The Dust Analysis
After taking pictures every day for 40 days (from 6 March to 14 April) and collecting data (check the divisions at the end of page to check data) a graph – Visibility VS Days – was constructed to be able to visualise when was the days with the highest and lowest amount of dust in the air.
WHY?
Visibility is defined as a measure of the distance at which an object or light can be clearly distinguished and that can be weakened by the scattering or absorption of light by gases and particles. Thus, visibility plays a major role in understanding what our atmosphere is composed of.
What Causes Poor Visibility?
We mainly noticed that days where the visibility was low, haze and/or clouds and/or fog was present in the atmosphere (according to weather.com). This can occur anytime , mainly during the winter and are often the consequence of the arrival of an unsettled weather front.
So, what is haze? When sunlight is absorbed by pollutants in the air, haze is formed. Thus, a proportional relationship between the pollutant concentration and the amount of light absorbed can be found. Therefore, the more sunlight absorbed, the higher concentration of toxic particles is present in the atmosphere, the less clarity exists and thus the lower the visibility. However, such particles and molecules impose a threat to one’s health.
How is Visibility Calculated?
Visibility is calculated mathematically based this equation:
V=2.99/ bext
bext in this case denotes the atmospheric extinction coefficients and V denotes the atmospheric visibility.
Now bext can be calculated using the following equation: bext= bsp + bap + bsg +bag
- Where bsg = light scattering by gas molecules. Gas scattering is attributable to oxygen and nitrogen molecules in the air and is known as Rayleigh .
- bag = light absorption by gases. Nitrogen dioxide (NO2) is the common atmospheric gaseous species that absorbs light.
- bsp = light scattering by particles. This scattering usually is dominated by fine particles, because particles 0.1–1.0 µm have the greatest scattering efficiency. Numerous pollutant airborne particles are in this size range.
- bap = light absorption by particles. Absorption arises mainly from black carbon particles.
