Whei-May Grace Lee

Hygroscopic properties of inorganic-salt aerosol with surface-active organic compounds

Abstract This paper investigates the hygroscopic characteristics of inorganic-salt aerosols with surface-active organic compounds (SAOCs). The experimental system includes a Tandem Differential Mobility Analyzer and a Scanning Mobility Particle Sizing System.The aerosols were prepared by mixing calcium chloride with SACs at five mass fraction of SAOCs, which are 0, 10, 16.7, 20, 25%. Four SAOCs, sodium dodecyl sulfate (SDS), sodium oleate (SO), Tween 80, and Span 80 were chosen according to the hydrophile lipophile balance (HLB) values. First, the hygroscopic growth of SAOCs aerosol was observed. Then the hygroscopic growth of calcium chloride with SAOCs were observed from 7.5% to 85% relative humidity in this study. The results show that the maximum growth ratio of four SAOCs in only 7.5% at relative humidity of 85%. Thus, four SAOCs used in this study have low hygroscopic growth. However, the relative hygroscopic growth ratio of inorganic-salt aerosols compared with inorganic-salt aerosols with SAOCs is between 56 to 83% even at SAOCs mass fraction of 25%.The relative hygroscopic growth ratio of inorganic-salt aerosols with SAOCs appears to decrease with increasing SAOCs concentration but to increase with the HLB values of SAOCs. In other words, SAOCs may inhibit the hygroscopic growth ratio but 56 to 83% relative hygroscopic growth ratio can still be observed. Although the relative hygroscopic growth ratio appears to decrease with increasing SAOC concentration, the growth ratio tends to be at stable value as the mass fraction of SAOCs greater than 20%.Moreover, the spreading rate of SAOCs was compared with the surface growth rate of aerosols calculated in this study. The presence of surface organic film can not inhibit the absorption of water vapor by calcium chloride completely should be caused by the high surface growth rate of aerosols in phase transition period. On the contrary, the spreading rates of SAOCs are much larger than surface growth rate of calcium chloride aerosol in the stable growth period, therefore, the absorption of water vapor can be inhibited significantly by the surface organic film.

Enhanced naphthalene solubility in the presence of sodium dodecyl sulfate: effect of critical micelle concentration.

Surfactants can increase the solubility of non-polar compounds, and have been applied in areas such as soil washing and treatment of non-aqueous phase liquids (NAPLs). This investigation explored the feasibility of removing vapor phase polycyclic aromatic hydrocarbon (PAH) from gases using an anionic surfactant. The solubility of vapor phase naphthalene was measured herein using gas chromatograph (GC) with a photon ionization detector (PID). The measurement results indicated that surfactant molecules were not favorable to micelle formation when temperatures increased from 25 degrees C to 50 degrees C. Regardless of whether solutions were quiescent or agitated, equilibrium naphthalene apparent solubility increased linearly with surfactant concentrations exceeding critical micelle concentration (CMC). The pH effects on naphthalene apparent solubility were small. Agitation increased naphthalene apparent solubility and lumped mass transfer coefficients. Furthermore, lumped mass transfer coefficients decreased with increasing surfactant concentration owing to increase in interfacial resistance and viscosity and decreased spherical micelle diffusion coefficients. Finally, the net absorption rate increased because the solubilization effects of micelles exceeded the reduction effects of mass transfer coefficient above the CMC. The enhanced naphthalene apparent solubility from the addition of surfactant can be expressed by an enrichment factor (EF). The EF value of naphthalene for the surfactant solution at 0.1 M with agitation at 270 rpm relative to quiescent water could reach 18.6. This work confirms that anionic surfactant can improve the removal efficiency of hydrophobic organic compound (HOC) from the gas phase.

The partitioning model of polycyclic aromatic hydrocarbon between gasous and particulate (PM 10μ) phases in urban atmosphere with high humidity

