Annular Denuder Research Articles

Field Measurement of Diesel Particulate Matter Emissions

A primary means to reduce environmental levels of diesel particulate matter (DPM) exposure to miners is to reduce the amount of DPM emission from the engine. A quick and economic method to estimate engine particulate emission levels has been developed. The method relies on the measurement of pressure increase across a filter element that is briefly used to collect a DPM sample directly from the engine exhaust. The method has been refined with the inclusion of an annular aqueous denuder to the tube which permits dry filter samples to be obtained without addition of dilution air. Tailpipe filter samples may then be directly collected in hot and water-supersaturated exhaust gas flows from water bath-cooled coal mine engines without the need for dilution air. Measurement of a differential pressure (DP) increase with time has been related to the mass of elemental carbon (EC) on the filter. Results for laboratory and field measurements of the method showed agreement between DP increase and EC collected on the filter with R(2) values >0.86. The relative standard deviation from replicate samples of DP and EC was 0.16 and 0.11, respectively. The method may also have applications beyond mining, where qualitative evaluation of engine emissions is desirable to determine if engine or control technology maintenance may be required.

Characteristics of Atmospheric Aerosol and Acidic Gases from Urban and Forest Sites in Central Taiwan

Measurements of atmospheric fine aerosols, acidic gases and ammonia were made at National Chung Hsing University (Urban) and Huisun forest area (Forest) sites in central Taiwan region during October (highest ozone month). Annular Denuder System (ADS) was used for sampling gaseous (nitrous acid, nitric acid, sulfur dioxide and ammonia) and fine aerosol species (ammonium, nitrate and sulfate). The results showed a significant diurnal variation in nitrous acid and nitric acid concentrations. Nitric acid was produced primarily during daytime in both sites. In the urban site, the average concentration of nitric acid during daytime was 5.8 times higher compared to nighttime while the average nitrous acid concentration during daytime was lower compared to nighttime, due to the photo-dissociation of nitrous acid. Sulfate, nitrate and ammonium were the major constituents of PM(2.5). Higher concentrations of nitrous acid, nitric acid, particulate nitrate and ammonium were recorded at urban site.

A Review on the Sampling and Analytical Methods for Ammonia in Air

The quantification of ammonia concentrations has received a lot of scientific attention. Numerous devices for the quantification of <TEX>$NH_3$</TEX> in the ambient air have been developed to provide more technical possibilities for research in abating <TEX>$NH_3$</TEX> emission from various source processes. For the proper quantification of <TEX>$NH_3$</TEX>, a number of sampling methods have been discussed by grouping them into different categories based on the principle of functioning. In general, active samplers employ pumps to draw air in, while passive samplers are exposed to air over a certain period of time to obtain integrated signature of <TEX>$NH_3$</TEX>. In case of the former, impingers and absorption flasks can be employed simultaneously with suitable absorbents to capture <TEX>$NH_3$</TEX> passing through them. The methods of analysis include both in-situ and laboratory determination. In the laboratory, colorimetric or ion chromatographic methods are generally used for its quantification. In the field, a number of real time analyzers have been proven to be useful. These real time analyzers can be grouped according to their principle of operation. These analyzers may use the principle of spectroscopy (e.g. DOAS), photoacousticics (e.g. photoacoustic monitor) or Chemiluminescence (<TEX>$NO_x$</TEX> analyzer). The automated annular denuder sampling system with on-line analyzer is also suitable for continuous monitoring of ammonia in air.

