Abstract
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.
Highlights
Ozone (O3) is a key component of the troposphere: it is known to be damaging for human health and vegetation and to reduce crop yields, and it is an important greenhouse gas (Monks et al, 2015)
2 relies on well-known kinetic parameters and implicitly takes into account the real distribution of flow paths through the reactor; it provides a simple test of the Total Ozone Reactivity System (TORS) functionality using NO instead of a biogenic volatile organic compounds (BVOCs)
After these tests showed that the instrument was behaving as expected under controlled conditions, it was deployed in a glasshouse containing various aromatic plants to demonstrate that TORS can measure total ozone reactivity under quasi-ambient conditions (Sect. 5.3)
Summary
Ozone (O3) is a key component of the troposphere: it is known to be damaging for human health and vegetation and to reduce crop yields, and it is an important greenhouse gas (Monks et al, 2015). Because of its importance to tropospheric chemistry, the ozone budget has long been a subject of considerable interest. Ozone is not directly emitted but is formed in the troposphere via photolysis of nitrogen dioxide (NO2), followed by reaction of atomic oxygen with molecular oxygen (Reactions R1 and R2). Ozone is destroyed in the troposphere via a series of processes, both physical (e.g. dry and wet deposition) and chemical (Monks et al, 2015). The latter involve photolysis (Reactions R3 and R4) and reactions with a range of inorganic molecules and unsaturated volatile organic compounds (Reactions R5–R9)
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