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In several previous studies emission of ozone (O3) during fireworks has been reported, which was attributed to either photolysis of molecular oxygen (O2) or nitrogen dioxide (NO2) by short/near UV radiation emitted during the high-temperature combustion of fireworks. In contrast, in the present study no O3 formation was observed using a selective O3-LOPAP instrument during the combustion of pyrotechnical material in the laboratory, while a standard O3 monitor using UV absorption showed extremely high O3 signals. The artificial O3 response of the standard O3 monitor was caused by known interferences associated with high levels of co-emitted VOCs and could also be confirmed in field measurements during New Year's Eve in the city of Wuppertal, Germany. The present results help to explain unreasonably high ozone levels documented during ambient fireworks, which are in contradiction to the fast titration of O3 by nitrogen monoxide (NO) in the night-time atmosphere.

SSCI-VIDE+CARE+ABO:YDU:CGO; International audience; Emission factors (EFs) of pollutants emitted by light-duty vehicles (LDV) were investigated in the Leopold II tunnel in Brussels city center (Belgium), in September 2011 and in January 2013, respectively. Two sampling sites were housing the instruments for the measurements of a large range of air pollutants, including non-methane volatile organic compounds (NMVOCs), nitrogen oxides (NOx) and carbon dioxide (CO2). The NMVOCs and NOx traffic EFs for LDV were determined from their correlation with CO2 using a single point analysis method.The emission factor of NOx is (544 ± 199) mg vehicle−1 km−1; NMVOCs emission factors vary from (0.26 ± 0.09) mg vehicle−1 km−1 for cis-but-2-ene to (8.11 ± 2.71) mg vehicle−1 km−1 for toluene. Good agreement is observed between the EFs determined in the Leopold II tunnel and the most recent EFs determined in another European roadway tunnel in 2004, with only a slight decrease of the EFs during the last decade. An historical perspective is provided and the observed trend in the NMVOCs emission factors reflect changes in the car fleet composition, the fuels and/or the engine technology that have occurred within the last three decades in Europe.

In the present study, problems of different methods used for quantifying the air remediation activity of photo-catalytic active surfaces are described. It is demonstrated that in bed photo-reactors (e.g. ISO), transport limitations can lead to underestimation of the activity, if fast heterogeneous reactions are investigated. In contrast, in stirred tank photo-reactors (e.g. UNI), complex secondary chemistry may lead to an overestimation of the photo-catalytic remediation of NOx, if NO2 is also present. In addition, the quantities, used for ranking the photo-catalytic air remediation activity in the different methods are not independent of the applied experimental conditions, and thus, make any intercomparison between the different methods or the extrapolation to atmospheric conditions very difficult. Furthermore, unrealistic high NOx levels are used, for which the chemical kinetics may already be affected by surface saturation problems. Finally, it is shown that the use of only nitrogen monoxide (NO) will not enable users to judge about the quality and effectiveness of a photo-catalytic surface for improving air quality, since surfaces which are active toward NO may be completely non-reactive toward other important atmospheric pollutants. A modified method for quantifying the air remediation activity of photo-catalytic surfaces is proposed here to overcome these problems.

A simple O 3 -LOPAP (Long Path Absorption Photometer) instrument for the selective detection of O 3 in the atmosphere is presented, which is mainly intended to be used as an extension of a recently developed NO 2 -LOPAP. O 3 is sampled in a stripping coil by a selective chemical reaction with the highly absorbing Indigo dye. The reduction of the optical absorption of the dye is detected in a liquid core waveguide. The instrument has a detection limit of 0.4 ppbv, an accuracy of 10%, a precision of 2% for 6 min time resolution and allows the absolute quantification of O 3 according to Lambert–Beer's law. Interferences towards nitrogen oxides (NO and NO 2 ), N 2 O 5 , H 2 O 2 and several VOCs were quantified in the laboratory and found to be negligible for atmospheric conditions. The new instrument was successfully validated against a commercial UV-absorption instrument during an urban field campaign and against the FTIR technique in a smog chamber under complex photosmog conditions. For the UV-absorption instrument significant positive interferences towards aromatic species were observed in the smog chamber.

