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<p>Air quality emission levels by mode are only compiled at a national level by the
National Atmospheric Emissions Inventory. Its estimates are updated annually. Emissions
from road vehicles are by far the greatest source of nitrous dioxide levels in Greater
London.</p><br /><p>The main impact of aviation on ground local air quality relates
to emissions during the landing and take-off phase up to about 3000 feet. Above this
height the oxides of nitrogen and particulate matter which can cause respiratory problems
get dispersed.</p><br />
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