Interrelations between surface, boundary layer, and columnar aerosol properties derived in summer and early autumn over a continental urban site in Warsaw, Poland
Authors: Wang Dongxiang , Szczepanik Dominika , Stachlewska Iwona S. 
Published: October 2019

Abstract. PollyXT Raman polarization lidar observations were
performed at the Remote Sensing Laboratory (RS-Lab) in Warsaw
(52.2109∘ N, 20.9826∘ E), Poland, in the framework of
the European Aerosol Research Lidar Network (EARLINET) and the Aerosol,
Clouds, and Trace gases Research Infrastructure (ACTRIS) projects. Data collected in
July, August, and September of 2013, 2015, and 2016 were analysed using the
classical Raman approach. In total, 246 sets of intact profiles, each set
comprising particle extinction (α) and backscatter coefficients
(β) as well as linear particle depolarization ratios (δ) at 355 nm
and 532 nm, were derived for statistical investigations and stored in the
EARLINET/ACTRIS database. The main analysis was focused on intensive
optical properties obtained within the atmospheric boundary layer (ABL). Their
interrelations were discussed for different periods: the entire day; nighttime, with respect to the nocturnal boundary layer (NL) and the residual boundary layer (RL); at sunrise, with respect to the morning transition boundary layer (MTL); and from late afternoon until sunset, with respect to the well-mixed boundary layer (WML). Within the boundary layer, the lidar-derived optical
properties (entire day, 246 sets) revealed a mean aerosol optical depth
(AODABL) of 0.20±0.10 at 355 nm and 0.11±0.06 at 532 nm;
a mean Ångström exponent (ÅEABL) of 1.54±0.37; a
mean lidar ratio (LRABL) of 48±17 sr at 355 nm and 41±15 sr at
532 nm; a mean linear particle depolarization ratio (δABL) of 0.02±0.01 at 355 nm and 0.05±0.01 at 532 nm; and
a mean water vapour mixing ratio (WVABL) of 8.28±2.46 g kg−1. In
addition, the lidar-derived daytime boundary layer optical properties (for the
MTL and WML) were compared with the corresponding daytime columnar aerosol
properties derived from the multi-filter rotating shadowband radiometer (MFR-7) measuring within the
National Aerosol Research Network (PolandAOD-NET) and the CE318 sun photometer of the Aerosol Robotic NETwork (AERONET). A high linear correlation of the
columnar aerosol optical depth values from the two latter instruments was obtained in
Warsaw (a correlation coefficient of 0.98 with a standard deviation
of 0.02). The contribution of the aerosol load in the summer and early-autumn
free troposphere can result in an AODCL value that is twice as high as the AODABL
over Warsaw. The occurrence of a turbulence-driven aerosol burst from the
boundary layer into the free troposphere can further increase this
difference. Aerosol within the ABL and in the free troposphere was interpreted
based on comparisons of the properties derived at different altitudes with
values reported in the literature, which were characteristic for different
aerosol types, in combination with backward trajectory calculations,
satellite data, and model outputs. Within the boundary layer, the aerosol consisted of
either urban anthropogenic pollution (∼ 61 %) or mixtures of anthropogenic aerosol with biomass-burning aerosol (< 14 %), local pollen
(< 7 %), or Arctic marine particles (< 5 %). No
significant contribution of mineral dust was found in the boundary layer.
The lidar-derived atmospheric boundary layer height (ABLH) and the AODABL
exhibited a positive correlation (R of 0.76), associated with the local
anthropogenic pollution (most pronounced for the RL and WML). A
positive correlation of the AODABL and LRABL and a negative
correlation of the ÅEABL and LRABL, as well as the expected
negative trends for the WVABL (and surface relative humidity, RH) and
δABL, were observed. Relations of the lidar-derived aerosol
properties within the ABL and the surface in situ measurements of particulate
matter with an aerodynamic diameter less than 10 µm (PM10) and less than 2.5 µm (PM2.5) measured by the Warsaw Regional Inspectorate
for Environmental Protection (WIOS) network, and the fine-to-coarse mass
ratio (FCMR) were investigated. The FCMR and surface RH showed a positive
correlation even at nighttime (R of 0.71 for the MTL, 0.63 for the WML, and 0.6 for the NL), which generally lacked statistically
significant relations. A weak negative correlation of the FCMR and δABL
(more pronounced at 532 nm at nighttime) and no casual relation
between the FCMR and ÅEABL were found. Most interestingly, distinct
differences were observed for the morning transition layer (MTL) and the
well-mixed layer (WML). The MTL ranged up to 0.6–1 km, and was
characterized by a lower AODABL(<0.12), wetter conditions
(RH 50–80 %), smaller particles (ÅEABL of 1–2.2; FCMR from 0.5 to
3), and a low LRABL of between 20 and 40 sr. The WML ranged up to 1–2.5 km
and exhibited a higher AODABL (reaching up to 0.45), drier conditions
(RH 25–60  %), larger particles (ÅEABL of 0.8–1.7; FCMR of
0.2–1.5), and a higher LRABL of up to 90 sr.