Experimental Study of the Effects of Environmental and Fog Condensation Nuclei Parameters on the Rate of Fog Formation and Dissipation Using a New Laboratory Scale Fog Generation Facility

Abstract

The IIT Kanpur Fog Chamber Facility has been conceptualized and built indigenously to study the fog formation and dissipation under various environmental conditions. The chamber has been designed such that all governing parameters can be controlled and optimized. The effects of relative humidity, temperature and size distribution, number and chemical composition of fog condensation nuclei (FCN) on the formation, stability and dissipation of fog has been studied. The visibility measurements were carried out using a He-Ne 632.8 nm monochromatic laser. It was found that aerosol number concentration, size distribution and chemical nature of FCN have significant effects on visibility reduction in fog. Direct comparisons were made for theoretical droplet growth and settling times in predicting the period for which stable fog was expected Vs the actual experimentally measured times for stable fog generated using different types of FCN. Effective radius, R eff , of fog droplet size distribution (DSD), a parameter that describes the optical properties of the droplet distribution was also calculated. It was noted that even for the same R eff (i.e. similar visibility), DSDs show notable differences depending on other conditions, implying the differences in the microphysical nature of fog. Fog dissipation results show that, with the decrease in temperature, the rate of fog dissipation decreases for all FCNs except for uncoated graphite, where no particular pattern has been observed maybe due to its less hygroscopic nature. The results from this study will help us in better understanding the optical nature of fog and designing of future fog vision devices.

Characterization of organic residues of size‐resolved fog droplets and their atmospheric implications

“…(iv) The ambient residence time of fine droplets can be expected to be generally higher (slower settling) as compared to larger droplets, so organics inside the fine droplets might be processed for longer duration. (v) It is possible that fine and coarse droplets have formed on condensation nuclei with different composition [ Gupta et al ., ; Singh et al ., ]. It seems likely that all of these reasons might have contributed to the observed trends to some extent; however, based on the current data set, only (i) and (ii) can be considered as more certain, whereas the other ones are rather speculative.…”

A Comparative Morphological Study of Primary and Aged Particles Emitted from a Biodiesel (B20) vis-à;-vis Diesel Fuelled CRDI Engine

“…This water vapor gets condensed in the photochemical chamber due to low ambient temperature. Condensation of water vapors to liquid form may lead to faster settling of fully grown water droplets in photochemical chamber, which may also remove several other particles by sweeping mechanism,while settling to the bottom of the photochemical chamber (Singh et al, 2011). Ruiz et al (2007) also reported 21-40% loss for 50-1000 nm size range particles in their photochemical chamber study used for determining the toxicity of coalfired power plant emissions.…”

“…At 75% and 100% engine load, surprisingly, lower particulate collection on the filter paper was observed, possibly due to loss of aged particulates in the photochemical chamber itself. This might be due to rapid growth of primary particles well above sub-micron sizes (Baumgard and Kittelson, 1985;Singh et al, 2011). At higher engine loads, more fuel quantity is injected into the engine cylinder, which produces higher quantity of water vapor as a combustion product.…”

LOAC: a small aerosol optical counter/sizer for ground-based and balloon measurements of the size distribution and nature of atmospheric particles – Part 1: Principle of measurements and instrument evaluation

“…This result validates the correction procedure applied to the LOAC measurements in the case of dense medium of liquid particles. Figure 11 presents the size distribution at the beginning of a fog event, with the typical enhancement around a diameter of 10 µm (e. g. Singh et al, 2011), and at the end of the event. Both LOAC and WELAS found a bimodal size distribution but disagree for the size and the position of the second mode.…”