Dr James Ciarlo`, a post-doctoral scholar at the Earth System Physics Section of the Abdus Salam International Centre for Theoretical Physics (ICTP) and the National Institute of Oceanography and Experimental Geophysics (OGS) in Trieste, Italy and Dr Noel Aquilina from the Department of Chemistry at the University of Malta published “A Modified Gas-Phase Scheme for Advanced Regional Climate Modelling with RegCM4” in Climate Dynamics.
The study is a follow-up of Dr Ciarlo`’s doctoral research which was funded by Malta Government Scholarship Scheme (Grant No.: MEDE541/2013/39).
Atmospheric chemical processes are complex due to the numerous natural and anthropogenic emission sources that are found in different environments, as well as the atmospheric dynamics present in a given region. Urban, rural, or maritime environments impact the local or regional atmospheric chemistry in ways that over short time scales modulate the air quality but over longer time scales drive the climate system.
Volatile Organic Compounds (VOCs) are chemical species that include a wide range of compounds such as isoprene, limonene, and α-pinene which are naturally released namely from vegetation, plants, and trees (biogenic), as well as those directly emitted from anthropogenic activities, such as ethyne, benzene, toluene, and xylene. Once released in the atmosphere they are oxidized and transformed into radicals that contribute to the production of surface ozone and secondary organic aerosols (SOAs).
Moreover, VOCs interact with the hydroxyl radical, the atmosphere’s principal oxidizing agent, that controls, among others, the lifetime of a powerful greenhouse gas such as methane, thus, overall VOCs are pivotal to changes in air quality and climate.
The Regional Climate Model (RCM), RegCM4 is a community model, developed and operated by the ICTP. This RCM is one of the most commonly used in the regional climate modelling community as it can project scenarios at high resolution and allows simulation of atmospheric chemistry and climate, accounting for both surface and chemistry feedbacks on regional climate, and vice versa. The old chemistry module (CBM-Z) of RegCM4 dealt with the formation, deposition, and transport of a number of VOCs. In this publication, a new gas-phase mechanism module, the CB6-C, has been combined with RegCM4 to produce a more realistic representation of atmospheric VOCs (notably including benzene, terpenes and acetylene) and their corresponding chemical reactions that produce several peroxy-compounds and radicals as by-products.
The performance of the new, CB6-C and the old, CBM-Z chemistry modules were evaluated together by comparison with gridded and station data. Albeit benzene was an important addition to the CB6-C gas-phase module, it was under predicted, resulting in lower concentrations of NO or emission sources, however substantial improvement in the representation of surface carbon monoxide and ozone was encouraging. Although additional studies are in progress to reduce these biases, the model is freely available for public use.
The CB6-C combined with the numerous physical parametrizations available in RegCM4, provides the user with a useful tool to study atmospheric organic compounds. It is also a platform to study further chemical mechanisms and test them on different climate scenarios. The work is ongoing to couple the CB6-C module with the aerosol formation parameterization in order to study the radiative properties of SOAs in climate projections.
This project was carried out using computational facilities procured through the European Regional Development Fund, Project ERDF-080 ‘A supercomputing laboratory for the University of Malta’, as well as the supercomputer cluster ‘Argo’, at the Abdus Salam International Centre for Theoretical Physics.