Abstract At present, temperature is usually the only environmental factor in the partitioning model of PAHs between gaseous and particulate phases in atmosphere. In this study, the effect of humidity on the partition of semi-volatile polycyclic aromatic hydrocarbons (PAHs), fluoranthene and pyrene, between gaseous phase and PM 10μ particulate was first investigated, which has not yet been done before. It was shown that there was a relation between partition coefficient, K p , i.e. F /[A (PM10)], and humidity (g/m 3 ), which range from 8.2 to 25.8 g/m 3 corresponding to 52–93% of relative humidity. A and F stand for PAH amount in gaseous and particulate phases, respectively. PM 10μ stands for concentration of PM10μ in ng/m 3 . The partition coefficient increases with increasing humidity. However, the coefficient of humidity variable in the regression model indicated that the effect of the humidity on the partition coefficient is low. Furthermore, the partitioning model incorporated humidity was set up in the form of log ( K p ) = b 0 + b 1 (1/ T ) + b 2 H + b 3 (1/ T ) H and was evaluated by stepwise regression in the humid atmosphere at Taipei. T is ambient temperature and H is humidity in g/m 3 , b 0 , b 1 and b 3 are coefficients of the multiple regression between log ( K p ) and 1/ T , H and (1/ T ) H . The results indicated that the model with the inverse of temperature is sufficient and in the form of log ( K p ) = b 0 + b 1 (1/ T ) The coefficient of correlation is 0.86 and 0.89 for fluoranthene and pyrene, respectively. The sampling experiments of gaseous and particulate PAHs were conducted using PUF plugs and PM10μ. Sampler in the downtown area of Taipei city from June 1988 to May 1990. The samples were analyzed by GC/MS for the PAH substances.

Effect of surfactant film on solubility of hydrophobic organic compounds in fog droplets

Abstract A HOCs-enrichment reactor was developed to investigate the elevated solubility of n-octane, a surrogate of the hydrophobic organic compounds (HOCs), in the artificial fog droplets containing sodium dodecyl sulfate (SDS), a surrogate of the natural surfactants. The enrichment of n-octane is strongly related to the SDS concentration. In comparison with the solubility of n-octane based on the Henrys law for the ideal aqueous solution, the enrichment factors of n-octane in the fog droplets are between 27.2 and 1.87, depending on the SDS concentration (2.85 × 10−3 to 5.15 × 10−5 M). In addition, when SDS concentration is below the specific concentration, 1.03 × 10−4 M, the larger fog droplets show higher enrichment effect than the smaller fog droplets do. Moreover, we present an enrichment model to describe the micro-states of the n-octane molecules partitioning in the SDS organic film at the air/fog interface and the SDS monomers inside the fogwater. The experimental results can easily be expounded and discussed by use of this model.

THE EFFECT OF SURFACTANTS ON THE DELIQUESCENCE OF SODIUM CHLORIDE

This study investigated the deliquescence of sodium chloride aerosol with surfactants at a retention time of 4.24 sec. Two surfactants used in this study, glutaric acid and pyruvic acid, are found in atmospheric aerosol and have a high hydrophile-lipophile balance (HLB) value. The experimental system consisted of a relative humidity conditioner, a tandem differential mobility analyzer (TDMA) and a scanning mobility particle sizing (SMPS) system. Results obtained from the observation of TDMA presented the deliquescence point of sodium chloride aerosol at 75% RH. In addition, the growth size of sodium chloride aerosol was observed to be79.47nm and thegrowth ratio was 77.94%, when theinitial sizeof aerosol was 101.82nm. Surfactants were internally mixed with sodium chloride at six different weight fractions, i.e. 2.5, 5, 10, 20, 40, and 60% by weight of surfactants in dry aerosol. Both surfactants apparently decreased the deliquescence point of sodium chloride, in which the lowest deliquescence point appeared at about 71% RH when the weight fraction of surfactants is 60% by weight of surfactants in dry aerosol. Moreover, the smallest size of sodium chloride aerosol with surfactants was 142.7nm at 60% by weight of pyruvic acid in dry aerosol. Our results further demonstrate that the deliquescence point and size of sodium chloride aerosol with surfactants are related to the weight fraction of surfactants.

Aerosol penetration properties of an electret filter with submicron aerosols with various operating factors.

This study was undertaken to determine the effects of using an electret filter on aerosol penetration. Various factors, including particle size (0.05 to 0.5 μ m), aerosol charge state (neutral and single charge), face velocity (0.1, 0.3, 0.5 and 1.0 m/s), and relative humidity (RH 30% and RH 70%), were examined to assess their effects on aerosol collection characteristics. The results presented here demonstrate that the electric fields of the electret and discharged filter were −1.53 × 104 and −1.3 × 102 (V/m). The penetration through the electret filter with singly charged aerosol and neutral aerosol ranged from 0.4% to 13% and 14% to 29%, respectively. According to these results, the coulombic capture force was dominant for the smaller aerosol and the dielectrophoretic capture mechanism was considered important for the larger aerosol. The level of penetration through the electret filter increased with increasing face velocity and relative humidity. The temperature did not affect the penetration through the electret. Furthermore, from the regression analysis conducted during the operating conditions of this work, the aerosol charge was shown to exert the greatest influence on aerosol penetration.

