Articles | Volume 16, issue 5
Research article
07 Mar 2016
Research article |  | 07 Mar 2016

Urban stress-induced biogenic VOC emissions and SOA-forming potentials in Beijing

Andrea Ghirardo, Junfei Xie, Xunhua Zheng, Yuesi Wang, Rüdiger Grote, Katja Block, Jürgen Wildt, Thomas Mentel, Astrid Kiendler-Scharr, Mattias Hallquist, Klaus Butterbach-Bahl, and Jörg-Peter Schnitzler

Abstract. Trees can significantly impact the urban air chemistry by the uptake and emission of reactive biogenic volatile organic compounds (BVOCs), which are involved in ozone and particle formation. Here we present the emission potentials of "constitutive" (cBVOCs) and "stress-induced" BVOCs (sBVOCs) from the dominant broadleaf woody plant species in the megacity of Beijing. Based on the municipal tree census and cuvette BVOC measurements on leaf level, we built an inventory of BVOC emissions, and assessed the potential impact of BVOCs on secondary organic aerosol (SOA) formation in 2005 and 2010, i.e., before and after realizing the large tree-planting program for the 2008 Olympic Games. We found that sBVOCs, such as fatty acid derivatives, benzenoids, and sesquiterpenes, constituted a significant fraction ( ∼  40 %) of the total annual BVOC emissions, and we estimated that the overall annual BVOC budget may have doubled from  ∼  4.8  ×  109 g C year−1 in 2005 to  ∼  10.3  ×  109 g C year−1 in 2010 due to the increase in urban greening, while at the same time the emission of anthropogenic VOCs (AVOCs) decreased by 24 %. Based on the BVOC emission assessment, we estimated the biological impact on SOA mass formation potential in Beijing. Constitutive and stress-induced BVOCs might produce similar amounts of secondary aerosol in Beijing. However, the main contributors of SOA-mass formations originated from anthropogenic sources (> 90 %). This study demonstrates the general importance to include sBVOCs when studying BVOC emissions. Although the main problems regarding air quality in Beijing still originate from anthropogenic activities, the present survey suggests that in urban plantation programs, the selection of low-emitting plant species has some potential beneficial effects on urban air quality.

Short summary
Trees can impact urban air quality. Large emissions of plant volatiles are emitted in Beijing as a stress response to the urban polluted environment, but their impacts on secondary particulate matter remain relatively low compared to those originated from anthropogenic activities. The present study highlights the importance of including stress-induced compounds when studying plant volatile emissions.
Final-revised paper