Brown carbon light absorption over an urban environment in northern peninsular Southeast Asia.

Light-absorbing organic carbon (or brown carbon, BrC) has been recognized as a critical driver in regional-to-global climate change on account of its significant contribution to light absorption. BrC sources vary from primary combustion processes (burning of biomass, biofuel, and fossil fuel) to secondary formation in the atmosphere. This paper investigated the light-absorbing properties of BrC such as site-specific mass absorption cross-section (MACBrC), absorption Ångström exponent (AAEBrC), and the absorbing component of the refractive index (kBrC) by using light absorption measurements from a 7-wavelength aethalometer over an urban environment of Chiang Mai, Thailand in northern peninsular Southeast Asia (PSEA), from March to April 2016. The contribution of BrC to total aerosol absorption (mean ± SD) was 46 ± 9%, 29 ± 7%, 24 ± 6%, 20 ± 4%, and 15 ± 3% at 370, 470, 520, 590, and 660 nm, respectively, highlighting the significant influence of BrC absorption on the radiative imbalance over northern PSEA. Strong and significant associations between BrC light absorption and biomass-burning (BB) organic tracers highlighted the influence of primary BB emissions. The median MACBrC and kBrC values at 370 nm were 2.4 m2 g-1 and 0.12, respectively. The fractional contribution of solar radiation absorbed by BrC relative to BC (mean ± SD) in the 370-950 nm range was estimated to be 34 ± 7%, which can significantly influence the regional radiation budget and consequently atmospheric photochemistry. This study provides valuable information to understand BrC absorption over northern PSEA and can be used in model simulations to reassess the regional climatic impact with greater accuracy.

Simultaneous determination of carcinogenic PAHs and levoglucosan bound to PM2.5 for assessment of health risk and pollution sources during a smoke haze period.

Carcinogenic polycyclic aromatic hydrocarbons (cPAHs) in ambient PM2.5 and a specific molecular marker of biomass burning, levoglucosan, are used to investigate the influence on public health of biomass burning. In this work, we present an effective method for one-time analysis of cPAHs and levoglucosan by GC-MS without derivatization. The method was applied for the analysis of PM2.5 samples (64.3 ±â€¯17.6 µg m-3, n = 57) collected during a smoke haze period in Chiang Mai, Thailand. Levoglucosan was analyzed by using both the developed method (GC-MS) and a reference method (HPAEC-PAD) for comparison. Its average concentration obtained from GC-MS (0.31 ±â€¯0.21 µg m-3) was about 4 times less than the concentration obtained from the reference method (1.22 ±â€¯0.76 µg m-3). Therefore, a correcting factor (CF = 4) was used as a multiplying factor, to obtain a comparative value (1.23 ±â€¯0.86 µg m-3). The average concentration of cPAHs found in PM2.5 samples was 5.88 ±â€¯1.97 ng m-3 with the highest value of 10.86 ng m-3 indicating medium to high cancer risk due to PAHs exposure when referring to values of toxicity equivalence and inhalation cancer risk. Diagnostic ratios of BaA/(BaA + CHR) (0.48 ± 0.04) and IND/(IND + BPER) (0.58 ± 0.04) and strong correlations between PM2.5, levoglucosan and cPAHs concentrations implied that the major source of air pollution in the study period was biomass burning. PM2.5 concentration as a pollution indicator was labelled as BB-low, BB-medium, BB-high or BB-extreme; <50, 50-75, 75-100 and > 100 µg m-3, respectively. The levoglucosan and cPAHs concentration during BB-extreme pollution was 4.3 times and 2.34 times, respectively, that during BB-low pollution, and the correlation coefficient (r) between the concentrations of levoglucosan and cPAHs was as high as 0.987, indicating that the more intense the burning of biomass, the higher the carcinogenic risk in the urban air.

Development and evaluation of a novel personal sampler for PM1 using rotating porous media.

