Abstract
Abstract. Atmospheric furan is a primary and secondary pollutant in the atmosphere, and its emission contributes to the formation of ultrafine particles. We investigate the effects of NOx level and humidity on the formation of secondary organic aerosol (SOA) generated from the photooxidation of furan in the presence of NaCl seed particles. SOA mass concentration and yield were determined under different NOx and humidity levels. A significant difference is observed both in the variation of SOA mass concentration and SOA yield with the initial experimental conditions. Varying VOC (volatile organic compound) ∕ NOx ratios over the range 48.1 to 8.2 contributes to the effective formation of SOA in the presence of NaCl seed particles, with the SOA mass concentration and SOA yield ranging from 0.96 to 23.46 µg m−3 and from 0.04 % to 1.01 %, respectively. We found that there was a favourable relationship between the SOA yields and NOx concentration. In particular, the increase in SOA yield with increasing NOx concentration was continuously observed at high NOx levels owing to a corresponding increase in the amount of low-volatility hydroxyl nitrates and dihydroxyl dinitrates that can partition into the particle phase. In addition, varying relative humidity (RH) from 5 % to 88 % increased the SOA yield from 1.01 % to 5.03 %. The enhanced SOA formation from humid conditions may result from the high OH concentration, rapid furan decay rate, enhanced carbonyl-rich products condensation, and the aqueous-phase reactions. Using hybrid quadrupole-orbitrap mass spectrometer equipped with electrospray ionization (HESI-Q Exactive-Orbitrap MS), three carbonyl-rich products and three kinds of organonitrates were identified in the collected SOA. Based on the HESI-Q Exactive-Orbitrap MS analysis and Fourier transform infrared spectroscopy (FTIR), the reaction mechanism of furan photooxidation was proposed. This study demonstrates the effects of NOx and humidity on SOA formation during the furan–NOx–NaCl photooxidation and provides new insights into the oxidation regime and SOA composition in furan photooxidation. The results also illustrate the importance of studying SOA formation over a comprehensive range of environmental conditions. Only such evaluations can induce meaningful SOA mechanisms to be implemented in air quality models.
Highlights
Atmospheric particulate matter (PM) is primarily composed of organic carbon, elemental carbon, sulfate, nitrate, and other components (Donahue et al, 2009; Zhang et al, 2011), which have adverse effects on human health and global climate forcing (Hallquist et al, 2009; Pope III et al, 2013)
To get detailed information on the functional groups in secondary organic aerosol (SOA) formed during the photooxidation of furan, the collected particles were measured by Fourier transform infrared spectroscopy (FTIR), which has been proven to be an ideal technique for the detection of functional groups and bond information in aerosol samples
The effects of NOx and relative humidity (RH) on SOA formation from the photooxidation of furan in the presence of NaCl seed particles have been investigated in this study
Summary
Atmospheric particulate matter (PM) is primarily composed of organic carbon, elemental carbon, sulfate, nitrate, and other components (Donahue et al, 2009; Zhang et al, 2011), which have adverse effects on human health and global climate forcing (Hallquist et al, 2009; Pope III et al, 2013). An increase in SOA yield with increasing NOx was proposed to be due to the formation of low-volatility compounds including multifunctional nitrates and dinitrates, which partitioned to the particle phase and contribute significantly to isoprene SOA under high-NOx conditions (Schwantes et al, 2019). The chemical composition of furan SOA was investigated by heated electrospray ionization high-resolution orbitrap mass spectrometer (HESI-Q Exactive-Orbitrap MS), with a focus on the formation of organic nitrates. Strong evidence that both the RH and different NOx levels have a significant effect on SOA formation from furan photooxidation are presented
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