Dilution Chamber Research Articles

Feedback based gas sensing setup for ppb to ppm level sensing.

Sensing and quantification of gas at low concentrations is of paramount importance, especially with highly flammable and explosive gases such as hydrogen. Standard gas sensing setups have a limit of measuring ultra-low concentrations of few parts per billion unless the external gas cylinders are changed to ones with low concentrations. In this work, we describe a home-built resistance based gas sensing setup that can sense across a wide concentration range, from parts per billion to parts per million, accurately. This was achieved using two dilution chambers: a process chamber and a feedback assembly where a part of the output gas from the dilution chamber is fed back to the inlet mass flow controller, enabling enhanced dilutions without increasing the number of mass flow controllers. In addition, the gas-sensing setup can measure across a large temperature range of 77-900K. The developed setup was then calibrated using palladium thin films and ZnO nanoparticle thin films. The setup was tested for reproducibility, concentration response, temperature response, etc. Corresponding sensitivity values were calculated and found to be in good agreement with published values, validating our setup design.

Fabrication of PVDF cation exchange membrane for electrodialysis: Influence and mechanism of crystallinity and leakage of co-ions

The influence of crystallization behavior on membrane structure and performance has been extensively studied in many membrane fields. Some studies of proton exchange membranes used in fuel cells have involved the influence of crystallization. However, crystallization of ion exchange membranes (IEMs) used in electrodialysis (ED) has been rarely studied. Co-ion leakage in ED process is adverse, but there have been few mechanism studies regarding how co-ions cross IEM surfaces on the concentration chamber side and migrate into the dilution chamber to reduce current efficiency. Polyvinylidene fluoride is a kind of good crystalline material. In this study, sodium dodecyl benzene sulfonate was introduced as the functional material, with polyvinylpyrrolidone (PVP) as the hydrophilizing agent. They were blended to prepare cation exchange membranes (CEMs). Amorphous PVP was used to regulate membrane crystallization behavior. The results showed that, when the ion exchange capacity is basically equal, surface roughness of the prepared crystalline CEMs was low and the structure dense. The ED efficiency significantly surpassed amorphous CEMs. The co-ion leakage of amorphous CEMs was greater than those of crystalline CEMs due to the rough and non-dense surfaces of amorphous CEMs. However, after densification modification, although surface resistance increased, co-ion leakage was effectively suppressed. Combining simulation and theoretical analysis, it was presumed that dense membrane surfaces on the concentrated chamber side was very important for suppressing co-ion leakage. This study on the influence and mechanism of crystallinity and co-ion leakage was helpful for optimizing CEM mass transfer and improving current efficiency.

Emission inventory of inorganic trace gases from solid residential fuels over the National Capital Territory of India.

In developing nations, solid residential fuels are the major sources of primary energy for various domestic activities. To date, the emission inventory of inorganic trace gases over National Capital Territory (NCT) was prepared using either default or country-specific emission factors. In this paper, we report (for the first time) the spatial variation of emission factors (EFs) of inorganic trace gases (SO2, NO, NO2, CO, CO2, and CH4) from the residential fuels used in slums and rural areas of NCT determined using dilution chamber in the laboratory. 147 residential fuel samples, including fuelwood, dung cake, crop residues, coal, etc., were collected at 149 NCT locations out of 675 slum clusters and 146 rural villages. The range of EF(s) of SO2 (0.02 ± 0.01 to 0.04 ± 0.01gkg-1), CH4 (0.10 to 0.34gkg-1), NO2 (0.01 to 0.02gkg-1) is lower than the CO (3.55 ± 1.72 to 6.07 ± 1.53gkg-1) and CO2 (0 to 129.45 ± 46.94gkg-1). The north and north west districts of NCT are emission hotspots for CH4, NO, and NO2 emissions, whereas, the southern and northern areas of NCT are for CO2. These citywide emission inventories (0.05° × 0.05°) of inorganic trace gases are prepared using laboratory-determined EFs and available consumption data determined by recent survey information. Among solid residential fuels, fuel wood, and dung cake are two major contributors to inorganic trace gases in NCT.

