Modelling the formation and radiative effects of secondary organic aerosols in a climate model

Abstract

Aerosols are known to cause changes in temperature and precipitation as a result of their effect on radiation and cloud droplets, and hence have a strong influence on the climate. Organic aerosols that form via the chemical oxidation of a gaseous precursor are called Secondary Organic Aerosols (SO As). The organic nature of these SOAs results in very different optical properties than other aerosols. Most climate models do not take into account SOAs or their radiative properties, however, recent studies have started including small suites of SOAs in order to reduce model biases. The aim of this research is to include the SOAs and their radiative properties to the Regional Climate Model, RegCM4 model (which does not currently model SOAs) in order to reduce the model biases and produce more reliable climate simulations. To achieve this, a recent gas phase module, the CB6r2, was coupled with RegCM4 to produce a more holistic suite of VOCs and chemical mechanisms, most notably ethyne, benzene, and pinene and their corresponding oxidation products. These gas phase products were coupled to Secondary Organic Aerosol Model (SORGAM) to produce the SOAs in RegCM4. The resulting aerosols were aggregated into six categories to reduce the size of the output and group the optical properties. The CB6r2 and SORGAM modules were successfully coupled with RegCM4, and the model now produces SOAs that interact with the radiation scheme. However, the current configuration of emission and chemical boundary conditions used for the CB6r2 do not produce a reliable chemical output. As a result of this, the SOA products are not yet reliable. Nevertheless, RegCM4 simulations using CB6r2, and the coupled CB6r2-SORGAM were run and analysed to identify methods that would improve the SOA simulations with RegCM4. The analysis also revealed a reduction in temperature and shortwave radiation over Europe when running RegCM4 with SORGAM, thereby showing the potential of SOA system in RegCM4.