In this manuscript, the authors investigate evaporative emissions from in-use light-duty gasoline vehicles under China’s latest regulatory standards. They quantify and compare emission characteristics—including emission factors, chemical composition, and total hydroxyl radical reactivity (k_OH)—across three processes (HSL, DBL24h, and DBL48h) for vehicles compliant with the China VI and China V standards. The study identifies key reactive volatile organic compound (VOC) species contributing to atmospheric photochemical processes.

The methodology of this paper is innovative, through the collection of on-site observation data, combined with mass spectrometry and other qualitative and quantitative methods, the study integrates the use of online and offline techniques, making the analysis more comprehensive. This study fills the gap of evaporative emission data under the new emission standard, provides a high-precision scientific basis for the control of motor vehicle evaporative emission, and has an important reference value for motor vehicle pollution control policy. The manuscript deserves to be published in the journal after the authors address the concerns below.

Specific comments:

1. The authors note significant discrepancies in evaporative emission components and emission factors across different studies, attributing these differences primarily to the number of species measured (P4, Lines 105–112). However, the discussion lacks further analysis of other potential influencing factors such as vehicle operation conditions, fuel formulation, temperature variations, or carbon canister aging. It is recommended to include a more comprehensive discussion of these aspects in this section.
2. The study highlights the critical role of branched-chain alkenes (BC-alkenes) in accounting for missing OH reactivity, emphasizing the need for their inclusion in chemical analysis. However, the Introduction section does not mention this rationale. It is suggested to include a relevant discussion in the Introduction to better justify the novelty and significance of the study.
3. In the methodology, the China VI test procedure includes the carbon canister loading step after the first refueling. Was this adjustment intended to simulate the initial adsorption state of the canister following long-term vehicle parking? Please clarify the rationale behind this modification and its potential influence on test results.
4. The study emphasizes that BC-alkenes contribute 25.7–39% to OH reactivity (P23, Lines 520–523). However, Section 2.2 only mentions the use of seven BC-alkene standards for calibration (Line 212), without providing validation details. This could lead to potential over- or underestimation of highly reactive species. It is recommended to include (in the Methods or Supplementary Materials) the standard curve parameters, repeatability test results, and recovery rates from spiked blank matrices, as well as discussion on possible interferences and how they were mitigated.
5. Figures 4 and 7 present source profile information, but due to the high number of species displayed, it is difficult to identify key components. It is suggested to simplify the figures by grouping similar compounds and highlighting the top 10 individual species, or breaking the figures into subpanels with a clearer focus on critical contributors.
6. In the hot soak loss (HSL) test, China VI vehicles were tested at 38 °C after high-temperature driving, whereas China V vehicles were tested at ambient temperatures (23–31 °C). As temperature is a key variable, could this difference confound comparisons between standards? High temperatures promote the volatilization of high-boiling-point VOCs (e.g., aromatics), possibly resulting in a systematic overestimation of China VI emissions and underestimation for China V. (P13, Lines 320–334)
7. Section 3.2 establishes source profiles for China V/VI vehicles (Figure 4) and suggests their applicability in source apportionment and emission inventory improvement (Lines 682–684). However, all measurements were based on a single gasoline type (China VI 95# gasoline, Table S1) and a limited number of vehicles (9 sedans/SUVs). Please clarify the applicability scope of these profiles and suggest boundaries for their use in the Conclusions section.

This manuscript reports the VOCs and OH reactivity characteristics of vehicle evaporative emissions. The study selected two main emission standard stages from the Chinese vehicle fleet as test objects, which can to some extent reflect the important characteristics of evaporative emissions from Chinese vehicle fleet. The team also improved the measurement method and used direct measurement of OH total reactivity to measure evaporative emissions. The research results are relatively rare and have high scientific significance. Anyway, some revisions need to be made before acceptance.

Major comments:

1. In the research methodology, the author only selected gasoline vehicles in two emission standard stages, China VI and China V. Why were measurements not conducted on previous emission standard vehicles, such as China IV and China III, according to the China Mobile Source Environmental Management Annual Report (2024), these vehicles still have a high contribution to the emission of air pollutants.
2. The description of the method in Section 2.3 is not clear enough and needs to be revised accordingly. The calculation method of emission factors of VOCs species is described. In this experiment, the evaporative emission test using VT-SHED should emphasize whether there is gas exchange during the measurement. In addition, the calculation process of THC should also be given here. The calculation formula can refer to the relevant standard (GB 18352.6-2016).
3. In Section 3.1, in the analysis of emission factors, the measurement results of high emission vehicles (Vehicle I) are noted. This result is different from previous studies. It not only gives the emissions of normal vehicles, but also has abnormal vehicle results. This result has good novelty and scientific value. In this part, the results of high emission vehicles are included in the supplementary materials, which makes the important results not highlighted. It is suggested that the author adjust the content of this part to highlight the results of high emission vehicles.
4. There are still some problems in the language description of the manuscript, and the author is suggested to modify the language.

Specific comments:

1. L73 and L83: “Euro4” and “E4” writing need to be unified.
2. L98-101: there is ambiguity in the expression, whether it is pollutant emissions or vehicle population, and please provide the specific time of the data.
3. L115: “China IV/V” can provide specific explanations to express its meaning.
4. L74, L86 and L117: the author's writing of numbers and units is not standardized, at least consistency should be achieved in the manuscript. Please also check other parts of the manuscript for similar descriptions.
5. In Section 2.1, L143-145: the author conducted experiments using customized experimental gasoline. What is the purpose of this experiment and can be highlighted.
6. In Section 3.1, second paragraph, it is noted that abnormal carbon canister can lead to higher THC emissions, which is a significant conclusion and implies an important regulatory target for vehicle evaporative emissions. Suggest the author to conduct in-depth analysis, such as the proportion of this type of vehicle in the actual vehicle fleet.
7. L396: the writing of “PAMS (Photo Assessment Monitoring Stations)” is incorrect and needs to be corrected.
8. L398-400: this sentence description and logical analysis are not reasonable. The author mainly describes the emission characteristics here, and the “high reactivity” mentioned here is ambiguous.
9. L440-441: the explanation and description here are not sufficient, and the author can emphasize the differences in component composition between DBL process emissions and gasoline headspace.
10. Line 562: in the title, the beginning letter of "Calculation" needs to be lowercase. It is suggested that the author also check other similar problems in the manuscript.
11. L598 and L635: writing error, the first letter needs to be lowercase.
12. L607-609: additional references are needed.
13. The writing of figure titles in the manuscript is not standardized. In Figures S3 and S5, the initial letters of words are capitalized, which is inconsistent with the titles of other figures.
14. In Section 3.3, the author calculated the emission source profiles based on OH reactivity, and suggested supplementary the species classification and number of reactivity source profiles.
15. In the conclusion of the Section 4, the first paragraph can supplement the relevant conclusions of high emission vehicles.