Abstract
Abstract. In the Arctic polar vortex of the 2009/10 winter temperatures were low enough to allow widespread formation of polar stratospheric clouds (PSCs). These clouds occurred during the initial chlorine activation phase which provided the opportunity to investigate the impact of PSCs on chlorine activation. Satellite observations of gas-phase species and PSCs are used in combination with trajectory modeling to assess this initial activation. The initial activation occurred in association with the formation of PSCs over the east coast of Greenland at the beginning of January 2010. Although this area of PSCs covered only a small portion of the vortex, it was responsible for almost the entire initial activation of chlorine vortex wide. Observations show HCl (hydrochloric acid) mixing ratios decreased rapidly in and downstream of this region. Trajectory calculations and simplified heterogeneous chemistry modeling confirmed that the initial chlorine activation continued until ClONO2 (chlorine nitrate) was completely depleted and the activated air masses were advected throughout the polar vortex. For the calculation of heterogeneous reaction rates, surface area density is estimated from backscatter observations. Modeled heterogeneous reaction rates along trajectories intersecting with the PSCs indicate that the initial phase of chlorine activation occurred in just a few hours. These calculations also indicate that chlorine activation on the binary background aerosol is significantly slower than on the PSC particles and the observed chlorine activation can only be explained by an increase in surface area density due to PSC formation. Furthermore, there is a strong correlation between the magnitude of the observed HCl depletion and PSC surface area density.
Highlights
Heterogeneous chemistry on stratospheric aerosol and polar stratospheric clouds (PSCs) plays a crucial role in the formation of the Antarctic ozone hole (Solomon, 1999)
We have analyzed CALIOP and microwave limb sounder (MLS) observations in combination with modeled trajectories to quantify the initial chlorine activation phase for the winter 2009/10 and constrain the spatial and temporal scales on which chlorine activation occurred; this answers the question regarding the extent to which heterogeneous chemistry on PSC particles is responsible for chlorine activation and the timescales for this www.atmos-chem-phys.net/16/4569/2016/
Our analysis has shown that mesoscale PSCs can have a substantial effect on chlorine chemistry throughout the polar vortex, even though the PSCs themselves only cover a small fraction of the polar vortex
Summary
Heterogeneous chemistry on stratospheric aerosol and polar stratospheric clouds (PSCs) plays a crucial role in the formation of the Antarctic ozone hole (Solomon, 1999). On the other hand, Carslaw et al (1998) and Kühl et al (2004) showed that nearly complete chlorine activation can be achieved in a mountain-wave PSC at sufficiently low temperatures and large surface area densities. We use data from the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP, Winker et al, 2009) instrument for studying PSCs and data from the Microwave Limb Sounder (MLS, Waters et al, 2006) in combination with model calculations of the Chemical Lagrangian Model of the Stratosphere (CLaMS, McKenna et al, 2002) to examine the impact of a mesoscale PSC on the chemical composition of the Arctic vortex in January 2010. CALIOP backscatter observations are used to derive particle surface area density (SAD) which is used to calculate chlorine activation Through these analyses, we will examine the impact of PSC SAD enhancements on chlorine activation compared with the cold binary background aerosol
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