Gas-phase precursors, aerosol composition and new particle formation during TRACER using spatially resolved TRACER-MAP datasets; TRACER-MAP-NPF

Rebecca Sheesley, Baylor University (Principal Investigator)
Sascha Usenko, Baylor University (Co-Investigator)
James Flynn, University of Houston (Co-Investigator)
Subin Yoon, University of Houston (Co-Investigator)
Jeffrey Pierce, Colorado State University (Co-Investigator)
Shantanu Jathar, Colorado State University (Co-Investigator)

Collaborators:
Robert J. Griffin, Roger Williams University
Don Collins, University of California – Riverside

Introduction.

In 2021 – 2022, the Tracking Aerosol

aerosols

Small particles or droplets, such as wildfire smoke, volcanic gases, or salty sea spray, that float in the air. They are emitted by both natural events and human activities.

Source: NASA Global Climate Change Source

Convection Interactions Experiment (TRACER) was completed in Houston, Texas to exploit its high convective storm activity and broad range of polluted aerosol conditions. With the TRACER field experiment now completed, we will use the data collected during TRACER to investigate new particle formation and growth (NPFG) across the Houston area. NPFG is important to understand the life cycle of urban aerosol, which can impact local meteorology and be important for human health. As the pollutants (e.g., gas precursors, aerosol composition, particle number, and particle size distributions) and environmental conditions changed during TRACER both spatially and temporally, we will be able to use Houston as a natural laboratory to probe the driving factors of NPFG in an urban setting. For this work, we will investigate the observations and integrate those measurements with detailed modeling.

Methods:

For this study, we are using the field measurements that this group collected in 2022 during TRACER in addition to measurements collected by the Department of Energy (DOE) at their site in La Porte, Texas. We will be focusing on NPF events and understanding the specific conditions under which new particles form and grow in the Houston area. We have measurements of pollutants that can contribute to NPFG (e.g., sulfur dioxide and select volatile organic compounds)

volatile organic compound (VOC)

Compounds that have a high vapor pressure and low water solubility. Many VOCs are human-made chemicals that are used and produced in the manufacture of paints, pharmaceuticals, and refrigerants.

Source: EPA Environmental Protection Agency Source

as well as measurements of the local meteorology, which also affects NPFG. We also have particle size, number, and composition measurements, which will indicate to us when these NPFG events are occurring and what the composition of that resultant aerosol is. We will combine these observations to look for specific NPFG scenarios at different sites and under different environmental conditions across Houston. For example, we will investigate conditions of high local pollution, high biogenic contributions, and/or high relative humidity. We will combine this analysis of our observations with detailed modeling designed to specifically target aerosol processes: the DOE/ASR-supported Weather Research and Forecasting-Chemistry with the Model for Simulating Aerosol Interactions and Chemistry (WRF-Chem-MOSAIC) and the simple statistical oxidation

oxidation

A chemical reaction that takes place when a substance comes into contact with oxygen or another oxidizing substance. One example of oxidation is rusting of iron when the iron interacts with oxygen and water. In climate science, oxidation is important because it is one of the processes that leads to the formation of greenhouse gases.

Source: NIH Source

model (simpleSOM) organic aerosol chemistry/thermodynamics model. It is the combination of detailed analysis of observations plus detailed modeling that will inform our understanding of the NPFG across Houston during TRACER. 

Summary of Project Objectives:
1.1. Characterize different regimes for NPF events and NPFG-relevant precursor species
     a.Identify NPF events and classify into three categories: growth, limited growth, and no growth
     b.Calculate rates of change in precursor gases during NPFG events (e.g., removal rates)
     c.Understand the distribution of chemical regimes (SO2 and volatile organic compounds (VOCs)) across the TRACER domain
2.Statistically evaluate impacts of differences in background conditions on NPFG
     a.Consider the impact of meteorological conditions (solar radiation, wind direction and speed), diurnal differences, aerosol composition, precursor gases, and condensation sink on NPF frequency, growth rate and formation rate
3.Interpret the role of spatiotemporal variability in species concentrations and aerosol processes on observed NPF using the WRF Chem-simpleSOM-MOSAIC model
    a.Assess role of vertical mixing and convection

convection

The rising of warm air and the sinking of cool air. Convection can cause local breezes, winds, and thunderstorms.

Source: NASA earth observatory Source

on the surface observed NPFG
    b.Quantify horizontal advection influences on temporal changes in observed NPFG and aerosol
    c.Understand local versus regional representativeness for site-based measurements (e.g., the ARM Mobile Facility, AMF1)

Outcomes and benefits. This proposed work evaluates how differences in gas-phase precursors and other background conditions help explain NPF frequency, formation rate, and growth rate during the Baylor contribution to TRACER, TRACER-MAP, through statistical analysis of observations and modeling of the Houston domain.