Light Intensity and Light Source Influence on Secondary Organic Aerosol Formation for the <i>m</i>-Xylene/NO<sub><i>x</i></sub> Photooxidation System

A series of <i>m</i>-xylene/NO<sub><i>x</i></sub> photooxidation experiments were conducted to determine the influence of light intensity and radiation spectrum on secondary organic aerosol (SOA) formation within the UC Riverside/CE-CERT environmental chamber. The environmental chamber is equipped with 80 115-W black lights and a variable voltage 200 kW argon arc lamp that emits a wavelength spectrum more similar to natural light. SOA formation increased significantly with light intensity, measured as the photolysis rate of NO<sub>2</sub> to NO (<i>k</i><sub>1</sub>), increased from 0.09 to 0.26 min<sup>−1</sup>. The argon arc lamp produced ∼20% more SOA than black lights at a <i>k</i><sub>1</sub> of 0.09 min<sup>−1</sup> for similar amounts of <i>m</i>-xylene consumed. These results may help explain the variation of SOA formation between environmental chambers and the differences between measured SOA in the ambient atmosphere versus environmental chamber predictions.