Abstract
Abstract. Mercury was measured onboard the IAGOS-CARIBIC passenger aircraft from May 2005 until February 2016 during near monthly sequences of mostly four intercontinental flights from Germany to destinations in North and South America, Africa and South and East Asia. Most of these mercury data were obtained using an internal default signal integration procedure of the Tekran instrument but since April 2014 more precise and accurate data were obtained using post-flight manual integration of the instrument raw signal. In this paper we use the latter data.Increased upper tropospheric total mercury (TM) concentrations due to large scale biomass burning were observed in the upper troposphere (UT) at the equator and southern latitudes during the flights to Latin America and South Africa in boreal autumn (SON) and boreal winter (DJF). TM concentrations in the lowermost stratosphere (LMS) decrease with altitude above the thermal tropopause but the gradient is less steep than reported before. Seasonal variation of the vertical TM distribution in the UT and LMS is similar to that of other trace gases with surface sources and stratospheric sinks. Speciation experiments suggest comparable TM and gaseous elementary mercury (GEM) concentrations at and below the tropopause leaving little space for Hg2+ (TM − GEM) being the dominating component of TM here. In the stratosphere significant GEM concentrations were found to exist up to 4 km altitude above the thermal tropopause. Correlations with N2O as a reference tracer suggest stratospheric lifetimes of 72±37 and 74±27 years for TM and GEM, respectively, comparable to the stratospheric lifetime of COS. This coincidence, combined with pieces of evidence from us and other researchers, corroborates the hypothesis that Hg2+ formed by oxidation in the stratosphere attaches to sulfate particles formed mainly by oxidation of COS and is removed with them from the stratosphere by air mass exchange, gravitational sedimentation and cloud scavenging processes.
Highlights
Mercury is an element whose high vapor pressure leads to significant emissions into the atmosphere
The lowest total mercury (TM) concentrations are observed in the latitude bands of 10–20 and 20–30◦ S in summer (JA) and the same applies for CO, CH4 and acetonitrile
The highest TM concentrations in 20–30◦ S latitude band are observed in fall (SON) and the TM concentrations decrease in winter (DJF) as do the CO and acetonitrile mixing ratios in the 10–20◦ S latitude band
Summary
Mercury is an element whose high vapor pressure leads to significant emissions into the atmosphere. Measurements of mercury distribution in the troposphere and stratosphere by research aircraft are expensive and usually limited to short-term campaigns covering small regions of the globe (Ebinghaus and Slemr, 2000; Friedli et al, 2001, 2003a, 2004; Banic et al, 2003; Ebinghaus et al, 2007; Radke et al, 2007; Talbot et al, 2007, 2008; Swartzendruber et al, 2008; Slemr et al, 2009, 2014; Lyman and Jaffe, 2012; Brooks et al, 2014; Ambrose et al, 2015; Gratz et al, 2015; Shah et al, 2016; Weigelt et al, 2016a, b). Smaller but higher quality dataset here, in an attempt to unravel the behavior of mercury in the UT/LMS
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