Estimation of secondary organic aerosol formation parameters for the volatility basis set combining thermodenuder, isothermal dilution, and yield measurements

Abstract. Secondary organic aerosol (SOA) is a major fraction of the total organic aerosol (OA) in the atmosphere. SOA is formed by the partitioning onto pre-existent particles of low-vapor-pressure products of the oxidation of volatile, intermediate-volatility, and semivolatile organic compounds. Oxidation of the precursor molecules results in a myriad of organic products, making the detailed analysis of smog chamber experiments difficult and the incorporation of the corresponding results into chemical transport models (CTMs) challenging. The volatility basis set (VBS) is a framework that has been designed to help bridge the gap between laboratory measurements and CTMs. The parametrization of SOA formation for the VBS has been traditionally based on fitting yield measurements of smog chamber experiments. To reduce the uncertainty in this approach, we developed an algorithm to estimate the SOA product volatility distribution, effective vaporization enthalpy, and effective accommodation coefficient combining SOA yield measurements with thermograms (from thermodenuders) and areograms (from isothermal dilution chambers) from different experiments and laboratories. The algorithm is evaluated with “pseudo-data” produced from the simulation of the corresponding processes, assuming SOA with known properties and introducing experimental error. One of the novel features of our approach is that the proposed algorithm estimates the uncertainty in the predicted yields for different atmospheric conditions (temperature, SOA concentration levels, etc.). The uncertainty in these predicted yields is significantly smaller than that of the estimated volatility distributions for all conditions tested.

Development and Evaluation of an Innovative Method Based on Dilution to Sample Solid and Condensable Fractions of Particles Emitted by Residential Wood Combustion

An innovative and simple method based on dilution, named as the dilution chamber (DC), allowing the measurement of solid and condensable fractions of particulate matter emitted by residential wood ...

Ferrowax microvalves for fully automated serial dilution on centrifugal microfluidic platforms.

We herein describe a centrifugal microfluidic system to accomplish a fully automated serial dilution. The liquid flow on the disc was regulated by utilizing ferrowax microvalves systematically integrated into the channels within specially designed metering structures. By opening the differently positioned microvalves through irradiation of IR laser to allow metering, the same amount of diluent was serially eluted to the dilution chamber from the same diluent chamber. After dilution, the diluted samples were automatically delivered to the respective final product chambers by appropriately opening or closing the microvalves in the connecting channels, followed by rotating the disc. Based on this unique design principle, six consecutive two-fold and 10-fold dilutions were successfully achieved, yielding excellent accuracy in a wide dynamic range up to six orders of magnitude. Very importantly, the overall serial dilution process, including the diluent addition, mixing, and product transfer steps, was completed very rapidly within 5 min, due to the minimized procedures enabled by the automated actuation of the ferrowax microvalves at the rationally designed positions. We expect our centrifugal microfluidic system would serve as a powerful elemental tool to realize fully automated diagnostic microsystems involving the serial dilution process.

Regulation and control methods for the unattached fraction of 220Rn progeny in a 220Rn progeny chamber

The unattached fraction of 220Rn progeny is one of the key parameters in lung dose evaluation models. To study the behavior of unattached 220Rn progeny and to prepare for calibration of the unattached 220Rn progeny monitors, a 220Rn progeny chamber that could stably regulate different unattached fractions of 220Rn progeny was established. A recirculation loop to eliminate the effects of the sampling and a loop connected to the dilution chamber to supplement the carrier aerosol were set up. Also, a theoretical model regarding the regulation of the unattached fraction of 220Rn progeny was established. Continuous measurements of the unattached fraction were conducted using the combination of a single-layer wire screen and a filter membrane. The experimental results showed that, under different aerosol levels, the relative standard deviation (RSD) of 212Pb concentration during the continuous samplings was within 10.7% and the RSD of the unattached fraction of 212Pb was within 9.9%. The relative deviation between the theoretical and the experimental values of 212Pb concentration was within 16.7% and the model calculation values of the unattached fraction of 212Pb were consistent with measured results.

An Integrated Centrifugal Degassed PDMS-Based Microfluidic Device for Serial Dilution.

We propose an integrated serial dilution generator utilizing centrifugal force with a degassed polydimethylsiloxane (PDMS) microfluidic device. Using gas-soluble PDMS as a centrifugal microfluidic device material, the sample can be dragged in any arbitrary direction using vacuum-driven force, as opposed to in a single direction, without adding further actuation components. The vacuum-driven force allows the device to avoid the formation of air bubbles and exhibit high tolerance in the surface condition. The device was then used for sample metering and sample transferring. In addition, centrifugal force was used for sample loading and sample mixing. In this study, a series of ten-fold serial dilutions ranging from to with about 8 μL in each chamber was achieved, while the serial dilution ratio and chamber volume could easily be altered by changing the geometrical designs of the device. As a proof of concept of our hybrid approach with the centrifugal and vacuum-driven forces, ten-fold serial dilutions of a cDNA (complementary DNA) sample were prepared using the device. Then, the diluted samples were collected by fine needles and subject to a quantitative polymerase chain reaction (qPCR), and the results were found to be in good agreement with those for samples prepared by manual pipetting.

