GOAMAZON-TDCIMS

Observations and Modeling of the Green Ocean Amazon: Thermal Desorption Ionization Mass Spectrometer (TDCIMS)

1 January 2014 - 31 October 2014

Lead Scientist: James N. Smith

Observatory: AMF , MAO

As part of both GoAmazon2014 IOPs, the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS) performed measurements of the molecular composition of 10-50 nm diameter particles. TDCIMS observations were used to address two objectives the GoAmazon. For studying the interactions between anthropogenic and biogenic emissions, the TDCIMS quantified the composition of nanoparticles that nucleate from anthropogenic emissions Manaus and the role of biogenic precursors in the growth of these particles. Coincident measurements of gas phase sulfuric acid allowed us to determine the contribution of sulfuric acid condensation to growth, which we compared to TDCIMS-derived nanoparticle composition to determine the fraction of growth that can be attributed to the uptake of organic compounds. The molecular composition of sampled particles was used to attribute specific chemical species and mechanisms to growth, such as the condensation of low-volatility species or the oligomerization of -dicarbonyl compounds. The TDCIMS was used to determine the source of new ambient nanoparticles in the Amazon. We hypothesize that potassium salts formed from the evaporation of primary particles emitted by fungal spores provides a unique and important pathway for NPF in the Amazon. To explore this hypothesis, we obtained positive ion mass spectra of sampled ambient aerosol. Our tests performed using potassium salts show that the TDCIMS can detect potassium with high sensitivity; the fact that potassium has two stable isotopes aids in the identification of this ion. The location for these measurements was the T3 site, co-located with other key measurements such as sulfuric acid and PAM-AMS. The instrument that we deployed was configured with a quadrupole mass spectrometer, which is reliable, sensitive, and ideal for quantifying specific compounds (e.g., potassium) in sampled aerosol. The low concentrations of ambient nanoparticles that are often observed in the Amazon sometimes require collection times of up to 2 hours at the smallest diameters; however, we expected that for particles larger than 30 nm we could collect sufficient sample size in less than an hour. Data was processed in near-real-time.