In Houston’s air, there are many aerosols that can interact with convective storm systems: marine and urban aerosols, smoke from industry, and dust. Atmospheric scientists need to better understand how aerosols affect storm systems, and the U.S. Department of Energy (DOE) recently funded a new field campaign to study just that.

The TRACER campaign, short for TRacking Aerosol Convection interactions ExpeRiment, is a co-operated field study that will be carried out by the DOE Atmospheric Radiation Measurement (ARM) user facility from Oct. 1, 2021 to Sept. 30, 2022. Several Texas A&M University scientists from the Department of Atmospheric Sciences in the College of Geosciences will be an integral part of the field research.

Dr. Anita Rapp, associate professor, is serving as principal investigator, with co-investigators Dr. Sarah Brooks, professor, and Dr. Christopher Nowotarski, associate professor, on a DOE-funded project to lead a research team of graduate and undergraduate students to conduct a series of observations and experiments from June through Sept. 2022 during the TRACER intensive operational period (IOP).

During the campaign, the Texas A&M team and scientists from different laboratories and universities around the nation will use a suite of instruments to collect data on aerosols and atmospheric characteristics to learn more about aerosol-cloud interactions in deep convection systems over the Houston area.

Texas A&M’s Unique Role In TRACER

“To improve our understanding of the interactions between aerosols and convective systems, we need to understand both aerosol and meteorological conditions of the atmosphere,” Rapp said. “However, one of the difficulties in understanding the impact of aerosols on storms, especially from an observational standpoint, lies in separating the effects of aerosols from effects of the background meteorology.” 

In Houston, for instance, the sea breeze, soot, dust and smoke emitted by industrial pollution sources, and urban heat island all contribute to different aerosol and meteorology background conditions, raising the uncertainty of predicting aerosol’s impact on convection and climate in models.

To cope with this challenge, DOE deployed a suite of different platforms supplied by ARM at four locations outside Houston.

“But the DOE sites are fixed, that’s where when we come in,” Brooks said. “The sea breeze, which can help initiate storms, moves, so we need to be mobile to measure the meteorology and aerosol properties where the convection is developing.”

 A newly purchased mobile van by Texas A&M will be deployed to carry the instruments to different places.

“In the morning we will be at a coastal site where we can measure the aerosols and meteorology on the marine side of the sea breeze, while in the evening, we will move inland to the continental side,” Nowotarski said, “because we want to collect data on the opposite sides of the sea breeze from the similar observations being collected at fixed DOE ARM sites.”

Objectives And Outcomes

In order to answer questions of how aerosols act as cloud condensation nuclei (CCN) and ice nuclei (IN) that water condenses on to form cloud droplets, and then how variations in CCN and IN influence the properties of thunderstorms, scientists will collect data on aerosol concentrations, composition, size distributions, CCN/IN concentrations, and atmospheric characteristics by deploying a set of state-of-the-art instruments. 

Besides the radars and lidars provided at the fixed DOE ARM sites, the Texas A&M research team will provide additional mobile instruments such as a lidar, CCN counter, Continuous Flow Diffusion Chambers (CFDC), Scanning Mobility Particle Sizer (SMPS) Vocus PTR-TOF mass spectrometer, soot particle aerosol mass spectrometer (SP-AMS) etc., to analyze a wide range of aerosol samples including dust, sea salt, pollen, soot particles. The Texas A&M team will also launch weather balloons to measure vertical profiles of temperature, relative humidity and wind of the atmosphere.

Despite the importance of aerosol’s role as ice nucleating particles in determining the properties of clouds, scientists are still unable to assess the impact of atmospheric ice formation because our basic knowledge about it is insufficient, and thus leads to uncertainties in model simulations. “TRACER will fill in some of the missing data to help us improve climate and numerical weather forecasting models,” Brooks said.

All data collected during the course of the campaign will be saved in DOE’s archive and freely accessible online to anyone who wants to analyze it. “Houston experiences a wide range of meteorology and aerosol conditions, so the research results will be applicable beyond the Houston area in other major cities around the world as well,” Brooks said.

TRACER is aiming to focus on aerosol, cloud, precipitation and radiation processes and is anticipated to improve the accuracy of predictions made by weather forecasting and climate models, benefiting residents, agricultural activities, and disaster preparation and prevention.

By Joy Lai