Developing and applying atomic force microscopy methodologies to probe for physicochemical properties of sea spray aerosols

Every cloud grows on a preexisting aerosol, a tiny and microscopic particle suspended in air. Among many types of aerosols, sea spray aerosols are one of the most abundant and chemically diverse types of aerosols on Earth. They originate from waves breaking and bubbles bursting in the ocean. Sea spray aerosols and the clouds formed from them scatter and reflect sunlight, resulting in less of the sun’s heat reaching the Earth’s surface. Currently however, the extent of these effects is uncertain. One source of this uncertainty stems from the inherent uniqueness of individual aerosol particles. Because of their small size, one hundred times smaller than the diameter of a human hair strand, experiments often collect a large number of aerosol particles, combine them into a set, and obtain the average of the results. But if small aerosol particles are uniquely different than large aerosol particles, the averages may not accurately represent this diversity. Thus, to decrease the uncertainty, experimental techniques must overcome the problem of the small size of aerosol particles. Here, it is demonstrated that single particle microscopy techniques, such as atomic force microscopy and scanning electron microscopy, are excellent tools to directly study small, individual aerosol particles. Typically used to image and observe small objects, results show that they can also be applied to study sea spray aerosols. This is illustrated in this work, which begins by identifying key properties of aerosols that must be measured with microscopy. Next, how several methods were developed to measure these properties is discussed. Once proven to be accurate, how these methods were applied to real sea spray aerosols is discussed. Data revealed significant variability between individual sea spray aerosol particles. This work ends by summarizing the key discoveries on sea spray aerosols and suggestions for future studies.