Analysis of acidic components, heavy metals and PAHS of particulate in the Changwon–Masan area of Korea

This study is an analysis of the concentrations and components of heavy metals in PM2.5 and the total suspended particulate (TSP) collected at a mechanical industrial complex (IC) site in Changwon and at a residential site in Masan, Korea. Particulate was collected during two sampling periods, from the late summer to the early fall and from the middle to late fall, at the IC site and one sampling period, from the middle fall to the early winter, at the residential site. PM2.5 and TSP samples were taken by an annular denuder system and a hi-volume air sampler, respectively. The authors also identified the concentrations and components of heavy metals extracted from the PM2.5 and TSP filters, the acidic components extracted from the PM2.5 filters, and the polycyclic aromatic hydrocarbons (PAHs) extracted from polyurethane foam (PUF) plug. The average concentrations of the PM2.5 collected at the IC and residential sites were very similar. Major sources of PM2.5 at the study sites, however, were air emissions from vehicles and industry as well as emissions from residential heating and soil origins, respectively. The higher concentrations of the TSP at the IC site, as compared to those at the residential site, were due to either increased suspended dust from vehicle emissions or re-suspended road dust because of increased vehicle speeds near the IC site. Heavy metal concentrations in the TSPs were higher than those in the PM2.5. The heavy metal concentrations in the PM2.5 and TSP at the IC site with heavy traffic were substantially greater than those at the residential site. The concentrations of TSP and heavy metals and PAHs in PM during the period of the middle to late fall was much higher than those during the period of the late summer to early fall at the IC site. This is because of the difference in meteorological characteristics and energy uses between two periods. The residential site also showed higher concentrations of acidic anions while the IC site showed higher concentrations of acidic cation. Secondary aerosols or particulates, such as ammonium nitrate or ammonium nitrite, might have been important constituents of the PM2.5 at the residential site. The PAHs in the TSP collected at the IC site was greatly affected by traffic and industry emissions consisting mostly of high molecular weight PAHs with two to four rings. PAHs in the TSP at the site, however, were affected by residential heating and air emissions from small chemical plants having higher concentrations of low molecular weight PAHs with five to six rings.

Quinone Emissions from Gasoline and Diesel Motor Vehicles

Gas- and particle-phase emissions from gasoline and diesel vehicles operated on chassis dynamometers were collected using annular denuders, quartz filters, and PUF substrates. Quinone species were measured using O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine derivatization in conjunction with gas chromatography-mass spectrometry and high-performance liquid chromatography-mass spectrometry. Nine quinones were observed, ranging from C6 to C16. New species identified in motor vehicle exhaust include methyl-1,4-benzoquinone, 2-methyl-1,4-naphthoquinone (MNQN), and aceanthrenequinone. Gas-phase motor vehicle emissions of quinones are also reported for the first time. Six gas-phase quinones were quantified with emission rates of 2-28 000 microg L(-1) fuel consumed. The most abundant gas-phase quinones were 1,4-benzoquinone (BON) and MNQN. The gas-phase fraction was > or = 69% of quinone mass for light-duty gasoline emissions, and > or = 84% for heavy-duty diesel emissions. Eight particle-phase quinones were observed between 2 and 1600 microg L(-1), with BQN the most abundant species followed by 9,10-phenanthrenequinone and 1,2-naphthoquinone. Current particle-phase quinone measurements agree well with the few available previous results. Further research is needed concerning the gas-particle partitioning behavior of quinones in ambient and combustion source conditions.

Distribution of PM2.5 and Gaseous Species in Central Taiwan During two Chinese Festival Periods

Measurements of PM2.5 and acidic gases were conducted at an inland site of Taichung basin. The sampling site was Nantou, which is located at a distance of 25 km from the Taichung city. Nantou represents an inland area surrounded by Central Mountain Ranges and Baqua Hill. The sampling timings were in the month of April (during Tomb-Sweeping Festival) and in September (during Mid-Autumn Festival). PM2.5 samples were collected with an annular denuder system. Aerosol ionic species including sulfate (SO42−), nitrate (NO3−), ammonium (NH4+), chloride (Cl−), calcium (Ca2+), potassium (K+), and sodium (Na+) and gaseous nitric acid (HNO3), hydrochloric (HCl), and sulfur dioxide (SO2) were analyzed. Results showed that the average PM2.5 concentration were 41.3 μg m−3 during the Tomb-Sweeping Festival period and 65.3 μg m−3 during the Mid-Autumn Festival period. The major particle-phase ionic species was sulfate (SO42−) during both the Chinese Festival periods. Ozone concentration was higher during the Mid-Autumn Festival. Sulfate (SO42−) and nitrate (NO3−) concentrations were well correlated with daily maximum ozone (O3) concentration. The time weight mean concentration data showed that the increased concentration of gas-phase sulfur dioxide (SO2) and sulfate (SO42−) were transported from Taichung City, which is located close to the sampling site. Based on our above obtained results, the Mid-Autumn Festival period showed more anthropogenic impact on the aerosol and gaseous distribution favored by meteorological factors, higher ambient temperature, and wind direction.

