the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Jun 2023
Measurement report: Evaluation of the TOF-ACSM-CV for PM1.0 and PM2.5 measurements during the RITA-2021 field campaign
Xinya Liu
Bas Henzing
Arjan Hensen
Jan Mulder
Danielle van Dinther
Jerry van Bronckhorst
Rujin Huang
Ulrike Dusek
Abstract. The recently developed time of flight-aerosol chemical speciation monitor with the capture vaporizer and a PM2.5 aerodynamic lens (TOF-ACSM-CV-PM2.5) aims to improve the collection efficiency and chemical characterization of aerosol particles with a diameter smaller than 2.5 µm. In this study, comprehensive cross-comparisons were performed between real-time online measurements and offline filter analysis with 24-hour collection time. The goal was to evaluate the capabilities of the TOF-ACSM-CV-PM2.5 lens, as well as the accuracy of the TOF-ACSM-CV-PM2.5. The experiments were conducted at Cabauw Experimental Site for Atmospheric Research (CESAR) during the RITA-2021 campaign. The non-refractory fine particulate matter PM1.0 and PM2.5 were measured by two co-located TOF-ACSM-CV-PM2.5 by placing them behind a PM2.5 and PM1.0 inlet, respectively. A comparison between the ACSMs and PM2.5 and PM1.0 filter samples showed a much better accuracy than ±30 % less given in the previous reports, with average differences less than ± 10 % for all inorganic chemical species. In addition, the ACSMs were compared to a Monitoring Instrument for Aerosol and Gas (MARGA) (slope between 0.78–0.97 for inorganic compounds, R2 ≥ 0.93), and a Mobility Particle Size Spectrometer (MPSS) measuring the particle size distribution from around 10 to 800 nm (slope was around 1.00, R2 = 0.91). The intercomparison of the online measurements and the comparison between the online and offline measurements indicated a low bias (< 10 % for inorganic compounds) and demonstrated the high accuracy and stability of the TOF-ACSM-CV-PM2.5 lens for the atmospheric observations of particle matters. The two ACSMs exhibited an excellent agreement, with differences less than 7 %, which allowed a quantitative estimate of PM1.0 vs PM2.5 chemical composition. The result showed that the PM1.0 accounted for about 70–80 % of the PM2.5 on average. The NO3 mass fraction increased but the OC mass fraction decreased from PM1.0 to PM2.5, indicating the size-dependence on chemical composition.
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Xinya Liu et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2023-967', Anonymous Referee #1, 11 Sep 2023
Liu et al. reported the cross-comparison between the measurement of a flight-aerosol chemical speciation monitor with the capture vaporizer and a PM2.5 aerodynamic lens (TOF-ACSM-CV-PM2.5) and other offline chemical analyses. Their results show great agreement between online and offline measurements, suggesting TOF-ACSM-CV-PM2.5 has good collection efficiency. The experiments were well designed, the manuscript overall is well written, and the conclusions are well supported. I just have a few minor comments for the authors. Thus, I suggest a minor revision of this manuscript.
Comments:
- L115-117, “The mass … (6.6 m2/g).” I think 6.6 m2/g is a mass absorption cross section (MAC), not mass scattering cross section (MSC). Please confirm that and make changes accordingly.
- Section 2.32 has some issues:
- Did you pre-bake the quartz filter? Moreover, quartz filters can adsorb gas species. Could you discuss how that could affect your results? I assume that will introduce more OC due to adsorbed VOCs and SVOCs.
- Did you weight filters before analysis to see if there was any change in weight during storage?
- I would never store filter samples under room conditions since samples might evaporate and/or react during storage. A recently published paper shows that storing filters under room temperature can significantly change the OC due to evaporation and oxidation (Resch et al., 2023). Please add a discussion regarding to potential change of sample due to storage. This is related to your discussion of NO3 loss from the filter in section 3.1.1 since your storage temperature is 20 C. It can also explain why you see more OM from ACSM than filters.
- It is not clear which filter you used for which offline analysis.
- For the thermal-optical method, it distinguishes OC and EC based on the different temperature steps. All CO2 that comes from He/O2 steps are considered to have originated from EC. Moreover, OE-EC has few artifacts due to VOC and SVOCs in the sample (Y. Cheng et al., 2010; Z. Cheng et al., 2019; Turpin et al., 1994, 2000). Also, EC is typically overestimated due to the pyrolysis of OC and strongly absorbing BrC (Z. Cheng et al., 2019). Please add relevant discussion about these artifacts.
- Figure 1: The caption is not very clear. It should be stated that these dots are daily averages in the caption. What is the variance of online measurements?
- L198-201, “A well-known … Pakkanen and Hillamo, 2002).” If this is true, you should always see filter has lower NO3 than ACSM. It actually suggests the difference between filter and ACSM should even be larger.
- L257-263, “The eBC was … a reasonable result.” It is also due to MAAP measures eBC, which includes BC and any other species that absorb light at 637 nm (e.g., BrC). The MAAP also overestimates eBC due to multi-scattering effects and loading effects.
Citation: https://doi.org/10.5194/egusphere-2023-967-RC1 -
RC2: 'Comment on egusphere-2023-967', Anonymous Referee #2, 08 Dec 2023
Liu et al. compared the performance of online TOF-ACSM-CV measurements against offline filter sample analysis. The results show that ACSM has a difference less than 10% from filter analysis for all the inorganic species, which indicates the good collection efficiency of the capture vaporizer. Additionally, TOF-ACSM-CV measurements overall agrees with MARGA in terms of inorganic species and with MPSS in terms of particle volume. The reasons for the differences are analyzed and discussed. I find this manuscript easy to read and overall well written. The manuscript can be published after the following minor comments are addressed.
Comments:
- Line 112: Do you mean electrostatic losses? Why would stainless steel tubing reduce diffusional losses compared to other tubings?
- Line 165: Why are the filters stored at 20C instead of at low temperatures? How long is it between filter collection and subsequent analysis? Any estimation about OC losses? A discussion on this should be added to section 3.1.1
- Line 321: The newest WHO PM2.5 annual limit is 5ug/m3.
- Line 338: Why does a low fraction of OC in PM 2.5 indicate organic compounds are more abundant in the PM1.0-2.5 range? There is also a typo: similar in PM1.0 and PM2.5
- Figure S1: it should show chlorine and OA, not EC and OC.
- Do the authors suggest an aerosol drying protocol to decrease the effect of humidity on the cut-off size?
Citation: https://doi.org/10.5194/egusphere-2023-967-RC2
Xinya Liu et al.
Data sets
Datasets for " Evaluation of the TOF-ACSM-CV for PM1.0 and PM2.5 measurements during the RITA-2021 field campaign" Xinya Liu, Bas Henzing, Arjan Hensen, Danielle van Dinther, and Ulrike Dusek https://doi.org/10.5281/zenodo.7924288
Xinya Liu et al.
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