium, 0.08. Emissions from local sources, e.g., fossil fuel consumption by motorized transport and power plants, farming, burning of agricultural residues, industrial and construction activities contributed the major proportion of pollutants in Lahore. Concentrations of ionic species, e.g., NO 3 −, SO 4 2−, Na +, NH 4 +, Mg 2+, and Ca 2+, and gaseous species, e.g., HCl, HNO 3, SO 2 and (COOH) 2 showed a distinct diurnal variation. Mixing heights and photochemistry played major roles in defining the diurnal pattern. Fog appeared to profoundly enhance the oxidation of sulfur dioxide. High moisture content of fog resulted in uptake of the gases in fog droplets.

Characterisation of gaseous and particulate atmospheric pollutants in the East Mediterranean by diffusion denuder sampling lines

A field study aimed to characterize atmospheric pollutants in the gaseous and the particulate phases was conducted during the fall-winter of 2004 and the summer of 2005 in the Ashdod area, Israel. The site is influenced by both anthropogenic sources (power plants, refineries, chemical and metal industries, a cargo port, road traffic) and natural sources (sea-spray and desert dust). The use of diffusion lines--a series of annular diffusion denuders for sampling gaseous compounds followed by a cyclone and a filter pack for determining PM(2.5) composition--allowed a good daily characterization of the main inorganic compounds in both the gaseous (HCl, HNO(3), SO(2), NH(3)) and the particulate phase (Cl(-), NO(3)(-), SO(4)(=), NH(4)(+), and base cations). During the summer campaign two other activities were added: an intensive 3-h sampling period and the determination of PM(2.5) bulk composition. The results were interpreted on the basis of meteorological condition, especially the mixing properties of the lower atmosphere as determined by monitoring the natural radioactivity due to Radon progeny, a good proxy of the atmospheric ability to dilute pollutants. Several pollution episodes were identified and the predominance of different sources was highlighted (sea-spray, desert dust, secondary photochemical pollutants). During the summer period a considerable increase of nitric acid and particulate sulphate was observed. Secondary inorganic pollutants (nitrate, sulphate and ammonium) constituted, on the average, 57% of the fine particle fraction, organic compounds 20%, primary anthropogenic compounds 14%, natural components (sea-spray and crustal elements) 9%. The advantages of the diffusion lines in determining gaseous and particulate N- and S- inorganic compounds are discussed.

Carbonyl Emissions from Gasoline and Diesel Motor Vehicles

Carbonyls from gasoline-powered light-duty vehicles (LDVs) and heavy-duty diesel-powered vehicles (HDDVs) operated on chassis dynamometers were measured by use of an annular denuder-quartz filter-polyurethane foam sampler with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine derivatization and chromatography-mass spectrometry analyses. Two internal standards were utilized based on carbonyl recovery: 4-fluorobenzaldehyde for < C8 carbonyls and 6-fluoro-4-chromanone for > or = C8 compounds. Gas- and particle-phase emissions for 39 aliphatic and 20 aromatic carbonyls ranged from 0.1 to 2000 microg/L of fuel for LDVs and from 1.8 to 27 000 microg/L of fuel for HDDVs. Gas-phase species accounted for 81-95% of the total carbonyls from LDVs and 86-88% from HDDVs. Particulate carbonyls emitted from a HDDV under realistic driving conditions were similar to concentrations measured in a diesel particulate matter (PM) standard reference material. Carbonyls accounted for 19% of particulate organic carbon (POC) emissions from low-emission LDVs and 37% of POC emissions from three-way catalyst-equipped LDVs. This identifies carbonyls as one of the largest classes of compounds in LDV PM emissions. The carbonyl fraction of HDDV POC was lower, 3.3-3.9% depending upon operational conditions. Partitioning analysis indicates the carbonyls had not achieved equilibrium between the gas and particle phases under the dilution factors of 126-584 used in the present study.

