Abstract. Oxidation flow reactors (OFRs) complement environmental smog chambers
as a portable, low-cost technique for exposing atmospheric compounds
to oxidants such as ozone (O3), nitrate (NO3)
radicals, and hydroxyl (OH) radicals. OH is most commonly generated
in OFRs via photolysis of externally added O3 at
λ=254 nm (OFR254) or combined photolysis of
O2 and H2O at λ=185 nm plus
photolysis of O3 at λ=254 nm (OFR185) using
low-pressure mercury (Hg) lamps. Whereas OFR254 radical generation is
influenced by [O3], [H2O], and photon flux at
λ=254 nm (I254), OFR185 radical generation
is influenced by [O2], [H2O], I185, and
I254. Because the ratio of photon fluxes,
I185:I254, is OFR-specific, OFR185 performance varies
between different systems even when constant [H2O] and
I254 are maintained. Thus, calibrations and models developed
for one OFR185 system may not be applicable to another. To investigate
these issues, we conducted a series of experiments in which
I185:I254 emitted by Hg lamps installed in an OFR was
systematically varied by fusing multiple segments of lamp quartz
together that either transmitted or blocked λ=185 nm
radiation. Integrated OH exposure (OHexp) values
achieved for each lamp type were obtained using the tracer decay
method as a function of UV intensity, humidity, residence time, and
external OH reactivity (OHRext). Following previous
related studies, a photochemical box model was used to develop a
generalized OHexp estimation equation as a function of
[H2O], [O3], and OHRext that is
applicable for I185:I254≈0.001 to 0.1.
Supplementary material to "Technical Note: Effect of varying the λ = 185 and 254 nm photon flux ratio on radical generation in oxidation flow reactors"