<p><strong>Abstract.</strong> We present an instrument for the measurement of total ozone reactivity (<i>R</i>_O3), i.e. 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 organic compounds (BVOCs) as chemical sinks of tropospheric ozone. The instrument was extensively characterized and tested in the laboratory using individual compounds and small

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... ants (lemonthyme, <i>Thymus citriodorus</i>) in a Teflon bag and proved able to measure reactivities corresponding to >&amp;thinsp;4.5&amp;thinsp;&amp;times;&amp;thinsp;10^&amp;minus;5&amp;thinsp;s^&amp;minus;1, corresponding to 20&amp;thinsp;ppb of &amp;alpha;-pinene or 150&amp;thinsp;ppb of isoprene in isolation &amp;ndash; larger than typical ambient levels but consistent with levels commonly found in environmental chamber and enclosure experiments. 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 is consistent with mixing ratios of tens ppb of monoterpenes and several ppb of sesquiterpenes.</p>