Abstract. During the DOMINO (Diel Oxidant MechanismIn relation to Nitrogen Oxides) campaign in southwest Spain we measured simultaneously all quantities necessary to calculate a photostationary state for HONO in the gas phase. These quantities comprise the concentrations of OH, NO, and HONO and the photolysis frequency of NO 2 , j (NO 2 ) as a proxy for j (HONO). This allowed us to calculate values of the unknown HONO daytime source. This unknown HONO source, normalized by NO 2 mixing ratios and expressed as a conversion frequency (% h −1 ), showed a clear dependence on j (NO 2 ) with values up to 43 % h −1 at noon. We compared our unknown HONO source with values calculated from the measured field data for two recently proposed processes, the light-induced NO 2 conversion on soot surfaces and the reaction of electronically excited NO 2 * with water vapour, with the result that these two reactions normally contributed less than 10 % (<1 % NO 2 + soot + hν; and <10 % NO 2 * + H 2 O) to our unknown HONO daytime source. OH production from HONO photolysis was found to be larger (by 20 %) than the "classical" OH formation from ozone photolysis (O( 1 D)) integrated over the day.Correspondence to: M. Sörgel

Abstract. Measurements of the ambient aerosol, various trace gases and meteorological quantities using a mobile laboratory (MoLa) were performed on the banks of the Lower Elbe in an emission control area (ECA) which is passed by numerous private and commercial marine vessels reaching and leaving the port of Hamburg, Germany. From 25–29 April 2011 a total of 178 vessels were probed at a distance of about 0.8–1.2 km with high temporal resolution. 139 ship emission plumes were of sufficient quality to be analyzed further and to determine emission factors (EFs). Concentrations of aerosol number and mass as well as polycyclic aromatic hydrocarbons (PAH) and black carbon were measured in PM1 and size distribution instruments covered the diameter range from 6 nm up to 32 μm. The chemical composition of the non-refractory submicron aerosol was measured by means of an Aerosol Mass Spectrometer (Aerodyne HR-ToF-AMS). Gas phase species analyzers monitored various trace gases (O3, SO2, NO, NO2, CO2) in the air and a weather station provided wind, precipitation, solar radiation data and other quantities. Together with ship information for each vessel obtained from Automatic Identification System (AIS) broadcasts a detailed characterization of the individual ship types and of features affecting gas and particulate emissions is provided. Particle number EFs (average 2.6e+16 # kg−1) and PM1 mass EFs (average 2.4 g kg−1) tend to increase with the fuel sulfur content. Observed PM1 composition of the vessel emissions was dominated by organic matter (72%), sulfate (22%) and black carbon (6%) while PAHs only account for 0.2% of the submicron aerosol mass. Measurements of gaseous components showed an increase of SO2 (average EF: 7.7 g kg−1) and NOx (average EF: 53 g kg−1) while O3 decreased when a ship plume reached the sampling site. The particle number size distributions of the vessels are generally characterized by a bimodal size distribution, with the nucleation mode in the 10–20 nm diameter range and a combustion aerosol mode centered at about 35 nm while particles \\textgreater 1 μm were not found. "High particle number emitters" are characterized by a dominant nucleation mode. By contrast, increased particle concentrations around 150 nm primarily occurred for "high black carbon emitters". Classifying the vessels according to their gross tonnage shows a decrease of the number, black carbon and PAH EFs while EFs of SO2, NO, NO2, NOx, AMS species (particulate organics, sulfate) and PM1 mass concentration increase with increasing gross tonnages.

