Abstract
Abstract. Volatile organic compound (VOC) control is an important issue of air quality management in Hong Kong because ozone formation is generally VOC limited. Several oxygenated volatile organic compound (OVOC) and VOC measurement techniques – namely, (1) offline 2,4-dinitrophenylhydrazine (DNPH) cartridge sampling followed by high-performance liquid chromatography (HPLC) analysis; (2) online gas chromatography (GC) with flame ionization detection (FID); and (3) offline canister sampling followed by GC with mass spectrometer detection (MSD), FID, and electron capture detection (ECD) – were applied during this study. For the first time, the proton transfer reaction–mass spectrometry (PTR-MS) technique was also introduced to measured OVOCs and VOCs in an urban roadside area of Hong Kong. The integrated effect of ambient relative humidity (RH) and temperature (T) on formaldehyde measurements by PTR-MS was explored in this study. A Poly 2-D regression was found to be the best nonlinear surface simulation (r = 0.97) of the experimental reaction rate coefficient ratio, ambient RH, and T for formaldehyde measurement. This correction method was found to be better than correcting formaldehyde concentrations directly via the absolute humidity of inlet sample, based on a 2-year field sampling campaign at Mong Kok (MK) in Hong Kong. For OVOC species, formaldehyde, acetaldehyde, acetone, and MEK showed good agreements between PTR-MS and DNPH-HPLC with slopes of 1.00, 1.10, 0.76, and 0.88, respectively, and correlation coefficients of 0.79, 0.75, 0.60, and 0.93, respectively. Overall, fair agreements were found between PTR-MS and online GC-FID for benzene (slope = 1.23, r = 0.95), toluene (slope = 1.01, r = 0.96) and C2-benzenes (slope = 1.02, r = 0.96) after correcting benzene and C2-benzenes levels which could be affected by fragments formed from ethylbenzene. For the intercomparisons between PTR-MS and offline canister measurements by GC-MSD/FID/ECD, benzene showed good agreement, with a slope of 1.05 (r = 0.62), though PTR-MS had lower values for toluene and C2-benzenes with slopes of 0.78 (r = 0.96) and 0.67 (r = 0.92), respectively. All in all, the PTR-MS instrument is suitable for OVOC and VOC measurements in urban roadside areas.
Highlights
Volatile organic compounds (VOCs), which are important precursors of tropospheric ozone and secondary organic aerosols (SOAs) (Sillman, 2002), can be emitted from multiple anthropogenic sources and biogenic sources (Watson et al, 2001; Atkinson and Arey, 2003)
In order to investigate urban roadside VOCs in Hong Kong, multiple sampling and analytical techniques were used, such as offline 2,4-dinitrophenylhydrazine (DNPH) cartridge sampling followed by high-performance liquid chromatography (HPLC) analysis for oxygenated volatile organic compounds (OVOCs); online gas chromatography (GC) with flame ionization detection (FID); and offline canister sampling followed by GC with mass spectrometer detection (MSD), FID, and electron capture detection (ECD) for VOCs (Ho et al, 2013; Cheng et al, 2014; Ou et al, 2015)
The experimental reaction rate coefficient (k) of each compound was obtained by the original input k value multiplied by the slope of the measured concentration to the diluted concentration of standard gas, because the volume mixing ratio (VMR) of each species is inversely related to its reaction rate coefficient (k)
Summary
Volatile organic compounds (VOCs), which are important precursors of tropospheric ozone and secondary organic aerosols (SOAs) (Sillman, 2002), can be emitted from multiple anthropogenic sources (e.g., vehicular emissions, industrial emissions, and solvent usage) and biogenic sources (Watson et al, 2001; Atkinson and Arey, 2003). VOCs have adverse impact on human beings (von Schneidemesser et al, 2010; Lelieveld et al, 2015). Special attention has been paid to the characteristics of roadside VOCs and their impacts on the local air quality of Hong Kong during the past years (Lee et al, 2002; Ho et al, 2004; Guo et al, 2007; Louie et al, 2013; Ling and Guo, 2014). Previous studies have shown that vehicular emissions are one of the major contributors to ambient VOCs in Hong Kong (Guo et al, 2007). Lau et al (2010) found that 31–48 % of ambient VOCs in Hong Kong were generated by vehicle- and marine-vessel-related sources in 2002–2003, and the percentage increased to 40– 54 % in 2006–2007 Previous studies have shown that vehicular emissions are one of the major contributors to ambient VOCs in Hong Kong (Guo et al, 2007). Lau et al (2010) found that 31–48 % of ambient VOCs in Hong Kong were generated by vehicle- and marine-vessel-related sources in 2002–2003, and the percentage increased to 40– 54 % in 2006–2007
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