Environmental and biological controls on seasonal patterns of isoprene above a rain forest in central Amazonia

Abstract

The Amazon rain forest is a major global isoprene source, but little is known about its seasonal ambient concentration patterns. To investigate the environmental and phenological controls over isoprene seasonality, we measured isoprene mixing ratios, concurrent meteorological data, and leaf area indices from April 2014 to January 2015 above a rain forest in the central Amazon, Brazil. Daytime median isoprene mixing ratios varied throughout the year by a factor of two. The isoprene seasonal pattern was not solely driven by sunlight and temperature. Leaf age and quantity also contributed to the seasonal variations of isoprene concentrations, suggesting leaf phenology was a crucial variable needed to correctly estimate isoprene emissions. A zero-dimensional model incorporating the estimated emissions, atmospheric boundary layer dynamics, and air chemistry was used to assess the contributions of each process on the variability of isoprene. Surface deposition was an important sink mechanism and accounted for 78% of the nighttime loss of isoprene. Also, chemical reactions destroyed isoprene and during 6:00 to 18:00 h local time 56, 77, 69, and 69% of the emitted isoprene was chemically consumed in June, September, December, and January, respectively. Entrainment fluxes from the residual layer contributed 34% to the early-morning above-canopy isoprene mixing ratios. Sensitivity analysis showed that hydroxyl radical (HO) recycling and segregation of isoprene-HO played relatively lesser roles (up to 16%) in regulating ambient isoprene levels. Nitric oxide (NO) levels dominated isoprene chemical reaction pathways associated with consumption and production of HO under low-NO and high volatile organic compound (VOC) conditions. While surface deposition and oxidative processes altered isoprene levels, the relative importance of these factors varied seasonally with leaf phenology playing a more important role.

Investigation of Isoprene Dynamics During the Day‐to‐Night Transition Period

“…In the STD case, isoprene has a pronounced diurnal cycle with a peak in the early afternoon and a minimum just before sunrise ( Figure 1a). This diurnal pattern of isoprene has been observed in many forests ranging from deciduous to tropical under clear and well-mixed conditions (Apel, 2002;Wei et al, 2018) and is well captured by models of different scales (Ashworth et al, 2015;de Arellano et al, 2011). During the 2016 AMOS field campaign at UMBS, an EOD peak in isoprene was observed during clear and calm days.…”

Effects of a Detailed Vegetation Database on Simulated Meteorological Fields, Biogenic VOC Emissions, and Ambient Pollutant Concentrations over Japan

“…In contrast, the present study treated these variations as biases, and used average EFs in all measurements. If their monthly EFs represent actual situations, it is necessary to clarify additional mechanisms that might alter BVOC emissions, such as leaf phenology [33], stresses [39], and drought [40][41][42], other than those considered in MEGAN, such as dependence of emissions on solar radiation and temperature. Figure S12 in the Supplementary Materials shows the horizontal distributions of the mean surface SOA concentrations originating from isoprene, monoterpenes, and sesquiterpenes simulated in the NEW-VEGEF cases from 22 July to 10 August 2013 in d02, d03, and d04.…”

“…There are studies investigating factors causing seasonal variations of BVOC emissions in addition to solar radiation and temperature. For example, Wei et al [33] indicated that leaf phenology is a crucial variable causing seasonal variations. However, to date, it is difficult to attribute one of factors to the measured large variations due to lack of detailed information.…”

Amazonian biogenic volatile organic compounds under global change

“…(Alves et al, 2016;Bourtsoukidis et al, 2018;Jardine, Monson, et al, 2011;Jardine, Yañez Serrano, Arneth, Abrell, Jardine, Artaxo, et al, 2011;Jardine et al, 2014Jardine et al, , 2017Liu et al, 2016;Paralovo et al, 2015;Yáñez-Serrano, Nölscher, et al, 2018;Yáñez-Serrano et al, 2015, 2016Yee et al, 2018), although new studies should aim to characterize unknown reactive compounds to better understand atmospheric reactivity, particularly in the dry season (Nölscher et al, 2016;Pfannerstill et al, 2018). Progress has been made in understanding of the impact of BVOCs on oxidant and aerosol distributions (Andreae et al, 2018;de Sá et al, 2017de Sá et al, , 2019Liu et al, 2016;Nölscher et al, 2016;Pfannerstill et al, 2018;Schulz et al, 2018;Shrivastava et al, 2019), the processes controlling the seasonal (Alves et al, 2016(Alves et al, , 2018Wei et al, 2018;Yáñez-Serrano, Fasbender, et al, 2018;Yáñez-Serrano et al, 2015) and spatial (Barkley et al, 2009(Barkley et al, , 2011Bauwens et al, 2016;Salazar et al, 2018;Taylor et al, 2018;Taylor, Smith, Slot, & Feeley, 2019) variations of BVOCs, flooding (Bracho-Nunez et al, 2012) and ecological interactions (Salazar et al, 2018). However, more process-based studies are essential, such as those using laboratory and enclosure methods,…”