Acetone in the upper troposphere/lowermost stratosphere measured by the CARIBIC passenger aircraft: Distribution, seasonal cycle, and variability

Abstract

Mass-spectrometric measurements of acetone (CH 3 COCH 3) have been performed monthly using a Lufthansa Airbus A340-600 passenger aircraft between February 2006 and December 2008. In total, 106 measurement flights (4 per month) were conducted between Germany and South America, North America, South Asia, and East Asia. Here measurements collected between 33°N and 56°N in the upper troposphere (UT) and lowermost stratosphere (LMS) at 9-12 km altitude are analyzed. By integrating data collected at 12 ozonesonde stations, ozone concentrations measured on flight are translated into a representative (mixing-based) altitude above the thermal tropopause. A strong seasonal variation of acetone occurs at the midlatitude tropopause with maxima of ∼900 parts per 10 12 vol (pptv) in summer and minima of ∼200 pptv in midwinter. This seasonality propagates into the LMS in approximately 6 weeks with rapidly decreasing concentrations and increasing phase shifts reaching 2 km above the tropopause. Throughout the year, acetone and ozone are highly negatively correlated in the LMS with a mean linear correlation coefficient (R) of -0.93. This linear relationship marks the O 3 -acetone-based extratropical tropopause mixing layer (exTL). A "stratospheric intrusion height of acetone" (Z acetone) is defined that concurs with the vertical depth of the O 3 -CO-based exTL, namely, averaging ∼2.2 km but with slightly lower values in winter. Probability density functions (PDFs) and the course of the seasonal variation of acetone relative to the tropopause are interpreted regarding the in-mixing and subsequent dispersion of acetone in the LMS. Copyright 2010 by the American Geophysical Union.