An experimental campaign has been conducted in the frame of the European Commission funded network of excellence ECATS, at Athens International Airport (AIA), Greece, from 13 to 25 September 2007. In order to quantify the background air quality and study the influence of meteorological conditions and airport emissions to the broader region, the analysis was extended to the greater Messogia Plain of Attica, Greece. Mixing height was estimated taking into account measurements from remote sensing and surface based single point instrumentation. According to the analysis, the air quality over Messogia Plain is mainly controlled by the intensity and the direction of the background flow. Under low background wind conditions, the development of local flows (sea and land breeze cells) over the greater area preserves high concentrations of air pollutants which are mainly attributed to the airport emissions, the local activities and traffic. When the background flow is strong, the diurnal cycle of all concentrations was significantly reduced by more than 50%, due to the advection and the subsequent mixing of the lower atmosphere. In order to identify and quantify the various processes linked with meteorology and air quality, the Hilbert–Huang transform was selected to be applied on the air-quality time-series data. The calculated Hilbert spectra of the main pollutants showed that meteorology plays a prescriptive role on the evolution of air pollutants, determining the influence of the local scale characteristics at each station.

Gradients of HONO, NOx (NO + NO2) and O3 were measured during an early summer campaign on a high-rise building in downtown Santiago de Chile. Distinct gradients of decreasing concentrations with altitude were observed for HONO and NOx, while O3 concentrations were found to increase with altitude. From the observed daytime maximum of the HONO/NOx ratio the existence of a strong daytime source of HONO is proposed, thus confirming recent results from another measurement site in downtown Santiago, where a high contribution of HONO to the OH radical initiation sources of >50% was observed. Since the HONO/NOx ratio and its daytime maximum were found to be independent of the altitude, it is concluded that HONO is an important OH radical source in Santiago not only close to the ground surface, but also at higher altitudes of the boundary layer.

In the present study, photocatalytic reactions of nitrogen oxides (NOx = NO + NO2) were studied on commercial TiO2 doped facade paints in a flow tube photoreactor under simulated atmospheric conditions. Fast photocatalytic conversion of NO and NO2 was observed only for the photocatalytic paints and not for non-catalytic reference paints. Nitrous acid (HONO) was formed in the dark on all paints studied, however, it efficiently decomposes under irradiation only on the photocatalytic samples. Thus, it is concluded that photocatalytic paint surfaces do not represent a daytime source of HONO, in contrast to other recent studies on pure TiO2 surfaces. As main final product, the formation of adsorbed nitric acid/nitrate anion (HNO3/NO3−) was observed with near to unity yield. In addition, traces of H2O2 were observed in the gas phase only in the presence of O2. Formation of the greenhouse gas nitrous oxide (N2O) could be excluded. The uptake kinetics of NO, NO2 and HONO was very fast under atmospheric conditions (e.g. γ(NO + TiO2) > 10−5). Thus, the uptake on urban surfaces (painted houses, etc.) will be limited by transport. For a hypothetically painted street canyon, an average reduction of nitrogen oxide levels of ca. 5% is estimated. Since the harmful HNO3/NO3− is formed on the surface of the photoactive paints, whereas it is formed in the gas phase in the atmosphere, the use of photocatalytic paints may also help to reduce acid deposition, e.g. on plants, or nitric acid related health issues.