In Vitro primary human airway epithelial whole exhaust exposure

The method outlined in this article is a customization of the whole exhaust exposure method generated by Mullins et al. (2016) using reprogrammed primary human airway epithelial cells as described by Martinovich et al. (2017). It has been used successfully to generate recently published data (Landwehr et al. 2021). The goal was to generate an exhaust exposure model where exhaust is collected from a modern engine, real-world exhaust concentrations are used and relevant tissues exposed to assess the effects of multiple biodiesel exposures. Exhaust was generated, gently vacuumed into a dilution chamber where it was diluted 1/15 with air and then vacuumed into an incubator containing the primary cell cultures for exposure. Exhaust physico-chemical properties including combustion gas concentrations and particle spectra were then analyzed using a combustion gas analyzer and a Universal Scanning Mobility Particle Sizer. 24 h after exposure, cellular viability and mediator release were measured using Annexin-V/PI staining and meditator multiplexing kits respectively. This method was generated to test biodiesel exhaust exposures but can be easily adapted for any type of engine exhaust exposure or even potentially other respirable environmental exposures such as woodsmoke.The main customization points for this method are:•Exhaust generated by a diesel engine equipped with EURO VI exhaust after treatment devices including diesel particulate filter and diesel oxidation catalyst.•The generated exhaust was diluted 1/15 with air to replicate real world exposure concentrations.•Used primary human airway epithelial cells obtained from bronchoscope brushings from multiple volunteers and reprogrammed to allow multiple, comparative exposures from the same individual.

Theoretical equilibration time is supported by measurement study of residence time at dilution sampling on fine particulate matter emissions from household biofuel burning

Household biofuel burning contributes a large proportion of fine particulate matter (PM2.5), black carbon (BC), and organic carbon (OC) emissions in many parts of the world. Dilution sampling has been widely used to characterize PM2.5 emitted from biofuel burning. The residence time in the dilution chamber is a key parameter for accurate sampling. However, residence time has not yet been adequately characterized for biomass combustion. In this work, we investigated the effects of residence time of dilution sampling on PM2.5 emissions from a typical Chinese household stove burning typical biofuels including three major crop wastes and one type of wood. The filter based measurements indicated that the emission factors for PM2.5 and its main chemical components such as OC, EC, Cl−, and K+ did not vary with the residence time over the range of 1–80 s. Theoretical estimation of average time scale for achieving dynamic equilibrium (τs) between the gas and particle phase in the dilution sampling system was less than 1 s. Both the measurement study and theoretical simulations indicated that dilution sampling with a residence time of 1s can provide adequately reliable results for PM2.5 emissions from biofuel burning under the condition of these experiments. A simple way to estimate the equilibration time based on measured average PM2.5 concentration was proposed. Recommendations are provided for the residence time for dilution sampling of accurate measurements of PM2.5 emissions from biofuel burning.

Determination of calcium and magnesium by atomic absorption spectroscopy and flame photometry

The comparison of emission intensities of unknown samples to either that of standard solutions, the alkali and alkaline earth metals. Flame photometer has both quantitative and qualitative applications. Flame photometer with monochromators emits radiations of characteristic wavelengths which help to detect the presence of a particular metal in the sample. This help to determine the availability of alkali and alkaline earth metals. Simple direct analysis procedure calcium, magnesium, in test solution flow injection analysis using flame atomic absorption spectroscopy or flame photometry designed using a well-mixed dilution chamber to increase calibration range. Analysis results real samples correspond to those found in the flame batch atomic procedure. Using the dilution chamber allows possibility of calibration using a dilution profile a single concentrate standard for each element and an empirical dilution equation that can be used to all elements are defined in each sample.

Improved bauxite residue dealkalization by combination of aerated washing and electrodialysis.

