The first four sites are regional stations of the Global Atmosphere Watch program (GAW-WMO). Each site, with different characteristics, was classified on the basis of distance from pollution sources:  Naples urban site, Lecce suburban, Lamezia Terme and Capo Granitola coastal/marine sites and Monte Curcio remote location. PM₁₀ and PM_2.5 measurements were performed using the β-ray attenuation method, with a low volume samplers (2.3 m³/h) with two channels for automatic sampling and monitoring (SWAM 5a Dual Channel Monitor-FAI Instruments). The particulate matter was collected on quartz microfiber filters (Whatman Q-grade, diameter 47 mm), pre-fired for 2 h at 700°C in order to remove any residual carbon contamination. The analysis of Total Carbon TC = OC + EC (OC organic carbon and EC elemental carbon) was performed by the thermo-optical method (TOT) using a Sunset Laboratory OC/EC analyser (Sunset Laboratory, Tigard, OR, USA), implementing the EUSAARII temperature protocol.

Fig. 3.1) Map of Southern Italy with the observation sites

 The higher PM₁₀ and PM_2.5 mass concentration values were observed in the urban site of Naples (50.8 ± 21.7 and 37.8 ± 18.0 μg/m³), followed by Lecce (32.7 ± 13.0 and 25.7 ± 11.6 μg/m³), Capo Granitola (23.2± 8.6 and 10.4 ± 2.6 μg/m³), Lamezia Terme (10.1 ± 3.8 and 7.2 ± 3.5 μg/m³)  and Monte Curcio (3.4 ± 1.4 and 3.0 ±1.2 μg/m³). The PM_2.5/PM₁₀ average ratios ranged between 0.68 and 0.82 and show that more than 68% of the PM₁₀ is in the form of PM_2.5. Moreover, PM₁₀ and PM_2.5 concentrations were well correlated at sites of Lecce (R² = 0.98), Naples (R² = 0.95) and Lamezia Terme (R² = 0.88) indicating that the two fractions are driven by similar sources and controlled by common processes. A slightly lower correlation (R² = 0.77) was found at the Monte Curcio site with a PM_2.5/PM₁₀ average ratio of 0.82 that shows the predominant contribution of the fine fraction likely due to long-range transport.

The results of TC, OC and EC mass concentrations are summarized in Tables 3.1 and 3.2. The average OC mass concentrations, contained in the PM₁₀ and PM_2.5 fractions ranged, respectively, from 0.9 μg/m³ to 12.8 μg/m³ and from 0.9 μg/m³ to 11.8 μg/m³, while the average EC mass concentrations ranged from 0.06 μg/m³ to 2.3 μg/m³ (in PM₁₀) and from 0.05 μg/m³ to 1.8 μg/m³ (in PM_2.5) indicating the high  spatial variability between  remote and urban site. The highest OC and EC average values were observed in the sites of Naples and Lecce, more affected by primary emissions of anthropogenic sources and characterized by high levels of volatile organic compounds that favour the production of secondary organic aerosol (SOC) under favourable meteorological conditions. Lower values were found in Lamezia Terme and Capo Granitola not only because of relatively limited sources but even because the two sites are influenced by sea-breeze effects that favour the pollutant’s dispersion. The low concentrations measured in Monte Curcio are in good agreement with free tropospheric conditions characterizing a remote site. The higher TC percentage in the PM fractions (TC/PM) were found in Lamezia Terme (48% and 67%) followed by Lecce (35% and 40%), Naples (31% and 39%) and Monte Curcio (30% and 33%), while very low percentages were found in Capo Granitola (13% and 17%), in the PM₁₀ and PM_2.5 fractions, respectively.

Fig. 3.2) Temporal variability of (a) PM₁₀ and (b) PM_2.5 mass concentrations during the measuring campaign at each observation site. Horizontal dashed lines represent the legislative limit values set in Directive 2008/50 and suggested by WMO.

Table 3.1) TC, OC, EC, and SOC average concentrations (±STD) in PM₁₀ together with the OC/EC, TC/PM, OC/PM, EC/PM and SOC/PM average ratios, for each observation site.

Table 3.2) TC, OC, EC, and SOC average concentrations (±STD) in PM_2.5 together with the OC/EC, TC/PM, OC/PM, EC/PM and SOC/PM average ratios, for each observation site.