Abstract. The Aerodyne aerosol mass spectrometer (AMS) is a frequently used instrument for on-line measurement of the ambient sub-micron aerosol composition. With the help of calibrations and a number of assumptions on the flash vaporization and electron impact ionization processes, this instrument provides robust quantitative information on various non-refractory ambient aerosol components. However, when measuring close to certain anthropogenic or marine sources of semi-refractory aerosols, several of these assumptions may not be met and measurement results might easily be incorrectly interpreted if not carefully analyzed for unique ions, isotope patterns, and potential slow vaporization associated with semi-refractory species.Here we discuss various aspects of the interaction of aerosol particles with the AMS tungsten vaporizer and the consequences for the measurement results: semi-refractory components -i.e., components that vaporize but do not flashvaporize at the vaporizer and ionizer temperatures, like metal halides (e.g., chlorides, bromides or iodides of Al, Ba, Cd, Cu, Fe, Hg, K, Na, Pb, Sr, Zn) -can be measured semiquantitatively despite their relatively slow vaporization from the vaporizer. Even though non-refractory components (e.g., NH 4 NO 3 or (NH 4 ) 2 SO 4 ) vaporize quickly, under certain conditions their differences in vaporization kinetics can result in undesired biases in ion collection efficiency in thresholded measurements. Chemical reactions with oxygen from the aerosol flow can have an influence on the mass spectra for certain components (e.g., organic species). Finally, chemical reactions of the aerosol with the vaporizer surface can result in additional signals in the mass spectra (e.g., WO 2 Cl 2 -related signals from particulate Cl) and in conditioning or contamination of the vaporizer, with potential memory effects influencing the mass spectra of subsequent measurements.Laboratory experiments that investigate these particlevaporizer interactions are presented and are discussed together with field results, showing that measurements of typical continental or urban aerosols are not significantly affected, while measurements of semi-refractory aerosol in the laboratory, close to anthropogenic sources or in marine environments, can be biased by these effects.

Abstract. In this study air masses are characterized in terms of their total OH reactivity which is a robust measure of the "reactive air pollutant loading". The measurements were performed during the DOMINO campaign (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) held from 21/11/2008 to 08/12/2008 at the Atmospheric Sounding Station -El Arenosillo (37.1 • N-6.7 • W, 40 m a.s.l.). The site was frequently impacted by marine air masses (arriving at the site from the southerly sector) and air masses from the cities of Huelva (located NW of the site), Seville and Madrid (located NNE of the site). OH reactivity values showed strong wind sector dependence. North eastern "continental" air masses were characterized by the highest OH reactivities (average: 31.4 ± 4.5 s −1 ; range of average diel values: 21.3-40.5 s −1 ), followed by north western "industrial" air masses (average: 13.8 ± 4.4 s −1 ; range of average diel values: 7-23.4 s −1 ) and marine air masses (average: 6.3 ± 6.6 s −1 ; range of average diel values: below detection limit −21.7 s −1 ), respectively. The average OH reactivity for the entire campaign period was ∼18 s −1 and no pronounced variation was discernible in the diel profiles with the exception of relatively high values from 09:00 to 11:00 UTC on occasions when air masses arrived from the north western and southern wind sectors. The measured OH reactivity was used to constrain both diel instantaneous ozone production potential rates and regimes. Gross ozone production rates at the site were generally limited by the availability of NO x with peak values of around 20 ppbV O 3 h −1 . Using the OH reactivity based approach, derived ozone production rates indicate that if NO x would no longer be the limiting factor in air masses arriving from the continental north eastern sector, peak ozone production rates could double. We suggest that the new combined approach of in-situ fast measurements of OH reactivity, nitrogen oxides and peroxy radicals for constraining instantaneous ozone production rates, could significantly improve analyses of upwind point sources and their impact on regional ozone levels.

During the DOMINO (Diel Oxidant Mechanism In relation to Nitrogen Oxides) campaign in southwest Spain we measured simultaneously all quantities necessary to calculate a photostationary state for HONO in the gas phase. These quantities comprise the concentrations of OH, NO, and HONO and the photolysis frequency of NO₂, j(NO₂) as a proxy for j(HONO). This allowed us to calculate values of the unknown HONO daytime source. This unknown HONO source, normalized by NO₂ mixing ratios and expressed as a conversion frequency (% h⁻¹), showed a clear dependence on j(NO₂) with values up to 43 % h⁻¹ at noon. We compared our unknown HONO source with values calculated from the measured field data for two recently proposed processes, the light-induced NO₂ conversion on soot surfaces and the reaction of electronically excited NO₂* with water vapour, with the result that these two reactions normally contributed less than 10 % (<1 % NO₂ + soot + hν; and <10 % NO₂* + H₂O) to our unknown HONO daytime source. OH production from HONO photolysis was found to be larger (by 20 %) than the "classical" OH formation from ozone photolysis (O(¹D)) integrated over the day