1. a view from the Automotive Industry
NO2/NOx ratio :
a view from the Automotive Industry
Alain Petit, Renault
May, 2nd 2006

2. Average concentrations NO2 and NO in Europe in urban traffic conditions
A certain stabilisation of NO2 concentrations essentially seen at roadside stations
accross Europe. NO 2
source : ETC - ACC / AirBase 5 10 15 20 25 30 35 40 45 50 55 60 65 70
1998
1999
2000
2001
2002
2003
2004 80 90
100
110 UK
Belgium
Netherlands
Germany
Switzerland
Austria
Spain
Italy

3. NO2/NOx ratios in passenger cars
Emission Regulation expressed in NOx as NO2 equivalent. So, this assumes
that all NO is converted in NO2 in the air.
This leads to overestimate the actual NO + NO2 sum in the exhaust gas.

4. NO2/NOx ratios in gasoline passenger cars
No evolution of NO2/NOx ratios of gasoline vehicles.
NO2 represents of few percent of total NOx

5. NO2/NOx ratios in diesel passenger cars
Euro 3 (mean over 15 cars) Euro 4 (mean over 11 cars)
ECE 15 % %
EUDC 33 % %
NEDC 25% %
On average, increase of NO2/NOx ratios from diesel Euro 3 to diesel Euro 4.
But, further investigation needed to understand the car to car impact

6. Impact of aftertreatment on NO2/NOxemissions
Study based on simulations on a diesel 2.0 litre engine.
Reducing NOx by using high EGR rates leads to increase engine-out CO and HC.
Complying with CO and HC standards implies to improve the oxidation catalyst,
with increase of NO2/NOx ratio as a side-effect.
Relaxing CO and HC limits will help to decrease NO2/NOx ratios CO
NO2
NO2/NOx HC
NOx
Euro 5 with Euro 5
aftertreatment*
Euro 5 with Euro 4
aftertreatment
Euro 5 with Euro 3
aftertreatment
* Euro 5 based on EC proposal of dec. 2005
Source : PSA

7. Analysis of urban NO2 sources and the effect on NO2 air quality. Dr
Analysis of urban NO2 sources and the effect on NO2 air quality. Dr.-Ing. Christoph Kessler (AVISO GmbH, Aachen) Dr. Juliane Theis (BMW AG, München) Dr. Rainer Vogt (Ford Forschungszentrum Aachen GmbH) Antriebsleitertreffen München, 2.Mai 2006

8. Analysis of urban NO2 sources and the effect on NO2 air quality.
Scope: Modeling of NO2 concentrations at the roadside of main artery road
(Corneliusstreet Dusseldorf, Germany)
Step 1: Detailed calculation of traffic emissions (45000 vehicles/d)
Step 2: Air quality modeling
modeling of transport and chemistry with box model based on
RADM2 (161 chemical reactions and 59 chemical species)
input: traffic emissions and ambient background concentrations
 ambient background for a typical summer day
ambient mean [µg/m³]
NO2 NO O3 CO
VOC 26 6 59
112 56 2 2

9. Main artery road: vehicle count & NO2 emissions. Year 2005.
PC diesel 57.0%
PC gasoline 67.2%
vehicles/day per category
NO2 emission per category
the traffic is dominated by passenger cars
main NO2 emission source are diesel pass. cars,
but also busses + HD trucks are major contributors
Emission model results:
17% NO2/ NOx
12% NO2/ NOx
Base case
32 % NO2/ NOx
20 % NO2/ NOx
Max. case
2010
2005 2 2

10. NO2 concentration at road side: diurnal variations. Base case 2005.
12 % (7 µg/m³) of NO2 conc. due to direct NO2 emission
41% (25 µg/m³) of NO2 conc. due to chemistry NO + O3 NO2 + O2
47 % (30 µg/m³) of NO2 conc. due to background NO2 conc. 2 2

11. Contribution of specific phenomena to ambient NO2 concentration (base case 2005).
NO2 concentration is determined by location and transport:
at the city park:
- background NO2 conc.
- increasing influence of chemistry
- negligible influence of primary NO2 emission
at the road side:
background NO2 conc.
chemistry
primary NO2 emissions

12. Preliminary conclusions
By regulating NOx as NO2 equivalent, NO2 is already taken
into account in emission regulations.
Clear increase of NO2/NOx ratios from exhaust diesel cars
since the introduction of oxidation catalyst:
Chemistry seems to have a higher impact that primary NO2 from diesel cars
Further investigation is needed to reach a better understanding of NO to NO2 conversion in diesel exhaust gas. Relaxing CO and HC limits will help to reduce the NO2 concentrations.