The NASA ER-2 has been a workhorse for study of the chemistry of the lower stratosphere. It is operated by a single pilot. The plane can attain altitudes in excess of 21 km (71,000 ft.). Numerous instruments have been developed for this platform and continue to make discoveries about the photochemistry and dynamics of the lower stratosphere and upper troposphere.
The official ER-2 web page is found here.
Some of the chemistry mission descriptions are found here.