Experimental Evidence of the Feeding of the Free Troposphere with Aerosol Particles from the Mixing Layer

Abstract

Aerosol particles emitted by both natural and anthropogenic sources have direct and indirect radiative impacts. Within the planetary mixing layer (ML), these particles are subjected to a large number of removal processes, e.g., rain, sedimentation, coagulation, and thus have a relatively short lifetime. Once aerosols are transported into the free troposphere (FT), their atmospheric lifetime increases significantly and they tend to be representative of large spatial areas. The work presented here shows evidence of anthropogenic emissions being transported from the ML to the FT during a cold period in February 2012. Using a wide range of in-situ measurements of aerosol chemical and physical properties at the Puy de Dome (PUY) station, as well as LIDAR measurements (at the Cezeaux site) of atmospheric back scattering we studied the exchange between the ML and the FT. Criteria used to identify when the PUY station was sampling in the ML or in the FT included mixing layer height estimates from LIDAR measurements, trace gas measurements, and air mass trajectories. Within the FT, we observed a gradual change in aerosol physical properties with increases in aerosol mass concentrations of up to 2 times the starting concentration, as well as increases in the number of larger particles (particle diameter >150 nm). Aerosol chemical properties showed increases in organic and nitrate particles. A series of linear fits were made through the data providing information on how different parameters change as a function of time. The impact of these changing aerosol properties are discussed in relation to the potential influence on aerosol direct and indirect effects. This work presents a unique combination of observations, and provide valuable data for future model validation.

Seasonal Variation of Aerosol Size Distribution Data at the Puy de Dôme Station with Emphasis on the Boundary Layer/Free Troposphere Segregation

“…For instance, the long-term variation of the particle size distribution has been studied by Venzac et al (2009) [14], and the occurrence of the new particle formation (NPF) process was specifically investigated in several dedicated studies [24,[26][27][28]. Filter measurements, as well as online mass spectrometry analysis, have been used to document the particles chemical composition [19,29,30] and aerosol-cloud interactions were also investigated from this station which offers favorable conditions for such analysis [28,31,32]. The second site, Cézeaux, hereafter referred to as CZ, is located on the University campus in Clermont-Ferrand (420 m a.s.l.…”

“…As evidenced in earlier studies [16][17][18] new particle formation (NPF) may have specific characteristics at high altitudes. Once in the FT, aerosol particles have a longer residence time due to the lower frequency at which they are scavenged by clouds and precipitation, allowing them to be transported in the atmosphere for several days [19] increasing their impact on the climate. Additionally, aerosol particles transported into the FT or formed in the FT can be re-injected again into BL, affecting the air quality far from the source region [20,21].…”

“…Additionally, these measurements are needed to validate and improve numerical mesoscale or global scale transport models [22]. A number of studies focused on FT conditions from ground-based high altitude sites [3,14,19] or from airborne measurement campaigns [23,24], providing information on aerosol physical and chemical properties in this part of the atmosphere. Fröhlich et al (2015) [25] and Freney et al (2016) [19] showed that the FT air masses are strongly influenced by injections from BL, however, the number of studies comparing the transport from the BL to the FT over long periods of time are rare.…”

Atmospheric Processing and Variability of Biological Ice Nucleating Particles in Precipitation at Opme, France

“…Each cluster of trajectories is calculated every 15 min for 48 h of back-trajectories, for each day of precipitation sampling with a starting vertical level defined using ERA-Interim humidity and cloud parameters, and varying from 1 to 5 km. LACYTRAJ has previously been used to study long-range inter-hemispheric transport of carbon monoxide [38], interactions between the mixing layer and the free troposphere [39] or jet stream dynamics [40]. Based on previous studies of the atmosphere at this site [41], we distinguished categories in the geographical origin of air masses; here 3 sectors were defined: West (air masses from the Atlantic Ocean), North-East (Continental source) and South (Mediterranean Sea).…”

Overview of the Special Issue “Selected Papers from the 2nd Atmospheric Chemistry and Physics at Mountain Sites Symposium”

“…Evidence of anthropogenic emissions transported from the planetary mixing layer to the free troposphere was presented by Freney et al (2016) using in-situ measurements of aerosol chemical and physical properties during a cold period in February 2012 at the Puy de Dôme station, as well as LIDAR measurements (at the Cezeaux site) in France. A change in aerosol physical and chemical properties was observed in the free troposphere with an increase in aerosol mass concentrations, number of larger particles, and presence of organic and nitrate particles.…”