PNNL

The Science

Aerosol particles in the atmosphere can contribute to local and global climate change in many different ways, including scattering of sunlight. However, the climate-relevant properties of atmospheric aerosols vary strongly over time and across geography, particularly in coastal areas. These strong variations in size, chemical composition, and light scattering ability make it difficult to predict how aerosols contribute to climate change. A research team, led by scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory, analyzed aerosols’ physical, chemical, and optical properties collected by a suite of airborne instruments during winter as part of a year-long measurement campaign in Cape Cod, Massachusetts. The team also introduced an approach to assess the consistency and meaningfulness of the collected data.

The Impact

Frequent occurrence of clouds during winter make these observations more challenging because clouds introduce additional variability in observed scattering properties. There is also an increased number of large particles, which are typically ignored in this type of quality assessment because information on their chemical composition is often limited. To address these challenges, the researchers only analyzed measurements taken in cloud-free areas and incorporated chemical composition into predictions of light scattering based on particle size. Their results highlighted the need to account for the chemical composition of the particles when investigating how they interact with sunlight.

Summary

During the winter phase of the Two-Column Aerosol Project (TCAP), a U.S. Department of Energy research aircraft collected in situ data under challenging, partly cloudy conditions using several airborne instruments with different designs and uncertainties. The researchers used these data to develop an integrated dataset with climate-important aerosol properties, including size spectra, chemical composition, and scattering coefficient. They also performed a quality assessment of the developed dataset and demonstrated that the chemical composition of particles is needed to improve the description of their interactions with sunlight.

Airborne measurements of physical, optical, and chemical properties of aerosol particles at different spatial and temporal scales, such as those collected during the TCAP, are imperative additions for many climate studies. They also provide critical datasets for evaluating model performance and inter-comparison of aerosol optical properties obtained from in situ measurements and remote sensing. The extended comparison experiment of airborne data introduced by this team could also be used for data gathered in previous and/or future field campaigns.

PNNL Contact

Jerome Fast, Pacific Northwest National Laboratory, Jerome.Fast@pnnl.gov

Funding

The ARM Aerial Facility team is gratefully acknowledged for the contribution collecting the aircraft data during TCAP which was supported by the Department of Energy Atmospheric Radiation Measurement Facility and Atmospheric System Research (ASR) Program. This research was supported by Office of Science of the U.S. Department of Energy as part of the ARM Facility and ASR Program.