Evaluation of a Condensation Particle Counter Method for Measuring Sulfuric Acid Vapor Concentrations

DOMINIC CASALNUOVO, Darren Cheng, Coty Jen, Carnegie Mellon University

     Abstract Number: 447
     Working Group: Instrumentation and Methods

Abstract
Freshly formed particles from sulfuric acid nucleation affect the Earth’s radiative balance by forming cloud condensation nuclei (CCN). Accurately predicting global sulfuric acid nucleation rates requires high temporal and spatial resolution measurements of gaseous sulfuric acid. Accomplishing this is challenging due to the difficulties in deploying a chemical ionization mass spectrometer (CIMS) in remote regions of the atmosphere. We have developed a complementary technique to measure sulfuric acid vapor concentrations (SA-CPC). The SA-CPC consists of a compact nucleation flow reactor that uses dimethylamine to convert atmospheric sulfuric acid vapor into measurable 1-nm particles in a controlled environment. The concentration of particles is measured using a 1-nm condensation particle counter and converted to sulfuric acid concentration using a semi-empirical acid-base nucleation model. We present operational details on the SA-CPC, including computational fluid dynamic simulations of the nucleation flow reactor. In addition, laboratory comparisons of SA-CPC measured sulfuric acid concentrations (10⁶-10⁸ cm^-3 range) compared to those measured by the CIMS are shown. Results demonstrate that the SA-CPC measures sulfuric acid concentrations within 12% of those measured by the CIMS, with larger discrepancies at higher sulfuric acid concentrations. In addition, the effects of relative humidity, temperature, and presence of other potential nucleation precursor compounds were explored to determine how these parameters impact SA-CPC measured sulfuric acid concentrations. Overall, the SA-CPC is a helpful instrument in obtaining atmospheric sulfuric acid vapor concentration measurements in diverse locations around the world.