Fluxes of urban pollution from the city of Naples (IT)
A super-site for the measurement of atmospheric pollutants from urban sources has been established in Naples where the complex layout of the coasts and surrounding mountains favours the development of combined sea breeze upslope winds and the evolution of return flows with several layers of pollutants and subsidence. The metropolitan area of Naples has one of the highest population densities in Europe with an important impact in terms of emissions associated with diesel/gasoline exhaust, industrial emissions, agricultural burning and waste disposal problem. In the super-site, located at the meteorological observatory of San Marcellino, an eddy covariance tower has been installed recently on the rooftop of the building: a fast response ultrasonic anemometer (Gill WindMaster) has been mounted on a 10-m mast, alongside three insulated inlet lines through which the air is sampled for reactive, non reactive gases and particulate. The height of the terrace is on average 35 m above the irregular street level, resulting in an overall measuring height of 45 m. Mixing ratios of CO2, CH4 and H2O are measured by an infrared spectrometer (10 Hz, Los Gatos Research); O3 mixing ratios are measured by a fast analyser (10Hz, FOS Sextant) for the calculation of fluxes, and referred to concentrations measured by a slower analyser (2B-Technologies, 205). NO and NOx are continuously quantified (1 Hz) using a NOx analyzer Eco Physics model (CLD 88p) associated with a photolytic converter (PLC 860). Size segregated aerosol are measured by gravimetric method at an hourly/daily frequency through a SWAM 5A Dual Channel (PM10 and PM2.5, FAI Instruments). A faster optical particle counter (4 Hz, FAI Instruments) allows the estimate of fluxes - as well as concentrations - of 22 classes of particles diameter. All analysers outputs are synchronised with the sonic anemometer through a common acquisition at 10 Hz using a CR3000 datalogger (Campbell Scientific). A full weather station is also available as ancillary measurements at the site including two webcams to record exceptional events to aid interpretation of the results. The fluxes are representative of varying footprint source areas, covering the historical centre of Naples, the harbour, and some main traffic arteries of the city. Preliminary results show that, during a stable event in the month of November, the mean urban levels of CO2 are between 420-520 ppm; the mean levels of CH4 span between 1.85-2.48 ppm, and the O3 levels are extremely variable, between 2 and 62 ppb. These follow NOx abundance, with values ranging between 0.5 and 84 ppb for NO, and 5 and 29 ppb for NO2, with an average NO2/NO ratio around 30%. Daily PM10 levels vary between 18 and 55 ?g/m3, and PM2.5 between 12 and 47 ?g/m3. The largest concentrations were measured from air coming from the harbour, coinciding with the presence of cruise ships. The year-long planned measurements will allow to establish relationships between the fluxes of greenhouse gases and the other pollutant species measured, to investigate the controls of the emission and provide relative emission factors for the urban sources.