Atmospheric Environment (v.36, #3)

Engine performance and pollutant emission of an SI engine using ethanol–gasoline blended fuels by Wei-Dong Hsieh; Rong-Hong Chen; Tsung-Lin Wu; Ta-Hui Lin (403-410).
The purpose of this study is to experimentally investigate the engine performance and pollutant emission of a commercial SI engine using ethanol–gasoline blended fuels with various blended rates (0%, 5%, 10%, 20%, 30%). Fuel properties of ethanol–gasoline blended fuels were first examined by the standard ASTM methods. Results showed that with increasing the ethanol content, the heating value of the blended fuels is decreased, while the octane number of the blended fuels increases. It was also found that with increasing the ethanol content, the Reid vapor pressure of the blended fuels initially increases to a maximum at 10% ethanol addition, and then decreases. Results of the engine test indicated that using ethanol–gasoline blended fuels, torque output and fuel consumption of the engine slightly increase; CO and HC emissions decrease dramatically as a result of the leaning effect caused by the ethanol addition; and CO2 emission increases because of the improved combustion. Finally, it was noted that NO x emission depends on the engine operating condition rather than the ethanol content.
Keywords: Alternative fuels; Ethanol; Engine performance; Pollutant emission preface;

A new algorithm has been derived for trajectory models to determine the transfer coefficient of each source along or adjacent to a trajectory and to calculate the concentrations of SO2, NO x , sulfate, nitrate, fine particulate matter (PM) and coarse PM at a receptor. The transfer coefficient t f (s m−1) is defined to be the ratio between the contributed concentration ΔC (μg m−3) to the receptor from a ground source and the emission rate of the source q (μg m−2  s−1) at a grid, i.e. t f ≡ΔC/q. The model is developed by combining with a backward trajectory scheme and a circuit-type's parameterization. First, the transfer coefficients of grids along or adjacent a back-trajectory are calculated. Then, the contributed concentration of each emission grid is determined by multiplying its emission rate with the transfer coefficient of the grid. Finally, the concentration at the receptor is determined by the summation of all the contributed concentrations within the domain of simulation.
Keywords: Transfer coefficient; Trajectory; Contributed concentration; Circuit model; Inverse approach;

Quantification on source/receptor relationship of primary pollutants and secondary aerosols from ground sources—Part II. Model description and case study by Chien-Lung Chen; Ben-Jei Tsuang; Rong-Chang Pan; Chia-Ying Tu; Jen-Hui Liu; Pei-Ling Huang; Hsunling Bai; Man-Ting Cheng (421-434).
A Circuit Trajectory transfer-coefficient model (CTx) is developed in this study based on the parameterization presented in a companion paper (Tsuang et al., Atmos. Environ., in this issue). CTx was tested by applying it to Metropolitan Taipei for the entire year 1998. The model was calibrated in January and verified throughout the year. The results indicate that the correlation coefficients (r) for daily concentrations of CO, NO x , SO2, PM2.5 and PM10 were 0.75, 0.69, 0.39, 0.55 and 0.55, respectively, with biases of the means ranging from 0% to 20% during the verification period. According to contour plots of contributed concentrations to the city, “teleconnections” between source emissions and their contributions to the city can be identified. In addition, the model captures most of the dust episodes except during the periods of Asian dust storms. The sensitivity analysis shows that the calculated PM10 concentration is most sensitive to its dry deposition velocity as well as its emission rate. A more thorough study on the deposition velocity of PM2.5 is suggested.
Keywords: Transfer coefficient; Trajectory; Contributed concentration; Particulate matter; Sensitivity test; Taipei; Dust storm;