Atmospheric deposition of nitrogen, sulfur and chloride in Thessaloniki, Greece

In the present study, the wet and dry depositions of particulate NO 3 −, SO 4 2−, Cl − and NH 4 + were measured using a wet/dry sampler as a surrogate surface. Gas phase compounds of nitrogen, sulfur and chloride (HNO 3, NH 3, SO 2 and HCl) were measured by an annular denuder system (ADS) equipped with a back up filter for the collection of particles with diameter ≤ 5 μm. Ambient concentrations of NO, NO 2 and SO 2 were also taken into consideration. Sampling was conducted at an urban site in the center of the city of Thessaloniki, northern Greece. The presence of the aerosol species was examined by cold/warm period and the possible compounds in dry deposits were also considered. Dry deposition fluxes were found to be well correlated with ambient particle concentrations in order to be used for the calculation of particle deposition velocity. Average particulate deposition velocities calculated were 0.36, 0.20, 0.20 and 0.10 cm s − 1 for Cl −, NO 3 −, SO 4 2− and NH 4 +, respectively. Total dry deposition fluxes (gas and particles) were estimated at 3.24 kg ha − 1 year − 1 for chloride (HCl + p-Cl), 9.97 kg ha − 1 year − 1 for nitrogen oxidized (NO + NO 2 + HNO 3 + p-NO 3), 5.32 kg ha − 1 year − 1 for nitrogen reduced (NH 3 + p-NH 4) and 15.77 kg ha − 1 year − 1 for sulfur (SO 2 + p-SO 4). 70–90% total dry deposition was due to gaseous species deposition. The contribution of dry deposition to the total (wet + dry) was at the level of 60–70% for sulfur and nitrogen (oxidized and reduced), whereas dry chloride deposition contributed 35% to the total. The dry-to-wet deposition ratio of all the studied species was found to be significantly associated with the precipitation amount, with nitrogen species being better and higher correlated. Wet, dry and total depositions measured in Thessaloniki, were compared with other countries of Europe, US and Asia.

Field test of four methods for gas-phase ambient nitric acid

Three semi-continuous methods for detecting nitric acid (HNO 3) were tested against the annular denuder + filter pack (ADS) integrated collection technique at the Tampa Bay Regional Atmospheric Chemistry Experiment (BRACE) Sydney research station ∼ 20 km downwind of the Tampa, Florida, urban core. The semi-continuous instruments included: two slightly differing implementations of the NO Y - NO Y * (total oxides of nitrogen minus that total denuded of HNO 3) denuder difference technique, one from the NOAA Air Resources Lab (ARL), and one from Atmospheric Research and Analysis, Inc. (ARA); the parallel plate wet diffusion scrubber + online ion chromatography technique from Texas Tech University (TTU); and the chemical ionization mass spectrometer from the Georgia Institute of Technology (GIT). Twelve hour ADS samples were collected by the University of South Florida (USF). Results for 10 min samples computed from the various higher sampling frequencies of each semi-continuous instrument showed good agreement ( R 2 > 0.7 ) for afternoon periods of the highest production and accumulation of HNO 3. Further, agreement was within ± 30 % for these instruments even at HNO 3 concentrations < 0.30 ppb . The USF ADS results were biased low, however, by 44%, on average, compared to the corporate 12 h aggregated means from the semi-continuous methods, and by > 60 % for the nighttime samples; ADS results were below the corporate mean maximum HNO 3 concentration by > 30 % as well. The four instruments using semi-continuous methods, by contrast, were all within 10% of each other's 12 h mean mixing ratios. While only ARA employed a formal minimum detection limit at 0.050 ppb, error analysis with the other techniques established that at the same level of precision, TTU's effective limit was approximately the same as ARA's and that ARL's limit was 0.030 ppb; analysis for GIT showed no apparent effective limit at the levels of HNO 3 encountered in this field study. The importance of sample inlet height for HNO 3 measurements was indirectly shown through comparison to previous field work at this site when sample inlet heights ranged from 1.5–10 m and produced systematic discrepancies in HNO 3 concentrations correlated with height of more than a factor of 2.