Morphological and semi-quantitative characteristics of diesel soot agglomerates emitted from commercial vehicles and a dynamometer

Diesel soot aggregates emitted from a model dynamometer and 11 on-road vehicles were segregated by a micro-orifice uniform deposit impactor (MOUDI). The elemental contents and morphological parameters of the aggregates were then examined by scanning electron microscopy coupled with an energy dispersive spectrometer (SEM-EDS), and combined with a fractional Brownian motion (fBm) processor. Two mode-size distributions of aggregates collected from diesel vehicles were confirmed. Mean mass concentration of 339 mg/m3 (dC/dlogdp) existed in the dominant mode (180-320 nm). A relatively high proportion of these aggregates appeared in PM1, accentuating the relevance regarding adverse health effects. Furthermore, the fBm processor directly parameterized the SEM images of fractal like aggregates and successfully quantified surface texture to extract Hurst coefficients (H) of the aggregates. For aggregates from vehicles equipped with a universal cylinder number, the H value was independent of engine operational conditions. A small H value existed in emitted aggregates from vehicles with a large number of cylinders. This study found that aggregate fractal dimension related to H was in the range of 1.641-1.775, which is in agreement with values reported by previous TEM-based experiments. According to EDS analysis, carbon content ranged in a high level of 30%-50% by weight for diesel soot aggregates. The presence of Na and Mg elements in these sampled aggregates indicated the likelihood that some engine enhancers composed of biofuel or surfactants were commonly used in on-road vehicles in Taiwan. In particular, the morphological H combined with carbon content detection can be useful for characterizing chain-like or cluster diesel soot aggregates in the atmosphere.

Emissions of air pollutants from indoor charcoal barbecue

Ten types of commercial charcoal commonly used in Taiwan were investigated to study the potential health effects of air pollutants generated during charcoal combustion in barbecue restaurants. The charcoal samples were combusted in a tubular high-temperature furnace to simulate the high-temperature charcoal combustion in barbecue restaurants. The results indicated that traditional charcoal has higher heating value than green synthetic charcoal. The amount of PM10 and PM2.5 emitted during the smoldering stage increased when the burning temperature was raised. The EF for CO and CO2 fell within the range of 68-300 and 644-1225 g/kg, respectively. Among the charcoals, the lowest EF for PM2.5 and PM10 were found in Binchōtan (B1). Sawdust briquette charcoal (I1S) emitted the smallest amount of carbonyl compounds. Charcoal briquettes (C2S) emitted the largest amount of air pollutants during burning, with the EF for HC, PM2.5, PM10, formaldehyde, and acetaldehyde being the highest among the charcoals studied. The emission of PM2.5, PM10, formaldehyde, and acetaldehyde were 5-10 times those of the second highest charcoal. The results suggest that the adverse effects of the large amounts of air pollutants generated during indoor charcoal combustion on health and indoor air quality must not be ignored.

The relation between polycyclic aromatic hydrocarbons and organic carbon in fly ash from municipal incinerator

Abstract In this study, the relation between PAHs and organic carbon in fly ash from a municipal incinerator is investigated by regression models. It is shown that the relation exists for PAHs with a coefficient of correlation of 0.85 and the regression model obtained is as follows, Y = 0.81 IX ‐ 35.052. In addition, the relation between single PAH substance and organic carbon is also studied. The relation is confirmed for Acenaphthylene (AcPy), Fluoranthene (FL), Pyrene (Pyr), Benzo(a)anthracene + Chrysene (BaA + Chr), and Benzo(b)fluoranthene + Benzo(k)fluoranthene (B(b)FL + B(k)FL). The coefficients of correlation are in the range of 0.82 to 0.93.

EFFECT OF RELATIVE HUMIDITY ON MIXED AEROSOLS IN ATMOSPHERE

In this study, the effects of relative humidity on the deliquescent point and size of internally mixed aerosols diameter, NH4NO3 and (NH4)2SO4 were investigated using a Tandem Differential Mobility Analyzer (TDMA) with a relative humidity conditioner. The growth of mixed aerosols appears to have two deliquescent steps. The first one was at about 61.2 ∼ 61.3%, but the second one was at around 77 ∼ 78%. At the first deliquescence point, growth ratio at phase change was 7.5%, which agrees with the growth ratio of ammonium nitrate aerosol. Growth ratio of phase change at the second deliquescence point was about 20%, lower than the growth ratio of ammonium sulfate aerosol. In the relative humidity range of 80 ∼ 85%, the growth ratio of the mixed aerosols reached 60%. In other words, it appears that growth ratio increases with the size of aerosol. Furthermore, a theoretical growth model of mixed aerosols was developed and applied to estimate the amount of composition of the mixed aerosols dissolved at each deliquescence point. The results also show that some of ammonium sulfate already dissolved at the first deliquescence point according to the theoretical growth model.