Future inhibition of ecosystem productivity by increasing wildfire pollution over boreal North America

Abstract

Abstract. Biomass burning is an important source of tropospheric ozone (O 3 ) and aerosols. These air pollutants can affect vegetation photosynthesis through stomatal uptake (for O 3 ) and light scattering and absorption (for aerosols). Wildfire area burned is projected to increase significantly in boreal North America by the mid-century, while little is known about the impacts of enhanced emissions on the terrestrial carbon budget. Here, combining site-level and satellite observations and a carbon-chemistry-climate model, we estimate the impacts of fire emitted O 3 and aerosols on net primary productivity (NPP) over boreal North America. Fire emissions are calculated based on an ensemble projection from 13 climate models. In the present day, wildfire enhances surface O 3 by 2 ppbv (7 %) and aerosol optical depth (AOD) at 550 nm by 0.03 (26 %) in the summer. By mid-century, area burned is predicted to increase by 66 % in boreal North America, contributing more O 3 (13 %) and aerosols (37 %). Fire O 3 causes negligible impacts on NPP because ambient O 3 concentration (with fire contributions) is below the damage threshold of 40 ppbv for 90 % summer days. Fire aerosols reduce surface solar radiation but enhance atmospheric absorption, resulting in enhanced air stability and intensified regional drought. The domain of this drying is confined to the north in the present day but extends southward by 2050 due to increased fire emissions. Consequently, wildfire aerosols enhance NPP by 72 Tg C yr −1 in the present day but decrease NPP by 118 Tg C yr −1 in the future, mainly because of the soil moisture perturbations. Our results suggest that future wildfire may accelerate boreal carbon loss, not only through direct emissions increasing from 68 Tg C yr −1 at present day to 130 Tg C yr −1 by mid-century but also through the biophysical impacts of fire aerosols.

Indirect contributions of global fires to surface ozone through ozone–vegetation feedback

“…HEMCO is highly customizable in that it can automatically combinate, overlay, and update emission inventories and scale factors specified by the users. In general, the GEOS-Chem model overestimates summer surface O 3 concentrations in the eastern US and China (Zhang et al, 2011;Travis et al, 2016;Schiferl and Heald, 2018).…”

Local Arctic Air Pollution: A Neglected but Serious Problem

“…Changes in diffuse/direct radiation fraction induced by changes in atmospheric aerosol loading affect the efficiency of plant productivity (Rap et al, ). Fire‐produced aerosol particles were found to produce an increase in net primary productivity via diffuse radiation effects, although decreases in productivity were found in a future midcentury scenario due to drought induced by fire aerosol impacts on atmospheric stability and moisture (Yue et al, ).…”

“…Ozone is harmful to vegetation because it impairs photosynthesis via uptake through plant stomata (Sitch et al, ). A recent study showed only negligible effects from ozone sourced from boreal wildfires on forest productivity in boreal North America (Yue et al, ). But a study examining potential ecosystem damage due to ozone at the country scale found that ozone formed through NO x has the highest impact in the high northern latitudes (van Zelm et al, ).…”

Influence of Fire on the Carbon Cycle and Climate

“…Increased atmospheric ozone concentration due to air pollution by fire emissions, however, leads to plant damages and reduction in vegetation productivity. This effect was quantified with a model for the Amazon forest [28] and boreal North America [29]. In the Amazon forest ozone damage could double the effect of wildfires on carbon storage [28].…”