02409naa a2200337 a 450000100080000000500110000800800410001902400330006010000240009324501080011726000090022552014570023465000130169165000120170470000210171670000270173770000220176470000140178670000220180070000200182270000140184270000160185670000150187270000210188770000150190870000150192370000230193870000200196170000170198177300730199821066352022-05-25       2018    bl uuuu     u00u1 u    #d7 a10.3389/ffgc.2018.000122DOI1 aPFANNERSTILL, E. Y.  aTotal OH reactivity changes over the Amazon rainforest during an El Niño event.h[electronic resource]  c2018  aThe 2015/16 El Niño event caused unprecedented drought and warming in the Amazon basin. How tropical forests react to such extreme events in terms of volatile organic compound (VOC) emissions is of interest as the frequency of these events is predicted to increase through climate change. The diverse VOCs emitted can be significant for plants' carbon budgets, influence ozone and particle production, and through their reactivity impact OH concentrations. Total OH reactivity is a directly measureable quantity that gives the reaction frequency of OH radicals with all reactive species in the atmosphere in s?1. Here we present a comparison of the OH reactivity diel cycle from November 2015, i.e., extreme drought and elevated temperatures associated with strong El Niño conditions, with November 2012, a ?normal? El Niño Southern Oscillation (ENSO)-neutral period. Interestingly, the diel maximum of OH reactivity during the El Niño event occurred at sunset instead of, under normal conditions, early afternoon. The absolute total diel OH reactivity, however, did not change significantly. Daytime OH reactivity averages were 24.3 ± 14.5 s?1 in 2012 and 24.6 ± 11.9 s?1 in 2015, respectively. Our findings suggest that a combination of stronger turbulent transport above the canopy with stress-related monoterpene and, possibly, other biogenic volatile organic compound (BVOC) emissions were responsible for the increased reactivity at sunset.  aAmazonia  aEl Nino1 aNÖLSCHER, A. C.1 aYÁÑEZ-SERRANO, A. M.1 aBOURTSOUKIDIS, E.1 aKEBEL, S.1 aJANSSEN, R. H. H.1 aTSOKANKUNKU, A.1 aWOLFF, S.1 aSÖRGEL, M.1 aSÁ, M. O.1 aARAUJO, A. C. de1 aWALTER, D.1 aLAVRIC, J.1 aDIAS-JUNIOR, C. Q.1 aKESSELMEIER, J.1 aWILLIAMS, J.  tFrontiers in Forests and Global Changegv. 1, Article 12, Dec. 2018.