Overview

Biogenic Volatile Organic Compounds (BVOCs) are volatile gases produced by plants and other living organisms that are emitted into the atmosphere where they can produce atmospheric constituents, such as organic particles and ozone, that are important for air pollution and climate. As a result, BVOC emission algorithms are integral components of air quality and climate modeling frameworks. Although there are hundreds of BVOC with complex controlling processes, BVOC emission models have focused on a few dominant compounds (e.g., isoprene and alpha-pinene) and major controlling processes (e.g., temperature and light responses). The primary objectives of this project were to identify additional compounds and processes that should be included in BVOC models to improve the predictability of air quality and climate models. This was accomplished by synthesizing existing observations, conducting laboratory investigations, and incorporating the results into an improved BVOC emission model.

Intellectual merit

BVOC emission enclosure measurements were combined with a literature survey of reported observations to identify dozens of BVOC that make a significant contribution to the total BVOC emission of some plant species. However, when these measurements were extrapolated to the global scale, they show that these compounds make a relatively small contribution to annual global total BVOC emission. Acetate esters, with the general formula CH3CO2R, were identified as an important class of BVOC that have previously been excluded in BVOC emission models.  Other potentially important classes of compounds that were not included in earlier BVOC emission models include oxidation products and low volatility terpenoids such as diterpenes and oxygenated sesquiterpenes.  

Laboratory investigations of stress-induced emissions were conducted to examine BVOC response to both high temperature and freezing conditions. The heat stress results show that emission responses vary for different compounds and plant species but can be grouped into four categories: 1) decreased emissions, 2) increase similar to that expected for moderate temperature variations, 3) unexpectedly high increase, and 4) induction of emissions that were not observed prior to stress.  Heat stress induced emissions persisted for several weeks in some cases. Freezing conditions resulted in unexpectedly high terpenoid emissions that continued for days after the plant was brought back to optimal temperature conditions. Algorithms accounting for drought stress were developed to account for observed emission increases due to elevated leaf temperatures associated with mild drought and emission decreases due to reductions in photosynthetic activity. Chemistry and transport modeling simulations using the CESM model suggest that other stresses (e.g., air pollution and high winds) can result in BVOC emission changes that can have a significant impact on local air quality and climate. 

Broader impacts

A potential reason for the omission of some compounds in reported BVOC emission studies could be the lack of suitable measurement technique. Highly inert and heated plant enclosure systems were developed for sampling reactive or low volatility compounds that can be lost when using standard enclosure approaches. A comparison of this system with conventional approaches indicates that the specialized enclosure systems are required for some but not all BVOC.  An updated version of a BVOC emission model, the MEGANv3, with an expanded list of compounds and controlling algorithms was developed and made available to the scientific and air quality regulatory community for regional to global emission modeling.

Last Modified: 10/03/2021
Modified by: Alex Guenther