Temporal and spatial characteristics of ozone depletion events from measurements in the Arctic

Abstract

Abstract. Following polar sunrise in the Arctic springtime, tropospheric ozone episodically decreases rapidly to near zero levels during ozone depletion events (ODEs). Many uncertainties remain in our understanding of ODE characteristics, including the temporal and spatial scales, as well as environmental drivers. Measurements of ozone, bromine monoxide (BrO), and meteorology were obtained during several deployments of autonomous, ice-tethered buoys (O-Buoys) from both coastal sites and over the Arctic Ocean; these data were used to characterize observed ODEs. Detected decreases in surface ozone levels during the onset of ODEs corresponded to a median estimated apparent ozone depletion timescale (based on chemistry and the advection of O3-depleted air) of 11 h. If assumed to be dominated by chemistry, these timescales would correspond to larger-than-observed BrO mole fractions based on known chemical mechanisms and assumed other radical levels. Using backward air mass trajectories, the spatial scales for ODEs (defined by time periods in which ozone mole fraction ≤15 nmol mol−1) were estimated to be ~900 km (median), while areas estimated to represent major ozone depletions (<10 nmol mol−1) had dimensions of ~280 km (median). These observations point to a heterogeneous boundary layer with localized regions of active, ozone-destroying halogen chemistry, interspersed among larger regions of previously depleted air that retain reduced ozone levels through hindered atmospheric mixing. Based on the estimated size distribution, Monte Carlo simulations showed it was statistically possible that all ODEs observed could have originated upwind, followed by transport to the measurement site. Local wind speed averages were low during most ODEs (median of ~3.6 m s−1), and there was no apparent dependence on local temperature.