Remote Sensing Observation of New Particle Formation Events with a (UV, VIS) Polarization Lidar

Abstract

Observations of new particle formation events in free troposphere are rather seldom and limited in time and space, mainly due to the complexity and the cost of the required on-board instrumentation for airplane field campaigns. In this paper, a calibrated (UV, VIS) polarization elastic lidar (2β + 2δ) is used to remotely sense new particle formation events in the free troposphere in the presence of mineral dust particles. Using very efficient (UV, VIS) light polarization discriminators (1:107) and after robust calibration, the contribution of mineral dust particles to the co-polarized (UV, VIS) lidar channels could be removed, to reveal the backscattering coefficient of the newly nucleated particles after these numerous particles have grown to a size detectable with our lidar. Since our polarization and wavelength cross-talks are fully negligible, the observed variation in the (UV, VIS) particle backscattering time–altitude maps could be related to variations in the particle microphysics. Hence, day and nighttime differences, at low and high dust loadings, were observed in agreement with the observed nucleation process promoted by mineral dust. While light backscattering is more sensitive to small-sized particles at the UV lidar wavelength of 355 nm, such new particle formation events are here for the first time also remotely sensed at the VIS lidar wavelength of 532 nm at which most polarization lidars operate. Moreover, by addressing the (UV, VIS) backscattering Angstrom exponent, we could discuss the particles’ sizes addressed with our (UV, VIS) polarization lidar. As nucleation concerns the lowest modes of the particles’ size distribution, such a methodology may then be applied to reveal the lowest particle sizes that a (UV, VIS) polarization lidar can address, thus improving our understanding of the vertical and temporal extent of nucleation in free troposphere, where measurements are rather seldom.

Retrieving Dust Grain Sizes from Photopolarimetry: An Experimental Approach

“…The depolarization ratio (δ L ) obtained from lidar observations is widely used for characterizing atmospheric aerosols in Earth's atmosphere (e.g., Miffre et al 2019;Kahnert et al 2000). This quantity is not commonly used in astronomy although it has become of interest since the work of Sterzik et al (2012).…”

On the use of light polarization to investigate the size, shape, and refractive index dependence of backscattering Ångström exponents

“…(1, 3, 4) since our 2λ-polarization lidar exhibits a high sensitivity and accuracy [26], i.e. fully negligible polarization and wavelengths cross-talks (1:10 7 polarization discriminator, OD5 wavelength discriminator, [27]). For completeness, we recall that ( , ,…”

“…(1, 3, 4) since our 2λ-polarization lidar exhibits a high sensitivity and accuracy [26], i.e. fully negligible polarization and wavelengths cross-talks (1:10 7 polarization discriminator, OD5 wavelength discriminator, [27]). For completeness, we recall that (𝛽 𝑝 , 𝛽 𝑠 , 𝛽 𝑛𝑠 ) are retrieved at altitude z and wavelength 𝜆 𝑖 by applying the methodology described in [7,8], where the co-(𝛽 𝑝,// ) and cross-(𝛽 𝑝,⊥ ) polarized backscattering coefficients (Fig.…”

“…For completeness, we recall that (𝛽 𝑝 , 𝛽 𝑠 , 𝛽 𝑛𝑠 ) are retrieved at altitude z and wavelength 𝜆 𝑖 by applying the methodology described in [7,8], where the co-(𝛽 𝑝,// ) and cross-(𝛽 𝑝,⊥ ) polarized backscattering coefficients (Fig. 3a) providing 𝛽 𝑝,𝑖 are obtained from the lidar raw data after accurate calibration [27] by applying the Klett's algorithm, using constant lidar ratios (± 10 sr) taken from the literature [28]. At altitude z and wavelength 𝜆 𝑖 , (β s,i , β ns,i ) are obtained by following [7,8], using 𝛿 𝑛𝑠 (𝜆 1 ) = 35.0 % and 𝛿 𝑛𝑠 (𝜆 2 ) = 30.5 % [11,29].…”

Properties of Saharan Dust Versus Local Urban Dust—A Case Study

“…Hygroscopicity studies in relation to dust are of importance (Hara et al., 2018; Navas‐Guzmán et al., 2019; Wu et al., 2020). Finally, real‐time lidar studies of the dust‐cloud interaction are possible (Huang et al., 2017), especially impact of mineral dust on cloud formation (Weger et al., 2018) and new particle formation (Miffre et al., 2019) is of importance.…”