Comparing field performances of denuder techniques in the high Arctic

A field evaluation between two annular denuder configurations was conducted during the spring of 2003 in the marine Arctic at Ny-Ålesund, Svalbard. The IIA annular denuder system (ADS) employed a series of five single-channel annular denuders, a cyclone and a filter pack to discriminate between gas and aerosol species, while the EPA-Versatile Air Pollution Sampler (VAPS) configuration used a single multi-channel annular denuder to protect the integrity of PM 2.5 sample filters by collecting acidic gases. We compared the concentrations of gaseous nitric acid (HNO 3), nitrous acid (HONO), sulfur dioxide (SO 2) and hydrochloric acid (HCl) measured by the two systems. Results for HNO 3 and SO 2 suggested losses of gas phase species within the EPA-VAPS inlet surfaces due to low temperatures, high relative humidities, and coarse particle sea-salt deposition to the VAPS inlet during sampling. The difference in HNO 3 concentrations (55%) between the two data sets might also be due to the reaction between HNO 3 and NaCl on inlet surfaces within the EPA-VAPS system. Furthermore, we detected the release of HCl from marine aerosol particles in the EPA-VAPS inlet during sampling contributing to higher observed concentrations. Based on this work we present recommendations on the application of denuder sampling techniques for low-concentration gaseous species in Arctic and remote marine locations to minimize sampling biases. We suggest an annular denuder technique without a large surface area inlet device in order to minimize retention and/or production of gaseous atmospheric pollutants during sampling.

Cavity Ring-Down Spectroscopy of Ambient NO2 with Quantification and Elimination of Interferences

Ambientdetection of NO2 by cavity ring-down spectroscopy is examined in the wavelength region near 405.23 nm, and possible interferences by particulates, water vapor, and carbon dioxide are characterized. Particulates can be efficiently removed by the use of a 0.45 microm fluoropolymer filter. Water vapor has a response of 2.8 ppb (NO2 equivalent) for 1.0% water vapor (80% relative humidity at 10 degrees C) in air at 405.23 nm in a broad continuous absorption feature. Carbon dioxide has a response of 0.8 ppb (NO2 equivalent) for 1.0% CO2 attributable to Rayleigh scattering and would not contribute significant interference in ambient measurements due to the lower ambient CO2 levels. Water vapor interference and in general broad background in the absorption spectrum can be accounted for by removing NO2 selectively in the ambient air stream with an annular denuder coated with sodium hydroxide and methoxyphenol (guiacol). Subtraction of the resulting background signal provides NO2 measurements with a limit of detection of 150 ppt/10 s (SIN = 3). Reliable NO2 measurements could be obtained by this method without the need for frequent calibration with calibration gas. Ambient NO2 measurements are carried out to demonstrate this method.

Sampling Time Effect on 2,4‐Toluene Diisocyanate Concentration by using Different Samplers

In order to understand the sampling time effect on the 2,4‐TDI (Toluene diisocyanate) concentrations, laboratory and field tests were conducted in this study. An ADS (annular denuder sampler) and two OFFCs (open face filter holders) with different filters were tested for 1 to 120 minutes in the laboratory using 2,4‐TDI gas. In the field study, the standard sampling method, the dual filter the triple filter and annular denuder systems were used at two workplaces to study the change of 2,4‐TDI concentrations with sampling time from 15 to 60 minutes. The test results in both laboratory and field studies show that the sampling time influences the sampled TDI concentration considerably which may be due to reaction of TDI with water vapor and polyo in the sampling process. It is evident that as sampling time increases the TDI concentration decreases very significantly.

