Laboratory investigation on the role of organics in atmospheric nanoparticle growth.
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The uptake of organic vapors by 4-20 nm H(2)SO(4) particles has been investigated to assess the role of organics in atmospheric nanoparticle growth. Sulfuric acid nanoparticles are generated from homogeneous binary nucleation of H(2)SO(4) and H(2)O vapors in a laminar flow chamber. The growth factor of H(2)SO(4) nanoparticles exposed to methyglyoxal, ethanol, 1-butanol, 1-heptanol, and 1-decanol is measured using a nanotandem differential mobility analyzer (nano-TDMA). The measured growth factor is close to unity when nanoparticles are exposed to methylglyoxal, ethanol, 1-butanol, 1-heptanol, and 1-decanol, indicating no apparent growth within the experimental uncertainty. In addition, spectroscopic evolution of functional groups in H(2)SO(4) particles of 40 nm diameter size, deposited on ZnSe crystal and subsequently exposed to glyoxal and 2,4-hexadienal, is studied using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FT-IR). The ATR-FT-IR measurements present the first spectroscopic signatures of high molecular weight aldol and oligomer products and show that polymerization and oligomerization reactions are partially reversible. The implications of the present results to nanoparticle growth in the atmosphere are discussed.