Field testing of new-technology ambient air ozone monitors

Abstract

Multibillion-dollar strategies control ambient air ozone (O 3 ) levels in the United States, so it is essential that the measurements made to assess compliance with regulations be accurate. The predominant method employed to monitor O 3 is ultraviolet (UV) photometry. Instruments employ a selective manganese dioxide or heated silver wool "scrubber" to remove O 3 to provide a zero reference signal. Unfortunately, such scrubbers remove atmospheric constituents that absorb 254-nm light, causing measurement interference. Water vapor also interferes with the measurement under some circumstances. We report results of a 3-month field test of two new instruments designed to minimize interferences (2B Technologies model 211; Teledyne-API model 265E) that were operated in parallel with a conventional Thermo Scientific model 49C O 3 monitor. The field test was hosted by the Houston Regional Monitoring Corporation (HRM). The model 211 photometer scrubs O 3 with excess nitric oxide (NO) generated in situ by photolysis of added nitrous oxide (N 2 O) to provide a reference signal, eliminating the need for a conventional O 3 scrubber. The model 265E analyzer directly measures O 3 -NO chemiluminescence from added excess NO to quantify O 3 in the sample stream. Extensive quality control (QC) and collocated monitoring data are assessed to evaluate potential improvements to the accuracy of O 3 compliance monitoring.Implications: Two new-technology ozone monitors were compared with a conventional monitor under field conditions. Over 3 months the conventional monitor reported more exceedances of the current standard than the new instruments, which could potentially result in an area being misjudged as "nonattainment." Instrument drift can affect O 3 data accuracy, and the same degree of drift has a proportionally greater compliance effect as standard stringency is increased. Enhanced data quality assurance and data adjustment may be necessary to achieve the improved accuracy required to judge compliance with tighter standards.

Measurement of microenvironmental ozone concentrations in Durham, North Carolina, using a 2B Technologies 205 Federal Equivalent Method monitor and an interference-free 2B Technologies 211 monitor

“…The 205 and 211 monitors agree to within 4 ppb with the hourly-average Armory monitor concentration that would be used in APEX model simulations (since subhourly ambient data are often unavailable) and to within 1 ppb of each other. A comparable but more comprehensive 3-month Houston 2B 211-TE 49C monitor comparison is reported by Ollison et al (2013). Results of special tests to identify potential sources of monitor interference…”

O3, CH4, CO2, CO, NO2 and NMHC aircraft measurements in the Uinta Basin oil and gas region under low and high ozone conditions in winter 2012 and 2013

“…In 2012, ozone measurements were made with a 2B Technologies UV photometric analyzer with the solid phase scrubber. In 2013, measurements of O 3 were made with a 2B Technology analyzer that used nitric oxide (NO) in place of a solid phase scrubber to avoid potential inference from aromatics and mercury (Ollison et al, 2014). The O 3 instruments were calibrated before and after each campaign against a NOAA GMD standard that is regularly compared with a U.S. NIST standard.…”

Use of a heated graphite scrubber as a means of reducing interferences in UV-absorbance measurements of atmospheric ozone

“…Average concentrations of interfering species found in outdoor air would normally be expected to cause errors of only a few ppb at most, but this is well within measurement limits of UV ozone photometers when averaged over the 1 h time frame typical for compliance monitoring. Since high levels of interferences often coincide with high levels of ambient outdoor ozone (Leston et al, 2005;Ollison et al, 2013), a small, unpredictable bias would be difficult to discern and could result in regions being in noncompliance with the EPA ozone standard. The recent downward revision of the standard from 75 to 70 ppb (8 h average) is expected to increase the number of U.S. counties being out of compliance from 224 to 241 (McCarthy and Lattanzio, 2016), making small ppb-level interferences a more critical issue.…”

“…This desorption can be caused by temperature or relative humidity (RH) changes within the scrubber that alter the adsorption characteristics of a species and allows it to be released back into the gas phase. Because UV-absorbing compounds and mercury are commonly present to some degree in both indoor and outdoor air, these interferences may be responsible in part for the baseline drift that occurs in photometric ozone monitors (Birks et al, 2013;Ollison et al, 2013). Therefore, development of a solid-phase scrubber that effectively destroys ozone (≥ 99 % destruction) but efficiently passes interfering species is desirable.…”

“…Past studies of VOC interferences have typically been of three types: (1) measurement of total net ozone biases during irradiation of simulated atmospheres in smog chambers (Kleindeist et al, 1993;Leston et al, 2005), (2) simultaneous atmospheric measurements by different analyzers using different measurement techniques (Ollison et al, 2013;Dunlea et al, 2006), and (3) addition of selected VOCs to ozone analyzers to determine the interference from that particular VOC (Grosjean and Harrison, 1985;Spicer et al, 2010). All of these approaches contribute to our understanding of the significance of VOC interferences in ozone monitors; however, we have chosen the latter approach to initially evaluate our heated graphite scrubber because it is a more direct approach and reproducible signals can be easily quantified.…”