Chemical characterization of particles in winter-night smog in Tokyo by Katsumi Saitoh; Koichiro Sera; Koichiro Hirano; Tadashi Shirai (435-440).
Continuous measurement of PM10, PM2.5 and carbon (organic, elemental composition) concentrations, and samples of PM10 and PM2.5 collected on a polycarbonate membrane filter (Nuclepore®, pore size: 0.8 μm), were carried out during a period from December 1998 to January 1999 at Shinjuku in Tokyo in order to investigate the chemical characterization of particles in winter-night smog within a large area of the Japan Kanto Plain including the Tokyo Metropolitan area. These were measured using an ambient particulate monitor (tapered element oscillating microbalance—TEOM) and a carbon particulate monitor. Elemental compositions in the filter samples of PM10 and PM2.5 were determined by means of particle-induced X-ray emission (PIXE) analysis. Ionic species (anion: F, Cl, NO3 , SO4 2− and C2O4 2−; cation: Na+, NH4 +, K+, Ca2+ and Mg2+) in the filter samples were analyzed by ion chromatography. The temporal variation patterns of PM2.5 were similar to those of PM10 and carbon. PM2.5 made up 90% of the PM10 at a high concentration, and 70% at a low concentration. Concentrations of 22 elements in both the PM10 and PM2.5 samples were consistently determined by PIXE, and Na, Mg, Al, Si, S, Cl, K, Ca, Fe, Zn and Pb were found to be the major components. Among these S and Cl were the most dominant elements of the PM2.5 and PM10 at high concentrations. Ionic species were mainly composed of Cl, NO3 , SO4 2− and NH4 +. The component proportion of carbon, the other elements (total amount of measured elements other than S and Cl) and secondary-formed particles of PM2.5 was similar to that of PM10. The major component was carbon particles at a low concentration and secondary-formed particles at a high concentration. The proportion of NH4NO3 and NH4Cl plus HCl in secondary-formed particles at a high concentration, in particular, was as high as 90%.
Keywords: Atmospheric aerosol; PM10; PM2.5; Elemental compostions; Secondary-formed particles; Winter-night smog; Tokyo;

Development of an automatic continuous analyzer for water-soluble gases in air by combining an artificial lung with an ion chromatograph by Kazuhiko Sakamoto; Masaki Takeno; Kazuhiko Sekiguchi; Osamu Ishitani; Tsutomu Fukuyama; Masahiro Utiyama (441-448).
An automatic measurement system for the simultaneous monitoring of sulfur dioxide (SO2) and ammonia (NH3) in air was developed by combining an artificial lung and an ion chromatograph. An artificial lung was used as a new technique for concentrated collection of trace amounts of gaseous pollutants in air. It was found that SO2 and NH3 were effectively absorbed into ultra-pure water in the artificial lung. Collection efficiencies for SO2 and NH3 were 100% and 98%, respectively, at a gas flow rate of 1 l min–1, and material balances >90% were obtained. No interference from the simultaneous collection of SO2 and NH3 was found. When a 400 ppb standard NH3 gas was measured automatically with this system, the recovery rate was 98%, and the relative standard deviation was 2.7% (n=8). In the case of a 200 ppb standard SO2 gas, the recovery rate was 87%, and the relative standard deviation was 1.6% (n=7). Results from the simultaneous measurement of SO2 and NH3 with the automatic system were equally as good as those obtained by measuring a single component at a time. Calibration curves for SO2 and NH3 showed good relationships between concentration and peak intensity. The linear correlation coefficients were 0.997 and 0.998 for SO2 and NH3, respectively. The detection limits of SO2 and NH3 were 0.06 and 0.1 ppb, respectively, in a 40 l air volume. The system was tested in air and found to be capable of simultaneous measurement of SO2 and NH3 with a 20 min cycle.
Keywords: Sulfur dioxide; Ammonia; Simultaneous measurement; Artificial lung; Automatic measurement system;

The stratosphere–troposphere exchange of ozone and aerosols over Korea by Y.K. Kim; H.W. Lee; J.K. Park; Y.S. Moon (449-463).
Vertical profiles of ozone, partial pressure, and meteorological parameter are obtained from ozonesondes and rawinsondes launched at Pohang (36.03°N, 129.40°E) in Korea. Stratosphere–troposphere exchanges (STE) of ozone and aerosols associated with the upper trough/surface high pressure system have been analyzed by TOMS data, and reanalyzed data of NCEP/NCAR and meteorological mesoscale model such as potential temperature, geopotential height, potential vorticity, and ageostrophic and vertical wind velocity. The secondary ozone peak in the upper troposphere over Pohang corresponded to the central axis of the jet stream near the tropopause, and then an enhancement of ozone in the upper troposphere was observed when the jet stream with a cut-off low was located over Korea. The maximum flux of ozone by STE over Korea occurs in wintertime and springtime. It was estimated that the downward fluxes observed in winter and spring for the period of 5 yr (1995–1998) at Pohang were the source of −7.72×107 ozone molecules/cm2  s between 100 and 300 hPa, and 5.72×107 ozone molecules/cm2   s between 300 and 500 hPa. The annual average flux during the period also was presented as a decrease of 3×107 ozone molecules/cm2  s between 100 and 500 hPa. It indicates that ozone flux is decreasing in the lower stratosphere and increasing in the troposphere. The gradients of potential temperature and isentropic potential vorticity near the upper troposphere in east Asia sloped steeply like the frontal zone between the polar and the subtropical jet core. Therefore, it was regarded that ozone and aerosols of the upper level over east Asia penetrated into the lower level or the ground over Korea because of the downstream due to tropopause folding near the jet streams and the sinking of surface high pressure. In particular, yellow-sand occurring in springtime in east Asia was determined by the distribution of weather systems associated with STE. The results of observation and modeling indicate that the enhancements of ozone and aerosols in springtime occur in the advection and the downward motion due to the upper trough/cut-off low and the high surface pressure.
Keywords: Ozone and aerosols; Stratosphere–troposphere exchange; The secondary ozone peak; Jet stream; Cut-off low; Ozone flux; Tropopause folding; Surface high pressure; Yellow-sand;

