Abstract. Volatile organic compounds (VOCs) play important roles in the tropospheric
atmosphere. In this study, VOCs were measured at an urban site in Guangzhou, one of the megacities in the Pearl River Delta (PRD), using a gas chromatograph–mass spectrometer/flame ionization detection (GC–MS/FID) and a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS). Diurnal profile analyses show that stronger chemical removal by OH radicals for more reactive hydrocarbons occurs during the daytime, which is used to estimate the daytime average OH radical concentration. In comparison, diurnal profiles of oxygenated volatile organic compounds (OVOCs) indicate evidence of contributions from secondary formation. Detailed source analyses of OVOCs, using a photochemical age-based parameterization method, suggest important contributions from both primary emissions and secondary formation for measured OVOCs. During the campaign, around 1700 ions were detected in PTR-ToF-MS mass spectra, among which there were 462 ions with noticeable concentrations. VOC signals from these ions are quantified based on the sensitivities of available VOC species. OVOC-related ions dominated PTR-ToF-MS mass spectra, with an average contribution of 73 % ± 9 %. Combining measurements from PTR-ToF-MS and GC–MS/FID, OVOCs contribute 57 % ± 10 % to the total concentration of VOCs. Using concurrent measurements of OH reactivity, OVOCs measured by PTR-ToF-MS contribute greatly to the OH reactivity (19 % ± 10 %). In comparison, hydrocarbons account for 21 % ± 11 % of OH reactivity. Adding up the contributions from inorganic gases (48 % ± 15 %), ∼ 11 % (range of 0 %–19 %) of the OH reactivity remains `missing”, which is well within the combined uncertainties between the measured and calculated OH reactivity. Our results demonstrate the important roles of OVOCs in the emission and evolution budget of VOCs in the urban atmosphere.
Nitrous
acid (HONO) plays an important role in the budget of hydroxyl
radical (•OH) in the atmosphere. Vehicular emissions
are a crucial primary source of atmospheric HONO, yet remain poorly
investigated, especially for diesel trucks. In this study, we developed
a novel portable online vehicular HONO exhaust measurement system
featuring an innovative dilution technique. Using this system coupled
with a chassis dynamometer, we for the first time investigated the
HONO emission characteristics of 17 light-duty diesel trucks (LDDTs)
and 16 light-duty gasoline vehicles in China. Emissions of HONO from
LDDTs were found to be significantly higher than previous studies
and gasoline vehicles tested in this study. The HONO emission factors
of LDDTs decrease significantly with stringent control standards:
1.85 ± 1.17, 0.59 ± 0.25, and 0.15 ± 0.14 g/kg for
China III, China IV, and China V, respectively. In addition, we found
poor correlations between HONO and NOx emissions, which indicate that
using the ratio of HONO to NOx emissions to infer HONO emissions might
lead to high uncertainty of HONO source budget in previous studies.
Lastly, the HONO emissions are found to be influenced by driving conditions,
highlighting the importance of conducting on-road measurements of
HONO emissions under real-world driving conditions. More direct measurements
of the HONO emissions are needed to improve the understanding of the
HONO emissions from mobile and other primary sources.
Abstract. Vehicular emissions are an important source for volatile organic compounds (VOCs) in urban and downwind regions. In this study, we conducted a chassis dynamometer study to investigate VOC emissions from vehicles using gasoline, diesel, and liquefied petroleum gas (LPG) as fuel. Time-resolved VOC emissions from vehicles are chemically characterized by a
proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) with
high frequency. Our results show that emission factors of VOCs generally
decrease with the improvement of emission standards for gasoline vehicles,
whereas variations in emission factors for diesel vehicles with emission
standards are more diverse. Mass spectrum analysis of the PTR-ToF-MS suggests that cold starts significantly influence VOC emissions of gasoline vehicles, while the influences are less important for diesel vehicles. Large differences in VOC emissions between gasoline and diesel vehicles are observed with emission factors of most VOC species from diesel vehicles being higher than gasoline vehicles, especially for most oxygenated volatile organic compounds (OVOCs) and heavier aromatics. These results indicate quantification of heavier species by the PTR-ToF-MS may be important in the characterization of vehicular exhausts. Our results suggest that VOC pairs (e.g., C14 aromatics / toluene ratio) could potentially provide good indicators for distinguishing emissions from gasoline and diesel vehicles. The fractions of OVOCs in total VOC emissions are determined by combining measurements of hydrocarbons from canisters and online observations of the PTR-ToF-MS. We show that OVOCs contribute 9.4 % ± 5.6 % of total VOC emissions for gasoline vehicles, while the fractions are significantly higher for diesel vehicles (52 %–71 %), highlighting the importance of detecting these OVOC species in diesel emissions. Our study demonstrated that the large number of OVOC species measured by the PTR-ToF-MS are important in the characterization of VOC emissions from vehicles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.