Influence of mixing layer height upon air pollution in urban and sub-urban areas

Abstract

The mixing layer height is an important parameter characterising the potential of the atmospheric boundary layer to take up emitted air pollutants. During continuous measurements in Hanover, Germany, from 2001 until 2003 and around Munich, Germany, in summer and winter 2003 were determined by different remote sensing systems mainly from the thermal structure and turbulence of the air (SODAR), for some time from the aerosol layering of the air (ceilometer), and for a short period directly from the temperature profile (RASS). The temporal variations of the concentrations of PM 10 and PM 2.5 as well as of CO and NO x simultaneously measured near the surface were investigated and correlated with the MLH derived from SODAR data. The pollution measurements were performed inside a street canyon and at an urban background station close to Hanover and at three measurement locations inside and outside of Munich complementing the available monitoring networks. The analyses show that the correlations of pollutant concentrations with MLH are smallest inside street canyons. Correlations at the urban background stations are larger in winter than in summer, and they are larger for the urban stations than for the rural stations. It turns out further that the correlation of NO x concentrations with MLH is larger than the correlation of particles concentrations. Explanations for these findings must consider the varying emission source strengths for NO x and particles and the influence of gas-to-particle conversion within air masses especially during daytime in summer. ZusammenfassungDie Mischungsschichthöhe ist ein wesentlicher Parameter, der die Aufnahmefähigkeit der atmosphärischen Grenzschicht für bodennah emittierte Luftschadstoffe charakterisiert. Bei kontinuierlichen Messungen in Hannover in den Jahren 2001 bis 2003 und im Raum München im Frühsommer und Winter 2003 wurden Mischungsschichthöhen (MLH) mit unterschiedlichen Fernmessverfahren detektiert, hauptsächlich mit SO-DAR aus der thermischen und dynamischen Struktur der Atmosphäre, zeitgleich mit einem Ceilometer aus dem Partikelgehalt und für eine kurze Zeitspanne mit einem RASS direkt aus dem Temperaturprofil. Die gemessenen NO x -und Partikelkonzentrationen wurden analysiert und mit der aus den SODAR-Daten bestimmten MLH korreliert. Die Schadstoffmessungen fanden in einer Straßenschlucht und einer nahe gelegenen städtischen Hintergrundstation in Hannover sowie an drei Messpositionen innerhalb und außerhalb von München statt, womit die bestehenden Messnetze ergänzt wurden. Die Analysen zeigen, dass die Korrelationen der Schadstoffkonzentrationen mit der MLH innerhalb der Straßenschlucht am geringsten sind. Generell sind die Korrelationen im Winter höher als im Sommer, in den Städten höher als im Umland, und für NO x höher als für Partikelkonzentrationen. Erklärungen hierfür müssen die verschiedenen Emissionsquellstärken der Schadstoffe und den Einfluss der Gas-zu-Partikel-Umwandlungsprozesse innerhalb einer Luftmasse insbesondere tagsüber im Sommer berücksichtigen.

Overview of the synoptic and pollution situation over Europe during the EUCAARI-LONGREX field campaign

“…The latter two stations showed minimum concentrations in the afternoon and maximum concentrations in the morning. Diurnal cycles of particulate matter in urban areas have been analysed in several previous studies (e.g., Kukkonen et al, 2005;Schäfer et al, 2006;Pernigotti et al, 2007;Pitz et al, 2008). Minimum concentrations of particulate matter frequently occur in the afternoon hours in polluted and urban background regions.…”

Monitoring Depth of Shallow Atmospheric Boundary Layer to Complement LiDAR Measurements Affected by Partial Overlap

“…Thus, the assessment of the effect of carbon sequestration and/or greenhouse gas emissions reduction activities, including attribution of sources and sinks by region and sector is a challenging but important task [38][39][40][41]. In estimating the CBL growth rate during the early morning transition or in studying dispersion in a shallow CBL [42][43][44], determination of z i below the height of full overlap of a LiDAR system is urgently required. Additionally, a growing CBL during the morning transition period first interacts with the overlying residual layer (RL) and then with the FA after reaching the quasi-stationary height.…”

Analysis of exceedances in the daily PM<sub>10</sub> mass concentration (50 μg m<sup>−3</sup>) at a roadside station in Leipzig, Germany

“…Another is the loss of moisture in air masses over land, which leads to a lesser degree of wet deposition in air masses that have travelled long over continents. Inversion situations and a low mixing layer height have, for example, been related to high concentrations of gases and particulates in other European (Kukkonen et al, 2005) or German cities (Schäfer et al, 2006).…”

“…Such emissions have been shown to lead to enhanced levels of PM 10 in certain hotspots as well as in the rural background (Herrmann et al, 2006). Second, temperature inversions that lead to pollution trapping near the ground are more frequent during the cold season (e.g., Schäfer et al, 2006;Birmili et al, 2010). In order to differentiate the influences of different particle source types, total PM 10 as well as the coarse particle subfraction PM [2.5;10] are distinguished after season in Fig.…”