Molecular characterization of polar organic aerosol constituents in off-road engine emissions using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS): implications for source apportionment

Min Cui,Yangzhi Mo,Bin Jiang,Gan Zhang,Fan Zhang,Zhiyong Xie,Jun Li,Caiqing Yan,Cheng Li,Mei Zheng,Junyu Zheng,Yingjun Chen,Jia Li

doi:10.5194/acp-19-13945-2019

Abstract

Abstract. The molecular compositions of polar organic compounds (POCs) in particles emitted from various vessels and excavators were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and possible molecular structures of POCs were proposed. POCs were extracted with purified water and sorted by elemental composition into three groups: CHO, CHON, and S-containing compounds (CHONS and CHOS). The results show the following. (i) CHO (accounting for 49 % of total POCs in terms of peak response) was the most abundant group for all tested off-road engines, followed by CHON (33 %) and CHOS (35 %) for diesel and HFO (heavy-fuel-oil)-fueled off-road engines. (ii) The abundance and structure of the CHON group in water extracts were different in terms of engine type and load. The relative peak response of CHON was the highest for excavator emissions in working mode, compared to the idling and moving modes. Furthermore, dinitrophenol and methyl dinitrophenol were potentially the most abundant emission species for high-rated speed excavators, while nitronaphthol and methyl nitronaphthol were more important for low-rated speed vessels. (iii) The composition and structure of the S-containing compounds were directly influenced by fuel oil characteristics (sulfur content and aromatic ring), with more condensed aromatic rings in the S-containing compounds proposed in HFO-fueled vessel emissions. More abundant aliphatic chains were inferred in diesel equipment emissions. Overall, higher fractions of condensed hydrocarbons and aromatic rings in POCs emitted from vessels using HFO cause strong optical absorption capacity. Different structures in POCs could provide a direction for qualitative and quantitative analysis of organic compounds as tracers to distinguish these emissions from diesel or HFO-fueled off-road engines.

Highlights

A rapid increase in the number of off-road engines has resulted in large quantities of pollutant emissions, which have severe impacts on air quality, human health, and climate change (Righi et al, 2011; Li et al, 2016; Liu et al, 2016; Wang et al, 2018; Zhang et al, 2018)
As reported by the US EPA, nearly 34 % of elemental carbon (EC) emissions originated from offroad diesel vehicle emissions in the United States (USEPA, 2015)
The range of detected peaks for excavators and vessels had molecular weights between 150 and 900 Da, but most of the intensive peaks occurred in the molecular weight range of 200–400 Da

Summary

Introduction

A rapid increase in the number of off-road engines (e.g., vessels and excavators) has resulted in large quantities of pollutant emissions, which have severe impacts on air quality, human health, and climate change (Righi et al, 2011; Li et al, 2016; Liu et al, 2016; Wang et al, 2018; Zhang et al, 2018). It was reported that emissions from fishing boats accounted for 18.3 % of total fine particulate matter (PM2.5) emitted by on-road vehicles (Deng et al, 2017). As reported by the US EPA, nearly 34 % of elemental carbon (EC) emissions originated from offroad diesel vehicle emissions in the United States (USEPA, 2015). Construction equipment, a typical offroad diesel vehicle, emitted abundant volatile organic compounds (VOCs). VOCs were considered one of the most important precursor of HUmic-LIke Substances (HULIS) like organosulfates (Zhang et al, 2010; Tao et al, 2014)

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Results