A rotating filtration device (RFD) that is filled with porous media is developed for sampling particulate matter with a diameter of 1 µm or less (PM1). An experiment is conducted on a test system using corn oil as a test aerosol. The RFD was evaluated using an aerodynamic particle sizer. The results yielded cutoff sizes of 1.68 µm and 1.04 µm at rotational speeds of 0 rpm and 9000 rpm, respectively, with foam with 80 pores per inch (ppi), a thickness of 80 mm, and a face velocity of 13.5 cm/s. When the foam was replaced with 94 ppi nickel mesh, the cutoff size decreased from 1.45 µm to 0.98 µm as the thickness increased from 17 to 68 mm. As the face velocity of the RFD increased from 13.5 to 108.3 cm/s, the cutoff size declined from 1.04 µm to 0.77 µm. Most of the changes in the cutoff sizes of the RFD were statistically significant (p < 0.05). The maximum pressure drops through the foam and the nickel mesh were 33.5 and 36.6 mm H2O, respectively. The experiment revealed that increasing the rotational speed and face velocity of the RFD, and the thickness and nominal size of the porous media reduced the penetration of oil aerosols.

Emissions of pollutant gases, fine particulate matters and their significant tracers from biomass burning in an open-system combustion chamber.

An open-system combustion chamber was designed and constructed for simulation of burning of various biomass types to estimate emission factors of pollutant gases, fine particulate matters and their composition to find out significant tracers. Rice straw (RS), maize residues (MR) and forest leaf litters (FLL) from mixed deciduous forest (MDF) and dry dipterocarp forest (DDF) were collected from various places in Northern Thailand based on land-use types. Approximately 1 kg of air-dried biomass sample was burned in the chamber, PM2.5 were collected. CO2 dominated during the flaming state while CO is predominant in the smoldering state. The highest EFPM2.5 was obtained from MDF burning (4.38 ±â€¯2.99 g kg-1), while the lowest value was from MR burning (2.15 ±â€¯0.95 g kg-1). Among water soluble ions, K+ (biomass burning (BB) tracer) was the most abundant species in PM2.5 followed by Cl- and SO42-. The average EFK+ from the burning of agricultural biomass was significantly higher than the burning of FLL. Scatter plot of K+/SO42- versus K+/Cl- can be used to distinguish between agricultural crop residues and FLL burning. Levoglucosan (BB tracer) was a dominant species among anhydrosugars and also a major component found in FLL burning. The ratios of levoglucosan/K+ and levoglucosan/mannosan obtained from forest and agricultural waste burnings were significantly different, therefore they can be used for BB source identification.

Molecular markers for biomass burning associated with the characterization of PM2.5 and component sources during dry season haze episodes in Upper South East Asia.

Severe air pollution in the form of smoke haze in the northern part of Southeast Asia (SEA) occurs annually in the dry season due to huge open area burning. Molecular markers of biomass burning were investigated by characterization of fine particles (PM2.5) collected in the dry season (23 February-28 April 2016). The average PM2.5, organic carbon (OC) and elemental carbon (EC) concentrations were 64.3 ±â€¯17.6 µg m-3, 23.6 ±â€¯8.1 µg m-3 and 2.85 ±â€¯0.98 µg m-3, respectively. SO42- was the dominant species (8.73 ±â€¯2.88 µg m-3) of water-soluble ion, followed by NH4+ (3.32 ±â€¯1.01 µg m-3) and NO3- (2.70 ±â€¯0.51 µg m-3). High concentrations of the biomass burning tracers K+ (1.27 ±â€¯0.38 µg m-3) and levoglucosan (1.22 ±â€¯0.75 µg m-3) were observed. The ratios of levoglucosan/K+ (0.92 ±â€¯0.35) and levoglucosan/mannosan (20.4 ±â€¯4.1) identified forest and agricultural waste burning as major contributors to the aerosol. Strong correlations (r > 0.800) between levoglucosan and OC, K+, anhydrosugar isomer (mannosan and galactosan) and other saccharides (mannose, arabitol and mannitol) verified that combustion of biomass was the major source of organic compounds associated with PM2.5 aerosols. Oxalate was the most abundant (0.75 ±â€¯0.17 µg m-3; 53%) of the carboxylates. The concentration of oxalate was strongly correlated to that of PM2.5 (r = 0.799) and levoglucosan (r = 0.615), indicating that oxalate originates mainly from primary emissions from biomass burning rather than secondary formation from photochemical processes. Backward trajectories indicated that long-range transport air masses influencing air quality in Northern Thailand originated to the west and southwest.

