Laboratory investigation on the role of organics in atmospheric nanoparticle growth

The uptake of organic vapors by 4-20 nm H₂SO₄ particles has been investigated to assess the role of organics in atmospheric nanoparticle growth. Sulfuric acid nanoparticles are generated from homogeneous binary nucleation of H₂SO₄ and H₂O vapors in a laminar flow chamber. The growth factor of H₂SO₄ 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 H₂SO₄ 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.