G. J. Engelhart

Constraining Particle Evolution from Wall Losses, Coagulation, and Condensation-Evaporation in Smog-Chamber Experiments: Optimal Estimation Based on Size Distribution Measurements

A goal of secondary organic aerosol (SOA) experiments performed in smog chambers is to determine the condensation of SOA onto suspended particles. Complicating the calculation of the condensation rate are uncertainties in particle wall-loss rates. Wall-loss rates generally depend on particle size, turbulence in the bag, the size and shape of the bag, and particle charge. In analyzing smog-chamber data, some or all of the following assumptions are commonly made regarding the first-order wall-loss rate constant: (a) that it is constant during an experiment; (b) that it is constant between experiments; and (c) that it is not a strong function of particle size for the relatively narrow size distributions in smog chamber experiments. Each of these assumptions may not be justified in some circumstances. We present the development and evaluation of the Aerosol Parameter Estimation (APE) model. APE is an inverse model that solves the aerosol general dynamic equation to determine best estimates for the size-dependent condensation rate and size-dependent wall-loss rate as a function of time. Size distribution measurements from a Scanning Mobility Particle Sizer (SMPS) provide time boundary conditions that constrain the general dynamic equation. The APE model is tested using data from a smog chamber experiment with dry ammonium sulfate particles in which no condensation occurred. Finally, we assess the variability in predicted SOA production between different wall-loss correction methods for relatively-fast-chemistry limonene-ozonolysis experiments and relatively-slow-chemistry toluene-oxidation experiments. In the fast limonene experiments, wall-loss correction methods agree within 10% for SOA production, and in the slow toluene experiments, wall-loss correction methods disagree up to a factor of 2.

New particle formation and growth in biomass burning plumes: An important source of cloud condensation nuclei

Experiments were performed in an environmental chamber to characterize the effects of photo-chemical aging on biomass burning emissions. Photo-oxidation of dilute exhaust from combustion of 12 diff ...

Properties of Aged Aerosols in the Eastern Mediterranean

Three month-long campaigns (FAME-07, -08, -09, -11) have been conducted at Finokalia in order to assess the water uptake, volatility and oxidation state of aged organic particulate matter (PM) along with aerosol nucleation. Finokalia is a remote coastal station located in the southeast of the Mediterranean Sea on the island of Crete, Greece. The site lacks local sources as there is no notable human activity at a range of approximately 15 km. The PM that reaches the site is heavily influenced by the surrounding source regions and the organic content highly oxidized. During the summer aerosols always contained water even under very low relative humidity (RH < 20%) possibly due to their acidity. Organic aerosol was highly and almost uniformly oxidized and the resulting mass spectra did not change throughout the summer campaign, even after it was thermally treated, indicating a high oxidation state. An organic aerosol evaporation model was used to simulate the behaviour of the thermally treated aerosol and showed that aged organic PM was two or more orders of magnitude less volatile than laboratory-generated secondary organic PM. Nucleation is controlled by the gas phase ammonia levels and the resulting PM acidity, at least during the summer, resulting in low number of particle formation events per year.

Characterization of Sesquiterpene Secondary Organic Aerosol: Thermodynamic Properties, Aging Characteristics, CCN Activity, and Droplet Growth Kinetic Analysis

Secondary Organic Aerosols (SOA) can be a considerable source of ambient organic aerosol. The generation of SOA from different hydrocarbon precursors yields different low volatile particulates that could affect aerosol hygroscopicity, CCN activity, and cloud droplet growth kinetics. In this work we investigate SOA from monoterpene and sesquiterpene ozonolysis experiments and characterize the ability of the organic component to depress surface tension, act as CCN, and affect growth kinetics. In addition, we provide experimental evidence that the aging of SOA yields hygroscopic materials.