The amount of particles and contaminants in the samples of snow decreases when collected further away from the city.
Pollution in snow
Snow normally looks white and clean. However, it's surprising that snow may actually contain many contaminants such as toxins, heavy metals, viruses and bacteria. Snow is contaminated when it is stepped on or when pollutants are splashed onto it.. Snow also collects dust and dirt carried by the wind. It also collects contaminants in the atmosphere as it falls to the ground.
Snow has the interesting "ability" to remove pollutants in the air by forming itself around dust particles. The formation of snow occurs in water vapor that moves in clouds of cold air. The water vapor "adheres" to pollutants or dust particles in the cloud and then other water molecules also begin to attach themselves to it, until snow crystals are formed.Snow crystals continue to grow in size and remain in the air for a few hours before they fall to the ground. During this time, snow crystals continue to collect pollutants and particles in the air. So, snow really isn't as clean as it looks.