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Abstract: During the course of one year (March 2004–March 2005), PM2.5 particulate nitrate concentrations were semi-continuously measured every 10min at a Madrid suburban site using the Rupprecht and Patashnick Series 8400N Ambient Particulate Nitrate Monitor (8400N). Gaseous pollutants (NO, NO2, O3, HCHO, HNO2) were simultaneously measured with a DOAS spectrometer (OPSIS AR-500) and complementary meteorological information was obtained by a permanent tower. The particulate nitrate concentrations ranged from the instrumental detection limit of around 0.2μgm−3, up to a maximum of about 25μgm−3. The minimum monthly average was reached during August (0.32μgm−3) and the maximum during November (3.0μgm−3). Due to the semi-volatile nature of ammonium nitrate, peaks were hardly present during summer air pollution episodes. A typical pattern during days with low dispersive conditions was characterized by a steep rise of particulate nitrate in the morning, reaching maximum values between 9 and 14UTC, followed by a decrease during the evening. On some occasions a light increase was observed at nighttime. During spring episodes, brief diurnal nitrate peaks were recorded, while during the autumn and winter episodes, later and broader nitrate peaks were registered. Analysis of particulate nitrate and related gaseous species indicated the photo-chemical origin of the morning maxima, delayed with respect to NO and closely associated with secondary NO2 maximum values. The reverse evolution of nitrate and nitrous acid was observed after sunrise, suggesting a major contribution from HNO2 photolysis to OH formation at this time of the day, which would rapidly produce nitrate in both gaseous and particulate phase. Some nocturnal nitrate maxima appeared under high humidity conditions, and a discussion about their origin involving different possible mechanisms is presented, i.e. the possibility that these nocturnal maximum values could be related to the heterogeneous formation of nitrous and nitric acid by the hydrolysis of NO2 on wet aerosols. [Copyright &y& Elsevier]

Experimental vehicle idle emission factors have been compared with calculated factors for 100 vehicles in Madrid. The vehicles were selected according to the distribution (by age and fuel type) of the official, national car fleet (up to 31 December 1997). They were then clustered following the criteria of the Computer Programme to Calculate Emissions from Road Transport (COPERT III) category classification. NOxand CO idle emission factors show a wide range of values in each category and an important deviation between the experimental values and the corresponding parameterised ones. Fifteen percent of tested vehicles in this study have been identified as gross emitters generating approximately 50% of the total CO emission volume. [Copyright &y& Elsevier]

The results of a field study carried out in September-October 2000 near Madrid, regarding Quercus ilex and Pinus pinea monoterpene emission and its relation to ambient and physiological parameters, are presented in this paper. The major compounds in diurnal Q. ilex emission were limonene, α-pinene and β-pinene. Emission rates during warm days fitted reasonably well to the temperature and light-dependent model of Guenther (E[sub S] = 13.4 µg g[sup -1, DW] h[sup -1]). However, during hot days at mid-day and afternoon hours, dramatic decreases of monoterpene emission, photosynthetic activity and stomatal conductance were observed. The poor soil-water availability combined with low relative humidity and high temperature is likely to be responsible for the observed emission drop. A parameterisation of emission, based on ambient atmospheric water vapour pressure deficit (WVPD), has been attempted in this study. Monoterpene diurnal emission from P. pinea was lower than that of Mediterranean oak (E[sub S] = 1.5 µg g[sup -1, sub DW]h[sup -1]). A reduction in the total emission during the hottest hours of the day was not observed in this monoterpene storing species. Limonene emission rates, accounting on average for nearly half of the emission, were well described by the temperature-dependent model of Tingey. The rest of the emission was comprised of several compounds (cineole, myrcene, α-pinene, linalool) and was reduced at high WVPD values. [ABSTRACT FROM AUTHOR]

Abstract: A seasonal comparison of aerosol secondary inorganic component (SIC) patterns on annual, weekly and daily timescales has been performed at urban Madrid and London and at rural sites in the central Iberian Peninsula and south-eastern UK alongside data for precursor gases. A database from winter 2004 to summer 2011 has been analysed. Results show the dominant processes affecting the formation and evolution of nitrate () and sulphate in both regions. In Madrid, photochemistry dominates formation of nitrate, which is mostly locally-generated. Strong thermal decomposition results in very low concentrations in summer. In contrast, in London high nocturnal values suggest the importance of heterogeneous formation processes as well as nitrate condensation at lower temperatures. The seasonal nitrate maximum in the UK is found in late winter-early spring, when the region typically receives the highest input of pollutants transported from mainland Europe. Daily evolution of nitrate in both cities is heavily influenced by meteorological factors. Seasonal sulphate patterns show no obvious trend, except at the Spanish rural site in summer where photochemical formation was apparent. In Madrid, daily SO2 and sulphate patterns exhibiting maximum concentrations at noon were found in winter. In previous studies this phenomenon was observed for SO2 in London, where it was explained by the entrainment of pollutants from aloft into the mixing layer. SIC weekend reductions were investigated at the urban background sites of Madrid and London, and in both cities statistically significant fine nitrate reductions of around 20% are found in summer. These values are consistent with the annual reductions observed by researchers in the US. Weekend sulphate reductions occurred in winter, reflecting a clear impact of anthropogenic sulphate in urban environments, in spite of the large reductions in sulphur emissions in Europe in the last decade. Ratios of nitrate and sulphate to oxidant gases and to one another have been calculated for Madrid, and are consistent with a contribution of local formation to sulphate in winter, while in summer a regional background unrelated to urban SO2 is observed. The strong differences in the behaviour seen in London and Madrid (and the rural sites) emphasises the need to study cities individually and not to extrapolate conclusions drawn in one city to others in different climate/topographic situations. [Copyright &y& Elsevier]