Bauxite residue, a major by-product of the alumina-producing Bayer process, is a serious environmental pollutant due to its high alkalinity. Here, we reported an operation system designed in our laboratory that included washing and electrodialysis dealkalization systems with aeration pipes. Washing with aeration releases a substantial amount of free alkali and attached alkali into water and increases the dealkalization efficiency. The washing liquid was treated with five steps of batch-mode electrodialysis. The average removal of total dissolved solids (TDS) after the aeration and non-aeration electrodialysis processes were 61.30% and 39.61%, respectively. The average removal of OH- under aeration conditions was 76.62%, a value that was greater than the value produced under non-aeration conditions (68.48%). This efficiency was also higher than that of some other reports (64.90-68.50%). Aeration decreased the energy consumption to a greater extent than the non-aeration condition. NaOH was recovered in terms of the concentration chamber, and the NaAl(OH)4 present in the dilution chamber was separated for the electrodialysis treatment. Membrane scaling was generated to a lesser amount under aeration conditions than that of non-aeration conditions, which would improve the dealkalization efficiency. The high repeatability of the experiments was indicated by the intraclass correlation coefficient (P < 0.05).

Estimation of the volatility distribution of organic aerosol combining thermodenuder and isothermal dilution measurements

Abstract. A method is developed following the work of Grieshop et al. (2009) for the determination of the organic aerosol (OA) volatility distribution combining thermodenuder (TD) and isothermal dilution measurements. The approach was tested in experiments that were conducted in a smog chamber using organic aerosol (OA) produced during meat charbroiling. A TD was operated at temperatures ranging from 25 to 250 °C with a 14 s centerline residence time coupled to a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a scanning mobility particle sizer (SMPS). In parallel, a dilution chamber filled with clean air was used to dilute isothermally the aerosol of the larger chamber by approximately a factor of 10. The OA mass fraction remaining was measured as a function of temperature in the TD and as a function of time in the isothermal dilution chamber. These two sets of measurements were used together to estimate the volatility distribution of the OA and its effective vaporization enthalpy and accommodation coefficient. In the isothermal dilution experiments approximately 20 % of the OA evaporated within 15 min. Almost all the OA evaporated in the TD at approximately 200 °C. The resulting volatility distributions suggested that around 60–75 % of the cooking OA (COA) at concentrations around 500 µg m−3 consisted of low-volatility organic compounds (LVOCs), 20–30 % of semivolatile organic compounds (SVOCs), and around 10 % of intermediate-volatility organic compounds (IVOCs). The estimated effective vaporization enthalpy of COA was 100 ± 20 kJ mol−1 and the effective accommodation coefficient was 0.06–0.07. Addition of the dilution measurements to the TD data results in a lower uncertainty of the estimated vaporization enthalpy as well as the SVOC content of the OA.

Nicotine, aerosol particles, carbonyls and volatile organic compounds in tobacco- and menthol-flavored e-cigarettes

BackgroundWe aimed to assess the content of electronic cigarette (EC) emissions for five groups of potentially toxic compounds that are known to be present in tobacco smoke: nicotine, particles, carbonyls, volatile organic compounds (VOCs), and trace elements by flavor and puffing time.MethodsWe used ECs containing a common nicotine strength (1.8%) and the most popular flavors, tobacco and menthol. An automatic multiple smoking machine was used to generate EC aerosols under controlled conditions. Using a dilution chamber, we targeted nicotine concentrations similar to that of exposure in a general indoor environment. The selected toxic compounds were extracted from EC aerosols into a solid or liquid phase and analyzed with chromatographic and spectroscopic methods.ResultsWe found that EC aerosols contained toxic compounds including nicotine, fine and nanoparticles, carbonyls, and some toxic VOCs such as benzene and toluene. Higher mass and number concentrations of aerosol particles were generated from tobacco-flavored ECs than from menthol-flavored ECs.ConclusionWe found that diluted machine-generated EC aerosols contain some pollutants. These findings are limited by the small number of ECs tested and the conditions of testing. More comprehensive research on EC exposure extending to more brands and flavor compounds is warranted.

A Feedback Control Approach to Organic Drug Infusions Using Electrochemical Measurement.

