AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Compaction of Soot Particles during Cloud Processing: Field and Laboratory Observations
JANARJAN BHANDARI, Gregory Kinney, Kamal Kant Chandrakar, Stefania Gilardoni, Stefano Decesari, M. Cristina Facchini, Nicola Zanca, Lynn Mazzoleni, Manvendra Dubey, Barbara Scarnato, Noopur Sharma, Paulo Fialho, Swarup China, Will Cantrell, Claudio Mazzoleni, Michigan Technological University
Abstract Number: 464 Working Group: Aerosols, Clouds, and Climate
Abstract Soot particles freshly emitted during combustion processes, are aggregates of nanometer size carbonaceous spherical monomers. These monomers are typically arranged in a fractal-like structure. After emission, soot aggregates undergo various atmospheric processes and their structure can become compact. These structural changes in turn, can affect the scattering and absorption cross sections of soot particles, and therefore, their radiative effects. During their transport in the atmosphere, soot particles can also act as cloud condensation nuclei and form cloud droplets. The condensation and evaporation of water vapor and other dissolved matter can result in the compaction of the soot aggregates. We investigated this last process in both laboratory and ambient studies.
Ambient samples were collected during cloudy (foggy) and sunny periods in the rural site of San Pietro Capofiume, in the Po Valley, Italy, in fall 2015. We used scanning electron microscopy (SEM) and image processing to analyze more than 950 individual soot particles and to quantify their degree of compaction. We found higher soot compaction during the foggy events with respect to the sunny events. We hypothesize that the compaction is due to cloud processing, as we postulated also in previous studies. To further investigate cloud processing in controlled laboratory conditions, we performed preliminary experiments in a turbulent cloud chamber at Michigan Technological University. We first injected kerosene flame soot particles and then produced a turbulent mixing cloud, and collected interstitial and residual soot particles using a pumped counterflow virtual impactor. We analyzed 361 individual soot particles from SEM images. The residual soot particles were found to be markedly more compact than the interstitial soot, supporting our hypothesis on cloud-induced compaction. We will present the results of these field and laboratory studies and discuss the implications on the optical properties of soot particles and the potential repercussions on their radiative effects.