Effects of various meteorological conditions and spatial emissionresolutions on the ozone concentration and ROG/NO_x limitationin the Milan area (I)

The three-dimensional photochemical model UAM-V is used to investigate the effects of various meteorological conditions and of the coarseness of emission inventories on the ozone concentration and ROG/NO_x limitation of the ozone production in the Po Basin in the northern part of Italy. As a base case, the high ozone episode with up to 200ppb on 13 May 1998 was modelled and previously thoroughly evaluated with measurements gained during a large field experiment. Systematic variations in meteorology are applied to mixing height, air temperature, specific humidity and wind speed. Three coarser emission inventories are obtained by resampling from 3x3km² up to 54x54km² emission grids. The model results show that changes in meteorological input files strongly influence ozone in this area. For instance, temperature changes peak ozone by 10.1ppb/&degC and the ozone concentrations in Milan by 2.8ppb/&degC. The net ozone formation in northern Italy is more strongly temperature than humidity dependent, while the humidity is very important for the ROG/NO_x limitation of the ozone production. For all meteorological changes (e.g. doubling the mixing height), the modelled peak ozone remains ROG limited. A strong change towards NO_x sensitivity in the ROG limited areas is only found if much coarser emission inventories were applied. Increasing ROG limited areas with increasing wind speed are found, because the ROG limited ozone chemistry induced by point sources is spread over a larger area. Simulations without point sources tend to increase the NO_x limited areas

Flux measurements of biogenic VOCs during ECHO 2003

International audienceWithin the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany using the eddy covariance (EC) technique. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. As a consequence, a considerable fraction of the measurements did not qualify for flux calculations by EC and had to be discarded. The validated results show light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average emissions (normalised to 30°C and 1000 µmoles m?2 s?1 PAR) of 1.5 and 0.39 µg m?2 s?1, respectively. Emissions of methanol reached on average 0.087 µg m?2 s?1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. The observed fluxes are consistent with upscalings from leaf-level emission measurements of representative tree species in this forest and, in the case of MVK and MACR, can plausibly be explained by chemical production through oxidation of isoprene within the canopy. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement

Volatile Organic Compounds in the Po Basin. Part A: Anthropogenic VOCs

Measurements of volatile organic compounds (VOCs) were performed in the Po Basin, northern Italy in early summer 1998 within the PIPAPO project as well as in summer 2002 and autumn 2003 within the FORMAT project. During the three campaigns, trace gases and meteorological parameters were measured at a semi-rural station, around 35 km north of the city center of Milan. Low toluene and benzene concentrations and lower toluene to benzene ratios on weekends, on Sundays, and in August enabled the identification of a ‘weekend' and a ‘vacation' effect when anthropogenic emissions were lower due to less traffic and reduced industrial activities, respectively. Recurrent nighttime cyclohexane peaks suggested a periodical short-term release of cyclohexane close to the semi-rural sampling site. A multivariate receptor model analysis resulted in the distinction of different characteristic concentration profiles attributed to natural gas, biogenic impact, vehicle exhaust, industrial activities, and a single cyclohexane sourc

Introduction

What are the strategies, modalities and aspirations of island-based, stateless nationalist and regionalist parties in the twenty-first century? Political independence is now easier to achieve, even by the smallest of territories; yet, it is not so likely to be pursued with any vigour by the world's various persisting sub-national (and mainly island) jurisdictions. Theirs is a pursuit of different expressions of sub-national autonomy, stopping short of independence. And yet, a number of independence referenda are scheduled, including one looming in Scotland in autumn 2014

The influence of traffic and wood combustion on the stable isotopic composition of carbon monoxide

Carbon monoxide in the atmosphere is originating from various combustion and oxidation processes. Recently, the proportion of CO resulting from the combustion of wood for domestic heating may have increased due to political measures promoting this renewable energy source. Here, we used the stable isotope composition of CO (δ<sup>13</sup>C and δ<sup>18</sup>O) for the characterization of different CO sources in Switzerland, along with other indicators for traffic and wood combustion (NO<sub>x</sub>-concentration, aerosol light absorption at different wavelengths). We assessed diurnal variations of the isotopic composition of CO at 3 sites during winter: a village site dominated by domestic heating, a site close to a motorway and a rural site. The isotope ratios of wood combustion emissions were studied at a test facility, indicating significantly lower δ<sup>18</sup>O of CO from wood combustion compared to traffic emissions. At the village and the motorway site, we observed very pronounced diurnal δ<sup>18</sup>O-variations of CO with an amplitude of up to 8‰. Solving the isotope mass balance equation for three distinct sources (wood combustion, traffic, clean background air) resulted in diurnal patterns consistent with other indicators for wood burning and traffic. The average night-time contribution of wood-burning to total CO was 70% at the village site, 49% at the motorway site and 29% at the rural site based on the isotope mass balance. The results, however, depend strongly on the pure source isotope values, which are not very well known. We therefore additionally applied a combined CO/NO<sub>x</sub>-isotope model for verification. Here, we separated the CO emissions into different sources based on distinct CO/NO<sub>x</sub> emissions ratios for wood combustion and traffic, and inserted this information in the isotope mass balance equation. Accordingly, a highly significant agreement between measured and calculated δ<sup>18</sup>O-values of CO was found (<i>r</i>=0.67, <i>p</i><0.001). While different proxies for wood combustion all have their uncertainties, our results indicate that the oxygen isotope ratio of CO (but not the carbon isotope ratio) is an independent sensitive tool for source attribution studies

