Volatile organic compounds (VOCs) are important precursors of atmospheric ozone (O3) and secondary organic aerosol (SOA), making their emissions an important concern for urban air quality. In this study, two light-duty gasoline vehicles (LDGVs), including one China V vehicle and one China VI vehicle, were tested over the Worldwide harmonized Light vehicles Test Cycle (WLTC) under normal TWC and simulated first-stage TWC failure conditions. VOC emissions were analyzed by driving phase, chemical group, and individual species, and their ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) were evaluated. Chemical kinetic simulations were further conducted to investigate the combustion-side formation and transformation behavior of representative aromatic VOCs under controlled conditions. Simulated first-stage TWC failure markedly increased VOC emissions from both tested vehicles, with the total VOC emission factors of the tested China VI and China V vehicles increasing from approximately 22 and 31 mg/km to 78 and 103 mg/km, respectively. For the two tested vehicles, the low-speed phase exhibited the highest phase-specific VOC emission factor under normal TWC conditions, whereas the phase-specific VOC emission factor of the extra-high-speed phase increased markedly following simulated first-stage TWC failure. The VOC profile shifted toward higher contributions of alkanes, alkenes/alkynes, and aromatics. OFP was dominated by oxygenated VOCs (OVOCs) under normal TWC conditions but by aromatics and alkenes/alkynes under the simulated first-stage TWC failure condition, whereas SOAFP was primarily controlled by aromatic species. Under the controlled simulation conditions, xylene isomers mainly accumulated at 800-850 K through side-chain oxidation and HCO-elimination pathways, while toluene peaked at around 900 K and was related to the secondary conversion of xylene-derived intermediates. Increasing equivalence ratio enhanced H-assisted aromatic conversion and weakened oxidative consumption, thereby promoting the accumulation of toluene and xylene isomers.
Atmospheric tall-tower measurements of radiocarbon ( CO 2 14 ), carbon monoxide ( CO ), and nitrogen oxides ( NO x ) show great potential for determining fossil fuel (ff) CO 2 emissions. While CO 2 14 relaxed eddy accumulation (REA) enables F ff CO 2 estimation during individual hours, F CO and F NO x , measured directly and continuously by eddy covariance (EC), can be used as proxies for continuous F ff CO 2 once local F proxy / F ff CO 2 ratios ( R proxy ) are known. We combined for the first time half-hourly EC F CO and F NO x , measured along F CO 2 at a tall tower in Munich from July 2024 to February 2025, with co-located F ff CO 2 from 76 hour-long CO 2 14 REA measurements. First, we examined the general applicability of CO - and NO x -based F ff CO 2 estimation by analyzing the C 14 -based R proxy . Then, we applied the C 14 -calibrated 〈 R proxy 〉 to the F proxy time series to obtain continuous ff CO 2 and non-fossil (nf) CO 2 fluxes, and analyze the F CO 2 composition. We demonstrate the potential of the purely observation-based partitioning approach by comparing R proxy and half-hourly F ff CO 2 and F nf CO 2 with modeled fluxes obtained from a footprint-weighted state-of-the-art Munich emission inventory and biospheric flux model. Although variability in R proxy limits precision and accuracy of half-hourly, proxy-based F ff CO 2 , average daytime fluxes could be estimated with about 20% uncertainty. On average, F ff CO 2 accounted for 70% of F CO 2 during daytime. The absolute modeled F ff CO 2 was 46% higher due to increased modeled heating emissions in the cold months. Observation-based and modeled F nf CO 2 indicated substantial human respiration and minor biospheric flux contributions. The multi-proxy EC and REA measurements enabled unique analysis and independent evaluation of urban ff CO 2 and nf CO 2 fluxes.
Atmospheric tall-tower measurements of radiocarbon (CO214), carbon monoxide (CO), and nitrogen oxides (NOx) show great potential for determining fossil fuel (ff) CO2 emissions. While CO214 relaxed eddy accumulation (REA) enables FffCO2 estimation during individual hours, FCO and FNOx, measured directly and continuously by eddy covariance (EC), can be used as proxies for continuous FffCO2 once local Fproxy/FffCO2 ratios (Rproxy) are known. We combined for the first time half-hourly EC FCO and FNOx, measured along FCO2 at a tall tower in Munich from July 2024 to February 2025, with co-located FffCO2 from 76 hour-long CO214 REA measurements. First, we examined the general applicability of CO- and NOx-based FffCO2 estimation by analyzing the C14-based Rproxy. Then, we applied the C14-calibrated 〈Rproxy〉 to the Fproxy time series to obtain continuous ffCO2 and non-fossil (nf) CO2 fluxes, and analyze the FCO2 composition. We demonstrate the potential of the purely observation-based partitioning approach by comparing Rproxy and half-hourly FffCO2 and FnfCO2 with modeled fluxes obtained from a footprint-weighted state-of-the-art Munich emission inventory and biospheric flux model. Although variability in Rproxy limits precision and accuracy of half-hourly, proxy-based FffCO2, average daytime fluxes could be estimated with about 20% uncertainty. On average, FffCO2 accounted for 70% of FCO2 during daytime. The absolute modeled FffCO2 was 46% higher due to increased modeled heating emissions in the cold months. Observation-based and modeled FnfCO2 indicated substantial human respiration and minor biospheric flux contributions. The multi-proxy EC and REA measurements enabled unique analysis and independent evaluation of urban ffCO2 and nfCO2 fluxes.
Health benefits from emission controls are often inferred from reductions in fine particulate matter (PM 2.5 ) mass, yet this metric can underrepresent toxicity from PM 2.5 -bound metals. Using the COVID-19 lockdown as an intervention-like natural experiment, this study quantified how PM 2.5 -bound metals, emission sources, and inhalation health risks changed in Guangzhou, China. Hourly measurements of 16 metals were coupled with positive matrix factorization and source-specific risk apportionment for pre-lockdown, lockdown, and post-lockdown periods. The lockdown controls reduced PM 2.5 mass by 28.8% and total metal concentrations by 36.3%, while total non-carcinogenic and carcinogenic risks decreased by 50.4% and 41.7%, respectively. However, carcinogenic risks during the lockdown remained approximately 9.6 times the safety criteria adopted in this study (1 × 10 −6 ) for children and 38 times for adults, driven mainly by Cr(VI) and As. Vehicle emissions remained the dominant carcinogenic-risk source, contributing more than 70% even under strict mobility restrictions, indicating a persistent role of non-exhaust brake and tire wear. Ship-related non-carcinogenic risks rebounded after the lockdown, consistent with port congestion and prolonged berthing during logistics recovery. Under the proportional-reduction assumption used in the scenario analysis, reaching the safety criteria would require further uniform reductions of 89.5–97.4% in source-attributed carcinogenic metal concentrations relative to the lockdown conditions, which is impractical as a single-step mass-reduction target. These findings support phased risk-oriented management that combines source-specific controls with feasible interim risk-reduction benchmarks and progressively tightens them toward the long-term health-protective criteria.
