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 However, the ethylene-chemiluminescence FRM for O 3 has been replaced by the UV photometric FEM by most state and local monitoring agencies because of its relative ease of operation.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

Employing bias-prone instruments for measurement of ambient ozone or nitrogen dioxide from inlets at inappropriate heights above ground level may result in collection of positively biased data. This paper discusses tests of new regulatory instruments, recent developments in bias-free ozone and nitrogen dioxide measurement technology, and the presence/extent of a near-ground O gradient (NGOG). Collection of unbiased monitor inlet height-appropriate data is crucial for determining accurate design values and meeting National Ambient Air Quality Standards.

Its chief objectives were to expand the chemical characterization of organic compounds and to estimate the source contributions of carbonaceous fine particles at urban and background monitoring sites. Two major challenges were faced in order to successfully implement the SOAP sampling network. First, collection of adequate fine PM mass was necessary for successful quantitation of organic marker compounds. Second, sufficiently low blank levels were required for each marker compound for accurate identification and quantitation needed for source-receptor modeling. Initial field tests of representative samplers designed for sampling PM chemical species indicated insufficient sample mass collection, unless analytical sensitivity for organic markers could be greatly improved. Adequate PM mass was collected using a Tisch TE-1202 sampler that operated at a much higher flow rate (113 lpm). Preliminary field tests also revealed unacceptably high travel blank levels for n-alkanes and carboxylic acids. The mass of organic marker compounds observed on travel blank filters was reduced significantly by shipping filters in sealed filter holders. Further evaluation of the Tisch TE-1202 sampler also demonstrated the sampler was free of organic components and impactor grease upstream of the filter. These features also reduced the contribution of carbonaceous species to system blanks and therefore, to the total mass collected. As a result, blank levels for hopanes, PAHs, and dicarboxylic acids were below limits of detection (LOD), and n-alkanes (C25 to C32), n-alkanoic acids (C12, C14, C16, and C18), and phthalic acid exhibited acceptable low levels in all SOAP blanks ranging from 1 to 10 times the limit of detection for each compound class. Overall, adequate sample mass and sufficiently low blank levels were achieved successfully with the SOAP fine particle collection protocol.

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