Volatile Organic Compounds in the Po Basin. Part B: Biogenic VOCs

Measurements of volatile organic compounds (VOCs) were performed in the Po Basin, northern Italy in early summer 1998, summer 2002, and autumn 2003. During the three campaigns, trace gases and meteorological parameters were measured at a semi-rural station, around 35 km north of the city center of Milan. Bimodal diurnal cycles of isoprene with highest concentrations in the morning and evening were found and could be explained by the interaction of emissions, chemical reactions, and vertical mixing. The diurnal cycle could be qualitatively reproduced by a three-dimensional Eulerian model. The nighttime decay of isoprene could be attributed mostly to reactions with NO3, while the decay of the isoprene oxidation products could not be explained with the considered chemical reactions. Methanol reached very high mixing ratios, up to 150 ppb. High concentrations with considerable variability occurred during nights with high relative humidities and low wind speeds. The origin of these nighttime methanol concentrations is most likely local and biogenic but the specific source could not be identifie

Dimethylamine and ammonia measurements with ion chromatography during the CLOUD4 campaign

The CLOUD project investigates the influence of galactic cosmic rays on the nucleation of new particles in an environmental chamber at CERN. Dimethylamine (DMA) was injected intentionally into the CLOUD chamber to reach atmospherically relevant levels away from sources (up to 100 pptv) in order to study its effect on nucleation with sulphuric acid and water at 278 K. Quantification of DMA and also background ammonia (NH<sub>3</sub>) was performed with ion chromatography (IC). The IC method used together with the sampling line developed for CLOUD in order to measure NH<sub>3</sub> and DMA at low pptv levels is described; the overall sampling efficiency of the method is discussed; and, finally, mixing ratios of NH<sub>3</sub> and DMA measured during CLOUD4 are reported

Investigations of primary and secondary particulate matter of different wood combustion appliances with a high-resolution time-of-flight aerosol mass spectrometer

A series of photo-oxidation smog chamber experiments were performed to investigate the primary emissions and secondary aerosol formation from two different log wood burners and a residential pellet burner under different burning conditions: starting and flaming phase. Emissions were sampled from the chimney and injected into the smog chamber leading to primary organic aerosol (POA) concentrations comparable to ambient levels. The composition of the aerosol was measured by an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and black carbon (BC) instrumentation. The primary emissions were then exposed to xenon light to initiate photo-chemistry and subsequent secondary organic aerosol (SOA) production. After correcting for wall losses, the average increase in organic matter (OM) concentrations by SOA formation for the starting and flaming phase experiments with the two log wood burners was found to be a factor of 4.1±1.4 after five hours of aging. No SOA formation was observed for the stable burning phase of the pellet burner. The startup emissions of the pellet burner showed an increase in OM concentration by a factor of 3.3. Including the measured SOA formation potential, average emission factors of BC+POA+SOA, calculated from CO<sub>2</sub> emission, were found to be in the range of 0.04 to 3.9 g/kg wood for the stable burning pellet burner and an old log wood burner during startup respectively. SOA contributed significantly to the ion C<sub>2</sub>H<sub>4</sub>O<sub>2</sub><sup>+</sup> at mass to charge ratio <i>m/z</i> 60, a commonly used marker for primary emissions of wood burning. This contribution at <i>m/z</i> 60 can overcompensate for the degradation of levoglucosan leading to an overestimation of the contribution of wood burning or biomass burning to the total OM. The primary organic emissions from the three different burners showed a wide range in O:C atomic ratio (0.19−0.60) for the starting and flaming conditions, which also increased during aging. Primary wood burning emissions have a rather low relative contribution at <i>m/z</i> 43 (<i>f</i> 43) to the total organic mass spectrum. The non-oxidized fragment C<sub>3</sub>H<sub>7</sub><sup>+</sup> has a considerable contribution at <i>m/z</i> 43 for the fresh OA with an increasing contribution of the oxygenated ion C<sub>2</sub>H<sub>3</sub>O<sup>+</sup> during aging. After five hours of aging, the OA has a rather low C<sub>2</sub>H<sub>3</sub>O<sup>+</sup> signal for a given CO<sub>2</sub><sup>+</sup> fraction, possibly indicating a higher ratio of acid to non-acid oxygenated compounds in wood burning OA compared to other oxygenated organic aerosol (OOA)

The formation, properties and impact of secondary organic aerosol: current and emerging issues

Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed