title: Soil surface acidity plays a determining role in the atmospheric-terrestrial exchange of nitrous acid.
abstract: Nitrous acid (HONO) is an important hydroxyl (OH) radical source that is formed on both ground and aerosol surfaces in the well-mixed boundary layer. Recent studies report the release of HONO from nonacidic soils, although it is unclear how soil that is more basic than the pKa of HONO (∼ 3) is capable of protonating soil nitrite to serve as an atmospheric HONO source. Here, we used a coated-wall flow tube and chemical ionization mass spectrometry (CIMS) to study the pH dependence of HONO uptake onto agricultural soil and model substrates under atmospherically relevant conditions (1 atm and 30% relative humidity). Experiments measuring the evolution of HONO from pH-adjusted surfaces treated with nitrite and potentiometric titrations of the substrates show, to our knowledge for the first time, that surface acidity rather than bulk aqueous pH determines HONO uptake and desorption efficiency on soil, in a process controlled by amphoteric aluminum and iron (hydr)oxides present. The results have important implications for predicting when soil nitrite, whether microbially derived or atmospherically deposited, will act as a net source or sink of atmospheric HONO. This process represents an unrecognized mechanism of HONO release from soil that will contribute to HONO emissions throughout the day.
authors.affiliation: School of Public and Environmental Affairs, Indiana University, Bloomington, IN 47405-2204;
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Donaldson
authors.affiliation: Department of Geological Sciences, Indiana University, Bloomington, IN 47405-1405; and.
authors.forename: David L
authors.initials: DL
authors.lastname: Bish
authors.affiliation: School of Public and Environmental Affairs, Indiana University, Bloomington, IN 47405-2204; Department of Chemistry, Indiana University, Bloomington, IN 47405-7102 jdraff@indiana.edu.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Raff
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000737:chemistry*; D008956:Models, Chemical; D009608:Nitrous Acid / Q000737:chemistry*; D011199:Potentiometry; D012987:Soil / Q000737:chemistry*
chemical_list: D012987:Soil; D017665:Hydroxyl Radical; D009608:Nitrous Acid
keywords: air pollution; nitrite; nitrogen cycle; nitrous acid; surface acidity