Biomass burning influence on high-latitude tropospheric ozone and reactive nitrogen in summer 2008: a multi-model analysis based on POLMIP simulations

S R Arnold,S Tilmes,J L Thomas,S Steenrod,V Huijnen,Y Long,Y Yoshida,S Turquety,S A Monks,J Flemming,D A Ridley,J Langner,I Bouarar,J Mao,L K Emmons,K S Law,B N Duncan

doi:10.5194/acp-15-6047-2015

Abstract

Abstract. We have evaluated tropospheric ozone enhancement in air dominated by biomass burning emissions at high latitudes (> 50° N) in July 2008, using 10 global chemical transport model simulations from the POLMIP multi-model comparison exercise. In model air masses dominated by fire emissions, ΔO3/ΔCO values ranged between 0.039 and 0.196 ppbv ppbv−1 (mean: 0.113 ppbv ppbv−1) in freshly fire-influenced air, and between 0.140 and 0.261 ppbv ppbv−1 (mean: 0.193 ppbv) in more aged fire-influenced air. These values are in broad agreement with the range of observational estimates from the literature. Model ΔPAN/ΔCO enhancement ratios show distinct groupings according to the meteorological data used to drive the models. ECMWF-forced models produce larger ΔPAN/ΔCO values (4.47 to 7.00 pptv ppbv−1) than GEOS5-forced models (1.87 to 3.28 pptv ppbv−1), which we show is likely linked to differences in efficiency of vertical transport during poleward export from mid-latitude source regions. Simulations of a large plume of biomass burning and anthropogenic emissions exported from towards the Arctic using a Lagrangian chemical transport model show that 4-day net ozone change in the plume is sensitive to differences in plume chemical composition and plume vertical position among the POLMIP models. In particular, Arctic ozone evolution in the plume is highly sensitive to initial concentrations of PAN, as well as oxygenated VOCs (acetone, acetaldehyde), due to their role in producing the peroxyacetyl radical PAN precursor. Vertical displacement is also important due to its effects on the stability of PAN, and subsequent effect on NOx abundance. In plumes where net ozone production is limited, we find that the lifetime of ozone in the plume is sensitive to hydrogen peroxide loading, due to the production of HOx from peroxide photolysis, and the key role of HO2 + O3 in controlling ozone loss. Overall, our results suggest that emissions from biomass burning lead to large-scale photochemical enhancement in high-latitude tropospheric ozone during summer.

Highlights

Vegetation fires play an important role in ecosystem function and regulation (Bonan, 2008) and contribute substantially to atmospheric CO2, with gross emissions from biomass burning estimated to be between 2 and 4 PgC a−1 globally, equivalent to 40 % of those from fossil fuel combustion (Ciais et al, 2013)
European Centre for Mediumrange Weather Forecasts (ECMWF)-forced models produce larger peroxyacetyl nitrate (PAN)/ CO values (4.47 to 7.00 pptv ppbv−1) than GEOS5-forced models (1.87 to 3.28 pptv ppbv−1), which we show is likely linked to differences in efficiency of vertical transport during poleward export from mid-latitude source regions
We use results from POLARCAT Model Intercomparison Project (POLMIP) (POLARCAT model intercomparison Project) (Emmons et al, 2014) and observations collected in the Arctic troposphere as part of the ARCTAS-B mission (Jacob et al, 2010), to evaluate simulated summertime tropospheric ozone and its precursors in the northern high latitudes and how it is influenced by boreal fire emissions in a series of state-of-the-art global atmospheric chemical transport models

Summary

Introduction

Vegetation fires play an important role in ecosystem function and regulation (Bonan, 2008) and contribute substantially to atmospheric CO2, with gross emissions from biomass burning estimated to be between 2 and 4 PgC a−1 globally, equivalent to 40 % of those from fossil fuel combustion (Ciais et al, 2013). We use results from POLMIP (POLARCAT model intercomparison Project) (Emmons et al, 2014) and observations collected in the Arctic troposphere as part of the ARCTAS-B mission (Jacob et al, 2010), to evaluate simulated summertime tropospheric ozone and its precursors in the northern high latitudes and how it is influenced by boreal fire emissions in a series of state-of-the-art global atmospheric chemical transport models. Using the fixed-lifetime CO tracers from the POLMIP simulations, in conjunction with observed and simulated CO, Monks et al (2015) investigated the contributions from differences in model transport and oxidants to inter-model variability in simulated seasonal CO in the Arctic They showed that emissions from Asian fires are the dominant source of CO tracer in the lower and middle summertime Arctic troposphere, and are approximately equal to the contribution from Asian anthropogenic sources in the upper troposphere. Do not generally support this offsetting of positive biases in HNO3 with under-prediction of PAN

Model ozone production in fire-dominated Arctic air masses

High-latitude PAN enhancement in POLMIP models

Lagrangian chemical model simulations

Simulated plume ozone change and sensitivities to transport and chemistry

Findings

Summary and conclusions