Diurnal and Seasonal Trends of Freshly Nucleated Sulfuric Acid Clusters Observed in Pittsburgh, PA

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

     Abstract Number: 235
     Working Group: Aerosol Chemistry

Abstract
Atmospheric aerosol particles play a crucial role in the Earth’s climate by altering the amount of solar radiation reflected or absorbed. A major source of aerosol particles is nucleation, which occurs when gaseous molecules known as nucleation precursors react to form stable particles. These particles can grow into cloud condensation nuclei (CCN) and influence cloud properties such as lifetime and brightness. Previous research shows a major driver of nucleation is sulfuric acid, which forms primarily from the photooxidation of sulfur dioxide. Pittsburgh, PA has a history of high concentrations of sulfur dioxide as local industries emit the pollutant via fossil fuel burning while the valley geography of the region traps it. Previous field campaigns have measured nucleation events in Pittsburgh but did not directly measure sulfuric acid concentrations. To better understand nucleation events happening in Pittsburgh, the Jen Lab measured concentrations of nucleation precursors, composition of sulfuric acid containing nanoclusters, and concentrations of newly formed particles. Measurements were obtained using a nitrate chemical ionization mass spectrometer (CIMS) and a suite of particle instruments. The instruments were deployed during the spring and fall of 2023, during which multiple nucleation events were measured. Freshly formed sulfuric acid-base clusters important to nucleation were identified by relating CIMS-measured clusters to nucleation events. In addition, the CIMS measured high gaseous sulfuric acid concentrations at night. Possible reasons for this phenomenon were investigated using gas monitors and meteorological models. The CIMS and particle measurements contribute to a better understanding of the molecules driving nucleation in Pittsburgh and provide insight into the events seen during previous field campaigns.