Target-controlled infusion of anesthesia is a closed-loop automated drug delivery method with a computer-aided control. Our goal is to design and test an automated drug infusion platform for propofol delivery in total intravenous anesthesia (TIVA) administration. In the proposed method, a dilution chamber with first-order exponential decay characteristics was used to model the pharmacodynamics decay of a drug. The dilution chamber was connected to a flow system through an electrochemical cell containing an organic film-coated glassy carbon electrode as working electrode. To set up the feedback-controlled delivery platform and optimize its parameters, ferrocene methanol was used as a proxy of the propofol. The output signal of the sensor was connected to a PI controller, which prompted a syringe pump for feedback-controlled drug infusion. The result is a bench-top drug infusion platform to automate the delivery of a propofol based on the measurement of concentration with an organic film-coated voltammetric sensor. To evaluate the performance characteristics of the infusion platform, the propofol concentration in the dilution chamber was monitored with the organic film-coated glassy carbon electrode and the difference between the set and measured concentrations was assessed. The feasibility of measurement-based feedback-controlled propofol delivery is demonstrated and confirmed. This platform will contribute to high-performance TIVA application of intravenous propofol anesthesia.

Afterglow of a microwave microstrip plasma as an ion source for mass spectrometry

A microwave-induced plasma that was previously used for optical emission spectrometry has been repurposed as an afterglow ion source for mass spectrometry. This compact microwave discharge, termed the microstrip plasma (MSP), is operated at 20–50W and 2.45GHz in helium at a flow of 300mL/min. The primary background ions present in the afterglow are ionized and protonated water clusters. An exponential dilution chamber was used to introduce volatile organic compounds into the MSP afterglow and yielded limits of detection in the 40ppb to 7ppm range (v/v). A hydride-generation system was also utilized for detection of volatile hydride-forming elements (arsenic, antimony, tin) in the afterglow and produced limits of detection in the 10–100ppb range in solution. The MSP afterglow was found capable of desorption and ionization of analyte species directly from a solid substrate, suggesting its use as an ion source for ambient desorption/ionization mass spectrometry.

Chemical properties of emission from biomass fuels used in the rural sector of the western region of India

This paper presents the emission factors (EF) of particulate matter (PM), organic carbon (OC), elemental carbon (EC), SO2, NO, NO2 and water soluble ions emitted by residential biomass fuels collected from the rural sector of Western India. Burning process has been simulated using a dilution chamber. Average EF of PM, OC and EC from fuel wood (FW), agricultural residues (AR) and dung cakes (DC) from Western India are estimated as: PM: 1.69 ± 0.98 g kg−1, 2.15 ± 1.00 g kg−1 and 5.37 ± 3.90 g kg−1; OC: 0.43 ± 0.29 g kg−1, 00.54 ± 0.22 g kg−1, 1.14 ± 0.67 g kg−1; EC: 0.25 ± 0.16 g kg−1, 0.23 ± 0.11 g kg−1 and 0.14 ± 0.08 g kg−1 respectively. Similarly, the average EF of SO2, NO and NO2 from FW, AR and DC are determined to be: SO2: 0.66 ± 0.37 g kg−1, 0.29 ± 0.45 g kg−1 and 0.74 ± 0.48 g kg−1; NO: 0.55 ± 0.25 g kg−1, 0.74 ± 0.37 g kg−1 and 0.50 ± 0.23 g kg−1; NO2: 1.05 ± 0.49 g kg−1, 1.41 ± 0.81 g kg−1 and 0.91 ± 0.45 g kg−1 respectively. Cl− has the highest average EF (FW: 97.03 ± 74.98 mg kg−1, AR: 175.71 ± 145.78 mg kg−1, DC: 158.15 ± 109.07 mg kg−1) among the anions, followed by PO43−(FW: 116.59 ± 63.43 mg kg−1, AR: 58.45 ± 1.42 mg kg−1, DC: 85.77 ± 78.85 mg kg−1) and NO3− (FW: 64.23 ± 68.38 mg kg−1, AR: 36.78 ± 22.80 mg kg−1, DC: 50.25 ± 49.33 mg kg−1). Similarly, among the cations, the highest emitters are Na+ (FW: 40.25 ± 26.64 mg kg−1; AR: 47.96 ± 18.35 mg kg−1, DC: 30.51 ± 23.39 mg kg−1), K+ (FW: 29.32 ± 23.95 mg kg−1, AR: 50.89 ± 34.62 mg kg−1, DC: 18.23 ± 14.54 mg kg−1) and NH4+ (FW: 27.93 ± 22.59 mg kg−1; AR: 46.37 ± 41.79 mg kg−1, DC: 41.74 ± 36.01 mg kg−1). The total emissions of trace gases, PM and its chemical composition from FW, AR and DC have been calculated using laboratory generated EFs over Western India.

