UC Riverside

Sulfur dioxide (SO2), nitrate radical (NO3), and nitrous acid (HONO) play important roles in the atmosphere. SO2 is associated with the combustion of fossil fuels and contributes to acidification of the ecosystem, particulate sulfate formation and SO2 is an EPA regulated species. NO3 is the major oxidation species at night often reacting with biogenic volatile organic hydrocarbons emitted during the nighttime air, which lead to peroxyl radical and nitric acid formation. HONO is a major source of hydroxyl radical (OH) in the early morning. All of these three pollutants exhibit strong absorptions in the UV and visible region and their absorption bands are exploited for measurements using the ultrasensitive absorption spectroscopy techniques, cavity ring-down spectroscopy (CRDS) and broadband cavity enhanced absorption spectroscopy (BBCEAS). SO2 is measured by CRDS near 308 nm in the UV region with a limit of detection of 3.5 ppb/10 seconds (S/N = 2) and ambient measurements are attempted. Instruments based on light emitting diode (LED) based BBCEAS are developed for measurements of NO3 and HONO. NO3 is monitored using the 662 nm absorption feature with a limit of detection of 10 ppt/2 minutes (1σ) and the technique is demonstrated by sampling from an environmental chamber. HONO is measured in the UV region using the 368 nm absorption with a limit of detection of 10 ppb/2 minutes (1σ).