Abstract. In recent years wildland fires in the United States have had significant
impacts on local and regional air quality and negative human health
outcomes. Although the primary health concerns from wildland fires come from
fine particulate matter (PM2.5), large increases in ozone (O3)
have been observed downwind of wildland fire plumes (DeBell et al., 2004;
Bytnerowicz et al., 2010; Preisler et al., 2010; Jaffe et al., 2012;
Bytnerowicz et al., 2013; Jaffe et al., 2013; Lu et al., 2016; Lindaas et
al., 2017; McClure and Jaffe, 2018; Liu et al., 2018; Baylon et al., 2018;
Buysse et al., 2019). Conditions generated in and around wildland fire
plumes, including the presence of interfering chemical species, can make the
accurate measurement of O3 concentrations using the ultraviolet (UV)
photometric method challenging if not impossible. UV photometric method
instruments are prone to interferences by volatile organic compounds (VOCs)
that are present at high concentrations in wildland fire smoke. Four
different O3 measurement methodologies were deployed in a mobile
sampling platform downwind of active prescribed grassland fire lines in
Kansas and Oregon and during controlled chamber burns at the United States
Forest Service, Rocky Mountain Research Station Fire Sciences Laboratory in
Missoula, Montana. We demonstrate that the Federal Reference Method (FRM)
nitric oxide (NO) chemiluminescence monitors and Federal Equivalent Method
(FEM) gas-phase (NO) chemical scrubber UV photometric O3 monitors are
relatively interference-free, even in near-field combustion plumes. In
contrast, FEM UV photometric O3 monitors using solid-phase catalytic
scrubbers show positive artifacts that are positively correlated with carbon
monoxide (CO) and total gas-phase hydrocarbon (THC), two indicator species
of biomass burning. Of the two catalytic scrubber UV photometric methods
evaluated, the instruments that included a Nafion® tube dryer
in the sample introduction system had artifacts an order of magnitude
smaller than the instrument with no humidity correction. We hypothesize that
Nafion®-permeating VOCs (such as aromatic
hydrocarbons) could be a significant source of interference for catalytic
scrubber UV photometric O3 monitors and that the inclusion of a
Nafion® tube dryer assists with the mitigation of
these interferences. The chemiluminescence FRM method is highly recommended
for accurate measurements of O3 in wildland fire plume studies and at
regulatory ambient monitoring sites frequently impacted by wildland fire
smoke.