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Atmospheric Environment (v.40, #31)

Editorial board (pp. i).

13th International Symposium on Transport and Air Pollution by Sasha Madronich; John Orlando (pp. 5943-5943).

Real-world European driving cycles, for measuring pollutant emissions from high- and low-powered cars by Andre Michel André; Robert Joumard; Robert Vidon; Patrick Tassel; Pascal Perret (pp. 5944-5953).

Pollutant emissions from cars are usually measured on a test bench using driving cycles. However, the use of one unique set of driving cycles to test all cars can be seen as a weak point of emission estimation, as vehicles could conceivably be tested differently depending on their performance levels and usage characteristics. A specific study was then conducted to characterize driving conditions and vehicle usage as a function of vehicle categories, as well as to derive driving cycles specially designed for high- and low-powered cars which have significantly different driving conditions.Pollutant emissions were measured on a sample of 30 passenger cars, using on the one hand the three real-world ARTEMIS driving cycles (urban, rural road and motorway), representative of European driving, and on the other hand specific driving cycles. The comparison of the resulting aggregated emissions demonstrates that the usual test procedure (i.e. with a unique set of driving cycles) can lead to strong differences in emissions, particularly for the most recent vehicle categories.

Keywords: Test procedure; Driving cycle; Speed; Acceleration; Passenger cars

Emissions of unregulated pollutants from European gasoline and diesel passenger cars by Isabelle Caplain; Fabrice Cazier; Habiba Nouali; Agnès Mercier; Jean-Claude Déchaux; Valérie Nollet; Robert Joumard; Jean-Marc André; Robert Vidon (pp. 5954-5966).

Within the framework of the European Artemis project, the emissions of unregulated compounds were measured on new technology passenger cars. A sample of passenger cars was tested on a chassis dynamometer with constant volume sampling (CVS). The measurement of unregulated compounds comprised about 100 different volatile organic campounds (VOC) in the C₂–C₆ and C₇–C₁₅ range and carbonyl compounds. The sampling of these compounds was made using sorbent tubes followed by analysis with liquid and gas phase's chromatography. The influence of cold and warm starting conditions on the VOC composition was determined. The emission factors were determined and compared for both gasoline and diesel vehicles. The influence of the technology was evaluated and a first approach to understand the effect of recent technology on the ozone formation was developed.

Keywords: Voc; Carbonyl compounds; Speciated emissions; Driving cycle; Emission factors

The role of inspection and maintenance in controlling vehicular emissions in Kathmandu valley, Nepal by Asif Faiz; Bhakta Bahadur Ale; Ram Kumar Nagarkoti (pp. 5967-5975).

Motor vehicles are a major source of air pollutant emissions in Kathmandu valley, Nepal. In-use vehicle emission limits were first introduced in Nepal in 1998 and updated in 2000. The emission regulations for gasoline vehicles limit CO emissions to 3–4.5% by volume and HC emissions to 1000 ppm for four-wheeled vehicles, and 7800ppm for two- and three- wheelers. Emission limits for LPG/CNG vehicles are 3% for CO and 1000ppm for HC. For diesel vehicles, smoke density must not exceed 65–75 HSU depending on the age of the vehicle. The Government operates a rudimentary inspection and maintenance (I/M) program based on an idle engine test, utilizing an exhaust gas analyzer (for gasoline/LPG/CNG vehicles) and an opacimeter for diesel vehicles. The I/M program is confined to four-wheeled vehicles and occasional three-wheelers. The inspections are required at least once a year and are conducted at designated vehicle testing stations. The I/M program is supplemented by roadside checks. This paper is based on the findings of an analysis of vehicle emissions test data for the period June 2000 to July 2002, covering some 45,000 data sets. Each data set includes information on vehicle type and ownership, the model year, and CO/HC test emission values. The analysis reported in this paper covers the characteristics and statistical distribution of emissions from gasoline-fuelled vehicles, including the impact of gross emitters. The effects of vehicle age, model year (with or without catalysts), usage, and ownership (private vs. public) on emissions of gasoline-fuelled vehicles are discussed. The findings for diesel vehicles have been reported earlier by Ale and Nagarkoti (2003b. Evaluation of Kathmandu valley inspection and maintenance program on diesel vehicles. Journal of the Institute of Engineering 3(1)). This study identifies the limitations of the current I/M program, given that it does not include 70% of the fleet consisting of two-wheelers and concludes with proposed changes to the I/M program to make it more effective.

