Sub-3 nm particle observations in the atmosphere of two sites in Eastern United States

Direct measurement of sub-3 nm particles is crucial for understanding the new particle formation process and its contribution to cloud condensation nuclei (CCN) formation. Sub-3 nm particles measured at Long Island, New York (coastal site) and Kent, Ohio (inland continental site) show that high concentrations of nighttime sub-3 nm particles were present at the coastal site only with marine air masses, whereas nighttime sub-3 nm particle concentrations were significantly low in continental air masses and at the inland continental site. The coastal nighttime sub-3 nm particles did not grow larger. Measured sulfuric acid and Volatile Organic Compounds (VOCs) indicate that the potential source precursors of nighttime sub-3 nm particles may be unknown ocean-originated chemical species other than sulfuric acid and biogenic VOCs (isoprene and monoterpenes).