The effect of spruce bark beetle on BVOC, secondary organic aerosol and ozone: Integrating biotic stress in a chemical transport model

Abstract.

Droughts and other weather extremes affect the resilience of trees and facilitate herbivore insect infestation. In the last decade, the spruce bark beetle population expanded over mid to northern Europe, infesting large spruce forest areas. Spruce bark beetles bore holes into the stem of the trees, which activates a stress response and causes the release of large amounts of stored BVOC. Based on BVOC measurements from the stem of healthy and infested Norway spruces, a biotic stress parametrization was developed integrating stress-related BVOC emissions into the chemical transport model COSMO-MUSCAT (COnsortium for Small scale MOdelling - MUltiScale Chemistry Aerosol Transport). This study investigates a high impact scenario representing an intensive Europe wide spruce bark beetle infestation. With the stress parametrization, the BVOC emissions of spruces were increased substantially which affects atmospheric chemistry. The parametrization leads to higher nighttime emissions and concentrations of α-pinene and limonene. The altered diurnal cycle of the monoterpenes concentration is in closer agreement with measurements. The enhanced BVOC affect ozone concentration with local variations between −7 % and +10 % and significantly elevate secondary organic aerosol (SOA). On the regional scale, the SOA concentration increases in summer by 55 % and at spruce-abundant locations by ~150 %. The largest increases occur during night, with major contributions by the oxidation of lumped α-pinene by NO₃ and O₃. The higher SOA concentration during bark beetle infestation contributes to elevated fine particulate matter concentration. The study highlights the importance for integrating stress related BVOC emissions into chemical transport models.