Showing papers by "Tuukka Petäjä published in 2005"

Evaluation of an automatic algorithm for fitting the particle number size distributions

Abstract: The multi log-normal distribution function is widely in use to parameterize the aerosol particle size distributions. The main purpose of such a parameterization is to quantitatively describe size distributions and to allow straightforward comparisons between different aerosol particle data sets. In this study, we developed and evaluated an algorithm to parameterize aerosol particle number size distributions with the multi log-normal distribution function. The current algorithm is automatic and does not need a user decision for the initial input parameters; it requires only the maximum number of possible modes and then it reduces this number, if possible, without affecting the fitting quality. The reduction of the number of modes is based on an overlapping test between adjacent modes. The algorithm was evaluated against a previous algorithm that can be considered as a standard procedure. It was also evaluated against a long-term data set and different types of measured aerosol particle size distributions in the ambient atmosphere. The evaluation of the current algorithm showed the following advantages: (I) it is suitable for different types of aerosol particles observed in different environments and conditions, (2) it showed agreement with the previous standard algorithm in about 90% of long-term data set, (3) it is not time-consuming, particularly when long-term data sets are analyzed, and (4) it is a useful tool in the studies of atmospheric aerosol particle formation and transformation.

The contribution of sulfuric acid and non-volatile compounds on the growth of freshly formed atmospheric aerosols

Abstract: [1] The formation of atmospheric aerosol particles (homogeneous nucleation, forming of stable clusters ∼1 nm in size), their subsequent growth to detectable sizes (>3 nm), and to the size of cloud condensation nuclei, remains one of the least understood atmospheric processes upon which global climate change critically depends. However, a quantitative model explanation for the growth of freshly formed aerosols has been missing. In this study, we present observations explaining the nucleation mode (3-25 nm) growth. Aerosol particles typically grow from 3 nm to 60-70 nm during a day, while their non-volatile cores grow by 10-20 nm as well. The total particle growth rate is 2-8 nm/h while the non-volatile core material can explain 20-40%. According to our results, sulfuric acid can explain the remainder of the growth, until the particle diameter is around 10-20 nm. After that secondary organic compounds significantly take part in growth process.

Design and performance characteristics of a condensation particle counter UF-02proto

Abstract: In this paper we present a design of a new swirling flow condensation particle counter UF-02proto, which has a continuous sampling flow. The performance and characteristics of the instrument were investigated. We studied experimentally the concentration range of the instrument and the detection efficiency as a function of particle diameter for silver.particles. The lower cut-off size of the CPC, i.e. the limiting size when 50% of the particles are successfully accounted for, was determined to be 4.35-4.46 nm, depending slightly on a form of a fitted exponential step-function. The counting efficiency of the CPC at high particle concentrations was experimentally investigated using 20 nm silver particles. The maximum observable number concentration with a single particle counting method was approximately 100 000 cm -3 with an accuracy of 20%. The operation of the CPC UF-02proto was also compared with that of a commercially available CPC when operating both instruments in parallel. The CPC proved to be suitable for a variety of applications with a wide range of particle concentrations and particle sizes.