Interactions between the boundary layer new particle formation and cloud systems: observations from ARMs Southeast U.S. field campaign

Atmospheric aerosols

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

affect the earth’s radiation budget directly by scattering solar radiation and indirectly by serving as cloud condensation nuclei

cloud condensation nuclei

Tiny airborne particles suspended in the atmosphere that serve as the seeds around which cloud droplets form.

Source: Source

(CCN) and affecting cloud properties. Among various atmospheric processes, new particle formation (NPF) is an important source of atmospheric aerosols, contributing almost half of the atmosphere’s CCN. NPF events in the boundary layer are frequently observed and are of great interest, because the new particles can be facilely transported to cloud level and contribute to CCN after they grow to sizes above the Hoppel minimum. Boundary layer NPF events are also ubiquitous around the world, ranging from the high-latitude Arctic and Antarctic regions, through mid-latitude boreal

boreal

Boreal forests (sometimes called "taiga") are a mosaic of forest types — from sunny aspen groves to spruce bogs-intermingled with meadows, marshes, lakes, and rivers — in the northern high latitude regions. This ecosystem is characterized by cold weather, long winters, and permafrost.

Source: Alaska Department of Fish and Game Source

forests, farmlands, cities, and coastal regions, to tropical forests and ocean. Many efforts have been devoted to studying the physio-chemical mechanisms of NPF in the boundary layer and the contribution of newly formed particles to CCN. However, understanding the climate impact of aerosols requires improved knowledge of aerosol-cloud processes. At present, the interactions between NPF and cloud systems are still relatively understudied.
Cloud systems can play a key role in creating conditions favoring NPF, such as allowing the actinic fluxes

flux

The amount of some type of particle or energy crossing a unit area per unit time.

Source: NRC Library Source

and photochemical reactions, generating a low surface area of pre-existing aerosols, and convecting precursors emitted from the land surface. Our recent studies show that NPF in the upper boundary layer may occur regularly after cold frontal passages. Understanding the dependence of NPF on cloud processes can help predict when and where NPF occurs more accurately. As for the impact of NPF on cloud systems, many studies showed that newly formed particles can grow to CCN-related sizes. However, particle growth is strongly dependent on the species and concentration of condensing vapors, meaning that the geographic and seasonal variabilities of particle growth processes need to be studied. Moreover, to completely understand the impact of NPF on cloud systems, cloud properties, such as cloud droplet size and number and cloud supersaturation, need to be examined and contrasted for NPF and non-NPF events. But currently, there is a scarcity of such studies due to the challenges in combining and comprehending aerosol and cloud data. These knowledge gaps signify the importance of understanding the interactions between NPF and cloud systems.
This project plans to investigate the dependence and impact of boundary layer NPF on cloud systems at the third ARM Mobile Facility (AMF3) in Southeast U.S. The Southeast U.S. region is a warm and humid region with abundant locally forced, atmospheric 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

inland and enhanced convection along coasts. The wide range cloud conditions resulted from these shallow to deep convections creates an opportunity to examine their impact and dependence on boundary layer NPF. We propose to analyze aerosol, trace gas, cloud, and meteorological data collected from the early observations at AMF3. This project is aimed at the following objectives: (1) Gaining a quantitative

quantitative

Data represented numerically, including anything that can be counted, measured, or given a numerical value.

Source: National Library of Medicine Source

understanding of the impact of cloud systems on NPF occurrence; (2) Examining the impact of boundary layer NPF on CCN population; (3) Investigating the impact of boundary layer NPF on cloud systems. The proposal is responsive to the FOA as it addresses the connection between aerosol formation and cloud processes, a specific subtopic of the FOA for Biological and Environmental Research.
To achieve the research objectives, we will perform the following tasks: (1) Identifying NPF events using aerosol data and analyzing the frequency and evolution of such events at AMF3; (2) Analyzing cloud, meteorological, and synoptic conditions during boundary layer NPF events; (3) Estimating the contribution of aerosols in different modes to CCN during and after NPF events; (4) Studying the hygroscopicity,

hygroscopicity

The ability of a particle to take up moisture from the environment and is important for understanding the ability of particles to act as cloud condensation nuclei (CCN).

Source: ARM Source

mixing state, and growth mechanisms of particles during NPF events; (5) Examining the impact of boundary layer NPF on cloud properties. This study addresses the interactions between boundary layer NPF and cloud systems in the Southeast U.S. and helps improve the estimation of aerosol-climate effects in both pre-industrial and present-day atmosphere. The results of this study will improve the parameterization of NPF, reducing uncertainties in climate and earth system models,

earth system model (ESM)

A model that simulates how chemistry, biology, and physical forces work together. These models are similar to, but much more comprehensive than, global climate models.

Source: U.S. Department of Energy Source

leading to sustainable solutions for the Nation’s energy and environmental challenges.