Eric-Michel ASSAMOI* and Catherine LIOUSSE** *assem@aero.obs-mip.fr ; **lioc@aero.obs-mip.fr Laboratoire d’Aérologie, CNRS, Toulouse, France

A two-wheel emission inventory for West Africa for the year 2002

Anthropogenic pollution : a real concern in West African megacities…

though still largely undocumented…

BC (!gC/m3) at Bamako (Mali)

0

50

100

150

10:50

16:20

21:20

2:20

7:20

14:15

19:15

0:25

5:25

10:25

17:55

22:55

4:35

9:40

14:40

19:40

0:40

5:45

10:45

16:15

22:10

5:20

22:30

5:20

16:00

22:25

5:25

10:40

16:40

0:35

6:15

2:45

8:30

14:15

19:25

1:05

6:15

12:00

17:30

23:40

5:00

April, 09, 2008 April, 23, 2008

From Liousse, Galy, Diop, Ndiaye et al., POLCA program

Bamako 25

Beijing 12

Paris 3

BLACK CARBON (BC) MEASUREMENTS : High concentrations at Bamako, Mali

•  2 wheel vehicles highly contribute to such high air pollution in Western Africa

Why ? - Low road quality. - Adulterated petrol sold in Nigeria, Benin and Togo. -  Deregulation of the public transport sector. -  Economic solution : increasing number of Asian

motorcycles «Jakartas» 2 stroke engines twice cheaper than motorcycles from Europe.

Are these emissions really accounted for in present inventories? :

Data are quite few, not consistent and sometimes not « official » (specially in Benin with smuggled oil...)

=> In this work, we propose a first inventory based on several assumptions with maximum and minimum hypotheses.

•  Where Ei,j is total emissions in g, •  Ci, motor gasoline fuel consumptions in kg, and •  EFi,j emission factors in g/kg, for country i and aerosol species j (BC or OCp).

TWO-WHEEL VEHICLE EMISSION INVENTORIES FOR THE YEAR 2002 over West Africa

•  Estimate the number of two-wheel vehicles

•  Number of days per week of two-wheel vehicles circulation •  Daily consumptions

•  Fuel density

  Motor gasoline fuel consumption estimation (Ci)

Ei,j = Ci x EFi,j

16 countries

1- Estimate the number of two-wheel vehicles

COUNTRIES NUMBER OF TWO-WHEEL

VEHICLES

BENIN 320,000

BURKINA FASO 300,000

CAMEROON 53,000

CHAD 16,000

MALI 300,000

NIGER 5,000

NIGERIA 1,309,000

TOGO 90,000

COUNTRIES ESTIMATED NUMBER OF TWO-WHEEL VEHICLES

GAMBIA** 1,026 – 12,578

GHANA** 11,892 – 145,758

GUINEA** 1,827 – 22,392

GUINEA-BISSAU** 948 – 11,625

IVORY-COAST** 41,460 – 508,177

LIBERIA** 1,159 – 14,205

SENEGAL** 13,685 – 167,739

SIERRA-LEONE** 1,319 – 16,170

  Minimum assumption = Niger RATIO (minimum of number of two-wheel vehicles) : 0.12

  Maximum assumption = Nigeria RATIO (maximum of number of two-wheel vehicles) : 1.44

RATIO = number of two-wheel vehicles / number of four-wheel vehicles

whether published data (left) or fully evaluated(**) from RATIO (right)

Minimum assumption Maximum assumption

“clean” two wheels

« motorcycle-taxis »

“clean” two wheels

« motorcycle-taxis »

Number of traffic day(s) per week 5 days per week 7 days per week

Daily consumptions (in litres) 0.5 2 1 4

Fuel density (kg/m3) 2% oil : ρ = 750.1 8% oil : ρ = 757.8

2) Characteristics in the minimum and maximum assumptions

In situ urban emissions measurements in Cotonou - AMMA, May 2005

Direct measurements of emission factors

example zems in Cotonou (Benin): CO/CO2 = 0.42

EF(BC) = 2.31 g/kg EF(OCp) =30.56 g/kg

Typical EF traffic values in developed countries: 0.28 for BC and 7.36 for OCp

Emission factors (g/kg) (Guinot et al., 2009)

BC = 0.28 OC = 7.36

BC = 2.31 OC = 30.56

Minimum assumption Maximum assumption

  New emission factors (EFi,j)

Differences between the maxi. and mini. assumptions variable : •  in Niger = 2,220 tons •  in Nigeria = 581,110 tons

IMPORTANCE OF FUEL CONSUMPTION DUE TO TWO-WHEEL VEHICLES : mini./maxi. (in tons per year)

Relative differences (maxi. – mini. / maxi.) •  97% in countries with estimated number of two-wheel vehicles •  64% in countries with available number of two-wheel vehicles

324,006 | 905,116

CONTRIBUTIONS TO BC EMISSIONS DUE TO TWO-WHEEL VEHICLES :

mini. / maxi. (in tons per year)

EF(MO) in the maxi. assumption is ~8 times greater than in the mini. assumption

Differences between the maxi. and mini. assumptions variable : •  in Niger = 7.6 tons •  in Nigeria = 1,998.3 tons

Relative differences (maxi. – mini. / maxi.)

•  96% in countries with available numbers of two-wheel vehicles

2,089

EF(MO) in the maxi. assumption is ~4 times greater than in the mini. assumption

Much higher impact for OCp than for BC for 2 stroke motorbikes

Differences between the maxi. and mini. assumptions variable : •  in Niger = 96.5 tons •  in Nigeria = 25,273.1 tons

Relative differences (maxi. – mini. / maxi.)

•  91% in countries with available numbers of two-wheel vehicles

CONTRIBUTIONS TO OCp EMISSIONS DUE TO TWO-WHEEL VEHICLES :

mini. / maxi. (in tons per year)

27,657 6,761

Bond et al., 2004 Junker and Liousse, 2008 vs. mini.

assumption vs. maxi.

assumption vs. mini.

assumption vs. maxi.

assumption (%) (%) (%) (%)

Consumption 5.7 18.4 6.0 19.5 BC emissions 12.9 344.8 11.2 300.6

OCp emissions 23.0 310.1 60.7 817.7

COMPARISON OF ALL TRAFFIC (BOND et al., 2004 and JUNKER and LIOUSSE, 2008) VS. OUR ASSUMPTIONS FOR MOTOR GASOLINE

Example for OCp comparisons for all West African countries

JL, 2008

JL,2008

JL,2008 + our maximum assumption

JL,2008 + our maximum assumption

maximum : 39 tons/year

tons/year

tons/year

1,265 tons/year 5,067 tons/year

6,157 tons/year 56,502 tons/year

maximum : 122 tons/year

maximum : 1281 tons/year maximum : 191 tons/year

New spatialization at 0.25° x 0.25° resolution (vs. normalized population densities, SEDAC 2005)

CONCLUSION   Large underestimates of fuel consumptions in West Africa within the global database.

  This work, focused on two-wheel emissions, shows the urgent need to integrate African specificities in BC and OCp emissions (both on fuel consumptions and emission factors).

  But, high uncertainties (cf. the min. and max. assumptions) => strong message to improve official data in each country.

  More generally, all traffic emissions need to be constantly updated not only two-wheel vehicles but also trucks, buses,… for motor gasoline and also for diesel.

  From this work we can stress a new emission «hot spot» along the coast of the Guinean Gulf and north of Nigeria this «hot spot» is expected to increase in future projections in case of no traffic regulation.