Primary Organic Aerosols

Abstract

Primary organic aerosol (POA) constitutes the emissions from both natural (vegetation and micro-organisms) and anthropogenic sources such as combustion of fossil fuels and biofuels, and open biomass burning (forest fire). Semi-volatile nature of POA emissions leads to overestimation in the traditional emission inventories and chemical transport models. Another class of primarily emitted volatile species, i.e., intermediate volatile organic compounds (IVOCs), present around 0.28–2.5 times of POA, potential secondary organic aerosols (SOAs) precursors, also goes unnoticed. Phase partitioning mechanisms depending on their source, dilution, and volatility distribution make the contribution of POA to overall organic aerosols (OA) budget controversial. Further, the complex and higher particle emission rates and the gas-phase chemical transformation processes lead to the conceptual ambiguity between primary and secondary organic aerosol, thus rendering physico-chemical and optical properties to be least understood. Researchers have overcome the need of complete molecular identification of gaseous species to simulate the gas-particle partitioning by developing a two-dimensional volatility basis scheme (2-D-VBS) that employs the vapor pressure and degree of oxygenation. Here, we also illustrate the chemical composition-dependent volatility distributions for different sources used to ascertain the correct POA emission factors. This suggest that the policymakers and environmental regulating authorities need to take into account the SVOCs and IVOCs causing positive and negative sampling artifacts in order to correctly account for POA source contributions.