Nano/micron particles released from newspapers under different reading conditions.

Despite the extensive use of the Internet, printed newspapers remain a primary information source. In this study, reading a newspaper in a relatively confined or poorly ventilated indoor space was simulated to determine the profile of particles released from the newspaper into the air. The consecutive simulated conditions were reading without agitation of the newspaper (NoAg), followed by reading with agitation of the newspaper (Ag) and post-reading absent the newspaper (PostR), repeated with four newspapers. We found that particle number concentration (ΣN) fell during Ag owing to electroadhesion of ultrafine particles (<200 nm) caused by static charges created by friction between the paper surface and the air as a result of newspaper agitation. Conversely, particle surface area concentrations (ΣA) and particle volume concentrations (ΣV) increased significantly during Ag. This was because the larger, fine (1-2.5 µm) and coarse mode (2.5-10 µm), particles were detached from the newspaper during agitation due to inertial detachment - the release of even a small number of these particles contributing greatly to ΣA and ΣV. The critical particle number diameter (CPND) occurred at 207-310 nm. Particles smaller than this were subject to electroadhesion during Ag. The critical particle volume diameter (CPVD) occurred at 130-497 nm. Particles larger than this were subject to inertial detachment during Ag. These observations indicate that the electroadhesion of smaller particles and the inertial detachment of larger particles occur simultaneously. Particle mass concentrations were found to be as high as 168.7-534.3 µg m-3. However, these findings of high potential concentrations were based on the measurement in relative small micro-environment. The inhalation of such concentrations is a health risk for people who regularly read newspapers in a relatively confined or poorly ventilated indoor space.

Ambient PM2.5 in the residential area near industrial complexes: Spatiotemporal variation, source apportionment, and health impact.

This study systemically investigated the ambient PM2.5 (n=108) with comprehensive analyses of the chemical composition, identification of the potential contributors, and estimation of the resultant respiratory physician visits in the residential regions near energy-consuming and high-polluting industries in central Taiwan. The positive matrix fraction (PMF) model with chemical profiles of trace metals, water-soluble ions, and organic/elemental carbons (OC/EC) was applied to quantify the potential sources of PM2.5. The influences of local sources were also explored using the conditional probability function (CPF). Associations between the daily PM2.5 concentration and the risk of respiratory physician visits for the elderly (≥65years of age) were estimated using time-series analysis. A seasonal variation, with higher concentrations of PM2.5, metals (As, Cd, Sb, and Pb), OC/EC and ions (i.e., NO3-, SO42- and NH4+) in the winter than in the spring and summer, was observed. Overall, an increase of 10µgm-3 in the same-day PM2.5 was associated with an ~2% (95% CI: 1.5%-2.5%) increase in respiratory physician visits. Considering the health benefits of an effective reduction, we suggest that the emission from coal combustion (23.5%), iron ore and steel industry (17.1%), and non-ferrous metallurgy (14.4%), accounting for ~70% of the primary PM2.5 in the winter are prioritized to control.

Emission characteristics of allergenic terpenols in PM2.5 released from incense burning and the effect of light on the emissions.