The city of Santiago, Chile experiences frequent high pollution episodes and as a consequence very high ozone concentrations, which are associated with health problems including increasing daily mortality and hospital admissions for respiratory illnesses. The development of ozone abatement strategies requires the determination of the potential of each pollutant to produce ozone, taking into account known mechanisms and chemical kinetics in addition to ambient atmospheric conditions. In this study, the photochemical formation of ozone during a summer campaign carried out from March 8–20, 2005 has been investigated using an urban photochemical box model based on the Master Chemical Mechanism (MCMv3.1). The MCM box model has been constrained with 10 min averages of simultaneous measurements of HONO, HCHO, CO, NO, j(O1D), j(NO2), 31 volatile organic compounds (VOCs) and meteorological parameters. The O3–NOx–VOC sensitivities have been determined by simulating ozone formation at different VOC and NOx concentrations. Ozone sensitivity analyses showed that photochemical ozone formation is VOC-limited under average summertime conditions in Santiago. The results of the model simulations have been compared with a set of potential empirical indicator relationships including H2O2/HNO3, HCHO/NOy and O3/NOz. The ozone forming potential of each measured VOC has been determined using the MCM box model. The impacts of the above study on possible summertime ozone control strategies in Santiago are discussed.

In order to quantify the contribution of solvent use and road traffic to the total non-methane volatile organic compound (NMVOC) emissions in Germany, the composition of air in the city of Wuppertal was investigated during three campaigns at different locations. The measurements covered NMVOCs in the range of C3–C10 hydrocarbons and C1–C6 oxygenated compounds. An assessment of the contribution from different emission sources to the observed NMVOC concentrations was attempted with the chemical mass balance (CMB) modelling technique. Emission profiles for traffic were obtained from measurements performed in a traffic tunnel, at a downtown street intersection and during drives through the city and on motorways. Solvent emission profiles were investigated in the vicinity of different factories and workshops using solvents in Wuppertal. Apportionment analyses were performed for several receptor points located down-wind from the city centre, in residential, dense traffic and industrial areas. The results of the present work show that traffic emission rather than solvent use determines the ambient NMVOC composition. The maximum contribution of solvent use to the NMVOC emission estimated on the basis of experimentally obtained results amounts to about 23% in the whole area of Wuppertal. It can be concluded that the contribution of solvent use to the NMVOC concentrations also in other German cities falls in the range of few to about 20%, assuming that Wuppertal can be considered as a typical German urban area with certain proportions of domestic, traffic and various industrial activities. These results are in strong disagreement with the German Emission Inventory, which states, that in the reference year 2003 about 51% of the total NMVOC emissions originate from solvent use and only 14% from traffic.

In May 2001, the large-scale field project BAB II was performed at the highly frequented motorway BAB (Bundesautobahn) A656 with two traffic lanes in each direction between the German cities Heidelberg and Mannheim. Extensive measurements of air pollutants were carried out on both sides of the motorway. In a distance of 60 m (north side) and 84 m (south side) to the traffic lanes, two 52-m-high towers were installed, at which electrically powered elevators were fixed. In these elevators, two NOx analysers, an Electrical Low Pressure Impactor (ELPI; measurement of the particle number size distribution in the diameter range D between 30 nm and 10 μm) and a Diffusion Charger (DC; measuring the particle surface area concentration), were operated to record continuous vertical profiles from 5 to 50 m above the earth's surface. On the upwind side, particle number and surface area concentration as well as NOx values were constant over the entire height profile. On the downwind side, increased concentrations appeared in the near-ground range: in the forenoon, a monotonous decrease in pollutant concentrations with increasing height was found, while around noon the concentration maximum of the particles was slightly shifted to 10 m above ground. This height dependence was found for two different size ranges, i.e., for particles with D 300 nm (consisting of soot particles and nucleation mode particles formed by condensation as a result of cooling of the exhaust gas after emission), and for coarse particles ( D > 1 μ m , abrasion and resuspension products). In the size range between 300 and 700 nm, no height dependence was found, corroborating the fact that motor traffic emits only few particles in this size range. On the downwind side of the motorway, only background concentrations were measured above 25 m. The results of the profile measurements were confirmed by stationary measurements of particle size distributions with Scanning Mobility Particle Sizers (SMPS) at various heights. A good correlation between particle surface area and NOx concentration was observed. Vehicle emission factors were determined for the particle surface area, number and volume of several size ranges.