Characterization of 58 Species Non-Methane Hydrocarbons from a Typical Coke Production Plant in Northern China

The profile of 58 species non-methane hydrocarbons (NMHCs) emissions from a typical coke production plant in northern China was studied. Source samples were taken using a dilution chamber system and were quantified by a gas chromatography/mass spectrometry (GC/MS) system. Based on the measurement of source profiles, aromatic hydrocarbons were found in highest concentration (48.5%), followed by alkanes (42.9%) and alkenes (8.6%), respectively. The emission of C6-C7species took the largest proportion of the NMHCs, toluene and n-hexane were primary species, accounted for 27.4% and 25.1% of total NMHCs. The OH loss rate of NMHCs were estimated, indicated that alkenes (46.5%) played the most important role in LOH, followed by aromatic hydrocarbons (34.3%) and alkanes (19.2%). The top 5 species in LOHwere: 1-butylene, toluene, n-hexane, trans-2-butene and cis-2-pentene.

Active Cage Mechanism of Chaperonin-Assisted Protein Folding Demonstrated at Single-Molecule Level

The cylindrical chaperonin GroEL and its lid-shaped cofactor GroES of Escherichia coli have an essential role in assisting protein folding by transiently encapsulating non-native substrate in an ATP-regulated mechanism. It remains controversial whether the chaperonin system functions solely as an infinite dilution chamber, preventing off-pathway aggregation, or actively enhances folding kinetics by modulating the folding energy landscape. Here we developed single-molecule approaches to distinguish between passive and active chaperonin mechanisms. Using low protein concentrations (100pM) to exclude aggregation, we measured the spontaneous and GroEL/ES-assisted folding of double-mutant maltose binding protein (DM-MBP) by single-pair fluorescence resonance energy transfer and fluorescence correlation spectroscopy. We find that GroEL/ES accelerates folding of DM-MBP up to 8-fold over the spontaneous folding rate. Accelerated folding is achieved by encapsulation of folding intermediate in the GroEL/ES cage, independent of repetitive cycles of protein binding and release from GroEL. Moreover, photoinduced electron transfer experiments provided direct physical evidence that the confining environment of the chaperonin restricts polypeptide chain dynamics. This effect is mediated by the net-negatively charged wall of the GroEL/ES cavity, as shown using the GroEL mutant EL(KKK2) in which the net-negative charge is removed. EL(KKK2)/ES functions as a passive cage in which folding occurs at the slow spontaneous rate. Taken together our findings suggest that protein encapsulation can accelerate folding by entropically destabilizing folding intermediates, in strong support of an active chaperonin mechanism in the folding of some proteins. Accelerated folding is biologically significant as it adjusts folding rates relative to the speed of protein synthesis.

Primary Gas- and Particle-Phase Emissions and Secondary Organic Aerosol Production from Gasoline and Diesel Off-Road Engines

Dilution and smog chamber experiments were performed to characterize the primary emissions and secondary organic aerosol (SOA) formation from gasoline and diesel small off-road engines (SOREs). These engines are high emitters of primary gas- and particle-phase pollutants relative to their fuel consumption. Two- and 4-stroke gasoline SOREs emit much more (up to 3 orders of magnitude more) nonmethane organic gases (NMOGs), primary PM and organic carbon than newer on-road gasoline vehicles (per kg of fuel burned). The primary emissions from a diesel transportation refrigeration unit were similar to those of older, uncontrolled diesel engines used in on-road vehicles (e.g., premodel year 2007 heavy-duty diesel trucks). Two-strokes emitted the largest fractional (and absolute) amount of SOA precursors compared to diesel and 4-stroke gasoline SOREs; however, 35-80% of the NMOG emissions from the engines could not be speciated using traditional gas chromatography or high-performance liquid chromatography. After 3 h of photo-oxidation in a smog chamber, dilute emissions from both 2- and 4-stroke gasoline SOREs produced large amounts of semivolatile SOA. The effective SOA yield (defined as the ratio of SOA mass to estimated mass of reacted precursors) was 2-4% for 2- and 4-stroke SOREs, which is comparable to yields from dilute exhaust from older passenger cars and unburned gasoline. This suggests that much of the SOA production was due to unburned fuel and/or lubrication oil. The total PM contribution of different mobile source categories to the ambient PM burden was calculated by combining primary emission, SOA production and fuel consumption data. Relative to their fuel consumption, SOREs are disproportionately high total PM sources; however, the vastly greater fuel consumption of on-road vehicles renders them (on-road vehicles) the dominant mobile source of ambient PM in the Los Angeles area.