Retrievals of dust-related particle mass and ice-nucleating particle concentration profiles with ground-based polarization lidar and sun photometer over a megacity in central China

Abstract

Abstract. The POLIPHON (polarization lidar photometer networking) method is a powerful pathway to retrieve the height profiles of dust-related particle mass and ice-nucleating particle (INP) concentrations. The conversion factors fitted from the sun photometer observation data are the major part of the POLIPHON computations, which can convert the polarization-lidar-derived dust extinction coefficients into dust-related particle mass and INP concentrations. For the central Chinese megacity of Wuhan (30.5∘ N, 114.4∘ E), located at the downstream area several thousands of kilometers far away from the source regions of Asian dust, dust particles always mix with other aerosols from local emissions. Therefore, very few dust case data sets can be available when using the column-integrated Ångström exponent (for 440–870 nm) <0.3 and aerosol optical depth (at 532 nm) >0.1 recorded by a sun photometer as the filtering criteria. Instead, we present another dust case data set screening scheme that applies the simultaneous polarization lidar observation to verify the occurrence of dust. Based on the 33 dust-intrusion days identified during 2011–2013, the extinction-to-volume (cv,d) and extinction-to-large particle (with radius >250 nm) number concentration (c250,d) conversion factors are determined to be (0.52±0.12)×10-12Mmm3m-3 and 0.19±0.05 Mm cm−3, respectively. The c250,d for Wuhan is 27 % larger than that observed at Lanzhou SACOL (36.0∘ N, 104.1∘ E), a site closer to the Gobi Desert, and tends to be closer to those observed in North Africa and the Middle East, indicating dust aerosols from these two sources are also possibly involved in the dust events observed over Wuhan. As a comparison, the conversion factor c290,c of 0.11±0.02Mmcm-3 for continental aerosol is much smaller than c250,d, indicating that there is no significant influence of urban aerosols on the retrievals of dust-related conversion factor over Wuhan. The conversion factors are applied in a dust event in Wuhan to reveal the typical dust-related immersion-mode INP concentration over East Asian cities. The proposed dust case data set screening scheme may potentially be extended to the other polluted city sites that are more influenced by mixed dust.

Technical note: Identification of two ice-nucleating regimes for dust-related cirrus clouds based on the relationship between number concentrations of ice-nucleating particles and ice crystals

“…Both cases are observed in central China. The conversion factors obtained in Wuhan city (30.5 • N, 114.4 • E) are applied in POLIPHON calculation (He et al, 2021b). For the first case, the estimated INPC and ICNC values generally realize successful closure within the upper part of cirrus clouds; i.e., they are generally in good agreement within an order of magnitude (Ansmann et al, 2019a), indicating the ice formation rule that one ice-nucleating particle generates one ice crystal by heterogeneous nucleation.…”

“…The dust-cloud interaction is generally considered to take place if a cirrus cloud is embedded in a dust layer (Ansmann et al, 2019a;Marinou et al, 2019;He et al, 2021b); in this case, the dust layer and cloud layer should have a spatial overlap either vertically or horizontally so that they can be considered coupled. The dust-related INPC is estimated from the CALIOP observations in dust-existing regions in the vicinity of cirrus clouds.…”

Vertical Structure of Dust Aerosols Observed by a Ground-Based Raman Lidar with Polarization Capabilities in the Center of the Taklimakan Desert

“…where ρd is the dust particle density, ρd = 2.9 g cm −3 for Asian dust, and cv,d is o a sun photometer observation [47]. The AOD was used as an input to retriev radius (Reff) using the GRASP algorithm (https://www.grasp-open.com, ( The LR can be retrieved using the sun photometer [42] or by integrating cloud-aerosol lidar with orthogonal polarization (CALIOP) total attenuated backscatter coefficients (TABC) and moderate resolution imaging spectroradiometer (MODIS) aerosol optical depths (AOD) [43].…”

“…where ρ d is the dust particle density, ρ d = 2.9 g cm −3 for Asian dust, and c v,d is obtained from a sun photometer observation [47]. The AOD was used as an input to retrieve the effective radius (Reff) using the GRASP algorithm (https://www.grasp-open.com, (accessed on 1 October 2021)) [48].…”

Natural Seeder‐Feeder Process Originating From Mixed‐Phase Clouds Observed With Polarization Lidar and Radiosonde at a Mid‐Latitude Plain Site

“…The volume (aerosol + molecular) depolarization ratio δ can be obtained by the ratio of perpendicular‐to parallel‐oriented signals multiplied by the gain ratio. The relative error in δ was evaluated to be ≤5% (He, Zhang, et al., 2021). The δ values characterize the nonspherical shape of backscattering targets and thus can be used to distinguish the water droplets and ice crystals in cloud observations (Wu & Yi, 2017).…”