Non-methane hydrocarbons (NMHC) were measured vertically resolved up-wind and down-wind of the motorway BAB A656 Heidelberg–Mannheim, Germany, for 4 weeks in April and May 2001. The horizontal distribution of C2–C9 aliphatic and aromatic hydrocarbons was monitored by using two compact quasi on-line gas chromatography (GC) instruments. The vertical distribution of NMHC was determined by using adsorption tubes, which were analysed off-line by GC in the laboratory. More than 50 NMHC were detected and 26 of them were quantified. From the measured data, the emission source strength for a variety of NMHC were calculated and discussed.

The quality of an emission calculation model based on emission factors measured on roller test stands and statistical traffic data was evaluated using source strengths and emission factors calculated from real-world exhaust gas concentration differences measured upwind and downwind of a motorway in southwest Germany. Gaseous and particulate emissions were taken into account. Detailed traffic census data were taken during the measurements. The results were compared with findings of similar studies. The main conclusion is the underestimation of CO and NO x source strengths by the model. On the average, it amounts to 23% in case of CO and 17% for NO x . The latter underestimation results from an undervaluation by 22% of NO x emission factors of heavy-duty vehicles (HDVs). There are significant differences between source strengths on working days and weekends because of the different traffic split between light-duty vehicles (LDVs) and HDVs. The mean emission factors of all vehicles from measurements are 1.08 g km −1 veh −1 for NO x and 2.62 g km −1 veh −1 for CO. The model calculations give 0.92 g km −1 veh −1 for NO x and 2.14 g km −1 veh −1 for CO. The source strengths of 21 non-methane hydrocarbon (NMHC) compounds quantified are underestimated by the model. The ratio between the measured and model-calculated emissions ranges from 1.3 to 2.1 for BTX and up to 21 for 16 other NMHCs. The reason for the differences is the insufficient knowledge of NMHC emissions of road traffic. Particulate matter emissions are dominated by ultra-fine particles in the 10–40 nm range. As far as aerosols larger than 29 nm are concerned, 1.80×10 14 particles km −1 veh −1 are determined for all vehicles, 1.22×10 14 particles km −1 veh −1 and an aerosol volume of 0.03 cm 3 km −1 veh −1 are measured for LDVs, and for HDVs 7.79×10 14 particles km −1 veh −1 and 0.41 cm 3 km −1 veh −1 are calculated. Traffic-induced turbulence has been identified to have a decisive influence on exhaust gas dispersion near the source.

The main objective of the field project BAB II (Bundesautobahn—Federal motorway) was to calculate the emissions of a motorway from ambient air measurements upwind and downwind of the lanes. The project was accompanied by a series of quality assurance measures, because all results have to be comparable to each other. Consequently, NO/NOx, CO, and VOC analysers participated in an inter-calibration with calibration gases. Subsequent results of ambient air measurements with all analysers for all measured components—NO/NOx, CO, O3, VOCs, elemental carbon (EC), and particulate matter (mass and number concentration)—were compared to each other. The quality assurance program had two main objectives: On the one hand, the data were harmonised after the detection of systematic deviations between the readings of the different analysers by applying individual correction equations or correction factors. On the other hand, the harmonised data were used for the determination of measurement uncertainty. In general, the measurement uncertainties determined were about 3–9%, except for VOCs and the particle number concentration. For all components, the upwind–downwind concentration differences in the actual experiment were much higher than the measurement uncertainties determined, thus bending confidence to the concentration differences being due to the traffic emissions rather than to measurement uncertainties.

Roadside measurements were performed in order to document the size distribution of particulate matter (PM) under dilution conditions similar to those found in real world. These activities covered measurements at engine test beds, at different locations in a road tunnel as well as in an urban environment. In order to get a clear picture of the evolution of the PM in different size classes, the in-tunnel locations ranged from curb-side to different locations inside the exhaust air system. Additional measurements were performed in the ambient air at curb-side at a street crossing as well as in urban background. At those times when heavy traffic occurs, tunnel measurements show size distributions similar to those derived from engine/vehicle measurements. During times with little traffic the size distributions are closer to those recorded in ambient air. As soon as the traffic load increases the size distribution changes, due to rapid coagulation of the smallest particles with the accumulation mode. As the travel time of the particles through the tunnel and up the stacks is very long “aging” effects could be observed. Thus, these spectra are quite different from ambient measurements in urban air, especially in the region above 30–40 nm.