A wintertime PM2.5 episode at the Fresno, CA, supersite by John G. Watson; Judith C. Chow (465-475).
A winter PM2.5 episode that achieved a maximum 24-h average of 138 μg m−3 at the Fresno Supersite in California's San Joaquin Valley between 2 and 12 January, 2000 is examined using 5-min to 1-h continuous measurements of mass, nitrate, black carbon, particle-bound PAH, and meteorological measurements. Every day PM2.5 sampling showed that many episodes, including this one, are missed by commonly applied sixth-day monitoring, even though quarterly averages and numbers of US air quality standard exceedances are adequately estimated. Simultaneous measurements at satellite sites show that the Fresno Supersite represented PM2.5 within the city, and that half or more of the urban concentrations were present at distant, non-urban locations unaffected by local sources. Most of the primary particles accumulated during early morning and nighttime, decreasing when surface temperatures increased and the shallow radiation inversion coupled to a valleywide layer. When this coupling occurred, nitrate levels increased rapidly over a 10–30 min period as black carbon and gaseous concentrations dropped. This is consistent with a conceptual model in which secondary aerosol forms above the surface layer and is effectively decoupled from the surface for all but the late-morning and early afternoon period. Primary pollutants, such as organic and black carbon, accumulate within the shallow surface layer in urban areas where wood burning and vehicle exhaust emissions are high. Such a model would explain why earlier studies find nitrate concentrations to be nearly the same among widely separated sites in urban areas, as winds aloft of 1 to 6 m s−1 could easily disperse the elevated aerosol throughout the valley.
Keywords: Supersite; PM2.5; Nitrate; Black carbon; Conceptual model; Fresno;

Characterization of n-alkanes in PM2.5 of the Taipei aerosol by Li-Hao Young; Chiu-Sen Wang (477-482).
Ambient concentrations of n-alkanes with carbon number ranging from 17 to 36 were determined for PM2.5 samples collected in Taipei city during September 1997–February 1998. The measured concentrations of particulate n-alkanes were in the range of 69–702 ng m−3, considerably higher than the concentration levels observed in Los Angeles and Hong Kong. The concentration distributions of n-alkanes homologues obtained in this study exhibited peaks at C19, C24 or C25. This suggests that fossil fuel utilization, such as vehicular exhaust and lubricant residues, was an important contributor to the Taipei aerosol. Source apportionment of PM2.5 was conducted using carbon preference index (CPI, defined as the ratio of the total concentration of particulate n-alkanes with odd carbon number to that with even carbon number) and U : R ratio (the concentration ratio of unresolved components to resolved components obtained from chromatograms). The low CPI value (0.9–1.9) and high U : R ratio (2.6–6.4) for each sample further confirmed that fossil fuel utilization was the major source of n-alkanes in ambient PM2.5 of Taipei city. Estimates from these results showed that 69–93% of the n-alkanes in PM2.5 of the Taipei aerosol originated from vehicular exhaust. The higher concentration level of particulate n-alkanes in the Taipei aerosol was mainly a result of vehicular emissions.
Keywords: Urban aerosols; Fine particles; Carbon preference index; Vehicular exhaust; Source apportionment;

