# Car Exhaust after Catalytic Converter

**URL:** <https://boards.straightdope.com/t/car-exhaust-after-catalytic-converter/527107>\
**Category:** Factual Questions\
**Created:** [January 31, 2010, 2:21pm UTC](https://boards.straightdope.com/t/car-exhaust-after-catalytic-converter/527107 "2010-01-31T14:21:46Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Redfishhunter930](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Redfishhunter930](https://boards.straightdope.com/u/Redfishhunter930)\
**Post date:** [January 31, 2010, 2:21pm UTC](https://boards.straightdope.com/t/car-exhaust-after-catalytic-converter/527107/1 "2010-01-31T14:21:46Z")

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After car exhaust goes through the Catalytic converter what percent  
of the exhaust gas is water.And what is the percent of other pollutants.  
Any cites or previous columns would be helpful.Thanks in advance

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**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\
**Post date:** [January 31, 2010, 3:04pm UTC](https://boards.straightdope.com/t/car-exhaust-after-catalytic-converter/527107/2 "2010-01-31T15:04:15Z")

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I can’t give you a percentage, but for every gallon of gasoline you burn you will create just about 1 gallon of water in the combustion process.  
Going into the converter you have (in no particular order)  
Unburned hydrocarbons (HC)  
Carbon Monoxide (CO)  
Carbon Dioxide (CO2)  
Oxygen (O2)  
Oxides of Nitrogen (NOX)  
In the converter the following reactions occur:  
NOX - O2 = NO2 + O2  
CO + O2 = CO2  
HC + O2 = H2O + CO2

Modern converters convert over 99% of the pollutants in the car’s exhaust.

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**Author:** ![Redfishhunter930](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Redfishhunter930](https://boards.straightdope.com/u/Redfishhunter930)\
**Post date:** [January 31, 2010, 4:20pm UTC](https://boards.straightdope.com/t/car-exhaust-after-catalytic-converter/527107/3 "2010-01-31T16:20:19Z")

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Thanks Rick I had a couple of friends  
over last night and that’s what I said.I couldn’t work the keyboard last night  
to log in (beer) to back me up.  
Never underestimate the power of the Straight Dope  
Any cites

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**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\
**Post date:** [January 31, 2010, 4:43pm UTC](https://boards.straightdope.com/t/car-exhaust-after-catalytic-converter/527107/4 "2010-01-31T16:43:58Z")

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> [@Rick](#):
>
> I can’t give you a percentage, but for every gallon of gasoline you burn you will create just about 1 gallon of water in the combustion process.  
> Going into the converter you have (in no particular order)  
> Unburned hydrocarbons (HC)  
> Carbon Monoxide (CO)  
> Carbon Dioxide (CO2)  
> Oxygen (O2)  
> Oxides of Nitrogen (NOX)  
> In the converter the following reactions occur:  
> NOX - O2 = NO2 + O2  
> CO + O2 = CO2  
> HC + O2 = H2O + CO2
> 
> Modern converters convert over 99% of the pollutants in the car’s exhaust.

One nit:  
NOX - O2 = NO2 + O2 should be NOx = N2 + O2

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**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\
**Post date:** [January 31, 2010, 5:13pm UTC](https://boards.straightdope.com/t/car-exhaust-after-catalytic-converter/527107/5 "2010-01-31T17:13:29Z")

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> [@beowulff](#):
>
> One nit:  
> NOX - O2 = NO2 + O2 should be NOx = N2 + O2

My bad, I wrote that before caffeine this morning. That is my only excuse.