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IACETH
Institute for Atmospheric and Climate Science

Road traffic emissions in ff Switzerland: Results from the Results Gubrist tunnel
Institute for Atmospheric and Climate Science (IACETH), Swiss Federal Institute of Technology ZЭrich (ETHZ) UniversitДtstrasse 16 CH-8092 ZЭrich, Switzerland email: Johannes.Staehelin@env.ethz.ch

Johannes Staehelin


1. Introduction Introduction
· Road traffic important anthropogenic source of primary pollutants · Emission inventory description: Ei = EFi x A i Ac where: Ei: Amount of emission ss of compound i (e.g. CO) - EFi: Emission factor (e.g. CO emission by road traffic per 1 km) - Aci: Activity: road traffic


Overview
2. Road traffic emission models and Road emission tunnel measurements 3. Determination of EFs from road tunnel measurements 4. Measurements of the Gubrist tunnel Measurements of 5. Long-term evolution 6. Conclusions


2. Road traffic emission models and tunnel measurements
Road traffic emission model e.g. ,,Hand book of emission factors (HBEFA)": Required:- Large number of dynamometric test data (different technologies (e.g. with/without controlled catalysts), fuel (gasoline, diesel), engine size, etc.) - Typical conditions (e.g. high way driving) derived from extend. analysis of on-road measurements - Typical (Swiss) vehicle fleet composition including long-term changes


Time series of EF (HBEF)
Passenger Car Delivery Van Heavy Duty vehicle


Road tunnel measurements measurements
· Quantification of road traffic emissions · Comparison with road traffic emission models emission · Evaluation of new technologies, valuable measurements from the same tunnel (e.g. from the Tauerntunnel, Schmid et al., 2001) · Advantage: Large collective (,,real world emissions") · Limitation: Restricted condition (e.g. high way driving), difficulties for generalization


Approach for comparison in this study


3. Determination of EFs from road tunnel measurements
1. Calculate EFk,t of compound k of fleet passing the tunnel during given time interval t
EF
kt

=

C

k ,t

u t dq

nts

Where: Ck,t: difference in concentration of compound k (exit-entrance); ut: air velocity; d: duration of time interval; q: tunnel cross section; of interval; tunnel cross nt: number of vehicles; s: distance between measurements sites distance between


EF for vehicle classes vehicle classes
EFk,t = k + k pHDV +
k,t

Where: k: EF of light duty vehicles (LDV: passenger cars and delivery vans, mostly vans gasoline driven) k: EF of heavy duty vehicles (HDV, diesel (HDV engine); pHDV: proportion of HDV; k,t : random error random


Data analysis tunnel measurements (NOx)
10

8

EF derived from measurements linear regression

EF / g km h

-1

6

4

2

Linear Regression-Modell

EFi = + pHDVi +
0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

i

1.0

fraction HDV HDV

Gubristtunnel-Measurements 2002


Example of analysis of measurements of tunnel study (Staehelin et al., 1997): LDV emit more m-ethyltoluene whereas HDV emit more n-decane (triangles include all data, circles only those with vehicle speed >90 km/h and tunnel ventilation u >5.2 m/s


Statistical analysis
· EF for categories based on variability of fleet composition: · Heavy duty traffic forbidden in CH fro week ends (pHDV very small on weekends, but never exceeds 25%) · Determination of EF of HDV: Limited precision


4. Measurements Gubrist tunnel (close to ZЭrich, Switzerland)
Tunnel installation: Passively ventilated tunnel, sampling in one tube with two lanes (traffic in one direction, road gradient: 1.3 %) · Simultaneous measurements of NOx, CO and t-VOC (regulated) and others (VOCs) at entry and exit site · Traffic data from loop detectors (number and speed from loop of vehicles and classification in LDV and HDV · Wind speed measurements inside the tunnel inside the Det.: EF(time) of entire vehicle collective


(Earlier) tunnel studies and HBFA tunnel studies
NOx emissions of HDV: tunnel measurements larger than expected from road traffic emission model (HBEFA, vs. 1999): vs Plabutsch tunnel (Austria): 1998/99 (Sturm et al., 2001) Gubrist tunnel (Switzerland): tunnel 1993 (John et al., 1999)


Comparison of Gubrist tunnel EFs with HBEFA (1999), (John et al., 1999 - data from license plates) li


5. Long-term evolution
NOx LDV


Long-term development: NOx HDV


Long-term development: CO LDV


Long-term development: t-VOC LDV


VOC measurements from Gubrist tunnel (Legreid et al., 2007)


VOCs and OVOCs from tunnel studies
· Only limited data of organic species available from dynamometric tests · Large uncertainties of EF for different vehicle classes · EF of hydrocarbons strongly decreased over time for gasoline driven vehicles (introduction of catalytic converters and converters further improvements of vehicle technology)


6. Conclusions
- Tunnel measurements suitable for quantification of road traffic emissions - Advantage: "Real flight"/disadvantage: problem of generalization (no cold cold start) - Simple desgin of experiment (measurements at entry/exit site, fleet composition)


Conclusions cont.
- Pronounced disagreement for NOx HDV emissions with HBFA (1999) - Much better agreement tunnel measurements with HBEF (2004) - Suitable for EF of VOCs - Tunnel measurements at same site (Gubrist tunnel): Documentation of success of new vehicle technology