This study investigated allergenic terpenol compounds in incense powder and smoke. The powder of two Thai brands contained higher concentrations of terpenols up to 6.15 times higher than those of two Taiwanese brands. Consequently, Thai incense makers face a higher potential risk of contact dermatitis than Taiwanese incense makers do. d-Limonene was the primary terpenol compound in the powder of Thai B (64.0%) and Thai Y (31.5%), sold in Thailand. By contrast, anisyl alcohol was the primary terpenol compound in the powder of LST (40.3%) and SC (37.7%), sold in Taiwan. After the four brands of incense were ignited, their mean PM2.5 emission factor was 18.02±6.20mgg-1 incense. The PM2.5 mass emission factors of the Taiwanese brands were far higher than those of the Thai brands, and so were the PM2.5 terpenol emission factors, showing that the smokes of the Taiwanese incense were potentially more allergenic than those of the Thai incense. Geraniol, the most allergenic terpenol compound, was 2.8%-10.7% of total terpenol compounds in the powder of the four brands, yet was the main contributor to PM2.5, constituting 66.3%-83.5% of terpenol compounds in the smokes of the four brands. Furthermore, geraniol exhibited an IP ratio, defined as the incense/powder (IP) ratio of terpenol-related species, >1 in all four brands, and >5 in the Taiwanese brands, suggesting a greater health risk with the smoke from the Taiwanese incense. The IP ratios of other terpenol species were all <1, indicating decomposition through combustion. Additionally, the light/darkroom ratios of the terpenol species were >1, meaning that the generation of PM2.5 terpenol compounds was potentially enhanced by indoor lighting.

Potential PM2.5 impacts of festival-related burning and other inputs on air quality in an urban area of southern Taiwan.

The Mid-Autumn Festival (MAF), or Moon Festival, is a harvest festival in Taiwan, celebrated by families across the island with evening barbecues outside. This study investigated the potential impact of these activities on the air quality in Tainan, a city in southern Taiwan. Fine particulate matter (PM2.5) was examined in the period leading up to the MAF (pre-MAF), during the Festival (MAF), after the Festival (post-MAF), and in the period after this (a period of moderate air quality: MAQ). Gaseous pollutants in PM2.5 were, from highest to lowest mean concentration, NH3, SO2, HCl, HNO3, HNO2, and oxalic acid, while inorganic salts were mainly in the form of the photochemical products SO4(2-), NH4(+), and NO3(-). These inorganic salts accounted for 37.6%-44.5% of the PM2.5 mass concentration, while a further 26.3%-42.8% of the PM2.5 mass was total carbon (TC). TC was mostly composed of organic carbon (OC) produced by photochemical reactions. Of this, 9.8%-14.9% was carboxylates, of which oxalate was the most abundant compound, accounting for 22.8%-31.9% of carboxylates. The presence of phthalates in the PM2.5 indicated emissions from the plastics industry. Although a noticeable amount of aerosol was produced by festival activities and burning of softwood and hardwood, onshore air currents during the festival prevented potential high aerosol loading. During the moderate air quality period following post-MAF, the concentration of total carbohydrates was 1.44-2.64 times the amount during the festival. Levoglucosan and myo-inositol accounted for 81.7%-89.6% of the total carbohydrate concentration. The average Levo/Manno ratio was 18.64 ± 5.24. The concentration of levoglucosan was closely related to that of PO4(3-), erythritol, and galactose. Backward trajectories indicated that biomass burning in China affected the air quality of Tainan City.

Carbonaceous composition changes of heavy-duty diesel engine particles in relation to biodiesels, aftertreatments and engine loads.

