Interrelations between surface, boundary layer, and columnar aerosol properties derived in summer and early autumn over a continental urban site in Warsaw, Poland

• Main Authors: D. Wang, D. Szczepanik, I. S. Stachlewska
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-10-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/19/13097/2019/acp-19-13097-2019.pdf
• ISSN: 1680-7316; 1680-7324

<p>PollyXT Raman polarization lidar observations were performed at the Remote Sensing Laboratory (RS-Lab) in Warsaw (52.2109<span class="inline-formula">^∘</span>&thinsp;N, 20.9826<span class="inline-formula">^∘</span>&thinsp;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 (<span class="inline-formula"><i>α</i></span>) and backscatter coefficients (<span class="inline-formula"><i>β</i></span>) as well as linear particle depolarization ratios (<span class="inline-formula"><i>δ</i></span>) at 355&thinsp;nm and 532&thinsp;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 (AOD<span class="inline-formula">_ABL</span>) of <span class="inline-formula">0.20±0.10</span> at 355&thinsp;nm and <span class="inline-formula">0.11±0.06</span> at 532&thinsp;nm; a mean Ångström exponent (ÅE<span class="inline-formula">_ABL</span>) of <span class="inline-formula">1.54±0.37</span>; a mean lidar ratio (LR<span class="inline-formula">_ABL</span>) of <span class="inline-formula">48±17</span>&thinsp;sr at 355&thinsp;nm and <span class="inline-formula">41±15</span>&thinsp;sr at 532&thinsp;nm; a mean linear particle depolarization ratio (<span class="inline-formula"><i>δ</i>_ABL</span>) of <span class="inline-formula">0.02±0.01</span> at 355&thinsp;nm and <span class="inline-formula">0.05±0.01</span> at 532&thinsp;nm; and a mean water vapour mixing ratio (WV<span class="inline-formula">_ABL</span>) of <span class="inline-formula">8.28±2.46</span>&thinsp;g&thinsp;kg<span class="inline-formula">⁻¹</span>. 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 AOD<span class="inline-formula">_CL</span> value that is twice as high as the AOD<span class="inline-formula">_ABL</span> 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 (<span class="inline-formula">∼</span>&thinsp;61&thinsp;%) or mixtures of anthropogenic aerosol with biomass-burning aerosol (<span class="inline-formula">&lt;</span>&thinsp;14&thinsp;%), local pollen (<span class="inline-formula">&lt;</span>&thinsp;7&thinsp;%), or Arctic marine particles (<span class="inline-formula">&lt;</span>&thinsp;5&thinsp;%). No significant contribution of mineral dust was found in the boundary layer. The lidar-derived atmospheric boundary layer height (ABLH) and the AOD<span class="inline-formula">_ABL</span> exhibited a positive correlation (<span class="inline-formula"><i>R</i></span> of 0.76), associated with the local anthropogenic pollution (most pronounced for the RL and WML). A positive correlation of the AOD<span class="inline-formula">_ABL</span> and LR<span class="inline-formula">_ABL</span> and a negative correlation of the ÅE<span class="inline-formula">_ABL</span> and LR<span class="inline-formula">_ABL</span>, as well as the expected negative trends for the WV<span class="inline-formula">_ABL</span> (and surface relative humidity, RH) and <span class="inline-formula"><i>δ</i>_ABL</span>, 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&thinsp;<span class="inline-formula">µ</span>m (PM<span class="inline-formula">₁₀</span>) and less than 2.5&thinsp;<span class="inline-formula">µ</span>m (PM<span class="inline-formula">_2.5</span>) measured by the Warsaw Regional<span id="page13098"/> 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 (<span class="inline-formula"><i>R</i></span> 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 <span class="inline-formula"><i>δ</i>_ABL</span> (more pronounced at 532&thinsp;nm at nighttime) and no casual relation between the FCMR and ÅE<span class="inline-formula">_ABL</span> 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&thinsp;km, and was characterized by a lower AOD<span class="inline-formula">_ABL(&lt;0.12</span>), wetter conditions (RH 50–80&thinsp;%), smaller particles (ÅE<span class="inline-formula">_ABL</span> of 1–2.2; FCMR from 0.5 to 3), and a low LR<span class="inline-formula">_ABL</span> of between 20 and 40&thinsp;sr. The WML ranged up to 1–2.5&thinsp;km and exhibited a higher AOD<span class="inline-formula">_ABL</span> (reaching up to 0.45), drier conditions (RH 25–60 &thinsp;%), larger particles (ÅE<span class="inline-formula">_ABL</span> of 0.8–1.7; FCMR of 0.2–1.5), and a higher LR<span class="inline-formula">_ABL</span> of up to 90&thinsp;sr.</p>