The calculation of particle trajectories in the extra-tropical troposphere is improved by a hybrid model that employs the temperature and geopotential fields to supplement the velocity field. The hybrid model uses the temperature and geopotential fields to construct the Montgomery Stream function, which, together with a Rayleigh friction force and the Coriolis force determine the evolution of a “correctional velocity” based on Newton's 2nd law of motion. This velocity, however, is decoupled from the continuity equation so its horizontal divergence does not affect the pressure. The improvement of the trajectory calculation is obtained by integrating a linear combination of National Centers for Environmental Predictions’ (NCEP) velocity field and the “correctional velocity” computed from NCEP's temperature and geopotential fields. The improvement of the model-generated trajectories over those obtained from a straightforward advection by the velocity field is verified by comparing the calculated trajectories to the observed trajectories of 379 constant-level balloons launched in 1971 as part of the EOLE experiment. For flight times between 2 and 10 weeks the new algorithm generates trajectories that are statistically closer to the observed EOLE trajectories than those obtained from advection by the velocity field only. There are, however, several balloon flights where for certain, isolated, values of its parameters the hybrid model generates trajectories that are actually less accurate than those of straightforward advection. For balloon flights between 2 and 9 weeks the worst hybrid model trajectories are only about 4% less accurate than those of straightforward advection. The model's improvement over advection by the velocity field reaches a maximum value of over 15% for 4–7 week long trajectories while for 1 week long, or longer than 10 week long trajectories the model offers no improvement over straightforward advection by the velocity field.
Keywords: Lagrangian dispersion; Constant Level Balloons;

The concentrations of air pollutants varied inherently with meteorological conditions and pollutant emission level. From the statistical properties (probability density) of air pollutants, it is easy to estimate how many times the exceedance compared with air quality standards occurs. In this paper, three distributions (lognormal, Weibull and type V Pearson distribution) were utilized to simulate the PM10 concentration distribution in Taiwan areas. Air quality data of three monitoring stations, Hsin-Chu, Sha-Lu and Gian-Jin, were taken to compare the characters of PM10 concentrations during a five-year period (1995–1999). Two parametric estimating methods, method of moments and method of least squares, were used to estimate the parameters of these three theoretic distributions. Therefore, the exceedance frequency of air pollutant concentration and emission source reduction can be predicted from these theoretic distributions. These results show that the lognormal is the best distribution to represent the PM10 daily average concentration. Between these two parametric estimation methods, the method of least squares has more accurate results than the moments method. The PM10 concentration distributions of Hsin-Chu and Sha-Lu stations are all unimodal distributions, but the distribution of Gian-Jin is a bimodal distribution. The measured PM10 concentrations of Gian-Jin station were divided into two seasons, and the parameters were computed individually. The reproduced bimodal distribution, which combined with the two unimodal distributions, agrees well with measured data. This result shows that the distribution type of PM10 concentration varied greatly in different areas, and could be influenced by local meteorological conditions in different seasons. In addition, the probabilities exceeding the air quality standard (PM10>125 μg m−3) and emission sources reduction of PM10 concentration to meet the air quality standard for Hsin-Chu, Sha-Lu and Gian-Jin stations are predicted successfully.
Keywords: Lognormal distribution; Weibull distribution; Type V Pearson distribution; Method of moments; Method of least squares;

Trend of acid rain and neutralization by yellow sand in east Asia—a numerical study by Hiroaki Terada; Hiromasa Ueda; Zifa Wang (503-509).
Acid rain and its neutralization by yellow sand in East Asia were investigated numerically by an Air Quality Prediction Modeling System (AQPMS). AQPMS consists of advection, diffusion, dry and wet deposition, gas-phase chemistry and the liquid-phase chemistry. A new deflation module of the yellow sand (Asian soil dust) was designed to provide explicit information on the dust loading. Different from the previous ones for Sahara and Australian deserts, this new one includes three major predictors, i.e., the friction velocity, the surface humidity and the predominant weather system, while this module was linked to the AQPMS. For model validation, the predicted pH values and sulfate- and nitrate-ion levels of precipitation, together with the surface concentrations of gaseous pollutants, were compared with the measured values at atmospheric monitoring stations, and a reasonable agreement was obtained. Firstly, the trend of the acid rain in East Asia due to the rapid increase of Chinese pollutants emission was investigated, and a remarkably rapid increase of acid rain area was predicted in the period from 1985 to 1995, the monthly mean pH values showing the decrease of 0.3–0.8 in the area from the center to northeast in China, and 0.1–0.2 even in Japan and Korea. Secondly, the simulation results of April 1995 exhibited a strong neutralization of the precipitation by the yellow sand. The monthly mean pH values in the northern China showed a remarkable increase of 0.6–1.8 by neutralization effect of the yellow sand, while the increases in the southern China were less than 0.1. Even in Korea and Japan the yellow sand caused the increase of the pH value of rain by 0.1–0.2.
Keywords: Acid rain; Numerical model; Yellow sand; Deflation module; Soil dust; Acidity; Sulfate; Nitrate;

