The effects of forest canopy shading and turbulence on boundary layer ozone

P A Makar,P Cheung,C Mclinden,J Zhang,Q Zheng,A Akingunola,S K Kharol,B Pabla,R M Staebler

doi:10.1038/ncomms15243

P A Makar, P Cheung + Show 7 more

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https://doi.org/10.1038/ncomms15243

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Journal: Nature Communications	Publication Date: May 18, 2017
Citations: 71	License type: open-access

Affiliation: Environment and Climate Change Canada

Abstract

The chemistry of the Earth’s atmosphere close to the surface is known to be strongly influenced by vegetation. However, two critical aspects of the forest environment have been neglected in the description of the large-scale influence of forests on air pollution: the reduction of photolysis reaction rates and the modification of vertical transport due to the presence of foliage. Here we show that foliage shading and foliage-modified vertical diffusion have a profound influence on atmospheric chemistry, both at the Earth’s surface and extending throughout the atmospheric boundary layer. The absence of these processes in three-dimensional models may account for 59–72% of the positive bias in North American surface ozone forecasts, and up to 97% of the bias in forested regions within the continent. These processes are shown to have similar or greater influence on surface ozone levels as climate change and current emissions policy scenario simulations.

Highlights

The chemistry of the Earth’s atmosphere close to the surface is known to be strongly influenced by vegetation
We found that the fraction of above-canopy photosynthetic photon flux density (PPFD), transmitted through the foliage to the ground, minimized in the summer months (Fig. 2b,c)
The canopy parameterization has a larger local effect than these scenarios ( À 23 p.p.b.v., GEM-MACHv2), underscoring its importance for accurate simulation of the atmosphere, we note that the magnitude of the changes from the referenced work may in part depend on the resolution of the underlying model framework. We note that these comparisons are for surface ozone changes only—while we have shown in Fig. 5 that the impacts of the forest on ozone levels extend throughout the atmospheric boundary layer, we are unable to show similar comparisons for the references quoted

Summary

Introduction

The chemistry of the Earth’s atmosphere close to the surface is known to be strongly influenced by vegetation. We show that foliage shading and foliage-modified vertical diffusion have a profound influence on atmospheric chemistry, both at the Earth’s surface and extending throughout the atmospheric boundary layer The absence of these processes in three-dimensional models may account for 59–72% of the positive bias in North American surface ozone forecasts, and up to 97% of the bias in forested regions within the continent. The chemistry of the Earth’s atmosphere close to the surface is known to be strongly influenced by the presence, absence, and type of vegetation, via hydrocarbon emissions[1,2] and deposition to the foliage[3,4] These factors are common components of the computational models of atmospheric chemistry[5,6,7,8], which are in turn used for air pollution forecasting for current and future climates, and to formulate public policy with respect to regulation[9]. WRF-CHEM/NC GGEEM-M-EMCMAAMCCWHWHvRFMv-1F.-1AE.[5].CC5R.1WHAC1/b1ERf/aMFeMF-s/eSOAteCdUZLacbtMCALaaeA3ARsckTDUReQ transcontinental transport[15,16], the larger summer bias within continents indicates missing processes as opposed to transport from abroad

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Conclusion