Numerical simulations with a comprehensive mesoscale- γ model system were carried out to study the relative importance of individual sources for nitrous acid (HONO) on the daily cycle of the HONO concentration during the course of the day. The sources are the gas phase production, direct emissions of HONO, and heterogeneous reactions at aerosol surfaces and at the ground. The results of the simulations were compared to observations made during 18–19 October 2001 at the 200 m research tower at the Forschungszentrum Karlsruhe, Germany. We found that currently used chemical transport models are using a rate constant for the gas-phase reaction of NO with OH which is a factor of two lower than the recently published IUPAC data. The old rate constant gives 50% lower daytime HONO concentrations than the new one. The simulations showed that the direct emissions and the heterogeneous reactions at the ground are the most important sources of HONO during the night. While the observed nocturnal HONO concentrations close to the surface are reproduced by the simulations the daytime HONO concentrations are underestimated by 30–50%. We introduced an artificial photolytic HONO source which is proportional to the photolysis rate constant of NO 2 . This leads to a much better agreement between observed and simulated HONO concentrations during the day. In addition, we compared the production of the hydroxyl radical by the photolysis of HONO with its production via the photolysis of ozone. During 18 October 2001 when the ozone concentrations were low the photolysis of HONO is the dominant source of the OH radical while during a typical summer day the photolysis of HONO contributes only 20% of the photolysis of ozone.

Simultaneous nighttime HONO, NO, NO 2 and particle surface area density gradients in the altitude range 10–190 m were measured for the first time on the meteorological tower at the Forschungszentrum Karlsruhe/Germany using a new, very sensitive HONO instrument, a commercial NO x monitor and a SMPS system. For all gradient measurements during the campaign it was observed that the [HONO]/[NO 2 ] ratio decreased with increasing altitude below 100 m. In contrast, the particle surface area density was found to be more or less constant. Accordingly, no correlation between the [HONO]/[NO 2 ] ratio and the particle surface area density was observed showing that HONO formation was dominated by processes on ground surfaces and that significant HONO formation on particle surfaces could be excluded for the measurement site. Besides the nighttime gradient measurements, high daytime HONO concentrations were observed at constant altitude, which point to a significant and yet unknown daytime source of HONO. In addition, a HONO/NO x ratio from direct emissions of 0.8% was estimated from the field campaign.

Simultaneous measurements of nitrous acid (HONO) and nitrogen dioxide (NO2) using a differential optical absorption spectroscopy system, nitrogen oxide (NO) by an in situ chemiluminescence analyser and carbon dioxide (CO2) by a gas chromatographic technique were carried out in the Wuppertal Kiesbergtunnel. At high traffic density HONO concentrations of up to 45 ppbV were observed. However, at low traffic density unexpectedly high HONO concentrations of up to 10 ppbV were measured caused by heterogeneous HONO formation on the tunnel walls. In addition to the tunnel campaigns, emission measurements of HONO, NO2, NO and CO2 from different single vehicles (a truck, a diesel and a gasoline passenger car) were also performed. For the correction of the HONO emission data, the heterogeneous HONO formation on the tunnel walls was quantified by two different approaches (a) in different NO2 emission experiments in the tunnel without traffic and (b) on tunnel wall residue in the laboratory. The HONO concentration corrected for heterogeneous formation on the tunnel walls, in relation to the CO2 concentration can be used to estimate the amount of HONO, which is directly emitted from the vehicle fleet. From the measured data, emission ratios (e.g. HONO/NOx) and emission indices (e.g. mg HONO kg−1 fuel) were calculated. The calculated emission index of 88±18 mg HONO kg−1 fuel allows an estimation of the HONO emission rates from traffic into the atmosphere. Furthermore, the heterogeneous formation of HONO from NO2 on freshly emitted exhaust particles is discussed.