Isoprene and cloud processing
Isoprene epoxy diol, otherwise known as IEPOX, is a common derivative of the molecule isoprene. Isoprene is a compound emitted from terrestrial vegetation that accounts for around 30% of all biogenic emissions and reacts quickly to form many different derivatives. IEPOX is the major outcome of isoprene in low NOx environments, and, since it is highly reactive due to its epoxide ring strain, it can also react further to form a variety of products including secondary organic aerosols (SOA).
SOAs are nonvolatile, contribute significantly to particulate mass, and can play key roles in the atmosphere’s oxidizing capacity. This means that they have direct impacts on climate, air quality, and human health, and therefore, understanding their properties and mechanisms of formation is important. The mechanism for many SOA’s formation, including IEPOX-derived SOAs, however, is not particularly well understood and there are often large discrepancies between atmospheric chemistry models and experimental observations.
In the case of IEPOX in the atmosphere, once it is formed, it can either dissolve into cloud droplets and react in aqueous solution, or undergo chemistry on aerosol particles. Anything acidic enables the ring opening of IEPOX allowing further reactions, meaning acidity is a major factor in controlling the rate of IEPOX reacting. In the atmosphere, this matters because cloud droplets are much larger than aerosols (more volume for IEPOX to go into), but aerosols are much more acidic.
In the Thornton group, some of our research has been focused on determining how important cloud uptake is for IEPOX compared to aerosol processing via chemical modeling.
Aerosol enhancement of lightning
Without aerosol particles, water cannot condense to form clouds. Changing aerosol number, size, and composition can therefore influence a cloud’s precipitation and lifetime. In the Thornton group, we study how these aerosol species impact deep clouds (cumulonimbus) through the lens of lightning.
Because lightning is an indicator of cloud water content and intensity, we can use the relationship between aerosols and lightning to better understand how these tiny particles might be changing deep clouds on a local scale (i.e. over shipping lanes) or on a global scale.
