Ultrafine Aerosol Particle Formation and Impacts in Houston During TRACER

Abstract

This project combines a unique suite of instruments and facilities for understanding the chemical species and mechanisms that are responsible for the formation of nanometer-sized particles in the Houston atmosphere during the Tracking Aerosol Convection Interactions Experiment (TRACER). Our approach will combine direct measurements of low volatility precursors and size-resolved ultrafine (sub-100 nm diameter) particles together with measurements of gas-particle partitioning of ambient vapors onto size-selected nanoparticles of known composition, the latter using the Captive Aerosol Growth and Evolution (CAGE) chamber. Measurements from the CAGE chamber will directly inform model development of ultrafine particle growth by our research team. While the focus of this project is on the formation and evolution of new ultrafine particles, the measurements and insights gained will be directly applicable to the formation and evolution of larger particles, with implications for air quality and climate in this important urban region.

The main hypothesis of the proposed project is that new particle formation and growth in the anthropogenically dominated Houston area will be controlled by different species than those we have previously found in well-characterized remote regions, such as in the northern boreal forests and the Southern Great Plains in the United States. In addition, we hypothesize that the high relative humidity (RH) typical of the Houston region plays an important, unexplored role in new particle formation at this site. This project will have three main objectives that will directly address our hypotheses. In Objective I, we will perform measurements of ambient gas and size-resolved ultrafine particle composition, as well as climatologically important particle hygroscopicity under sub- and supersatured water vapor conditions during TRACER. Leveraging other relevant observations, including convective transport, we will seek to understand the dominant species that participate in particle formation and their potential impacts on clouds and climate. Concurrently, in Objective II we will perform measurements of size-resolved growth of particles of known initial size and composition during TRACER using the CAGE chamber. Using the data from Objectives I and II, Objective III is to build a process-level model that describes new particle formation in the Houston atmosphere, comparing model predictions of size-resolved ultrafine particle growth with measurements in order to test our mechanistic understanding of particle formation in this region. As part of Objective III, we will work with Department of Energy research partners to incorporate our mechanisms into regional and global models.