Brake wear emissions with a special focus on particle number (PN) concentrations were investigated during a chassis dynamometer measurement campaign. A recently developed, well-characterized, ...measurement approach was applied to measure brake particles in a semi-closed vehicle setup. Implementation of multiple particle measurement devices allowed for simultaneous measurement of volatile and solid particles. Estimated PN emission factors for volatile and solid particles differed by up to three orders of magnitude with an estimated average solid particle emission factor of 3∙109 # km−1 brake−1 over a representative on-road brake cycle. Unrealistic high brake temperatures may occur and need to be ruled out by comparison with on-road temperature measurements. PN emissions are strongly temperature dependent and this may lead to its overestimation. A high variability for PN emissions was found when volatile particles were not removed. Volatiles were observed under high temperature conditions only which are not representative of normal driving conditions. The coefficient of variation for PN emissions was 1.3 without catalytic stripper and 0.11 with catalytic stripper. Investigation of non-braking sections confirmed that particles may be generated at the brake even if no brakes are applied. These “off-brake-event” emissions contribute up to about 30% to the total brake PM10 emission.
An autocatalytic mechanism for halogen release from sea-salt aerosol is proposed in which gaseous HOBr is scavenged by the aerosol and converted to only slightly soluble BrCl and Br2, which are ...released into the gas phase.
•Different driving styles were characterized by driving parameters, such as relative positive acceleration.•Driving dynamics were correlated with exhaust emissions measured by a PEMS.•An accurate ...road grade calculation method based on reference altitude data was applied.•The impact of road grade on NOx and CO2 emissions was investigated.
Motivated by the upcoming Euro-6c regulation including Real Driving Emissions (RDE), the present study addresses the impact of different driving styles and route characteristics on on-road exhaust emissions. Gaseous emissions of two Diesel test vehicles (Euro-5 and Euro-6) were measured using a Portable Emission Measurement System (PEMS) on an RDE compliant test route.
The driving parameters relative positive acceleration (RPA), mean positive acceleration (MPA) and v∗apos95 allowed a favorable classification of different driving styles. The comparison of driving parameters for normal PEMS trips with reference data obtained from the World harmonized Light-duty Test Cycle (WLTC) and from Field Operational Tests (FOT) indicated a good representation of normal driving. Severe driving led to elevated CO2 and NOx emissions as compared to normal trips while CO and HC did not allow a distinct classification of different driving styles.
Route characteristics of four different routes were investigated applying the parameter cumulated altitude gain using Google Elevation data. The distance specific NOx emissions were in the same range for trips with comparable driving dynamics on routes with similar cumulated altitude gain. Based on repetitive measurements the road grade was calculated within 100m segments. CO2 and NOx emissions measured by a PEMS showed a linear increase with road grade. Larger emissions at higher road grades could be explained by more frequent high engine load points. In this study cumulated altitude gain and road grade were directly correlated to emissions measured by the PEMS and the step from 0 to 5% road grade led to a CO2 increase of 65–81% and a NOx increase of 85–115%.
A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and ...Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O arrow right 2OH, HO2 + O3 arrow right OH + 2O2, and OH + O3 arrow right HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.PUBLICATION ABSTRACT
There has been some discussion in the literature on the generation of ultrafine particles from tire abrasion of studded and non-studded tires tested in the laboratory environment.
In the present ...study, the potential generation of ultrafine particles from the tire road interface was investigated during real driving. An instrumented Sport Utility Vehicle equipped with summer tires was used to measure particle concentrations with high temporal resolution inside the wheel housing while driving on a regular asphalt road. Different driving conditions, i.e., straight driving, acceleration, braking, and cornering were applied. For normal driving conditions no enhanced particle number concentration in the size range 6–562 nm was found. Unusual maneuvers associated with significant tire slip resulted in measurable particle concentrations. The maximum of the size distribution was between 30 and 60 nm. An exponential increase of the particle concentration with velocity was measured directly at the disc brakes for full stop brakings. A tracer gas experiment was carried out to estimate the upper limit of the emission factor during normal straight driving.
► New experimental setup to measure ultrafine particles from the tire road interface. ► Emission factor for steady straight driving estimated with a tracer gas experiment. ► Compared to exhaust emissions (DPF-car), the emission factor is of minor importance. ► Under normal driving conditions no enhanced particle generation was found. ► Under extreme driving conditions, ultrafine particles (30–80 nm) could be measured.
Brake wear emissions are investigated during on-road driving with a midsize passenger car on a closed test track. A novel sampling system is designed that aims at monitoring the entire aspiration of ...brake wear particles. The wear particles are collected by a cone-shaped sampler, which is attached at the outer side of the wheel rim. Thus, the air flow direction penetrating the brake assembly from the vehicle underbody to the vehicle outside is preserved. For analysis, the wear aerosol is routed to the trunk of the car. In addition to the emission measurements, the setup flow is monitored, which enables quantification of the acquired emission data. A 3 h subsection of the Los Angeles City Traffic (LACT) cycle, representative for realistic driving behavior, is used as test cycle. For two different brake materials, PM10 emission factors are ranging from 1.4 mg km−1 brake−1 to 2.1 mg km−1 brake−1, while one material is found to be 18% less emissive. Due to high brake disc temperatures exceeding 170 °C, high particle number emissions occur through ultrafine particle generation. The unrealistic temperatures are caused by the limited brake cooling in the semi-closed measurement setup. In contrast, the reference brake temperature does not exceed 153 °C during the same test, thus ultrafine brake particle emissions are not expected during normal driving. Furthermore, well run-in brake material shows emission factors near the lower measurement limit at the unrealistic temperatures, suggesting that ultrafine particle emissions are characteristic for brand-new materials in combination with high brake temperatures observed due to the semi-closed housing of the measurement setup.
•On-road driving investigation of brake wear particles in a semi-closed vehicle setup.•Known aspiration and setup flow enable quantification of emission data.•Robust setup design and repeatable tests allow material comparisons.
A novel measurement setup is designed, constructed, and validated by theoretical simulations and by experiments enabling sensitive and loss-free brake particle emission investigations. With the goal ...to simulate realistic driving, a 3 h subsection of the Los Angeles City Traffic (LACT) cycle is selected as test cycle. The tests are performed with the front brake of a midsize passenger vehicle under both static laboratory and more dynamic realistic conditions that include parasitic drag and vehicle brake temperatures (advanced vehicle simulations). A PM10 emission factor of around 4.6 mg km–1 brake–1 is determined. During five cycle runs the emission factor in terms of particle number decreases by 1 order of magnitude. This decrease is accompanied by a shift of the critical brake temperature T crit, at which ultrafine particle emissions occur, from 140 to 170 °C. Investigations with advanced vehicle simulations generate brake temperatures below T crit and consequently do not show ultrafine particle emissions above background level. A particle number emission factor of approximately 4.9 × 1010 km–1 brake–1 is estimated for realistic vehicle brake temperatures. Particle formation during cruising is clearly identified. The brake drag is estimated to contribute about 34% to the total airborne particle mass emission.
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