The effect of viscosity and diffusion on the HO<sub>2</sub> uptake by sucrose and secondary organic aerosol particles

Abstract

Abstract. We report the first measurements of HO 2 uptake coefficients, γ , for secondary organic aerosol (SOA) particles and for the well-studied model compound sucrose which we doped with copper(II). Above 65 % relative humidity (RH), γ for copper(II)-doped sucrose aerosol particles equalled the surface mass accommodation coefficient α = 0.22 ± 0.06, but it decreased to γ = 0.012 ± 0.007 upon decreasing the RH to 17 %. The trend of γ with RH can be explained by an increase in aerosol viscosity and the contribution of a surface reaction, as demonstrated using the kinetic multilayer model of aerosol surface and bulk chemistry (KM-SUB). At high RH the total uptake was driven by reaction in the near-surface bulk and limited by mass accommodation, whilst at low RH it was limited by surface reaction. SOA from two different precursors, α-pinene and 1,3,5-trimethylbenzene (TMB), was investigated, yielding low uptake coefficients of γ < 0.001 and γ = 0.004 ± 0.002, respectively. It is postulated that the larger values measured for TMB-derived SOA compared to α-pinene-derived SOA are either due to differing viscosity, a different liquid water content of the aerosol particles, or an HO 2 + RO 2 reaction occurring within the aerosol particles.

Atmospheric oxidation in the presence of clouds during the Deep Convective Clouds and Chemistry (DC3) study

“…Laboratory studies show that the HO 2 effective uptake coefficient for moist aerosol particles that contain copper is probably much lower than 0.01 in the lower troposphere but may be greater than 0.1 in the upper troposphere (Thornton et al, 2008). However, other laboratory studies show that adding organics to the particles or lowering the relative humidity can reduce uptake coefficients (Lakey et al, 2015(Lakey et al, , 2016. These values are generally lower than the HO 2 effective uptake coefficient assumed in global chemical transport models.…”

“…Atmospheric oxidation is driven primarily by hydroxyl (OH), whose concentration is strongly dependent on ozone (O 3 ), especially in the upper troposphere (Logan et al, 1981). Ozone is a source of OH through its destruction by solar ultraviolet radiation, which produces an excited state oxygen atom that can react with water vapor to produce OH.…”

The frequency-dependent response of single aerosol particles to vapour phase oscillations and its application in measuring diffusion coefficients

“…12 This can influence reactive uptake [13][14][15][16] and greatly diminish the rate of water sorption and desorption.…”

Predictions of diffusion rates of large organic molecules in secondary organic aerosols using the Stokes–Einstein and fractional Stokes–Einstein relations

“…10074 E. Evoy et al: Predictions of diffusion rates of large organic molecules in secondary organic aerosols partition to the particle phase (Ervens et al, 2011;Hallquist et al, 2009). The exact chemical composition of SOA remains uncertain; however, measurements have shown that SOA contains thousands of different organic molecules, and the average oxygen-to-carbon (O : C) ratio of organic molecules in SOA ranges from 0.3 to 1.0 or even higher (Aiken et al, 2008;Cappa and Wilson, 2012;DeCarlo et al, 2008;Ditto et al, 2018;Hawkins et al, 2010;Heald et al, 2010;Jimenez et al, 2009;Laskin et al, 2018;Ng et al, 2010;Nozière et al, 2015;Takahama et al, 2011;Tsimpidi et al, 2018). SOA also contains a range of organic functional groups including alcohols and carboxylic acids (Claeys et al, 2004(Claeys et al, , 2007Edney et al, 2005;Fisseha et al, 2004;Glasius et al, 2000;Liu et al, 2011;Surratt et al, 2006Surratt et al, , 2010.…”