Keywords: Emission standards; Kathmandu valley I/M program; Roadside checks; Effectiveness

A case study of the impact of Winter road sand/salt and street sweeping on road dust re-entrainment by Alan Gertler; Hampden Kuhns; Mahmoud Abu-Allaban; Christopher Damm; John Gillies; Vicken Etyemezian; Russ Clayton; David Proffitt (pp. 5976-5985).

Resuspended road dust is an important contributor to ambient particulate matter (PM). In areas with significant snow events, the use of wintertime roadway abrasives for traction control can result in increased PM emissions. An alternative control measure is to use chemical deicers prior to a snow event to minimize ice formation and reduce the need for abrasives. Street sweeping is also commonly used to reduce the impact of re-entrained abrasive material after the snow pack on the road has cleared. In this study, we performed roadside measurements of PM flux and instrumented vehicle PM measurements to evaluate the effectiveness of street sweeping to reduce dust re-entrainment and assess the impact of abrasives and deicers on ambient PM near an alpine lake (Lake Tahoe). The results indicate use of liquid deicers contributes less to road dust emissions than abrasives. Street sweeping was found to increase the PM₁₀ re-entrainment rate of the remaining road dust. Emission factors for roads in the study area (a snowy mountain climate) tend to decrease significantly from late Spring to early Summer by as much as a factor of 4.

Keywords: Resuspended road dust; On-road emissions; PM; ₁₀; PM; _2.5; Emission factors

Three-way catalyst-induced formation of ammonia—velocity- and acceleration-dependent emission factors by Norbert V. Heeb; A.-M. Anna-Maria Forss; Bruhlmann Stefan Brühlmann; Luscher Roland Lüscher; Christian J. Saxer; Paul Hug (pp. 5986-5997).

Ammonia (NH₃) is classified as a toxic air pollutant but its release from vehicles is not regulated. Herein we report on the efficiency of the catalytic reduction of nitrogen monoxide (NO) and the selectivity towards NH₃. Chemical ionization mass spectrometry (CIMS) has been applied to monitor NH₃ and NO emissions at a time resolution of 2s. At real world driving, intense, catalyst-induced NH₃ formation was detected for a gasoline-fueled passenger car equipped with a Pd/Rh-based three-way-catalyst (TWC). Post-catalyst NH₃ emissions strongly depend on velocity and acceleration and varied by two orders of magnitude from 1 to 170mgkm⁻¹. For most vehicle conditions, tail-pipe NH₃ emissions exceeded those of NO. Excellent NO conversion above 95% was noticed as soon as catalyst light-off occurred. Post-catalyst NO emissions were lowest when NH₃ formation was most intense and vice versa. This complementary behavior indicates that a TWC can be operated in a way that either NH₃ or NO emissions dominate. The NH₃/NO mixing ratio was mainly influenced by the air-to-fuel ratio. At fuel-rich combustion ( λ<1), highest NH₃/NO mixing ratios clearly above one were observed, whereas ratios at or below one were found at lean conditions (λ>1). Catalyst temperature effected the selectivity of the DeNOx process. Highest NH₃ selectivity up to 0.45 was found when operating the catalyst below 280°C. Above this temperature, the selectivity was reduced to 0.02–0.05. The obtained results highlight those parameters, influencing the NH₃ output of a TWC vehicle at real world driving.

Keywords: Vehicle emissions; Conversion efficiency; Secondary pollutant; Time-resolved exhaust gas analysis; Chemical ionization mass spectrometry (CIMS)

The role of traffic emissions from weekends’ and weekdays’ fine PM data in Milan by G. Lonati; M. Giugliano; S. Cernuschi (pp. 5998-6011).

A receptor-oriented and a source-oriented approach are applied to assess the contribution of traffic emissions to concentration levels of fine particulate matter in Milan (Italy). Both the approaches are based on the comparison between seasonal weekends’ and weekdays’ data. Relative differences observed between Sundays’ and weekdays’ PM10 concentrations are analysed in terms of their probability distributions for the cold and warm season separately. As a consequence of the reduced circulating traffic flows, Sundays’ concentration levels are on average about 20% lower, but an increase of concentration levels is sometimes observed under unfavourable meteorological conditions. The effect of the reduced traffic on Sundays is assessed also in terms of particles’ number concentration. The results obtained by the analysis of weekly PM10 concentration data are compared to information derived from the emission inventory for traffic. From observed reduction of Sundays’ traffic flow, the corresponding expected variation in primary PM10 emissions from traffic is calculated accounting for both exhaust and non-exhaust contribution. Seasonal probability distribution of PM10 emission variations are obtained by implementing the COPERT III methodology in a Monte Carlo simulation: on Sundays estimated values of PM10 emissions always result lower than on weekdays and on average about 50% less. Based on estimated reductions for PM10 traffic emission and on observed reductions for PM10 ambient air concentrations, traffic emissions appear responsible for about 50% of the PM10 concentration levels in the urban area. This contribution is both due to exhaust and non-exhaust emissions: depending on site exposure to the traffic source, out of the 50% contribution of total traffic emissions to PM10 concentrations, a 4–40% share is estimated to come directly from the exhaust, whereas the remaining share derives from non-exhaust emissions and resuspension of soil dust.

