The standard sets a permissible exposure limit (PEL) of 25 parts methylene chloride per million parts of air (ppm) as an eight-hour time-weighted average (TWA). This refers to the average exposure during an eight-hour period. Employers must use engineering and work practice controls to limit employee exposures.
The state of the atmosphere at a particular time and place. Weather is described in terms of variable conditions such as temperature, humidity, wind velocity, precipitation, and barometric pressure. Weather on Earth occurs primarily in the troposphere, or lower atmosphere, and is driven by energy from the Sun and the rotation of the Earth. The average weather conditions of a region over time are used to define a region's climate.
Atmospheric Conditions. Weather is the state of the atmosphere at a specific time and place, with respect to temperature, precipitation, and other factors such as cloudiness. Weather is generated by many forces, some obvious, some not. Warm, humid air masses blowing in from oceans, for example, fuel rains.