PTR-TOF-MS eddy covariance measurements of isoprene and monoterpene fluxes from an eastern Amazonian rainforest

Abstract

Abstract. Biogenic volatile organic compounds (BVOCs) are important components of the atmosphere due to their contribution to atmospheric chemistry and biogeochemical cycles. Tropical forests are the largest source of the dominant BVOC emissions (e.g. isoprene and monoterpenes). In this study, we report isoprene and total monoterpene flux measurements with a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) using the eddy covariance (EC) method at the Tapajós National Forest (2.857∘ S, 54.959∘ W), a primary rainforest in eastern Amazonia. Measurements were carried out from 1 to 16 June 2014, during the wet-to-dry transition season. During the measurement period, the measured daytime (06:00–18:00 LT) average isoprene mixing ratios and fluxes were 1.15±0.60 ppb and 0.55±0.71 mg C m−2 h−1, respectively, whereas the measured daytime average total monoterpene mixing ratios and fluxes were 0.14±0.10 ppb and 0.20±0.25 mg C m−2 h−1, respectively. Midday (10:00–14:00 LT) average isoprene and total monoterpene mixing ratios were 1.70±0.49 and 0.24±0.05 ppb, respectively, whereas midday average isoprene and monoterpene fluxes were 1.24±0.68 and 0.46±0.22 mg C m−2 h−1, respectively. Isoprene and total monoterpene emissions in Tapajós were correlated with ambient temperature and solar radiation. Significant correlation with sensible heat flux, SHF (r2=0.77), was also observed. Measured isoprene and monoterpene fluxes were strongly correlated with each other (r2=0.93). The MEGAN2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) model could simulate most of the observed diurnal variations (r2=0.7 to 0.8) but declined a little later in the evening for both isoprene and total monoterpene fluxes. The results also demonstrate the importance of site-specific vegetation emission factors (EFs) for accurately simulating BVOC fluxes in regional and global BVOC emission models.

Total OH reactivity over the Amazon rainforest: variability with temperature, wind, rain, altitude, time of day, season, and an overall budget closure

“…Total OH reactivity diel cycles (Fig. 2) reflect the typical diurnal behaviour of BVOC concentrations previously measured in the rainforest (Langford et al, 2010;Yáñez-Serrano et al, 2015;Rizzo et al, 2010), which is broadened towards the evening hours in comparison to emission fluxes (Sarkar et al, 2020;Kuhn et al, 2007). Sunrise was around 06:00 local time (LT) and sunset around 18:00, independent of the season.…”

“…In all seasons, there was a negative vertical gradient of OH reactivity towards higher levels around noon. This is expected, because noon and early afternoon is the time when the vegetation reaches its emission maximum (Sarkar et al, 2020). Reactive…”

A new field instrument for leaf volatiles reveals an unexpected vertical profile of isoprenoid emission capacities in a tropical forest

“…Although strong, light-dependent monoterpene emissions have been reported from several species (K. J. Jardine et al, 2017;Kuhn et al, 2002), calibration relative to isoprene is the safest bet for a non-distinguishing sensor, as isoprene is demonstrated to be the dominant VI emitted from plants in the tropics (Alves et al, 2016;Sarkar et al, 2020;Yanez-Serrano et al, 2015) and worldwide (Alex Guenther, 2013).…”

Evidence of ketene emissions from petrochemical industries and implications for ozone production potential

“…CC BY 4.0 License. plants) using a high-sensitivity PTR-TOF-MS that enables high mass resolution with a detection limit of low ppb to ppt using H3O + as reagent ion (Lindinger et al, 1998;Jordan et al, 2009;Sarkar et al, 2016;Sarkar et al, 2020). The PTR-TOF-MS was operated over the mass range of 21-210 amu at a drift tube pressure of 2.2 mbar and temperature of ο C (E/N ~ 136 Td) that enabled collection of VOC data at 1 Hz resolution.…”

“…Calibrations were performed in the range of 2-10 ppb. In order to establish the instrumental background, VOC-free zero air was generated by passing the ambient air through a catalytic converter (stainless steel tube filled with platinum-coated glass wool) heated at 350 ο C. The measured ion signals were normalized to the primary ion (H3O + , m/z = 19) as follows (Sarkar et al, 2016;Sarkar et al, 2020):…”