A global model study of the impact of land-use change in Borneo on atmospheric composition

N J Warwick,D E Heard,J Lee,P K Misztal,B Langford,P M Edwards,J A Pyle,A T Archibald,K Ashworth,J Dorsey,L K Whalley

doi:10.5194/acp-13-9183-2013

Abstract

Abstract. In this study, a high resolution version of the Cambridge p-TOMCAT chemical transport model is used, along with measurement data from the 2008 NERC-funded Oxidant and Particle Photochemical Processes (OP3) project, to examine the potential impact of the expansion of oil palm in Borneo on atmospheric composition. Several model emission scenarios are run for the OP3 measurement period, incorporating emissions from both global datasets and local flux measurements. Using the OP3 observed isoprene fluxes and OH recycling chemistry in p-TOMCAT substantially improves the comparison between modelled and observed isoprene and OH concentrations relative to using MEGAN isoprene emissions without OH recycling. However, a similar improvement was also achieved without using HOx recycling, by fixing boundary layer isoprene concentrations over Borneo to follow the OP3 observations. An extreme hypothetical future scenario, in which all of Borneo is converted to oil palm plantation, assessed the sensitivity of the model to changes in isoprene and NOx emissions associated with land-use change. This scenario suggested a 70% upper limit on surface ozone increases resulting from land-use change on Borneo, excluding the impact of future changes in emissions elsewhere. Although the largest changes in this scenario occurred directly over Borneo, the model also calculated notable regional changes of O3, OH and other species downwind of Borneo and in the free troposphere.

Highlights

There are, significant uncertainties concerning isoprene chemistry and the degree to which OH is consumed by the oxidation of isoprene, which could alter our understanding of the atmospheric impact of future changes in isoprene emissions
Warwick et al.: Impact of land-use change in Borneo on atmospheric composition compared with 1 % less than 40 yr ago (Thoenes, 2007; Hewitt et al, 2010)
11 2 the calculated maximum increase of 70 % is applied to observed ozone mixing ratios, which are lower than the model calculated ozone levels, the ozone increase would result in monthly mean mixing ratios of only ∼20 ppb. These results demonstrate the importance of understanding nitrogen oxides (NOx) emissions when predicting the impact of oil palm expansion on air quality

Summary

Introduction

There are, significant uncertainties concerning isoprene chemistry and the degree to which OH is consumed by the oxidation of isoprene, which could alter our understanding of the atmospheric impact of future changes in isoprene emissions. Large discrepancies exist between measured and modelled OH concentrations in regions of high isoprene and low NOx emissions, suggesting the existence of an unknown chemical recycling mechanism for OH (Lelieveld et al, 2008; Hewitt et al, 2010; Whalley et al, 2011; Stone et al, 2011; Hofzumahaus et al, 2009). Lelieveld et al, 2008; Peeters et al, 2009; Da Silva et al, 2010; Paulot et al, 2009). Inclusion of these mechanisms in model chemistry schemes has the potential to influence our understanding of the extent to which changes in isoprene emissions could affect oxidising capacity (Archibald et al, 2010b)

Objectives

Methods

Findings

Conclusion