Sulfur dioxide monitoring

Sulfur dioxide is a nonflammable, colorless gas that can exist in the air either as a gas or dissolved in water droplets. It can be tested by most people at concentrations of about 900 ug/m3 or greater. Sulfur dioxide partially oxidizes in air to form sulfur trioxide, which readily combines with water vapor to form sulfuric acid. Procedures for monitoring SO2 may be of the automatic or manual type, manual techniques may be either static (e.g., sulfation plates) or mechanical (e.g. gas bubbler devices). The two procedures for SO2 monitoring described in this manual are both of the mechanical types and were selected because of their proven reliability and relatively moderate purchase and operating cost.