Source Identification and Trends in Concentrations of Gaseous and Fine Particulate Principal Species in Seoul, South Korea

Ambient measurements were made using two sets of annular denuder system during the four seasons (April 2001 to February 2002) and were then compared with the results during the period of 1996–1997 to estimate the trends and seasonal variations in concentrations of gaseous and fine particulate matter (PM2.5) principal species. Annual averages of gaseous HNO3 and NH3 increased by 11% and 6%, respectively, compared with those of the previous study, whereas HONO and SO2 decreased by 11% and 136%, respectively. The PM2.5 concentration decreased by ∼17%, 35% for SO4 2−, and 29% for NH4 +, whereas NO3 − increased by 21%. Organic carbon (OC) and elemental carbon (EC) were 12.8 and 5.98 μg/m-3, accounting for ∼26 and 12% of PM2.5 concentration, respectively. The species studied accounted for 84% of PM2.5 concentration, ranging from 76% in winter to 97% in summer. Potential source contribution function (PSCF) analysis was used to identify possible source areas affecting air pollution levels at a receptor site in Seoul. High possible source areas in concentrations of PM2.5, NO3 −, SO4 2−, NH4 +, and K+ were coastal cities of Liaoning province (possibly emissions from oil-fired boilers on ocean liners and fishing vessels and industrial emissions), inland areas of Heibei/Shandong provinces (the highest density areas of agricultural production and population) in China, and typical port cities (Mokpo, Yeosu, and Busan) of South Korea. In the PSCF map for OC, high possible source areas were also coastal cities of Liaoning province and inland areas of Heibei/Shandong provinces in China. In contrast, high possible source areas of EC were highlighted in the south of the Yellow Sea, indicating possible emissions from oil-fired boilers on large ships between South Korea and Southeast Asia. In summary, the PSCF results may suggest that air pollution levels in Seoul are affected considerably by long-range transport from external areas, such as the coastal zone in China and other cities in South Korea, as well as Seoul itself.

Fluxes of reactive gaseous mercury measured with a newly developed method using relaxed eddy accumulation

There is a qualitative understanding that gaseous elemental mercury (GEM) is oxidized during Arctic spring to reactive gaseous mercury (RGM) that afterwards is removed by fast deposition to snow surfaces. The conditional sampling or relaxed eddy accumulation (REA), technique represents the first opportunity to directly measure fluxes of reactive gaseous mercury (RGM) to the snow pack in the Arctic. Using a micrometeorological method REA system, with a heated sampling system specifically designed for Arctic use, the dry deposition of RGM is measured after polar sunrise, in Barrow, Alaska. Heated KCl-coated manual RGM annular denuders were used as the accumulators with an inlet allowing only fine particles to pass (Cut off diameter 2.5 μm). At 3 m above the snow pack significant RGM fluxes were measured each spring in 2001–2004. Both depositions and emissions were observed. The emissions were attributed to chemical formation of RGM at or near the snow surface. The surface resistance, R c, for RGM was found to be very small and set to zero as a first estimate.

Characteristics of gaseous HNO 2, HNO 3, NH 3 and particulate ammonium nitrate in an urban city of Central Taiwan

Simultaneous measurements of ambient gaseous species HNO 2, HNO 3, NH 3 and particulate NO 3 − and NH 4 + 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 HNO 2, HNO 3, NH 3, NO 3 − and NH 4 + 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 HNO 2 was found to be lower during the summer, whereas HNO 3 and NH 3 displayed higher concentrations. On the other hand, particulate NO 3 − exhibited significant seasonal variation with lower levels observed in autumn and summer. The average nitrogen conversion ratios (F n) 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 NO 2 to nitrate since F n was well correlated with O 3 during daytime in all seasons. During nighttime, F n 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.

