The Effect of Initial Conditions on the Growth of Particulate Matter from Aromatic Hydrocarbons

ISSAK PROAÑO LÓPEZ, Murray Johnston, University of Delaware

     Abstract Number: 408
     Working Group: Aerosol Chemistry

Abstract
The formation of secondary organic aerosol (SOA) from the growth of nanoparticles via the photooxidation of volatile organic compounds (VOCs) is of great atmospheric importance, due to their being a significant source of cloud condensation nuclei (CCN)-active particulate matter. An increasing prevalence of human industrialization since the beginning of the Industrial Revolution has led to increased interest in the effects of industrial emissions on these atmospheric processes. Despite contributing a minor fraction of total VOC content in the atmosphere and being relatively localized in nature, VOCs of anthropogenic origin (AVOCs) are of increasing interest due to their ability to both generate their own SOA while simultaneously influencing the SOA generated from their biogenic counterparts.

One of the most common classes of AVOCs present in the atmosphere is the aromatic class, capable of generating the low-volatility products found in SOA and whose preferential diurnal photooxidation mechanism involves the hydroxyl radical (∙OH). A custom flow-tube type photooxidation reactor with desirable flow characteristics is used to generate the SOA while approximating real-world precursor concentrations. Previous work has established that particle-phase reactions occurring within generated SOA plays a key role in the growth of atmospheric nanoparticles, both using reactive and inert seeds as a growth substrate, and using a scanning mobility particle sizer (SMPS) to elucidate changes in aerosol mobility diameter. The work presented here compares the diameter growth rates of aerosol produced from the photooxidation of aromatic hydrocarbons onto different composition seed particles having a range of sizes within the Aitken mode (10-100 nm). The relative humidity during these experiments is controlled to compare solid-to-aqueous seed surface conditions on aerosol growth. Understanding the mechanisms through which SOA from AVOCs grows across the Aitken mode becoming CCN-active is invaluable to understanding the effects that our activities have on global climate.