Tip Two to Clear the Air – Fill up in the Evening

Just what is this ozone stuff made of?

Ozone forms when oxides of nitrogen (NOx) and volatile organic compounds (VOCs) mix in the presence of sunlight.  NOx and VOCs are produced in the process of fuel combustion and emitted from our vehicles.  VOCs are known by another name – aromatic hydrocarbons.  That “gasoline smell” you smell at the pump?  That’s a volatile organic compound.

How does the process work?

When we top off our cars, those VOC vapors that come out mix with other NOx and VOCs in the air.  When this occurs in the sunlight, a chemical reaction takes place that produces single oxygen atoms (O) which bind with oxygen molecules (O2) to form ozone (O3).  When you fill up in the morning and afternoon, in the sunlight, those emissions from the pump can form ozone.  If we can reduce the amount of ozone formed, we can help improve air quality.  Fill up the car at night so those fumes have time to dissipate before sunrise and they don’t get a chance to become ozone.      

Why does it matter?

Ozone is harmful to our health.  An oxygen molecule is “stable” as O2, but as ozone (O3), it is trying to shed that extra oxygen atom.  When we breathe it in, the oxygen atom breaks free and can combine with other molecules to create chemicals that are harmful to lung tissue and other cellular structures.  When we take steps to reduce ozone, we improve air quality and our health.

Green Dallas, Office of Environmental Quality, Air Quality


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