Measurement of 2,4-toluene diisocyanate concentrations by different samplers

The standard sampling methods for toluene diisocyanate (TDI) only collect total TDI without separating the aerosol and gas phases. There are few other samplers, such as the dual filter, triple filter and annular denuder systems (ADS), which are able to sample the aerosol and gas phases simultaneously. This field study was conducted at two workplaces to access the total 2,4-TDI and the gaseous and aerosol TDI concentrations by different samplers simultaneously. In addition to the standard sampling time of 15 min, sampling was done for 30 and 60 min to study the effect of sampling time on the measured 2,4-TDI concentrations. Test results at two workplaces show that gas-phase 2,4-TDI is the predominant species and the aerosol phase concentration is very small. The measurements using various samplers show that the sampling time influences the sampled TDI concentration considerably which may be due to reaction of TDI with water vapor and polyo in the sampling process. It is evident that as sampling time increases the TDI concentration decreases. Laboratory test was also conducted using pure gas-phase 2,4-TDI to confirm the sampling time effect on the measured concentrations found in the field study.

Influence of Sampling Artefacts on Measured PM, OC, and EC Levels in Carbonaceous Aerosols in an Urban Area

Sampling of particulate matter (PM) with filter media is subject to the influence of positive and negative artefacts. The complexity of these measurements derives from the use of different instrumentation, face velocities, and filter types. Carbonaceous compounds are one of the main PM chemical components affected by these artefacts. In this study, two main types of artefacts were evaluated at an urban site in Ghent (Belgium) during the summer period: those related to the sampling procedure (high- or low-volume samplers) and those related to the adsorption and/or volatilization of carbonaceous species. For their measurement, two high-volume (PM10 and PM2.5) samplers with single quartz fiber filters and two low-volume PM2.5 samplers (one of them coupled to an annular diffusion denuder) with double quartz fiber filters (front and backup) were used. PM2.5 mass concentrations measured by means of the low-volume sampler (front filter) were, on average, 31% higher than those registered with the high-volume sampler. PM2.5 mass concentrations registered with the low-volume sampler coupled to the diffusion denuder represented 88% of the PM2.5 mass collected with the undenuded low-volume sampler. Similar values for organic carbon (OC) were recorded for the high- and low-volume samplers. Front filter OC levels for the denuded samples represented 66% of the front filter OC mass on the undenuded samples. Using the backup filter OC data to apply a correction to the front filter data as suggested by Mader et al. (2003) only marginally reduced the discrepancy between the undenuded and denuded OC data, indicating that such correction does not result in consistent OC data for an urban area in Western Europe during summer.

Organic and elemental carbon concentrations in carbonaceous aerosols during summer and winter sampling campaigns in Barcelona, Spain

Daily PM10 and PM2.5 samples were collected at an urban background monitoring site in Barcelona (Spain) in summer and winter 2004. The instrumentation used consisted of two high-volume (PM10 and PM2.5) and two low-volume samplers (PM2.5), one of them coupled to an annular diffusion denuder aiming to evaluate the influence of sampling artefacts related to the adsorption of volatile carbonaceous species. Quartz fibre filters of 15 cm and 47 mm diameter were used as collection substrates (Schleicher & Schuell QF20 and Whatman QM-A, respectively). The resulting samples were analysed for organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC). Total carbon (TC) was calculated as OC+EC. The present study aimed to (a) determine maximum (winter) and minimum (summer) OC/EC/TC/WSOC levels in the study area, and (b) assess the magnitude and influence of positive sampling artefacts. Mean levels of TC in PM2.5 ranged from 4 to 5 μg m −3 in summer to 7–10 μg m −3 in winter with the different samplers (5 and 8 μg m −3, respectively, in PM10, one sampler); OC levels in PM2.5 were 3–4 μg m −3 in summer and 6–7 μg m −3 in winter (4 and 6 μg m −3 in PM10); EC levels in PM2.5 ranged from 1 to 2 μg m −3 in summer to 1–3 μg m −3 in winter (1 and 2 μg m −3 in PM10). Thus, OC/EC/TC winter levels were higher than summer levels by a factor of 1.7–2. WSOC levels were 1.6 μg m −3 in PM2.5 and PM10 in summer, and 2.1 μg m −3 (PM2.5) and 1.9 μg m −3 (PM10) in winter. The results indicate that positive artefacts for OC accounted for 0.5–0.7 μg m −3, representing 11–16% of the raw OC mass and 3% of the PM2.5 mass. Sampling artefacts for OC were slightly higher in summer. EC levels were similar for the low-volume samplers and unusually low for the high-volume samplers, suggesting that EC determination could be influenced by the filter type.

