Potential Interference Bias in Ozone Standard Compliance Monitoring

Abstract

The U.S. Environmental Protection Agency has established a federal reference method (FRM) for ozone (O 3 ) and allowed for designation of federal equivalent methods (FEMs). However, the ethylene-chemiluminescence FRM for O 3 has been replaced by the UV photometric FEM by most state and local monitoring agencies because of its relative ease of operation. Accumulating evidence indicates that the FEM is prone to bias under the hot, humid, and stagnant conditions conducive to high O 3 formation. This bias may lead to overreporting hourly O 3 concentrations by as much as 20 -40 ppb. Measurement bias is caused by contamination of the O 3 scrubber, a problem that is not detected by dry air calibration. An adequate wet test has not been codified, although a procedure has been proposed for agency consideration. This paper includes documentation of laboratory tests quantifying specific interferant responses, collocated ambient FRM/FEM monitoring results, and smog chamber comparisons of the FRM and FEMs with alternative scrubber designs. As

Technical note: Evaluation of standard ultraviolet absorption ozone monitors in a polluted urban environment

“…The costs of reducing O 3 pollution are estimated in the billions of dollars (Leston et al, 2005). For example, a report by the Instituto Nacional de Ecología (INE) in Mexico (McKinley et al, 2003) found that the implementation of several control measures could achieve a 3% reduction in daily maximum ozone concentration at the cost of approximately two billion dollars.…”

“…3164 E. J. Dunlea et al: Evaluation of UV ozone monitors counties in the U.S. have O 3 concentrations in excess of the threshold as a result of measurement interferences (Leston et al, 2005).…”

“…The Federal Reference Method (FRM) for O 3 is a gas-phase ethylenechemiluminescence detector, however, by far the most common technique for determining the ambient concentration of O 3 is ultra-violet absorption (UV O 3 monitor), which has been designated as a Federal Equivalent Method (FEM). Indeed, UV O 3 monitors account for almost all of the UV monitoring in the U.S. (Leston et al, 2005). Monitoring networks in other countries have also adopted UV O 3 monitors making them the most ubiquitous instruments for O 3 monitoring worldwide.…”

“…Several studies have shown adequate performance of UV O 3 monitors in comparison to NOchemiluminescence (Ryerson et al, 1998) and spectroscopic (Stevens et al, 1993) instruments (note: neither technique is a FEM method). Alternatively, a number of studies have shown interferences due to scattering of UV radiation by fine particles within the instrument (Arshinov et al, 2002;Leston and Ollison, 2000) and anomalous sensitivity of the manganese dioxide scrubbers to ambient water vapor, causing a discrepancy compared with calibrations typically performed with dry gas (ASTM, 2003;Butcher and Ruff, 1971;Cavanagh and Verkouteren, 2001;Leston et al, 2005;Maddy, 1999;Parrish and Fehsenfeld, 2000). Aromatic hydrocarbons and oxidized or nitrated aromatics are known to absorb UV radiation and are the most likely to be present in sufficient quantities in an urban environment to potentially contribute to this type of interference (Cavanagh and Verkouteren, 2001;Grosjean and Harrison, 1985;Hudgens et al, 1994;Kleindienst et al, 1993;Leston et al, 2005).…”

“…Alternatively, a number of studies have shown interferences due to scattering of UV radiation by fine particles within the instrument (Arshinov et al, 2002;Leston and Ollison, 2000) and anomalous sensitivity of the manganese dioxide scrubbers to ambient water vapor, causing a discrepancy compared with calibrations typically performed with dry gas (ASTM, 2003;Butcher and Ruff, 1971;Cavanagh and Verkouteren, 2001;Leston et al, 2005;Maddy, 1999;Parrish and Fehsenfeld, 2000). Aromatic hydrocarbons and oxidized or nitrated aromatics are known to absorb UV radiation and are the most likely to be present in sufficient quantities in an urban environment to potentially contribute to this type of interference (Cavanagh and Verkouteren, 2001;Grosjean and Harrison, 1985;Hudgens et al, 1994;Kleindienst et al, 1993;Leston et al, 2005). Overall, there is still a need for field intercomparisons of these UV O 3 monitors, particularly intercomparisons done in urban locations with high O 3 concentrations typical of non-attainment conditions (Parrish and Fehsenfeld, 2000).…”