Halogen‐driven low‐altitude O3 and hydrocarbon losses in spring at northern high latitudes

Tao Zeng,Brian Ridley,Nicola Blake,Donald Blake,Yuhang Wang,Kelly Chance

doi:10.1029/2005jd006706

Abstract

Halogen‐driven ozone and hydrocarbon losses in springtime Arctic boundary layer are investigated using a regional chemical transport model. Surface observations of ozone at Alert and Barrow and aircraft observations of ozone and hydrocarbons during the Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment from February to May in 2000 are analyzed. We prescribe halogen radical distributions on the basis of GOME BrO observations. Tropospheric GOME BrO column shows an apparent anticorrelation with surface temperature over high‐BrO regions. The enhancements of tropospheric BrO columns coincide with movements of cold polar air masses. While GOME BrO measurements reach the maximum in March, simulated near‐surface ozone loss peaks in April because of the increasing daylight hours and hence the time for chemical processing. At its peak, the area of simulated near‐surface ozone depletions (O3 < 20 ppbv) covers >50% of the northern high latitudes. Analysis of surface measurements at Alert and Barrow points to the importance of long‐range transport of ozone‐poor air from high‐BrO regions. We find that specifying a BrO layer thickness of 300 m results in the best overall agreement between observed and simulated ozone. The apparent halogen‐driven ozone loss up to 1 km was reproduced in the model because of vertical transport of ozone‐poor air from low altitudes. When the empirical Cl/Br ratios derived from previous observations are used, the model can reproduce the observed halogen loss of light alkanes and acetylene. The Cl/Br ratios from a recent box model study using an accepted chemical mechanism are, however, much higher than the empirical results. We show that the hydrocarbon loss is not as sensitive to the prescribed thickness of the halogen layer as the ozone loss, therefore representing a more robust measure for evaluating satellite BrO column measurements.

Highlights

[1] Halogen-driven ozone and hydrocarbon losses in springtime Arctic boundary layer are investigated using a regional chemical transport model
Differential Optical Absorption Spectroscopy (DOAS) measurements of BrO showed the close associations of high BrO concentrations and ozone depletion events (ODEs) [e.g., Hausmann and Platt, 1994; Tuckermann et al, 1997]
Taking advantage of this new capability, Zeng et al [2003] prescribed BrO concentration on the basis of Global Ozone Monitoring Experiment (GOME) measurements in March and April 2000 in a regional chemical transport model (RCTM) to evaluate the model simulated low-altitude ozone losses driven by bromine chemistry with surface and aircraft observations and to investigate the spatial and temporal extents of nearsurface ozone depletions, which cannot be determined from available in situ or remote sensing observations

Summary

Introduction

[2] Near surface ozone depletion events (ODEs) at northern high latitudes during polar sunrise were first discovered two decades ago [Oltmans et al, 1986; Bottenheim et al, 1986]. ZENG ET AL.: SIMULATION OF ARCTIC O3 AND NMHCS LOSS [4] Several box model studies [Fan and Jacob, 1992; Tang and McConnell, 1996; Vogt et al, 1996; Sander and Crutzen, 1996; Sander et al, 1997; Michalowski et al, 2000; Evans et al, 2003] have investigated polar surface halogen chemistry by incorporating heterogeneous halogen chemical mechanisms. The spatial and temporal coverage of GOME far exceeds the available surface aircraft measurements of any chemical species related to halogen chemistry Taking advantage of this new capability, Zeng et al [2003] prescribed BrO concentration on the basis of GOME measurements in March and April 2000 in a regional chemical transport model (RCTM) to evaluate the model simulated low-altitude ozone losses driven by bromine chemistry with surface and aircraft observations and to investigate the spatial and temporal extents of nearsurface ozone depletions, which cannot be determined from available in situ or remote sensing observations.

Methodology

Findings

Conclusions