Project at a Glance

Title: Measurements of NOy, nitric acid, NO, and PAN in the South Coast Air Basin.

Principal Investigator / Author(s): Fitz, Dennis R

Contractor: UC Riverside

Contract Number: 01-318

Research Program Area: Atmospheric Processes

Topic Areas: Chemistry & Reactivity, Field Studies


NOy–NOy* analyzers and NO2/PAN gas chromatographs were used in the continuation of a study to evaluate the concentrations of nitrogenous species in Azusa and Riverside. These two sites are generally on the same afternoon wind trajectory with Azusa, approximately 35 miles to the west-northwest, being upwind. NOy-NOy* instruments are chemiluminescent NO-NOx analyzers equipped with dual converters, with one preceded by a NaCl-coated denuder to measure nitric acid by difference. NO2/PAN gas chromatographs separate NO2 and quantify the amount using luminol detection. This selective method of measuring NO2 and PAN is used to quantify the amount of these species contained in the NOy. The analyzers were operated from May 2001 through December 2002. Data were compiled, validated, and submitted for all of 2002. Data from 2001 were submitted as unvalidated data. In 2002 NOy values at Riverside ranged up to 250 ppb, and values at Azusa reached up to 500ppb. The diurnal pattern of nitric acid was observable nearly every day, although at each site one of the two collocated NOy-NOy* instruments was biased low, most likely due to a slight converter efficiency mismatch. While there was significant scatter in the nitric acid measured by all of the instruments, the concentrations at Riverside ranged up to about 5 ppb while maximum values at Azusa were 20 ppb. The lower concentrations at Riverside were expected since the afternoon wind trajectory from Riverside passes over dairy operations emitting large amounts of ammonia, which would remove nitric acid as ammonium nitrate. The conclusion was that nitric acid concentrations could be characterized, although the accuracy could not be established. In Riverside, the PAN concentrations typically peaked at 1 ppb, although concentrations of 4 ppb were observed in August. In Azusa, a more limited amount of data from the NO2/PAN GC showed PAN concentrations to be nearly a factor of two higher than in Riverside.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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