Investigating Volatile Organic Compound Emissions from Boreal Lake Water Exposed to Ultraviolet Light and Ozone

Abstract

Inland surface waters are an important part of the global carbon cycle through sedimentation, atmospheric emissions, dissolution of atmospheric carbon dioxide (CO2) and the transport of dissolved carbon in runoff. The surface microlayer (SML) is a thin film on the surface of waters consisting of fatty acids, lipids and other organic compounds which serve as the interface between the hydrosphere and atmosphere. The organic compounds in the SML can photooxidize and constitute a source of reactive organic compounds that contribute to the formation of tropospheric ozone (O3) and secondary organic aerosols, consequently affecting air quality and climate. This study investigated the volatile organic compound (VOC) emissions from ten boreal lake water samples exposed to ultraviolet (UV) light and atmospheric O3. The aim was to study the drivers of VOC emissions and examine if the main source of the emissions was the SML or subsurface water. High emissions of methanol, acetaldehyde, acetone/propanal, hexanal and nonanal were observed. UV light was the main driver of these emissions, and high UV intensities produced higher amounts of VOCs. Emissions of acetone/propanal and pentanal were formed by O3 exposure in one of the lakes studied. There was a correlation between the total organic carbon concentration and the VOC emission levels. The SML did not contribute to higher emissions than the subsurface water.