3. Temperature Profile as a Function of Height

Okay, so, let’s consider two things, first thing to be considered is what is called as the temperature profile as a function of height. So, we are saying that vertical convection happens as a result of thermal forces which means there’s a temperature difference. So, what is the temperature difference that will result in vertical movement of air masses? So, which means that I need to know what is the temperature profile as a function of height.

This chunk introduces the concept of a temperature profile with respect to height in the atmosphere. It explains that understanding this profile is essential because temperature differences in the atmosphere lead to vertical air movement (or convection). The key idea is that as the temperature varies with height, air masses will move vertically due to differences in their density, which is influenced by temperature.

Imagine a campfire; as the fire heats the air above it, the warm air rises because it is lighter than the cooler air surrounding it. This is similar to how temperature profiles in the atmosphere cause air to move: warmer air rises while cooler air sinks.

During daytime the radiation heats up the soil or the land faster than it heats the air. So, the radiation directly heats the soil. ... So, you are expecting to see this kind of a gradient in the temperature.

This section focuses on how solar radiation heats the ground more quickly than the air. As the ground heats up, it transfers heat to the air above, creating a vertical temperature gradient where the air closest to the ground is warmer. This gradient leads to more air movement as warmer, lighter air rises and cooler, denser air sinks.

Think of a hot asphalt road on a sunny day. The pavement gets much warmer than the air above it. If you've ever noticed that the air above the pavement seems to shimmer, that's the warm air rising, creating a visible effect of heat rising into the cooler air above.

Then you see a certain small decrease, the air is still hot but the soil has started cooling so, you start seeing this kind of behavior.

At night, the ground cools more quickly than the air, which can result in a reversal of the earlier temperature gradient. As the soil loses its heat, the warmer air above it still persists for a while. This behavior demonstrates that temperature gradients are dynamic and change throughout the day.

Think about a warm day turning into a cool night. The grass and soil cool down quickly as the sun sets, but the air above remains warm for a time. If you've ever felt a chill outside shortly after sunset while the air was still warm, you've experienced this phenomenon.

So this profile is called as an environmental lapse rate. It is called a lapse rate because it is temperature profile as a function of height.

The temperature profile that has been described is referred to as the environmental lapse rate. This term signifies how temperature typically decreases with height; however, if the temperature increases with height, it indicates a temperature inversion. This is significant for understanding air quality and pollution dispersion since pollutants can become trapped in the cooler air below the inversion layer.

Imagine a multilayered cake, where the top layers are cooler than the bottom layers. If pollution is released at the bottom layer (the cool layer) and there’s a warmer layer above, those pollutants might get trapped under the warm layer, similar to how your cake layers might stack up, preventing the bottom from rising to the top.

In the system if I drop a parcel of air coming from a pollutant source ... depending on what is the condition in the environmental lapse rate.

When pollutants are released from a source, their movement is influenced by the environmental lapse rate. If the released air is warmer than the surrounding air, buoyancy will cause it to rise. However, as it rises, it also cools and expands, which is described by the dry adiabatic lapse rate. Understanding these interactions helps predict how pollutants will disperse in the atmosphere.

Think about smoke rising from a chimney. If the smoke is warmer than the ambient air, it will rise. However, as it goes higher and encounters cooler air, it might start to cool and spread out. This is how pollutants can behave in the atmosphere, influenced by temperature differences and buoyancy.

Environmental lapse rate is known at different times of the day ... based on the pollution profile in that region.

The concept of stability relates to how air parcels behave when disturbed. If a parcel is warmer than its surroundings, it will rise; if cooler, it will sink. This leads to different stability conditions: stable, unstable, and neutral. The mixing height is crucial for predicting pollution dispersion as it determines how far pollutants can spread vertically.

Imagine a party balloon filled with helium. If you release it, it quickly shoots up because it's lighter (or less dense) than the surrounding air. But if you had a heavier balloon, it would sink. The interaction of these forces — buoyancy versus density — affects how pollutants spread in the atmosphere, similar to how balloons behave differently when released.

--