We present results of statistical trajectory source analyses applied on ozone concentrations measured at high mountain peaks within and at the fringes of the Alps supported by Lagrangian photochemical box model calculations. These analyses yielded coherent pictures of transport processes causing elevated ozone concentrations in the Alps, and of the amount of ozone produced during transport over high-emission areas. Using measurement data, specific emission areas like the Po Basin, southern Germany, the “ Black Triangle “ region and some areas in eastern Europe were identified as important source regions, causing elevated ozone concentrations in the Alps. These statistics were supported by model calculations of transport and formation of ozone, giving similar results. Mesoscale transport processes and ozone formation in the boundary layer along the pathways were found to play an important role in determining Alpine ozone concentration levels. Ozone concentration tendencies along transport pathways were quantified climatologically using the box model. During the last 24 h of transport, concentration increases of 6-13 ppb, on the average, were found along 60-80% of all trajectories reaching the Alps, depending on the specific location. These estimates were confirmed by a measurement-based analysis of ozone formation during transport over the Po Basin, obtaining values of similar order of magnitude.

Within 2 years of trace gas measurements performed at Arosa (Switzerland, 2030 m above sea level), enhanced ozone mixing ratios were observed during south foehn events during summer and spring (5–10 ppb above the median value). The enhancements can be traced back to ozone produced in the strongly industrialized Po basin as confirmed by various analyses. Backward trajectories clearly show advection from this region during foehn. NOy versus O3 correlation and comparison of O3 mixing ratios between Arosa and Mt. Cimone (Italy, 2165 m asl) suggest that ozone is the result of recent photochemical production (+5.6 ppb on average), either directly formed during the transport or via mixing of air processed in the Po basin boundary layer. The absence of a correlation between air parcel residence times over Europe and ozone mixing ratios at Arosa during foehn events is in contrast to a previous analysis, which suggested such correlation without reference to the origin of the air. In the case of south foehn, the continental scale influence of pollutants emission on ozone at Arosa appears to be far less important than the direct influence of the Po basin emissions. In contrast, winter time displays a different situation, with mean ozone reductions of about 4 ppb for air parcels passing the Po basin, probably caused by mixing with ozone-poor air from the Po basin boundary layer.

In this work, we present the first systematic identification of episodes of air mass transport from the lower stratosphere/upper troposphere (LS/UT) in the middle troposphere of the southern Himalayas. For this purpose, we developed an algorithm to detect LS/UT transport events on a daily basis at the Everest-Pyramid GAW station (EV-PYR, 5079 m a.s.l., Nepal). In particular, in situ surface ozone and atmospheric pressure variations as well as total ozone values from OMI satellite measurements have been analysed. Further insight is gained from three-dimensional backward trajectories and potential vorticity calculated with the LAGRANTO model. According to the algorithm outputs, 9.0% of the considered data set (365 days from March 2006 to February 2007) was influenced by this class of phenomena with a maximum of frequency during dry and pre-monsoon seasons. During 25 days of LS/UT transport events for which any influence of anthropogenic pollution was excluded, the daily ozone mixing ratio increased by 9.3% compared to the seasonal values. This indicates that under favourable conditions, downward air mass transport from the LS/UT can play a considerable role in determining the concentrations of surface ozone in the southern Himalayas.

Its location in the Mediterranean region and its physical characteristics render Mt. Cimone (44°11' N, 10°42' E), the highest peak of the Italian northern Apennines (2165 m asl), particularly suitable to study the transport of air masses from the north African desert area to Europe. During these northward transports 12 dust events were registered in measurements of the aerosol concentration at the station during the period June–December 2000, allowing the study of the impact of mineral dust transports on free tropospheric ozone concentrations, which were also measured at Mt. Cimone. Three-dimensional backward trajectories were used to determine the air mass origin, while TOMS Aerosol Index data for the Mt. Cimone area were used to confirm the presence of absorbing aerosol over the measurement site. A trajectory statistical analysis allowed identifying the main source areas of ozone and aerosols. The analysis of these back trajectories showed that central Europe and north and central Italy are the major pollution source areas for ozone and fine aerosol, whereas the north African desert regions were the most important source areas for coarse aerosol and low ozone concentrations. During dust events, the Mt. Cimone mean volume concentration for coarse particles was 6.18 µm3/cm3 compared to 0.63 µm3/cm3 in dust-free conditions, while the ozone concentrations were 4% to 21% lower than the monthly mean background values. Our observations show that surface ozone concentrations were lower than the background values in air masses coming from north Africa, and when these air masses were also rich in coarse particles, the lowest ozone values were registered. Moreover, preliminary results on the possible impact of the dust events on PM10 and ozone values measured in Italian urban and rural areas showed that during the greater number of the considered dust events, significant PM10 increases and ozone decreases have occurred in the Po valley.

L’ozono superficiale viene misurato utilizzando un analizzatore Thermo TEI49i: esso utilizza il principio dell’assorbimento UV. Nell’ambito del network I-AMICA esso sarà tarato attraverso un calibratore secondario riferito alla scala internazionale GAW-WMO. Instrument (Thermo 49i) is connected by a Teflon pipe (OD: ¼”) to the air intake manifold. Antiparticulate filter (Teflon material) are present at the instrument inlet (changed every 30 days). Internal span source (ozonator) and external zero source (Purafill© filled cartridge) allow the daily execution of zero/span check. Instrument will be calibrated in-situ on a yearly basis against a travelling calibrator (Thermo 49iPS) hosted at the “twin” I-AMICA station of Lecce. This travelling calibrator will be compared against the standard reference SRP15 hosted at the GAW WCC at EMPA. Data are recorded on a 1-minute basis by a station server and delivered in NRT mode to ISAC-CNR HQs in Bologna for publication on the web (http://www.i-amica.it/i-amica/?page_id=868). Information about instrument functioning and intervention are stored within an e-logbook. Instrument manual are present at the station. SOP are extracted by the GAW Report No. 209 “Guidelines for Continuous Measurements of Ozone in the Troposphere”