Three biodiesels and two aftertreatments were tested on a heavy-duty diesel engine under the US FTP transient cycle and additional four steady engine loads. The objective was to examine their effects on the gaseous and particulate emissions, with emphasis given to the organic and elemental carbon (OC and EC) in the total particulate matter. Negligible differences were observed between the low-sulfur (B1S50) and ultralow-sulfur (B1S10) biodiesels, whereas small reductions of OC were identified with the 10% biodiesel blend (B10). The use of diesel oxidation catalyst (DOC1) showed moderate reductions of EC and particularly OC, resulting in the OC/EC ratio well below unity. The use of DOC plus diesel particulate filter (DOC2+DPF) yielded substantial reductions of OC and particularly EC, resulting in the OC/EC ratio well above unity. The OC/EC ratios were substantially above unity at idle and low load, whereas below unity at medium and high load. The above changes in particulate OC and EC are discussed with respect to the fuel content, pollutant removal mechanisms and engine combustion conditions. Overall, the present study shows that the carbonaceous composition of PM could change drastically with engine load and aftertreatments, and to a lesser extent with the biodiesels under study.

Molecular markers in ambient aerosol in the Mahanadi Riverside Basin of eastern central India during winter.

Organic molecular markers are important atmospheric constituents. Their formation and sources are important aspects of the study of urban and rural air quality. We collected PM10 aerosol samples from the Mahanadi Riverside Basin (MRB), a rural part of eastern central India, during the winter of 2011. PM10 aerosols were characterized for molecular markers using ion chromatography. The concentration of PM10 ranged from 208.8 to 588.3 µg m(-3) with a mean concentration of 388.9 µg m(-3). Total concentration of anhydrosugars, sugar alcohols, primary sugars, and oxalate were found to be 3.25, 5.60, 10.52, and 0.37 µg m(-3), respectively, during the study period. Glucose was the most abundant species followed by levoglucosan and mannitol. Significant positive correlation between the molecular markers, anhydrosugars, sugar alcohols, primary sugars, and oxalic acid confirmed that biomass burning, biogenic activity, and re-suspension of soil particles were the main sources of aerosol in the eastern central India study area.

Reducing emissions of persistent organic pollutants from a diesel engine by fueling with water-containing butanol diesel blends.

The manufacture of water-containing butanol diesel blends requires no excess dehydration and surfactant addition. Therefore, compared with the manufacture of conventional bio-alcohols, the energy consumption for the manufacture of water-containing butanol diesel blends is reduced, and the costs are lowered. In this study, we verified that using water-containing butanol diesel blends not only solves the tradeoff problem between nitrogen oxides (NOx) and particulate matter emissions from diesel engines, but it also reduces the emissions of persistent organic pollutants (POPs), including polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated biphenyls, polychlorinated diphenyl ethers, polybrominated dibenzo-p-dioxins and dibenzofurans, polybrominated biphenyls and polybrominated diphenyl ethers. After using blends of B2 with 10% and 20% water-containing butanol, the POP emission factors were decreased by amounts in the range of 22.6%-42.3% and 38.0%-65.5% on a mass basis, as well as 18.7%-78.1% and 51.0%-84.9% on a toxicity basis. The addition of water-containing butanol introduced a lower content of aromatic compounds and most importantly, lead to more complete combustion, thus resulting in a great reduction in the POP emissions. Not only did the self-provided oxygen of butanol promote complete oxidation but also the water content in butanol diesel blends could cause a microexplosion mechanism, which provided a better turbulence and well-mixed environment for complete combustion.

Characteristics and sources of water-soluble ionic species associated with PM10 particles in the ambient air of central India.

PM(10) aerosol samples were collected in Durg City, India from July 2009 to June 2010 using an Andersen aerosol sampler and analyzed for eight water-soluble ionic species, namely, Na(+), NH(4) (+), K(+), Mg(2+), Ca(2+), Cl(-), NO(3) (-) and SO(4) (2-) by ion chromatography. The annual average concentration of PM(10) (253.5 ± 99.4 µg/m(3)) was four times higher than the Indian National Ambient Air Quality Standard of 60 µg/m(3) prescribed by the Central Pollution Control Board, India. The three most abundant ions were SO(4) (2-), NO(3) (-), and NH(4) (+), with average concentrations of 8.88 ± 4.81, 5.63 ± 2.22, and 5.18 ± 1.76 µg/m(3), respectively, and in turn accounting for 27.1 %, 16.5 %, and 15.5 % of the total water-soluble ions analyzed. Seasonal variation was similar for all secondary ions i.e., SO(4) (2-), NO(3) (-), and NH(4) (+), with high concentrations during winter and low concentrations during monsoon. Varimax Rotated Component Matrix principal component analysis identified secondary aerosols, crustal resuspension, and coal and biomass burning as common sources of PM(10) in Durg City, India.

