Evangelia Kostenidou

An Algorithm for the Calculation of Secondary Organic Aerosol Density Combining AMS and SMPS Data

An algorithm for the calculation of organic aerosol density in mixed organic-inorganic particles combining measurements by the Aerodyne Aerosol Mass Spectrometer (AMS) and the Scanning Mobility Particle Sizer (SMPS) was developed. The approach is applicable to particles with size-dependent composition. The estimated density of secondary organic aerosol (SOA) formed by α-pinene, β-pinene, and d-limonene ozonolysis was in the range of 1.4–1.65 g cm− 3. However, in two cases the SOA had much lower density (0.9–1.0 g cm − 3 )indicating that there may be changes in particle morphology depending on the conditions of SOA formation. The high estimated density for these systems suggests that SOA particles may be solid or waxy. Based on our results, SOA yields in smog chamber experiments may be a lot higher (up to 50%) than the currently assumed values. Most of the literature results have been calculated by measuring the SOA number distribution with an SMPS and then multiplying the volume concentration with a density equal to 1 or 1.2 g cm − 3 .

Vehicle and Driving Characteristics That Influence In-Cabin Particle Number Concentrations

In-transit microenvironments experience elevated levels of vehicle-related pollutants such as ultrafine particles. However, in-vehicle particle number concentrations are frequently lower than on-road concentrations due to particle losses inside vehicles. Particle concentration reduction occurs due to a complicated interplay between a vehicles air-exchange rate (AER), which determines particle influx rate, and particle losses due to surfaces and the in-cabin air filter. Accurate determination of inside-to-outside particle concentration ratios is best made under realistic aerodynamic and AER conditions because these ratios and AER are determined by vehicle speed and ventilation preference, in addition to vehicle characteristics such as age. In this study, 6 vehicles were tested at 76 combinations of driving speeds, ventilation conditions (i.e., outside air or recirculation), and fan settings. Under recirculation conditions, particle number attenuation (number reduction for 10-1000 nm particles) averaged 0.83 ± 0.13 and was strongly negatively correlated with increasing AER, which in turn depended on speed and the age of the vehicle. Under outside air conditions, attenuation averaged 0.33 ± 0.10 and primarily decreased at higher fan settings that increased AER. In general, in-cabin particle number reductions did not vary strongly with particle size, and cabin filters exhibited low removal efficiencies.

Physical and chemical properties of 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) aerosol

The properties and the chemical fate of later generation products of the oxidation of biogenic organic compounds are mostly unknown. The properties of fresh MBTCA aerosol, a later generation product of the oxidation of monoterpenes in the atmosphere, were determined combining an aerosol mass spectrometer (AMS), a thermodenuder, and a scanning mobility particle sizer. Based on its AMS spectrum m/z 141.055 (C7H9O3+) could be used as an MBTCA signature. The MBTCA particle density was 1.43 ± 0.04 g cm-3, its saturation concentration was (1.8 ± 1.3) × 10-3 μg m-3 at 298 K, and its vaporization enthalpy was 150 ± 15 kJ mol-1. After OH radical exposure (∼1.2 days) and UV illumination the average aerosol O:C ratio decreased from 0.72 to 0.58-0.64 suggesting net fragmentation. Our findings suggest that the reactions of MBTCA with OH lead to CO2 loss with or without an oxygen addition.

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

10 A method is developed following the work of Grieshop et al. (2009) for the determination of the organic aerosol (OA) volatility distribution combining thermodenuder 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 thermodenuder (TD) was operated at temperatures ranging from 25 to 250 o C with a 14 s 15 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 20 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 o C. The resulting volatility distributions suggested that around 60-75% of the cooking OA (COA) at concentrations 25 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 30 enthalpy as well as the SVOC content of the OA.