Retrieval of Atmospheric Fine Particulate Density Based on Merging Particle Size Distribution Measurements: Multi‐instrument Observation and Quality Control at Shouxian

Abstract

Density of fine mode particles is an important physical parameter. However, its measurement and validation in the actual atmosphere are still difficult. In this study, the measurements at Shouxian, Anhui province, China (32.56°N, 116.78°E, elevation 22.7 m) in winter, are used for density retrieval and quality control. The effective density and number size distribution of fine mode aerosol can be obtained in real time, by using the scanning mobility particle sizer and aerodynamic particle sizer. During the experiment, the average density is about 1.66 ± 0.15 g/cm 3 with the uncertainty of 0.19 g/cm 3 calculated from the residuals in the overlap region of scanning mobility and aerodynamic particle sizers. A multi-instrument measurement and quality control scheme is proposed to identify large measurement uncertainties. The extinction and scattering coefficients calculated from the merged fine particle number size distributions by Mie theory are comparable with the measurements from cavity-enhanced albedometer. The differences between the calculated and observed scattering and extinction coefficients are less than 2%. Meanwhile, the deduced aerosol complex refractive index n and k are obtained by minimizing the sum of squared residuals of extinction and scattering coefficients and comparable with the values retrieved from the Sun-sky radiometer CE318 measurements. The correlation coefficient on n is 0.72. However, the correlation on k is not optimized, explained by the influence of anthropogenic aerosol particles with strong absorption near ground and the poor accuracy of k. Compared with independent observations, a good agreement between the optical parameters is also obtained.

Comment on “Retrieval of Atmospheric Fine Particulate Density Based on Merging Particle Size Distribution Measurements: Multi‐instrument Observation and Quality Control at Shouxian” by Li et al.

“…Therefore, a C c ( D ) must be introduced to correct this reduction in the Stokes law (DeCarlo et al, ). Li et al () described that their experiments were carried out in Anhui Province, China (22.7 m above sea level), on 21–26 December 2016. The average temperature was approximately 280 K, and the barometric pressure approximated normal atmospheric pressure; so a calculation for the λ of gas molecules yielded 70 nm.…”

“…The average temperature was approximately 280 K, and the barometric pressure approximated normal atmospheric pressure; so a calculation for the λ of gas molecules yielded 70 nm. Based on that value of λ and D = 550 nm, the K n from experiments conducted in the work of Li et al () was 0.25 and indicated that those experiments were carried out in the transition regime ( K n > 0.1). Because of that, C c ( D ) should be introduced to conversions from D m and D a to D p theoretically.…”

“…This comment questions the omission of C c ( D ) in conversions of D p from D m and D a presented by Li et al (). We estimated the K n in the work of Z Q Li et al () and found the sampled aerosols were in the transition regime, which indicated that C c ( D ) should theoretically be introduced to correct the reduction drag force experienced by the particles. The D p conversion from D m and D a with and without C c ( D ) was calculated for the particles with different DSF values and/or density using a diameter ( D m or D a ) of 550 nm.…”

“…Li et al () showed that the overlap size range for density estimation was generally from a D a of 400 nm, obtained by aerodynamic particle sizer to a D m of 594 nm obtained by scanning mobility particle sizer. Thus, it is reasonable for this comment to set D m and D a as 550 nm to convert D p .…”

“…The derivation process of V is shown in equation : where D p , D m and D rs represent the geometric equivalent diameter, electric mobility equivalent diameter, and optical equivalent diameter, respectively. Li et al () also stated that D rs closely approximated D m and gave a conversion between D m and D p as shown in equation : …”