Uptake of gaseous formaldehyde by soil surfaces: a combination of adsorption/desorption equilibrium and chemical reactions

Abstract

Abstract. Gaseous formaldehyde (HCHO) is an important precursor of OH radicals and a key intermediate molecule in the oxidation of atmospheric volatile organic compounds (VOCs). Budget analyses reveal large discrepancies between modeled and observed HCHO concentrations in the atmosphere. Here, we investigate the interactions of gaseous HCHO with soil surfaces through coated-wall flow tube experiments applying atmospherically relevant HCHO concentrations of ∼ 10 to 40 ppbv. For the determination of uptake coefficients (γ ), we provide a Matlab code to account for the diffusion correction under laminar flow conditions. Under dry conditions (relative humidity = 0 %), an initial γ of (1.1 ± 0.05) × 10 −4 is determined, which gradually drops to (5.5 ± 0.4) × 10 −5 after 8 h experiments. Experiments under wet conditions show a smaller γ that drops faster over time until reaching a plateau. The drop of γ with increasing relative humidity as well as the drop over time can be explained by the adsorption theory in which high surface coverage leads to a reduced uptake rate. The fact that γ stabilizes at a non-zero plateau suggests the involvement of irreversible chemical reactions. Further back-flushing experiments show that two-thirds of the adsorbed HCHO can be re-emitted into the gas phase while the residual is retained by the soil. This partial reversibility confirms that HCHO uptake by soil is a complex process involving both adsorption/desorption and chemical reactions which must be considered in trace gas exchange (emission or deposition) at the atmosphere-soil interface. Our results suggest that soil and soil-derived airborne particles can either act as a source or a sink for HCHO, depending on ambient conditions and HCHO concentrations.

Light-induced protein nitration and degradation with HONO emission

“…Therefore two rate constants of 4.10 × 10 −6 and 5.2 × 10 −7 s −1 were obtained, respectively. Reactive uptake coefficients for NO 2 were calculated according to Li et al (2016). For both irradiation types the uptake coefficient γ was in the range of 7 × 10 −6 at the very beginning of each experiment.…”

Relative importance of gas uptake on aerosol and ground surfaces characterized by equivalent uptake coefficients

“…The real ambient multiphase processes are much more complex than the laboratory measurements; nevertheless, they use airborne aerosols. Ambient online measurements of γ eff will favor the model parameterization and improve our understanding of the multiphase processes within the PBL in the real world (Li et al, 2019). Moreover, more gaseous and aerosol species such as VOCs and bioaerosols should also be investigated (Zhou et al, 1996;Wagner et al, 2002;Fried et al, 2003;Beck et al, 2013;Li et al, 2014Ouyang et al, 2016;Liu et al, 2017;Meusel et al, 2017).…”

Technical note: Influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies

“…Coated-wall flow tube reactors have been extensively employed for investigations of uptake and reaction kinetics of gases with reactive liquid/semisolid/solid surfaces (Howard, 1979;Kolb et al, 2010). To simulate various heterogeneous or multiphase reactions relevant to atmospheric chemistry, these coated reactive surfaces can span a broad scale including aqueous inorganic acids (Jayne et al, 1997;Pöschl et al, 1998), inorganic salts (Davies and Cox, 1998;Chu et al, 2002;Qiu et al, 2011), organic acids and sugars (Shiraiwa et al, 2012;Steimer et al, 2015), proteins (Shiraiwa et al, 2011), soot (McCabe and Abbatt, 2009;Khalizov et al, 2010;Monge et al, 2010), mineral dust (El Zein and Bed-Guo Li et al: Technical note: Influence of surface roughness and local turbulence janian, 2012; Bedjanian et al, 2013), ice (Fernandez et al, 2005;McNeill et al, 2006;Petitjean et al, 2009;Symington et al, 2012;Hynes et al, 2001Hynes et al, , 2002Bartels-Rausch et al, 2005), and soils (Stemmler et al, 2006;Wang et al, 2012;Donaldson et al, 2014a, b;VandenBoer et al, 2015;Li et al, 2016). Reactive uptake kinetics to a condensed phase material are normally described in terms of the uptake coefficient, γ , which represents the net loss rate of a gas reactant at the surface normalized to its gas kinetic collision rate.…”

“…Data sources are https://neutrium.net/fluid_flow/absolute-roughness/ and http:// www.edstech.com/design-tools.html. The soil roughness refers to Li et al (2016) and the ice roughness refers to Onstott et al (2013) and Landy et al (2015Landy et al ( ). al., 2008Zhang et al, 2010;Zhou and Yao, 2011;Gloss and Herwig, 2010).…”

“…Although the surface roughness effects can be potentially important, there has been a long-lasting debate on whether the coating surface roughness could disturb the fully developed laminar flow in flow tube kinetic experiments (Taylor et al, 2006;Herwig et al, 2008), and its effects were usually not well quantified in most of the previous gas uptake and/or kinetic studies (Davies and Cox, 1998;Chu et al, 2002;McCabe and Abbatt, 2009;Khalizov et al, 2010;El Zein and Bedjanian, 2012;Bedjanian et al, 2013;Shiraiwa et al, 2012;Wang et al, 2012;Donaldson et al, 2014a, b;VandenBoer et al, 2015;Li et al, 2016). It is, however, conceivable that as the roughness of the coating surfaces increases it would eventually distort the steady laminar regime near tube walls, and small-scale eddies would evolve from roughness elements.…”