The role of in-canopy processes on biogenic VOC oxidation and formation of organic nitrogen aerosols

The balance between biogenic volatile organic compound (BVOC), nitrogen oxides (NOx), and hydrogen oxides (HOx) is key to determining photochemical regimes and aerosol formation. Field campaigns in forested regions have improved our understanding of the role of BVOC emissions on gas-phase tropospheric chemistry (e.g., isoprene oxidation under a range of NOx conditions), yet large uncertainties remain about the role of organic nitrates in aerosol formation. Typically, regional and global scale models represent the forest canopy and resulting BVOC emissions as a single lower boundary condition. However, the three-dimensional nature of the forest canopy has been shown to be important for BVOC emissions and atmospheric chemistry. Because BVOC are emitted from vegetation and react quickly in the atmosphere, the potential for oxidation and aerosol formation within the forest canopy remains an open question. Other physical processes, such as deposition, are also important for the loss of aerosol precursors and particulate matter. The large concentration gradients of reactive species within forest canopies coupled with large temperature gradients that influence partitioning highlight the need for evaluating these processes at a finer vertical scale than can be included in most regional models.

The proposed work use a 1-D canopy-chemistry model (FORCAsT, [Ashworth et al., 2015]) with existing field observations at two forests sites to address two scientific questions:

What are the role of physical and chemical in-canopy processes on BVOC oxidation and the formation of organic nitrate aerosol?

How do in-canopy processes inform emissions and chemistry of organic nitrates at the regional and global scales?

Work tasks will include adding new partitioning parameterizations for organic nitrates, evaluating these changes with existing field observations, and analyzing the chemical and physical processes that drive the formation of organic nitrates within and above a forest canopy. At the project conclusion, we will evaluate key processes to include in regional and global scale atmospheric chemistry models to accurately represent the formation of biogenically derived organic nitrates.