Molecular understanding of the suppression of new-particle formation by isoprene

Abstract

Abstract. Nucleation of atmospheric vapours produces more than half of global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products that can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together with isoprene (C5H8), which has the highest global emission of all organic vapours. Previous studies have shown that isoprene suppresses new-particle formation from monoterpenes, but the cause of this suppression is under debate. Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we show that isoprene reduces the yield of highly oxygenated dimers with 19 or 20 carbon atoms – which drive particle nucleation and early growth – while increasing the production of dimers with 14 or 15 carbon atoms. The dimers (termed C20 and C15, respectively) are produced by termination reactions between pairs of peroxy radicals (RO2⚫) arising from monoterpenes or isoprene. Compared with pure monoterpene conditions, isoprene reduces nucleation rates at 1.7 nm (depending on the isoprene ∕ monoterpene ratio) and approximately halves particle growth rates between 1.3 and 3.2 nm. However, above 3.2 nm, C15 dimers contribute to secondary organic aerosol, and the growth rates are unaffected by isoprene. We further show that increased hydroxyl radical (OH⚫) reduces particle formation in our chemical system rather than enhances it as previously proposed, since it increases isoprene-derived RO2⚫ radicals that reduce C20 formation. RO2⚫ termination emerges as the critical step that determines the highly oxygenated organic molecule (HOM) distribution and the corresponding nucleation capability. Species that reduce the C20 yield, such as NO, HO2 and as we show isoprene, can thus effectively reduce biogenic nucleation and early growth. Therefore the formation rate of organic aerosol in a particular region of the atmosphere under study will vary according to the precise ambient conditions.

Isoprene and monoterpene emissions from alder, aspen and spruce short-rotation forest plantations in the United Kingdom

“…However, this may be an over-prediction of the emissions as, on some occasions, demonstrated by our chamber measurements, winter BVOC emission may be very low or absent from this species. Similarly, rain events have been shown to alter BVOC emissions and may have different effects in the short term (increasing) and the longer term (decreasing), which are also not accounted for in the model (Holzinger et al, 2006). These factors are likely to lead to an overestimation of emissions from all species but in particular Sitka spruce on a per annum basis.…”

Influence of vegetation on occurrence and time distributions of regional new aerosol particle formation and growth

“…In the present study, we derived three compound vegetation properties -GPP, LAI and SCT -to evaluate the impact of BVOC sources on NPF event occurrence in urban environments. These three parameters can indirectly also be associated with vegetation emissions and finally with BVOC concentrations (Hidy et al, 2016). They were computed by the Biome-BGCMuSo biogeochemical model (v6; Thornton and Rosenbloom, 2005;Hidy et al, 2016).…”

“…These three parameters can indirectly also be associated with vegetation emissions and finally with BVOC concentrations (Hidy et al, 2016). They were computed by the Biome-BGCMuSo biogeochemical model (v6; Thornton and Rosenbloom, 2005;Hidy et al, 2016). This is a widely used, process-based model with a multilayer soil module that simulates the storage and flux of H 2 O, C and N between terrestrial managed agroecosystems and the atmosphere.…”

“…It also accounts for fertilisation, harvest and crop rotation. The system utilised here was parameterised specifically to the Carpathian Basin, and its proper functioning and outputs were validated by agriculturally related data products and eddy-covariance measurements (Barcza et al, 2010;Hidy et al, 2016).…”

Review of Cai et al.

“…mean transmission efficiency through the mass filter? If so, did the authors correct for this as shown in (Heinritzi et al, 2020;Zhao et al, 2010)? Also, the authors mention that the CIMS were calibrated for sulfuric acid concentration but how did they determine concentrations of the larger clusters?…”