Application of aerosol electrometer for ambient particle charge measurements

The charge on ambient atmospheric particles is an important parameter in the investigation of particle dynamics. Yet, there is only limited knowledge available on it, mainly due to the lack of instrumentation for its direct measurement. The aim of this study was to explore the application and suitability of the Aerosol Electrometer (AE) TSI Model 3068 as a direct instrument for measuring ambient particle charge concentration, thereby extending its use beyond the current applications. Through a set of experimental investigations the AE was applied to measure net concentration of charged particles in different environments. Results of the study showed the instrument is mostly suitable for outdoor field measurement, when particle charge concentrations are elevated, such as in the vicinity of strong ion emitting sources (high voltage powerlines, electricity substations, etc); and under conditions of air relative humidity of below 60%. Operating the instrument above this humidity value would require the use of a dehumidifier. 74% (R2) statistical correlation (P<0.05) was obtained between the readings of the AE and the Air Ion Counter, when both instruments were used to simultaneously sample ambient air

Quantitative Assessment of the Effect of Surface Deposition and Coagulation on the Dynamics of Submicrometer Particles Indoors

Exposure to airborne particles indoors depends on particle concentration, which is affected by air filtration, ventilation, and particle dynamics. The aim of this work was quantitative assessment of the effects of coagulation, surface deposition, and ventilation on the submicrometer particle concentration indoors. The assessment was obtained from measured particle loss rate and deposition velocity parameters. The experiments were conducted in an experimental chamber for three different types of aerosols: environmental tobacco smoke, petrol smoke, and ambient air aerosols. Particle number concentration and size distribution were measured in the size range between 0.017 and 0.898 wm by SMPS. The average values for the overall deposition loss rates varied from 4.3 2 10m5 sm1 (0.16 hm1) to 1.1 2 10m4 sm1 (0.39 hm1). The overall deposition velocities associated with surface deposition and coagulation ranged from 9.6 2 10m4 cm sm1 to 2.4 2 10m3 cm sm1, and for surface deposition only from 2.8 2 10m4 cm sm1 to 6.3 2 10m4 cm sm1. For indoor conditions with an air exchange rate above 1.3 hm1, (natural ventilation, no filters) only a reduction in particle number of about 20% is attributed to the surface deposition and coagulation

The effect of temperature and humidity on size segregated traffic exhaust particle emissions

The formation and behaviour of exhaust emissions is affected by environmental, traffic and meteorological conditions. The understanding of the governing processes and dependency between particles and other relevant parameters, as well as the magnitude of the impacts, is still limited and mostly based on a few laboratory studies. The focus of this work is the effect of temperature (TEMP) and relative humidity (RH) and their interaction on traffic emission particles in the size range of 15-850 nm. The relationship was assessed using a large data set collected over a period of six months at two road sites in Brisbane. A sequence of statistical analyses were designed and applied in order to quantify the relationships, comprising of exploratory correlation analysis to identify pairwise linear associations, factor analysis to assess multivariate effects and nonparametric regression tree methods to more carefully explore interactions. The results show that total particle number concentration was dominated by traffic flow rate and wind speed and to a lesser degree by RH and TEMP. In general, an inverse relationship between temperature and concentration, and a direct relationship between RH and concentration was observed. While TEMP was a dominant parameter for particle concentrations in the size range 15-30 nm, its role diminished and RH emerged as a stronger influence as particle size increased. The observed increase for particle concentrations in the size range 50-150 nm could be associated with particle transfer from a smaller to larger size group due to coagulation and condensation induced growth, as well as an increase in primary (engine) emissions. The significant influence of RH on particles in the 150-880 nm size range could be related to particle growth, changes in hygroscopic properties of traffic emissions and particles originating from sources other than traffic. Decreased combustion efficiency may also contribute to higher emissions of particles in this size range