1. You stated that "AQB-monitored PM concentration can be converted to dry particle mass concentration, aligning well with EPA data

after OPC sensitivity correction. The derived hygroscopicity provides the relationship between ambient relative humidity and

particle water content. By dividing PM10 into PM2.5 and PM2.5-10, considering the composition heterogeneity, we achieved more

280 precise dry PM10 concentrations with lower MAPE." Please state differences clearly with 2 different observing packages.

2. Provide units for the parameters in the equations.

3. How accurate your hygroscopicity calculation that needs to bediscussed.

4. please provide how did you convert ppm to mass for various species?

5. please provide your final conclusions in an itemized list.

General Comments:

The normalization and portability of atmospheric pollutant monitoring are crucial for in-depth research into local variations in atmospheric environment and pollution. This manuscript establishes a low-cost air quality monitoring device and applies it to estimate the hygroscopicity parameters of aerosols, comparing the results with site observation data. The study holds certain scientific and application value and aligns with the publication scope of the Atmospheric Measurement Techniques journal. However, there are some scientific and technical issues within the manuscript itself, suggesting major revisions before reconsidered.

Specific Comments:

1) The accuracy and error range of AQB in detecting aerosols and the application of AQB to estimate aerosol hygroscopicity parameters should be two separate research components with a sequential order. However, in this manuscript, the authors often fail to clearly distinguish between the two. The authors adopt a method of setting RH thresholds to classify AQB observation results into dry aerosols and humidified aerosols, and then compares and calibrates the observations of dry aerosols with EPA station data, which is a feasible approach. However, in Sections 3.1, 3.2, and Figures 2 and 3, the authors do not classify or analyze the data based on the RH threshold set by themselves. Meanwhile, as shown in Figure 2(b), the occurrence of RH below 50% during the observation period is rare. Can such a limited amount of data support the examination of the reliability of AQB detection?

2) Introducing aerosol chemical composition observations into a thermodynamic equilibrium model to calculate aerosol hygroscopic growth and comparing it with optical observations is a common research approach. However, contrasting different field experiments conducted at different times (with an 8-year difference) and different underlying surfaces by the authors doesn't have much significance.

3) In Table 1, the hygroscopicity parameter kappa for PM2.5 and PM2.5-10 is smaller than the hygroscopicity parameter kappa for PM10, which is abnormal. PM10 is the sum of PM2.5 and PM2.5-10, and its hygroscopicity should be intermediate between the two.

4) In Section 2.1, the author introduces the photo-ionization detector for monitoring VOCs, but in Figure 1 and subsequent manuscripts, the abbreviation used by the author is NMHC. These two abbreviations are not entirely equivalent.