Light Intensity and Light Source Influence on Secondary Organic Aerosol Formation for the m-Xylene/NO_x Photooxidation System

A series of m-xylene/NO_x 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 NO₂ to NO (k₁), increased from 0.09 to 0.26 min⁻¹. The argon arc lamp produced ∼20% more SOA than black lights at a k₁ of 0.09 min⁻¹ for similar amounts of m-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.