Fluxes of ammonia and sulfate over maize using relaxed eddy accumulation

The dry deposition of fine aerosol sulfate and ammonia was measured over maize using the relaxed eddy accumulation method (REA). This micrometeorological method determines the flux by sampling the concentrations in the “updraft” and “downdraft” eddy motions, with the flux being proportional to the difference in concentration between the “up” and “down” concentrations. The fine aerosol fraction and gas phase components were separated using annular denuders followed by filterpacks using Teflon filters. Measurements were made when the leaf area index was low (∼1) and later when the canopy was fully developed (LAI ∼ 4) to evaluate the role of LAI on the aerosol deposition velocity. The deposition measurements of sulfate aerosol yielded daytime deposition velocities larger than expected (∼2 cm s −1) from short crops but consistent with other field measurements over forests. Over a young fertilized stand of maize with a leaf area index of ∼1, large emissions of ammonia were observed for several days following the surface application of urea containing fertilizer. Measurements over a fully developed canopy with a leaf area index of about 4, showed both deposition and emission events.

Aerosol Counterflow Two-Jets Unit for Continuous Measurement of the Soluble Fraction of Atmospheric Aerosols

A new type of aerosol collector employing a liquid at laboratory temperature for continuous sampling of atmospheric particles is described. The collector operates on the principle of a Venturi scrubber. Sampled air flows at high linear velocity through two Venturi nozzles "atomizing" the liquid to form two jets of a polydisperse aerosol of fine droplets situated against each other. Counterflow jets of droplets collide, and within this process, the aerosol particles are captured into dispersed liquid. Under optimum conditions (air flow rate of 5 L/min and water flow rate of 2 mL/min), aerosol particles down to 0.3 microm in diameter are quantitatively collected in the collector into deionized water while the collection efficiency of smaller particles decreases. There is very little loss of fine aerosol within the aerosol counterflow two-jets unit (ACTJU). Coupling of the aerosol collector with an annular diffusion denuder located upstream of the collector ensures an artifact-free sampling of atmospheric aerosols. Operation of the ACTJU in combination with on-line detection devices allows in situ automated analysis of water-soluble aerosol species (e.g., NO2-, NO3-)with high time resolution (as high as 1 s). Under the optimum conditions, the limit of detection for particulate nitrite and nitrate is 28 and 77 ng/m(3), respectively. The instrument is sufficiently rugged for its application at routine monitoring of aerosol composition in the real time.

Gas‐aerosol partitioning of semi volatile carbonyls in polluted atmosphere in Hachioji, Tokyo

Gaseous and particulate semi volatile carbonyls have been measured in urban air using an annular denuder sampling system. Three dicarbonyls, five aliphatic aldehydes and two hydroxy carbonyls were observed. Concentrations of other biogenic and anthropogenic volatile organic compounds (VOCs), SO2, CO, NO2 and particle concentration were also measured. Estimated gas‐aerosol equilibrium constants for the carbonyls showed an inverse correlation with the concentrations of anthropogenic pollutants such as benzene, isopentane and SO2. This suggests that the increase in the fraction of non‐polar anthropogenic particles in the atmosphere could change the average property of the ambient aerosols and drive the gas particle equilibrium of the carbonyls to the gas phase. This trend is uncommon in remote forest air. In this study, we examined the factors controlling the equilibrium in the polluted atmosphere and show that there is a difference in gas‐aerosol partition between polluted and clean air.