An instrument for in situ measurement of total ozone reactivity
Abstract. We present an instrument for the measurement of total ozone
reactivity – the reciprocal of the chemical lifetime of ozone
( O3 ) – in the troposphere. The Total Ozone Reactivity
System (TORS) was developed with the objective to study the role of
biogenic volatile organic compounds (BVOCs) as chemical sinks of
tropospheric ozone. The instrument was extensively characterized and
tested in the laboratory using individual BVOCs and small plants
(lemon thyme, Thymus citriodorus) in a Teflon bag and proved
able to measure reactivities corresponding to > 4.5 × 10 - 5 s−1 (at 5 min averaging time), with an estimated total
uncertainty of ∼ 32%. Such reactivities correspond to > 20 ppb of α -pinene or > 150 ppb of isoprene in
isolation – larger than typical ambient levels but observable in
environmental chamber and enclosure experiments as well as in
BVOC-rich environments. The functionality of TORS was demonstrated
in quasi-ambient conditions with a deployment in a horticultural
glasshouse containing a range of aromatic plants. The measurements
of total ozone reactivity made in the glasshouse showed a clear
diurnal pattern, following the emissions of BVOCs, and are consistent
with mixing ratios of tens of parts per billion of monoterpenes and several
parts per billion of sesquiterpenes.