Effects of biodiesel, engine load and diesel particulate filter on nonvolatile particle number size distributions in heavy-duty diesel engine exhaust.

Diesel engine exhaust contains large numbers of submicrometer particles that degrade air quality and human health. This study examines the number emission characteristics of 10-1000 nm nonvolatile particles from a heavy-duty diesel engine, operating with various waste cooking oil biodiesel blends (B2, B10 and B20), engine loads (0%, 25%, 50% and 75%) and a diesel oxidation catalyst plus diesel particulate filter (DOC+DPF) under steady modes. For a given load, the total particle number concentrations (N(TOT)) decrease slightly, while the mode diameters show negligible changes with increasing biodiesel blends. For a given biodiesel blend, both the N(TOT) and mode diameters increase modestly with increasing load of above 25%. The N(TOT) at idle are highest and their size distributions are strongly affected by condensation and possible nucleation of semivolatile materials. Nonvolatile cores of diameters less than 16 nm are only observed at idle mode. The DOC+DPF shows remarkable filtration efficiency for both the core and soot particles, irrespective of the biodiesel blend and engine load under study. The N(TOT) post the DOC+DPF are comparable to typical ambient levels of ≈ 10(4)cm(-3). This implies that, without concurrent reductions of semivolatile materials, the formation of semivolatile nucleation mode particles post the after treatment is highly favored.

A novel method for determination of low molecular weight dicarboxylic acids in background atmospheric aerosol using ion chromatography.

This paper describes a novel gradient elution ion chromatographic method using a Dionex AS11 system for the determination of low molecular weight dicarboxylic acids (low-M(w) DCAs) in background atmospheric aerosol. Interference with the oxalic acid peak from sulfate in background PM(2.5) aerosol, 15.8 times the oxalic acid concentration, was remedied by removing sulfate using a barium cartridge, whilst interference with the malonic acid peak from carbonate was reduced by using a carbonate removal device. An alternative remedy to sulfate interference was use of an AS14 system using isocratic eluent, and this produced good resolution of oxalic acid from a high sulfate peak. In both the AS11 and the AS14 system, linear correlation coefficients were at all times >0.9990 with excellent linear range, the recoveries ranged from 92.8 to 106%, with relative standard deviation of 3.67-6.30%, whilst method detection limits (MDLs) ranged from 0.36microgL(-1) for malic acid to 3.87microgL(-1) for maleic acid. These data indicate that the analytical methods developed herein produce excellent separation efficiency and good determination of low-M(w) DCAs with satisfactory accuracy, recoveries, and MDLs. Samples left at room temperature (20 degrees C) for 300min in a simulation of the 'waiting time' involved in the proposed IC analysis decayed to between 86% (oxalic acid) and 39% (succinic and malonic acids) of their original concentration, whilst at 4 degrees C concentrations remained at 96-101% of original, indicating that maintaining samples at a low temperature prior to injection into the IC analyzer is vital for obtaining accurate results when analyzing low-M(w) DCAs. Oxalic acid was found to be the most prevalent low-M(w) DCA in background aerosol, comprising 57% of the total low-M(w) DCAs and 0.959% of the PM(2.5) aerosol mass, followed by succinic acid and malonic acid.

Long-term visibility trends in one highly urbanized, one highly industrialized, and two rural areas of Taiwan.