Keywords: Airborne fine particles; Weekend effect; PM traffic emissions; Particle number concentration.

Chemical evolution of gaseous air pollutants down-wind of tropical megacities: Mexico City case study by Sasha Madronich (pp. 6012-6018).

The photochemical evolution of a polluted air parcel originating in a tropical megacity was modeled for 3 days using a box model with detailed gas-phase chemistry. The parcel was initialized with concentrations typically observed in Mexico City for nitrogen oxides (80parts per billion on a molar basis, or ppbv), carbon monoxide (3000ppbv), non-methane hydrocarbons (1700ppb on a carbon basis, or ppbC) and formaldehyde (23.9ppbv). Vigorous ozone production occurred during day 1, followed by gradual net destruction during the next 2 days. Other major inorganic products were nitric acid and hydrogen peroxide (35 and 16ppbv, respectively at the end of day 3), while organic products included ketones (83ppbv), organic hydroperoxides (25ppbv), peroxyacyl nitrates (28ppbv), aldehydes (18ppbv), organic acids (16ppbv), alkyl nitrates (10ppbv) and alcohols (0.2ppbv). Also produced was multitude of different polyfunctional compounds, present individually at small concentrations, but with significant summed concentrations (68, 49 and 1.5ppbC, respectively, for compounds having 2, 3 or 4 functional groups), which could contribute to the formation of secondary aerosols. The overall reactivity of the parcel (daytime concentrations of hydroxy, hydroperoxy and organic peroxy radicals; and cumulative hydroxyl radical loss rates) remained relatively constant and high on days 2 and 3. This persistent gas-phase reactivity suggests that urban areas could affect regional and global tropospheric chemistry. However, it remains unclear whether heterogeneous losses, on aerosol particles, reduce this reactivity while simultaneously changing aerosol chemical, microphysical and radiative properties relevant to weather and climate.

Keywords: Hydrocarbon oxidation; Reactivity; Regional pollution; Mexico City

Satellite observations of aerosol and CO over Mexico City by Steven T. Massie; John C. Gille; David P. Edwards; Sreela Nandi (pp. 6019-6031).

The development of remote sensing satellite technology potentially will lead to the technical means to monitor air pollution emitted from large cities on a global basis. This paper presents observations by the moderate resolution imaging spectroradiometer (MODIS) and measurements of pollution in the troposphere (MOPITT) experiments of aerosol optical depths and CO mixing ratios, respectively, in the vicinity of Mexico City to illustrate current satellite capabilities. MOPITT CO mixing ratios over Mexico City, averaged between January–March 2002–2005, are 19% above regional values and the CO plume extends over 10°² in the free troposphere at 500hPa. Time series of Red Automatica de Monitoreo Ambiental (RAMA) PM10, and (Aerosol Robotic Network) AERONET and MODIS aerosol optical depths, and RAMA and MOPITT CO time series are inter-compared to illustrate the different perspectives of ground based and satellite instrumentation. Finally, we demonstrate, by examining MODIS and MOPITT data in April 2003, that satellite data can be used to identify episodes in which pollution form fires influences the time series of ground based and satellite observations of urban pollution.

Keywords: Mexico City; Satellite; Pollution; Monitoring

Combination of aerosol instrument data into reduced variables to study the consistency of vehicle exhaust particle measurements by Leonidas Ntziachristos; Zissis Samaras (pp. 6032-6042).

