Balloon-borne measurements yield new insights on boundary layer new particle formation
Smith, James — University of California, Irvine
Pierce, Jeffrey Robert — Colorado State University
Area of research:
New particles that form in the atmosphere can do so high above-ground before such events are observed by ground-based instruments. Once formed, these particles can take up significant amounts of water and become more liquid-like, which can impact the role that these particles play in atmospheric chemistry and cloud formation processes.
We know little about the location in the atmosphere where new particles are formed, nor how much water is contained in nascent particles. This study addresses both of these unknowns and shows that the researchers need to do a better job in measuring new particle formation above-ground and in measuring the water content of particles. Addressing both uncertainties will result in better models that represent potential impacts of atmospheric particle formation in, e.g., air pollution formation and cloud properties.
In the spring of 2013, during the New Particle Formation Study at the ARM Southern Great Plains field site, we performed measurements of the vertical distribution of atmospheric nanometer-sized particles (“nanoparticles”) using a lightweight instrument package attached to a tethered balloon. We compared these measurements to observations from ARM remote-sensing instruments that measured vertical distributions of temperature, water vapor, and vertical wind velocity. Our main findings are: (1) ground-based measurements may not always accurately represent the timing, distribution, and meteorological conditions associated with the onset of new particle formation; (2) atmospheric nanoparticles are highly hygroscopic, and typically contain up to 50% water by volume, and during conditions of high relative humidity combined with high particle water solubility, particles can be up to 95% water by volume; (3) increased water content of nanoparticles at high relative humidity greatly enhances the uptake of gas-phase, water-soluble species like organic acids into ambient nanometer-sized particles. This study emphasizes the importance of aerosol particle-water interactions even at low relative humidity.