In situ measurements of isoprene and monoterpenes within a south-east Asian tropical rainforest

J R Hopkins,A C Lewis,C E Jones

doi:10.5194/acp-11-6971-2011

J R Hopkins, A C Lewis + Show 1 more

Open Access

https://doi.org/10.5194/acp-11-6971-2011

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Abstract

Abstract. Biogenic volatile organic compounds (BVOCs) emitted from tropical rainforests comprise a substantial fraction of global atmospheric VOC emissions, however there are only relatively limited measurements of these species in tropical rainforest regions. We present observations of isoprene, α-pinene, camphene, Δ-3-carene, γ-terpinene and limonene, as well as oxygenated VOCs (OVOCs) of biogenic origin such as methacrolein, in ambient air above a tropical rainforest in Malaysian Borneo during the Oxidant and Particle Photochemical Processes above a south-east Asian tropical rainforest (OP3) project in 2008. Daytime composition was dominated by isoprene, with an average mixing ratio of the order of ~1 ppb. γ-terpinene, limonene and camphene were the most abundant monoterpenes, with average daytime mixing ratios of 102, 71 and 66 ppt respectively, and with an average monoterpene toisoprene ratio of 0.3 during sunlit hours, compared to 2.0 at night. Limonene and camphene abundances were seen to be related to both temperature and light conditions. In contrast, γ-terpinene emission continued into the late afternoon/evening, under relatively low temperature and light conditions. The contributions of isoprene, monoterpenes and other classes of VOC to the volatile carbon budget and OH reactivity have been summarised for this rainforest location. We observe good agreement between surface and aircraft measurements of boundary layer isoprene and methacrolein above the natural rainforest, suggesting that the ground-level observations are broadly representative of isoprene emissions from this region.

Highlights

Emissions of volatile organic compounds (VOCs) affect the oxidising capacity of the atmosphere (Kesselmeier et al, 2000), radiative forcing and the global carbon cycle (Kuhn et al, 2002; Fuentes et al, 2000)
VOCs scavenge oxidants such as the hydroxyl radical (OH), ozone (O3) and the nitrate radical (NO3) (Atkinson and Arey, 2003), and in polluted, high NOx (NO and NO2) environments, VOC emissions lead to net tropospheric O3 production through catalytic reactions between oxidised VOC derivatives and NO (Atkinson and Arey, 2003; Lelieveld et al, 2008)
Biosynthesis of isoprene and monoterpenes occurs within plants via the precursors dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP) (Fuentes et al, 2000), and has been linked with a number of physiological processes such as temperature regulation, reducing drought-induced stress and promotion of flowering (Kesselmeier and Staudt, 1999)

Summary

Introduction

Emissions of volatile organic compounds (VOCs) affect the oxidising capacity of the atmosphere (Kesselmeier et al, 2000), radiative forcing (through formation of secondary organic aerosol, Padhy and Varshney, 2005) and the global carbon cycle (Kuhn et al, 2002; Fuentes et al, 2000). Biogenic VOCs (BVOCs) such as isoprene, monoterpenes and sesquiterpenes are thought to provide the largest fraction (>90 %) of the total global non-methane VOC source term (Greenberg et al, 1999), with a total BVOC flux of the order of 1100 Tg C yr−1 (Guenther et al, 1995; Simpson et al, 1999), compared to 50–100 Tg C yr−1 anthropogenic VOCs (Holzke et al, 2006). BVOC emissions (by mass) are often dominated by isoprene (Guenther et al, 2000), and estimates of the annual global isoprene flux are comparable with annual global methane emissions (Wildermuth and Fall, 1996; Sharkey and Yeh, 2001).

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