Semisolidity and Reactivity of Atmospheric Organic Aerosol Particles

Harvard University, Cambridge MA

Investigators

Abstract

Secondary organic aerosols (SOA) are particulate phases that form in the atmosphere through oxidation, transformation and condensation of gas phase, or volatile organic compounds (VOCs). Source VOCs can be either biogenic or man-made compounds. Recent scientific investigations have demonstrated that some SOA particles exhibit the physical properties of a solid rather than those of liquids normally expected of aerosol. Intermediate behavior of a hard solid of negligible viscosity (>10^12 Pa s) and a thick liquid of high viscosity (<10^2 Pa s) is observed in a transitional range, herein termed semisolid. The diffusion of molecules in such a semisolid may be orders of magnitude slower than in a liquid, yet still fast enough that reactive chemistry can take place. The set of questions raised in this project are investigative, even speculative in nature, designed to shed light on the mechanical properties of semisolid SOA, individual (and bulk) properties of aerosols. A first objective is to quantify how semi-solidity varies with relative humidity and SOA chemistry. A second objective is to measure how chemical reactivity, including both the loss of gas-phase reactants and the appearance of particle-phase products, varies with SOA semi-solidity. The study will make extensive use of an environmental chamber in which VOCs will be oxidized. The atmospheric occurrence of organic semisolid particles may have important implications for gas uptake and subsequent chemical aging of SOA particles, which in turn are of interest to their climate forcing properties and their effects on public health.