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• Human-generated aerosols (smoke, other aerosols) have relatively short lifetimes in the atmosphere and are not created by processes in the atmosphere, and so will fairly quickly decline in concentration once emission stops.
• Aerosols of water – clouds – are created in the atmosphere, from water vapour which will continue to be emitted from the surface, and are also removed from the atmosphere as rain, but these processes balance out over time and so clouds will persist in the atmosphere. Clouds are not a pollutant of course: I just wanted to add them as another type of aerosol with another lifecycle in the atmosphere.
• $\mathrm{NO_x}$ has a relatively short lifetime in the atmosphere as it's not stable: its lifetime in the lower atmosphere is hours, and in the upper is not more than few weeks. I don't think $\mathrm{NO_x}$ is created in the atmosphere in significant quantities, so it will decline pretty quickly once emission from the surface stops.
• and so on.

• Human-generated aerosols (smoke, other aerosols) have relatively short lifetimes in the atmosphere and are not created by processes in the atmosphere, and so will fairly quickly decline in concentration once emission stops.
• Aerosols of water – clouds – are created in the atmosphere, from water vapour which will continue to be emitted from the surface, and are also removed from the atmosphere as rain, but these processes balance out over time and so clouds will persist in the atmosphere. Clouds are not a pollutant of course: I just wanted to add them as another type of aerosol with another lifecycle in the atmosphere.
• $\mathrm{NO_x}$ has a relatively short lifetime in the atmosphere as it's not stable: its lifetime in the lower atmosphere is hours, and in the upper is not more than few weeks. Some $\mathrm{NO_x}$ is created in the atmosphere by lightning, but I think the quantities are rather small compared to the amounts created by human emissions. So the amount in the atmosphere will decline pretty quickly once emission from the surface stops.
• and so on.

So, now, how lon things persist in the atmosphere depends on what they are: the term 'pollution' bundles together things which have radically different characteristics.

• Human-generated aerosols (smoke, other aerosols) have relatively short lifetimes in the atmosphere and are not created by processes in the atmosphere, and so will fairly quickly decline in concentration once emission stops.
• Aerosols of water – clouds – are created in the atmosphere, from water vapour which will continue to be emitted from the surface, and so will persist.
• $\mathrm{NO_x}$ has a relatively short lifetime in the atmosphere as it's not stable: its lifetime in the lower atmosphere is hours, and in the upper is not more than few weeks. I don't think $\mathrm{NO_x}$ is created in the atmosphere in significant quantities, so it will decline pretty quickly once emission from the surface stops.
• and so on.

• plants absorb about $120\,\mathrm{GtC/y}$ through photosynthesis;
• plants emit about $60\,\mathrm{GtC/y}$ thro through respiration;
• about $60\,\mathrm{GtC/y}$ is emitted from decay of plant matter;
• the oceans absorb about $90\,\mathrm{GtC/y}$;
• the oceans emit about $90\,\mathrm{GtC/y}$.

So, now, how long things persist in the atmosphere depends on what they are: the term 'pollution' bundles together things which have radically different characteristics.

• Human-generated aerosols (smoke, other aerosols) have relatively short lifetimes in the atmosphere and are not created by processes in the atmosphere, and so will fairly quickly decline in concentration once emission stops.
• Aerosols of water – clouds – are created in the atmosphere, from water vapour which will continue to be emitted from the surface, and are also removed from the atmosphere as rain, but these processes balance out over time and so clouds will persist in the atmosphere. Clouds are not a pollutant of course: I just wanted to add them as another type of aerosol with another lifecycle in the atmosphere.
• $\mathrm{NO_x}$ has a relatively short lifetime in the atmosphere as it's not stable: its lifetime in the lower atmosphere is hours, and in the upper is not more than few weeks. I don't think $\mathrm{NO_x}$ is created in the atmosphere in significant quantities, so it will decline pretty quickly once emission from the surface stops.
• and so on.

• plants absorb about $120\,\mathrm{GtC/y}$ through photosynthesis;
• plants emit about $60\,\mathrm{GtC/y}$ through respiration;
• about $60\,\mathrm{GtC/y}$ is emitted from decay of plant matter;
• the oceans absorb about $90\,\mathrm{GtC/y}$;
• the oceans emit about $90\,\mathrm{GtC/y}$.

How long something persists in the atmosphere once it's there depends, obviously, on how it gets removed from the atmosphere and also if anything is adding it to the atmosphere. However there is a very important distinction to be made:

So, now, how lon things persist in the atmosphere depends on what they are.

How long something persists in the atmosphere once it's there depends, obviously, on how it gets removed from the atmosphere and also if anything is adding it to the atmosphere. Different things we might consider pollutants will have different lifetimes, often very different, and it's confusing to lump them together as 'pollution'.

However there is a very important distinction to be made:

So, now, how lon things persist in the atmosphere depends on what they are: the term 'pollution' bundles together things which have radically different characteristics.