Marine boundary layer measurements of new particle formation and the effects nonprecipitating clouds have on aerosol size distribution

Abstract

Measurements of aerosol size distributions (0.005 < r < 20 /am), cloud droplet spectra, SO2, 03, CN, and other supporting quantities were made in the cloudtopped and clear marine boundary layer (MBL) from an airship operating within about 50 km of the Oregon coast. Comparison of size distribution of interstitial aerosol within the cloud with the size distribution below the cloud clearly indicates that the processing of the aerosol through (nonprecipitating) stratus can lead to increased mass of the subset of particles which had served as cloud condensation nuclei (CCN). This increase in mass in the CCN results in a distinct "cloud residue" mode in the size distribution measured below the cloud. In all cases the aerosol mass in the cloud residue mode greatly exceeded the mass in the interstitial mode, even though the number concentration of interstitial particles sometimes exceeded the CCN concentration. Evidence of new particle formation in clear air was also found on numerous occasions. Analyses of the data indicate that the growth of newly formed particles into the observed size range is consistent with gas phase oxidation of SO2 to sulfate and subsequent condensation on the aerosol. However, the exact nucleation process, whether by homogeneous nucleation, ion-assisted nucleation, or heterogeneous nucleation on precursor embryos, is still an open question. can be classified into three types of experiments: (1) clear air profiling of the MBL, (2) profiling the MBL when marine stratus is present, and (3) measurements of ship plumes.Results of the profiling measurements showing the effects of cloud processing on the aerosol size distribution and evidence of new particle formation by heteromolecular nucleation are presented in this paper. Airship and InstrumentationThe slow airspeed of an airship immediately suggests its candidacy as a research platform for experiments which Paper number 94JD00797. 0148-0227/94/94 JD-00797505.00 require (1) a nearly stationary platform within an air mass, e.g., Lagrangian measurements; (2) vertical profiling measurements downwind of localized sources where high spatial resolution is required, e.g., plumes from stationary and slowly moving sources; or (3) measurements where lowspeed sampling decreases the difficulty of sampling and/or sampling errors, e.g., sampling cloud droplets and hydrometers. The slow airspeed of the airship can also be a significant disadvantage by limiting the meteorological conditions under which it can operate and the range to the order of 150 km from its base of operation.The airship used in the experiments reported here was the US-LTA model 138S airship and is shown in Figure 1. A gasoline-powered generator which can provide 55 amps of 115 V, 60 Hz power was mounted external to the gondola; 500 kg of scientific equipment was mounted in three instrument racks inside the gondola and particle-sampling equipment was mounted 1.8 m below the nose of the airship (see Figure 1). In addition to the scientific payload, a pilot plus two scientists could be accommoda...

Measurements of aerosol and CCN properties in the Mackenzie River delta (Canadian Arctic) during spring–summer transition in May 2014

“…The minimum between the Aitken and the accumulation mode can be explained by previous cloud processing during which further material was added to activated droplets via aqueous phase oxidation. After the evaporation of cloud droplets this process creates the bimodal PNSD with the Hoppel minimum (Hoppel et al, 1994). In our case the Hoppel minimum can be found at around 90 nm.…”

Precipitation removal of ultrafine aerosol particles from the atmospheric boundary layer

“…Significant evidence of nucleation of new particles was found at continental boundary layer sites [Birmili and Wiedensohler, 2000;Verheggen and Mozurkewich, 2002;Birmili et al, 2003], including boreal forests [Mäkelä et al, 1997;Kulmala et al, 1998Kulmala et al, , 2001aKulmala et al, , 2001bKomppula et al, 2003] and Arctic regions [Wiedensohler et al, 1996;Pirjola et al, 1998]. The marine boundary layer (BL) provided evidence of homogeneous nucleation both in remote sites and near-coastal regions [Covert et al, 1992;Hoppel et al, 1994;Weber et al, 1998;Allen et al, 1999;O'Dowd et al, 1999]. New particles form also in urban environment, while the cases with low surface area of ambient aerosol are less frequent than in remote regions, and the direct emissions of UFP from road traffic and other sources make more difficult the observations of UFP generated by homogeneous nucleation [Kerminen and Wexler, 1996;Alam et al, 2003].…”

New Particle Formation in the Remote Troposphere: A Comparison of Observations at Various Sites

“…Evidence of homogenous nucleation has been observed in widely varying circumstances, such as in the remote marine boundary layer [Hoppel et al, 1994], in regions of cloud outflow [Hegg et al, 1990;Perry and Hobbs, 1994], and at a remote continental site [Weber et al, 1997]. Both models [Hamill et al, 1982] and indirect measurements of particle composition [Brock et al, 1995] suggest that in the upper troposphere (---10 km altitude), particles are formed via nucleating H2SOn and H20.…”