Effects of wind shear on pollution dispersion by Chris J. Walcek (511-517).
Using an accurate numerical method for simulating the advection and diffusion of pollution puffs, it is demonstrated that point releases of pollution grow into a shape reflecting the vertical wind shear profile experienced by the puff within a time scale less than 4 h. For distances beyond several 10 s of kilometers from a release point, shear-related dispersion effects are probably the dominant mechanism affecting the area and magnitude of surface impacts. For assessing long-range pollutant dispersion, the common assumption that pollutants disperse as horizontally spherical “puffs” in the atmosphere is inherently inaccurate since shear-induced horizontal spreading of pollution is not a homogeneous “turbulent-like” diffusion process. A Lagrangian puff model can simulate an area impacted by a pollution puff only if larger shear-dependent horizontal puff dispersions are assumed. However, even if impacted areas are reasonably simulated, peak concentrations will be severely underestimated since atmospheric puffs influenced by even small amounts of wind shear are nonspherical. If horizontal dispersion coefficients in a Lagrangian puff model are adjusted so that peak concentrations are correctly simulated, then the calculated pollution impact area will be severely skewed. In shear environments, no choice of horizontal dispersion coefficients in a single-puff Lagrangian model will yield reasonable correlations with puffs that are skewed into nonspherical shapes by atmospheric wind shear.
Keywords: Air pollution; Pollution dispersion; Gaussian dispersion; Trajectories; Lagrangian; Puff models; Long-range transport; Trajectory; Plume;

Methyl butenols are emitted by the vegetation to the atmosphere. The reaction with nitrate radicals produces semivolatile substances that may contribute to the atmospheric particular matter. In this preliminary laboratory study, measurements of particle concentration and size distribution were conducted with three methyl butenols, 3-methyl-2-butene-1-ol (MBO321), 3-methyl-3-butene-1-ol (MBO331), and 2-methyl-3-butene-2-ol (MBO232). There was little evidence for production of aerosol from the primary products; however, formation of secondary products caused particle nucleation. The result indicated that NO3 oxidation of primary products from MBO321 and 331 gave substances with a vapor pressure range from 4×10−9 to 4×10–7  Pa, while the range for MBO 232 was a factor of 10 higher.
Keywords: Aerosol formation; Particle nucleation; Nitrate radical; Unsaturated alcohol; Oxidation products;

On the escape of pollutants from urban street canyons by Jong-Jin Baik; Jae-Jin Kim (527-536).
Pollutant transport from urban street canyons is numerically investigated using a two-dimensional flow and dispersion model. The ambient wind blows perpendicular to the street and passive pollutants are released at the street level. Results from the control experiment with a street aspect ratio of 1 show that at the roof level of the street canyon, the vertical turbulent flux of pollutants is upward everywhere and the vertical flux of pollutants by mean flow is upward or downward. The horizontally integrated vertical flux of pollutants by mean flow at the roof level of the street canyon is downward and its magnitude is much smaller than that by turbulent process. These results indicate that pollutants escape from the street canyon mainly by turbulent process and that the net effect of mean flow is to make some escaped pollutants reenter the street canyon. Further experiments with different inflow turbulence intensities, inflow wind speeds, and street aspect ratio confirm the findings from the control experiment. In the case of two isolated buildings, the horizontally integrated vertical flux of pollutants by mean flow is upward due to flow separation but the other main results are the same as those from the control experiment.
Keywords: Flow and dispersion; Urban street canyon; Pollutant transport; Vertical turbulent flux of pollutants;

