Particle composition measurements during CLOUD7

The chemical composition of >8 nm diameter aerosol was measured using the Timeof-Flight Thermal Desorption Chemical Ionization Mass Spectrometer (TOF-TDCIMS) during CLOUD7 particle nucleation experiments in Fall 2012 at the CLOUD chamber at CERN in Geneva, Switzerland. Sulfate dominated the negative ion particle spectra during all events with enough particle mass to observe, both in experiments with amine and alpha-pinene. Ammonium was also a major particle constituent during all observable events, though gaseous ammonia was present in the chamber only as a contaminant. During nucleation events following the oxidation of alpha-pinene, highly oxidized organic acids such as oxalic and oxoacetic acid were observed to be significant components of the collected aerosol.