Separation of the optical and mass features of particle components in different aerosol mixtures by using POLIPHON retrievals in synergy with continuous polarized Micro-Pulse Lidar (P-MPL) measurements

Abstract. The application of the POLIPHON (POlarization-LIdar PHOtometer Networking)

method is presented for the first time in synergy with continuous

24/7 polarized Micro-Pulse Lidar (P-MPL)

measurements to derive the vertical separation of two or three particle

components in different aerosol mixtures, and the retrieval of their

particular optical properties. The procedure

of extinction-to-mass conversion, together with an analysis of the mass extinction efficiency (MEE) parameter, is described, and the relative mass

contribution of each aerosol component is also derived in a further step. The

general POLIPHON algorithm is based on the specific particle linear

depolarization ratio given for different types of aerosols and can be run in

either 1-step (POL-1) or 2 steps (POL-2) versions with dependence on either the

2- or 3-component separation. In order to illustrate this procedure, aerosol

mixing cases observed over Barcelona (NE Spain) are selected: a dust event

on 5 July 2016, smoke plumes detected on 23 May 2016 and a

pollination episode observed on 23 March 2016. In particular, the 3-component

separation is just applied for the dust case: a combined POL-1 with POL-2

procedure (POL-1/2) is used, and additionally the fine-dust contribution to

the total fine mode (fine dust plus non-dust aerosols) is estimated. The

high dust impact before 12:00 UTC yields a mean mass loading of

0.6±0.1 g m−2 due to the prevalence of Saharan coarse-dust

particles. After that time, the mean mass loading is reduced by two-thirds,

showing a rather weak dust incidence. In the smoke case, the arrival of fine

biomass-burning particles is detected at altitudes as high as 7 km.

The smoke particles, probably mixed with less depolarizing non-smoke

aerosols, are observed in air masses, having their origin from either North

American fires or the Arctic area, as reported by HYSPLIT back-trajectory

analysis. The particle linear depolarization ratio for smoke shows values in

the 0.10–0.15 range and even higher at given times, and the daily mean smoke

mass loading is 0.017±0.008 g m−2, around 3 % of that found

for the dust event. Pollen particles are detected up to 1.5 km in height from

10:00 UTC during an intense pollination event with a particle linear

depolarization ratio ranging between 0.10 and 0.15. The maximal mass loading

of Platanus pollen particles is 0.011±0.003 g m−2,

representing around 2 % of the dust loading during the higher dust

incidence. Regarding the MEE derived for each aerosol component, their values

are in agreement with others referenced in the literature for the specific

aerosol types examined in this work: 0.5±0.1 and

1.7±0.2 m2 g−1 are found for coarse and fine dust particles, 4.5±1.4 m2 g−1 is derived for smoke and

2.4±0.5 m2 g−1 for non-smoke aerosols with Arctic origin, and a MEE of 2.4±0.8 m2 g−1 is obtained

for pollen particles, though it can reach higher or lower values depending on

predominantly smaller or larger pollen grain sizes. Results reveal the high

potential of the P-MPL system, a simple polarization-sensitive elastic

backscatter lidar working in a 24/7 operation mode, to retrieve the

relative optical and mass contributions of each aerosol component throughout

the day, reflecting the daily variability of their properties. In fact, this

procedure can be simply implemented in other P-MPLs that also operate within the

worldwide Micro-Pulse Lidar Network (MPLNET), thus extending the aerosol

discrimination at a global scale. Moreover, the method has the advantage of also

being relatively easily applicable to space-borne lidars with an equivalent

configuration such as the ongoing Cloud-Aerosol LIdar with Orthogonal

Polarization (CALIOP) on board NASA CALIPSO (Cloud-Aerosol Lidar and Infrared

Pathfinder Satellite Observation) and the forthcoming Atmospheric

Lidar (ATLID) on board the ESA EarthCARE mission.