Alternative pathway for atmospheric particles growth

Abstract

Credible climate change predictions require reliable fundamental scientific knowledge of the underlying processes. Despite extensive observational data accumulated to date, atmospheric aerosols still pose key uncertainties in the understanding of Earth’s radiative balance due to direct interaction with radiation and because they modify clouds’ properties. Specifically, major gaps exist in the understanding of the physicochemical pathways that lead to aerosol growth in the atmosphere and to changes in their properties while in the atmosphere. Traditionally, the driving forces for particle growth are attributed to condensation of low vapor pressure species following atmospheric oxidation of volatile compounds by gaseous oxidants. The current study presents experimental evidence of an unaccounted-for new photoinduced pathway for particle growth. We show that heterogeneous reactions activated by light can lead to fast uptake of noncondensable Volatile Organic Compounds (VOCs) at the surface of particles when only traces of a photosensitizer are present in the seed aerosol. Under such conditions, size and mass increase; changes in the chemical composition of the aerosol are also observed upon exposure to volatile organic compounds such as terpenes and near-UV irradiation. Experimentally determined growth rate values match field observations, suggesting that this photochemical process can provide a new, unaccounted-for pathway for atmospheric particle growth and should be considered by models.

Secondary organic aerosol formation from semi‐ and intermediate‐volatility organic compounds and glyoxal: Relevance of O/C as a tracer for aqueous multiphase chemistry

“…For the bulk reaction case, the GLY-SOA product distribution depends strongly on the Henry's law constant of glyoxal and particle pH, and less on the gas-phase OH radical concentration. When the only source for aqueous phase OH radicals is transfer from the gas-phase, the SOA mass formed from aqueous phase OH radical reactions is very small (≤5% of GLY-SOA); additional radical sources from organic photochemistry are likely [Volkamer et al, 2009;Monge et al, 2012]. The dominant GLY-SOA formation route in the model is from the catalytic reaction with NH 4 + at the elevated particle pH in Mexico City (Table S1).…”

“…Gas-phase OH is the only OH source considered in particles during these model runs ( Figure S2). Additional radical sources are not considered, but may result from organic photochemistry in aerosol water [Volkamer et al, 2009;Monge et al, 2012]. With increasing H and pH, the ammonium reaction gains in relative importance because the NH 4 + availability is not mass transfer limited; at lower H the OH-radical reaction is relatively more important.…”

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

“…Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection. Physical Chemistry Chemical Physics, 18 (8), 5867-5882.…”

Similarities and differences of aerosol optical properties between southern and northern sides of the Himalayas

“…Intensive convection around noon could transport relatively large particles from natural emissions upwards, which may partly lead to larger column-integrated particle size around noon at QOMS_CAS. In addition, aerosol growth in the atmosphere partly related to solar irradiation leads to the increasing size and mass (Monge et al, 2012), which may possibly influence the column-integrated aerosol size. The aerosol load at QOMS_CAS in the upper atmosphere is possibly comparable to that in the lower atmosphere.…”