the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Emissions of Intermediate- and Semi-Volatile Organic Compounds (I/SVOCs) from Different Cumulative Mileage Diesel Vehicles under Various Ambient Temperatures
Abstract. The role of intermediate- and semi-volatile organic compounds (I/SVOCs) in heavy-duty diesel vehicle (HDDV) exhaust remains a significant research gap across previous studies, with limited focus on cumulative mileage and ambient temperature effects. This study analyzed gaseous and particulate I/SVOCs from four in-use HDDVs using thermal desorption two-dimensional gas chromatography-mass spectrometry (TD-GC×GC-MS). Total I/SVOC emission factors (EFs) ranged from 9 to 406 mg·km-1, with 79–99 % in the gaseous phase. High-mileage vehicles (HMVs) emitted I/SVOCs at levels eight times greater than low-mileage vehicles (LMVs), highlighting the influence of cumulative mileage. Emission deterioration occurred under both cold-start and hot-running conditions, though HMVs showed no extra sensitivity to cold starts. HMVs also exhibited increasing emissions with component volatility, alongside a higher share of oxygenated I/SVOCs (O-I/SVOC) than LMVs (65 % vs. 42 %). Compounds such as phenol, alkenes, and cycloalkanes appeared only in HMV emissions. Temperature effects were notable at 0 °C, only HMV emissions rose significantly, while LMV emissions remained stable. A strong linear correlation (R2 = 0.93) between I/SVOC EFs and modified combustion efficiency (MCE) suggests that reduced combustion efficiency drives higher I/SVOC emissions. HMVs also showed four times greater secondary organic aerosol formation potential (SOAFP) compared to LMVs. This increase was smaller than the eightfold rise in EFs, likely due to the higher O-I/SVOC content in HMV emissions.
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Status: open (until 09 Jan 2025)
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RC1: 'Comment on egusphere-2024-3290', Anonymous Referee #1, 10 Dec 2024
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In the current study, gaseous and particulate I/SVOCs emitted from four HDDVs were analyzed using GC×GC-MS. The emission factors as well as the composition of I/SVOCs were reported. Overall, the experiments were nicely done and the data are well analyzed. The current contribution is a welcome addition to the field. There are several places in the paper are a bit obscure as detailed in the comments below. Beyond these, I do not see any major obstacles to publication.
Specific comments:
(1) The experiments were well organized. My general question is the innovation of the current study. The I/SVOC emissions as well as their compositions from heavy diesel vehicles have been widely reported, including the studies from their own group. Any new findings that the authors would like to highlight in the current one?
(2) Line 24: “Compounds such as phenol, …. appeared only in HMV emissions”. These are compounds that are widely observed in vehicle emissions. Any reason for their disappearance in LMV emission? Are there any potential artifacts in the sample analysis?
(3) Line 179: “Oxy-PAH&Oxy-benzene”, I don’t think the abbreviations were pre-defined. Also, what compounds specifically do they represent? I noticed the authors also separately classify “phenol” instead of grouping them into “Oxy-benzene”.
(4) Line 190: the emission factors of ISVOCs between LMV and HMV differs quite a lot according to Figure 2a. And according to Figure 3, the fractional contributions from different components are also different for HMV and LMV. Hence, I’m not sure it is appropriate to present the average volatility distributions of I/SVOCs from the entire fleet. Could Figure 1 be separated into LMV and HMV?
(5) Line 225: How many sets of the tests were performed? Does each data point on Figure 2b represents the average emission factor for each entire 1800s test cycle? Also, I hesitate to agree that gaseous I/SVOCs show good correlation with THC because the datapoints on Figure 2b concentrates at two ends of the fitted line, which might affect the reliability of the linear regression. Any more evidence on this point? Or any other supporting references?
(6) The influence of temperature on emission is interesting. What are the variations of other pollutants with the changes in temperature, i.e., THC, NOX, CO, etc?
(7) The overall presentation is acceptable, but English could do with improvement in places.
Citation: https://doi.org/10.5194/egusphere-2024-3290-RC1
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