AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Ship Impacts on Marine Aerosol and Clouds
MATTHEW COGGON, Armin Sorooshian, Andrew Metcalf, Amanda Frossard, Zhen Wang, Taylor Shingler, Jill Craven, Lynn Russell, Haflidi Jonsson, John Seinfeld, Caltech
Abstract Number: 649 Working Group: Aerosol Chemistry
Abstract We present properties of background marine aerosol and clouds measured off the coast of central California using state-of-the art instrumentation. These measurements were performed in the shipping lanes between Monterey Bay and San Francisco and represent a unique set of measurements contrasting the properties of clean and emission-impacted marine airspace in below cloud aerosol and cloud drop residuals. Average mass and number concentrations of 2.3 micro-grams m$^-3 and 600 cm$^-3 were consistent with previous studies performed off the coast of California. Enhancement of vanadium and cloud droplet number concentration observed concurrently with a decrease in cloud water pH suggested that periods of high aerosol loading were primarily linked to increased ship influence. Mass spectra from a compact time-of-flight aerosol mass spectrometer illustrated an enhancement in the fraction of organic (forg) at m/z 42 and 99 in ship-impacted clouds. These ions were well correlated (r > 0.8) and most dominant during periods of enhanced sulfate. These ions were equally correlated outside of cloud and showed similar enhancement with increased sulfate. High-resolution analysis of these masses from ship measurements suggests that the ions responsible for this variation were oxidized, possibly due to cloud processing. We propose that these ions can be used as a metric for determining the extent of ship-impacted marine atmosphere where (forg41 > 0.15; forg99 > 0.04) would imply heavy influence from shipping emissions, (0.05 < forg42 < 0.15 ; 0.01 < forg99 < 0.04) would imply moderate, but persistent influences from shipping emissions and (forg42 < 0.05; forg99 < 0.01) would imply clean, non-ship-influenced air.