Several aerosol instruments are generally used to study the concentration and characteristics of exhaust particle emissions. These are based on different operational principles and usually record a different particle property. As a result, the definition of an absolute emission level is ambiguous and the consistency, i.e. the uniformity and response of the measurements to the input variables, becomes the main quality issue. Here we present four reduced variables, which are derived from the primary information provided by a condensation particle counter, a diffusion charger, an electrical low-pressure impactor and the gravimetric filter-based particulate matter measurement. The variables correspond to a total vs. solid particle number concentration, a mean diameter, an apparent density and a mass-specific surface. The variables were first compared on a relative scale, in order to examine the uniformity of the underlying measurements. Then they were compared on an absolute scale with particle properties found in the literature to confirm the validity of the measurement level of each instrument. Based on the values of the variables, it is verified that different aerosol instruments and methods may produce consistent measurements when attention is given to the sampling protocol and conditions. However, measurement particularities intrinsic to some methods, such as the adsorption of gaseous species on the gravimetric filter and the assumption of unit density for the calculation of the number concentration by the electrical low-pressure impactor, may lead to deviations from this general rule. Overall, our comparisons demonstrated that such reduced variables may serve both as a means to recognise abnormal measurement occasions and to discriminate the effects of fuel, driving condition and vehicle technology on particle emissions.

Keywords: Diesel aerosol; Particle properties; Density; Surface concentration

Simulation of traffic induced No _x-concentrations near the A 12 highway in Austria by D. Oettl; S. Hausberger; M. Rexeis; P.J. Sturm (pp. 6043-6052).

The A12 and A13 highways in Tyrol link the regions of Munich and Milan. Both regions possess a strong economy and the highways carry about 60% of the total transit heavy goods traffic in Austria. In recent year's, national as well as EU air quality limits for NO₂ have been exceeded at a monitoring site close to the A12 autobahn. In order to assess the pollution levels of NO₂ close to the highway, state-of-the-art methodologies for emission- and dispersion modeling were applied in the area. Emissions were calculated utilizing the Passenger cars and heavy duty vehicle emission model (PHEM). Recorded driving cycles for the A12 served as input to the emission model. Air quality was assessed applying Graz lagrangian model (GRAL). Both, GRAL and PHEM have been developed at the Institute for Internal Combustion Engines and Thermodynamics over several years, and have been validated for that purpose. Results show that heavy duty vehicles contribute to about 60% of the total No _x-emissions on the A12 highway. Modeled average No _x-concentrations were found to be in good agreement with observations at four sites near the A12. In addition, the effects of a night-time driving ban for vehicles >7.5t are discussed.

Keywords: PHEM; GRAL; Lagrangian dispersion model; Emission model; Air quality; Highway

Benzene, toluene and C₂-benzene emissions of 4-stroke motorbikes: Benefits and risks of the current TWC technology by Christian J. Saxer; A.-M. Anna-Maria Forss; Rudy Claudio Rüdy; Norbert V. Heeb (pp. 6053-6065).

Chemical ionization mass spectrometry has been applied to determine benzene, toluene and C₂-benzene emission rates of 4-stroke motorbikes. Extra emissions and duration of the cold start were deduced from the legislative urban driving cycle. The Common Artemis driving cycle was investigated to study the emission characteristics at transient driving from 0 to 135kmh⁻¹. In addition, the benefits and risks of the currently available 3-way catalyst technology (TWC) are explored. Benzene, toluene and C₂-benzene cold start emissions of 230–290, 920–980 and 950–1270mgstart⁻¹ were obtained for the TWC motorbikes, exceeding those without catalyst by more than a factor of 3. At hot engine/catalyst, benzene, toluene and C₂-benzene emission factors in the range of 10–140, 10–160 and 10–170mgkm⁻¹ were found for the TWC motorbikes. Without catalyst, the corresponding emission factors were higher, varying from 40 to 260, 100 to 500 and 110 to 480mgkm⁻¹, respectively. A comparison with the latest passenger car technology, with reported aromatic hydrocarbon (HC) emission factors of 0.2–3.0mgkm⁻¹, revealed that the investigated 4-stroke motorbikes, indeed, are an important source of air pollution. Furthermore, cold start duration, driving distance under cold start influence and velocity dependence of aromatic HC emissions were deduced from time-resolved data. In addition, variations of aromatic HC mixing ratios were studied. Narrow and unimodal distributions of, e.g. benzene/C₂-benzene mixing ratios with median values of 0.46–0.73 were found for all motorbikes but one. This motorcycle, equipped with a TWC, showed a broad and bimodal distribution with a median mixing ratio of 1.47. Catalyst-induced formation of benzene from alkylbenzenes is the assumed process, leading to increased benzene/alkylbenzene mixing ratios.

Keywords: Motorcycle emissions; Time-resolved exhaust gas analysis; Chemical ionization mass spectrometry; Cold start emissions; Transient driving

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Atmospheric Environment (v.40, #31)