Characterization of PM2.5 and conversion rate of sulfur dioxide to sulfate in inland areas of Taiwan

The purpose of this study was to investigate the sulfur conversion rate and the characterization of PM2.5 particulate matter and acidic gases in inland Taiwan region. The measurements were taken at two different sites located near the fossil fuel power plant in central Taiwan. First site was Wufong and the other site was Nantou, which is located 15 km south from Wufong. PM2.5 and gaseous acids were measured by annular denuder system. PM2.5 ionic species including SO42–, NO3–, NH4+, Cl–, Ca2+, K+, Na+, and H+and gaseous HNO3 and HCl were analyzed. Results showed that the average ratio of PM2.5 and SO42– was higher during daytime, probably due to the anthropogenic activities. Wind field map also clearly displayed that Wufong was located upwind and Nantou was located downwind during daytime. Sulfur conversion ratio in the downwind site was higher than upwind site. Experimental data showed that sulfur conversion rate between these sites was 5%–9% h–1. The increased PM2.5 and SO2 concentrations recorded in the Nantou site were from the direction of Taichung city during daytime.

Evaluating Relative Contribution of Atmospheric Mercury Species to Mercury Dry Deposition in Japan

In this study, we evaluated the relative contribution of atmospheric particulate mercury (Hg(p)) and divalent reactive gaseous mercury (RGM) to mercury dry deposition in Japan. The dry deposition fluxes (on a water surface sampler) and atmospheric PM concentrations of Hg, Cd, Cu, Mn, Ni, Pb and V, which were measured concurrently from April 2004 to March 2006 at 10 sites across the nation, were used in this evaluation. We considered that Hg(p) and RGM, but not Hg0, are deposited on the water surface, and that our method of sampling Hg(p) without the use of KCl-coated annular denuders enables the exclusion of a significant amount of RGM artifact. The monthly average dry deposition velocities (= deposition flux/atmospheric PM concentration) of Cd and Pb were found to be similar to each other (Cd/Pb deposition velocities = 1.06 ± 0.58). It was assumed that the deposition velocity of Hg(p) is identical to the mean deposition velocity of Cd and Pb, because the particle size distribution of Hg(p) is likely similar to those of both elements. Using this deposition velocity, the monthly dry deposition flux of Hg(p) was calculated. The average contribution (±1σ) of Hg(p) to the annual deposition flux at ten sites was 26 ± 15%. The mercury dry deposition flux increased generally from spring to early summer, which was attributed mostly to the deposition of RGM. This seasonal change correlated to that in photochemical oxidant (primarily O3) concentration in air at most sites. These suggest that mercury dry deposition in Japan is predominantly deposition of RGM, which was formed via oxidation of Hg0 by O3 in the atmosphere.

Evaluation of Laser Absorption Spectroscopic Techniques for Eddy Covariance Flux Measurements of Ammonia

An intercomparison was made between eddy covariance flux measurements of ammonia by a quantum cascade laser absorption spectrometer (QCLAS) and a lead-salt tunable diode laser absorption spectrometer (TDLAS). The measurements took place in September 2004 and again in April 2005 over a managed grassland site in Southern Scotland, U.K. These were also compared with a flux estimate derived from an "Ammonia Measurement by ANnular Denuder with online Analysis" (AMANDA), using the aerodynamic gradient method (AGM). The concentration and flux measurements from the QCLAS correlated well with those of the TDLAS and the AGM systems when emissions were high, following slurry application to the field. Both the QCLAS and TDLAS, however, underestimated the flux when compared with the AMANDA system, by 64%. A flux loss of 41% due to chemical reaction of ammonia in the QCLAS (and 37% in the TDLAS) sample tube walls was identified and characterized using laboratory tests but did not fully accountforthis difference. Recognizing these uncertainties, the agreement between the systems was nevertheless very close (R2 = 0.95 between the QCLAS and the TDLAS; R2 = 0.84 between the QCLAS and the AMANDA) demonstrating the suitability of the laser absorption methods for quantifying the temporal dynamics of ammonia fluxes.