Visibility trends on the island of Taiwan were investigated employing visibility and meteorological (1961-2003), and air pollutant (1994-2003) data from one highly urbanized center (Taipei), one highly industrialized center (Kaohsiung), and two rural centers (Hualien and Taitung). Average annual visibility (1961-2003) was significantly higher at the rural centers. Unlike at the other centers, visibility in Taipei improved between 1992 (6.6 km) and 2003 (9.9 km), and this can be linked to the construction and expansion of a mass transit rail system in Taipei, the use of which has helped reduce emissions of traffic related air pollutants, particles, and NO2. This has left Kaohsiung with the lowest annual visibility since 1994, despite its 1961-2003 average being superior to that of Taipei. Precipitation lowers visibility, as demonstrated by the all-centers correlation coefficient for visibility and precipitation of -0.92. Hence, frequency of precipitation is one of the factors contributing to the average annual visibility number. The poorest air quality category ('episode'), most commonly experienced in Taipei and Kaohsiung, was characterized by relatively high concentrations of PM10 and NOx at those centers, with comparatively high atmospheric pressure and comparatively low visibility and wind speed. Excepting O3, pollutant concentrations were slightly higher during weekdays, although there was no consistent, significant difference in weekday-weekend visibility. Principal component analysis demonstrated that visibility was markedly reduced in Taipei, Kaohsiung, and Hualien by increased vehicular emissions, road traffic dust, and industrial activity, but not in Taitung, where visibility was as a result superior to that at the other centers and degradation in visibility was likely a response to long-range transport of pollutants rather than local sources. Optimal empirical regression models indicated a negative impact on visibility for each of PM10, SO2 and NO2, particularly so for PM10, and validity of these models for Taipei, Kaohsiung, and Hualien was confirmed by correlation coefficients of simulated and observed average visibility of 0.63-0.72 for daily visibility and 0.85-0.88 for monthly visibility. For Taitung these figures were only 0.46 and 0.50, respectively, indicating that simulations for Taitung should include long-range transport as a pollutant source.

Effects of CH4 and CO on the reduction of nitric oxide to nitrogen in a discharge reactor.

Additives are often added to enhance the efficiency of NO removal. This study uses a radio frequency (rf) discharge to consider the effect of added CH4 and CO to simulated NO/N2/O2/H2O mixtures on the elevation of NO conversion and the reduction of NO into N2. The enhancement levels of NO conversion when using various additives were found to be in this order: +CH4 > +CO > no additive. NO conversion reached 99.3%, 86.2%, and 77.6% when adding CH4, CO, and without additive, respectively, at inlet additive/NO molar ratio (R) = 5 and at 120 W. Moreover, the fraction of total N atoms converted from NO into N2 (FN2) was very high, reaching 99.4% and 99.5% when adding CH4 and CO, respectively, at R = 1 and at 120 W. The better operating conditions are using CH4 as the additive at R > or = 1 and a power of > 60 W to reach a higher NO conversion with a higher FN2. However, it should be noted that this rf plasma approach is not practical at this stage because of its relative low pressure.

Characterization of chemical species in atmospheric aerosols in a metropolitan basin.

Ambient PM10 aerosol samples were collected from Taiwan's Taichung metropolitan basin between October 1997 and January 1998, and their chemical characteristics studied. The average mass concentration of PM10 was 109.0 +/- 54.1 microg/m3. Carbonaceous materials, sulfate, nitrate, and ammonium were the most important contributors to the PM10 component. On average, 64% of the PM10 was made up of fine particles. During PM10 episodes, average wind speed was 0.7 m/s and relative humidity was high, 83% on average, probably giving rise to stagnation of air pollutants and their entrapment close to the surface. With relative humidity < 70%, NO3-, NH4+, SO4(2-), carbonaceous materials, and PM10 mass showed high correlation with maximum hourly average ozone (O3M). Variation in atmospheric humidity may affect the gas-to-particle interactions of S and N species. The most significant contribution to PM10 in the Taichung urban basin was from the photochemical formation of secondary aerosols and carbonaceous materials in the atmospheric environment.