Modelling gaseous dry deposition in AURAMS: a unified regional air-quality modelling system by Leiming Zhang; Michael D. Moran; Paul A. Makar; Jeffrey R. Brook; Sunling Gong (537-560).
An upgraded parameterization scheme for gaseous dry-deposition velocities has been developed for a new regional air-quality model with a 91-species gas-phase chemistry mechanism, of which 48 species are “transported” species. The well-known resistance analogy to dry deposition is adopted in the present scheme, with both O3 and SO2 taken as base species. Stomatal resistances are calculated for all dry-depositing species using a “sunlit/shaded big-leaf” canopy stomatal resistance submodel. Dry-ground, wet-ground, dry-cuticle, and wet-cuticle resistances for O3 and SO2, and parameters for calculating canopy stomatal resistance and aerodynamic resistance for these two base species are given as input parameters for each of the 15 land-use categories and/or five seasonal categories considered by the scheme. Dry-ground, wet-ground, dry-cuticle, and wet-cuticle resistances for the other 29 model species for which dry deposition is considered to be a significant process are scaled to the resistances of O3 and SO2 based on published measurements of their dry deposition and/or their aqueous solubility and oxidizing capacity. Mesophyll resistances are treated as dependent only on chemical species. Field experimental data have then been used to evaluate the scheme's performance for O3 and SO2. Example sets of modelled dry-deposition velocities have also been calculated for all 31 dry-deposited species and 15 land-use categories for different environmental conditions. This new scheme incorporates updated information on dry-deposition measurements and is able to predict deposition velocities for 31 gaseous species for different land-use types, seasons, and meteorological conditions.
Keywords: Air-quality modelling; Gaseous species; Dry deposition; Deposition velocity; Big-leaf model; Surface resistance;

Simulation of the transport and dispersion of chemical tracer in complex terrain has been performed using artificial neural networks (ANN). The ANN method has been applied to relatively high temporal resolution data (hourly averages—long time series), and lower-resolution data (daily averages—short time series). The meteorological input consisting of surface and upper-air data was selected in such a way that it optimally represents the spatial inhomogeneity of the flow field, atmospheric stability, and synoptic conditions. In both cases, the inclusion of previous tracer concentrations as input has significantly improved the ANN performance. For the daily average case, several isolated single-point sharp peaks that were recorded in the series of daily concentrations were not resolved by the ANN. An improved correlation with measurements (from 0.946 to 0.997) was obtained after simple smoothing of the tracer concentrations. Because the number of data samples was small, a “leave-one-out” method was used. The hourly averages provided more cases and thus more significant input for ANN training; however, it brought more uncertainty into the selection of appropriate inputs because of the transport time due to the separation between the source and receptor. Here, training was performed using the first 85% of cases; the rest was used for testing. The ANN-simulated hourly concentrations agreed well with the measured concentrations and yielded correlation coefficients for the training and testing sets of 0.844 and 0.896, respectively. The sensitivity analysis revealed that previous concentration data contributed to resolving peaks in simulated concentrations while meteorological data provided more information on the temporal characteristics of the simulated tracer concentrations. A rudimentary comparison with traditional statistical methods revealed that the ANN performed better and showed fewer limitations as a tool for tracer modeling, especially for long-term prediction.
Keywords: Air quality modeling; Tracer concentration; Field program; Simulation; Artificial intelligence;

OH formation from the ozonolysis reactions of seven internal alkenes with 4–6 carbons, styrene, trans-β-methyl styrene, and α-methyl styrene was studied using complementary techniques. A small-ratio relative-rate technique in which small quantities of OH tracers are added to monitor OH formation yields provided the following results: trans-2-butene, 0.64±0.12; cis-2-butene, 0.33±0.05; trans-2-pentene, 0.46±0.08; cis-2-pentene, 0.29±0.06; trans-3-hexene, 0.53±0.08; cis-3-hexene, 0.36±0.07; and 2-methyl-2-butene, 0.98±0.24. For styrene, trans-β-methyl styrene, and α-methyl styrene, OH yields of 0.07±0.04, 0.22±0.09, and 0.23±0.12 were measured, respectively. A second method, which monitors product formation from the OH reaction with 2-butanol was used to derive OH formation yields from 2,3-dimethyl-2-butene, 2-methyl-2-butene and cis-2-pentene, and provided yields of 0.91±0.14, 0.80±0.12, and 0.27±0.07, respectively. The results are briefly discussed in terms of the relationship between structures of these alkenes and OH formation.
Keywords: Urban air; Alkene ozonolysis; OH radical; Indoor air;

This paper presents a direct approach to solving the aerosol coagulation equation. Newton–Cotes formulas are used to discretize the integral terms, and the semi-discrete system is built using collocation. A semi-implicit Gauss–Seidel time integration method is employed. The approach generalizes the semi-implicit method of Jacobson and is more accurate.
Keywords: Aerosol dynamics; Coagulation; Newton–Cotes integration;