title: Unexpected seasonality in quantity and composition of Amazon rainforest air reactivity.
abstract: The hydroxyl radical (OH) removes most atmospheric pollutants from air. The loss frequency of OH radicals due to the combined effect of all gas-phase OH reactive species is a measureable quantity termed total OH reactivity. Here we present total OH reactivity observations in pristine Amazon rainforest air, as a function of season, time-of-day and height (0-80 m). Total OH reactivity is low during wet (10 s(-1)) and high during dry season (62 s(-1)). Comparison to individually measured trace gases reveals strong variation in unaccounted for OH reactivity, from 5 to 15% missing in wet-season afternoons to mostly unknown (average 79%) during dry season. During dry-season afternoons isoprene, considered the dominant reagent with OH in rainforests, only accounts for ∼20% of the total OH reactivity. Vertical profiles of OH reactivity are shaped by biogenic emissions, photochemistry and turbulent mixing. The rainforest floor was identified as a significant but poorly characterized source of OH reactivity.
authors.affiliation: Air Chemistry and Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.
authors.forename: A C
authors.initials: AC
authors.lastname: Nölscher
authors.affiliation: Air Chemistry and Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.|Clima e Ambiente (CLIAMB), Instituto Nacional de Pesquisas da Amazônia (INPA), Avenue André Araújo 2936, Manaus, Amazonas CEP 69083-000, Brazil.
authors.forename: A M
authors.initials: AM
authors.lastname: Yañez-Serrano
authors.affiliation: Air Chemistry and Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.|Clima e Ambiente (CLIAMB), Instituto Nacional de Pesquisas da Amazônia (INPA), Avenue André Araújo 2936, Manaus, Amazonas CEP 69083-000, Brazil.
authors.forename: S
authors.initials: S
authors.lastname: Wolff
authors.affiliation: Embrapa Amazônia Oriental, Empresa Brasileira de Pesquisa Agropecuaria, Belem, Pará CEP 66095-100, Brazil.
authors.forename: A Carioca
authors.initials: AC
authors.lastname: de Araujo
authors.affiliation: Biogeochemical Systems Department, Max Planck Institute for Biogeochemistry, Jena 07745, Germany.
authors.forename: J V
authors.initials: JV
authors.lastname: Lavrič
authors.affiliation: Air Chemistry and Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Kesselmeier
authors.affiliation: Air Chemistry and Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Williams