The OC/EC ratio was used to quantify secondary organic aerosol (SOA) that can be  produced into the atmosphere by volatile organic compounds (VOC) oxidation. As summarized in Tables 3.1 and 3.2, the average SOC concentrations ranged from 0.4 to 7.6 μg/m³ in PM₁₀ and from 0.4 to 7.2 μg/m³ in PM_2.5, accounting from 37 to 59% of the OC in PM₁₀ and from 40 to 57% in PM_2.5. These results show that SOC particles are an important component of the PM mass in all sampling sites. In particular, the higher percentage of SOC observed at Naples and Lecce, can be attributed to the increased emission of volatile organic precursors that together with the stable atmospheric conditions and the prolonged residence time may strengthen atmospheric oxidation of volatile organic compounds.

[2] Inter-Comparison of Carbon Content in PM2.5 and PM10 Collected at Five Measurement Sites in Southern Italy, Dinoi, A., Cesari, D., Marinoni, A., Bonasoni, P., Riccio, A., Chianese, E., Tirimberio, G., Naccarato, A., Sprovieri, F., Andreoli, V., Moretti, S., Gullì, D., Calidonna, C.R., Ammoscato, I., Contini, D., 2017, Atmosphere 8, 243, http://dx.doi.org/10.3390/atmos8120243.

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Fig. 2.1) DOAS system at the observatory ECO I-AMICA in Lecce

 Figure 2.2 reports the seasonal variation of NO₂ vertical columns as measured by the GASCOD/NG4-MIGE system. The analogues measurements carried out with the NASA OMI (Ozone Monitoring Instrument) satellite instrument are also plotted. The values are referred to solar zenith angles of 90° at sunrise (AM) and sunset (PM). It can be noted that the PM observations  are systematically higher than the AM vertical columns.  The AM/PM variation is mainly due to the photochemical activity of NO2 that is produced during the day through the reactions:

N₂O₅ +hv –> NO₂ + NO₃                            NO + O₃ –> NO₂ + O₂

and removed during the night thanks to:

NO₂ + O₃ –> NO₃ + O₂                                NO₂ + NO₃ + M –> N₂O₅ + M

The photochemistry is responsible for the yearly maxima and minima occurring in summer and winter respectively. Similarly, the time series for O₃ total columns from NG4 and OMI are plotted in Figure 2.3. The considered period is shorter than in Figure 2.2, and it does not allow for an appreciation of the O₃ seasonal behaviour that present the maximum value in spring and the minima in autumn. Since the beginning of its history, DOAS evolved in many aspects, starting from the measurements obtained in active mode, using an artificial source of radiation placed at a certain distance of the sensor unit (Open Path configuration), in order to obtain the mean concentration along the measurements path.

Fig. 2.2) Seasonal variation of NO₂ vertical columns as measured by the GASCOD/NG4-MIGE system.

Fig. 2.3) Seasonal variation of O₃ vertical columns as measured by the GASCOD/NG4-MIGE system.

 The zenith sky passive mode, using the sun light as radiation source, was the following step aiming to characterize mainly the low stratospheric compounds from a climatological point of view. In the last 10 years, the MAX-DOAS  (Multi AXis-DOAS) configuration that make use of measurements obtained for different elevation angle of the instrument pointing device, is deeply used for the profiling of tropospheric compounds and air quality assessment. For the Open Path configuration, the retrieval of the main concentration along the optical path is quite easy since the distance between emitter and receiver is known. In contrast, for the passive mode configurations (Zenith-sky and MAX-DOAS) the computation of the main concentrations of the analysed species need the help of a radiative transfer model in order to evaluate the distance travelled by the photons before reaching the spectrometric system. The obtained values are primarily function of the sun elevation then of the actual distribution of the atmospheric compounds and many others parameters. This geometrical factor (called Air Mass Factor -AMF) correct the outputs of the DOAS algorithms – the so-called Slant Column Densities (SCDs) – in order to obtain the vertical columns (VC) of the selected tracer. In addition, the AMFs with the SCDs series allows for the retrieval of the vertical distribution for the main atmospheric  absorbers such as nitrogen dioxide (NO₂) and ozone (O₃). For MAX-DOAS configuration this feature is extended to weak tropospheric absorbers.

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The study, published in Science of the Total Environment [1], was carried out using data from the Environmental-Climate-Observatory (ECO, Figure 1.1) realized in Lecce as part of the PON I-Amica project (www.i-amica.it).

 Fig. 1.1) The Environmental-Climate-Observatory (ECO) of Lecce, regional station of Global Atmosphere Watch (GAW-WMO) network. 

Results showed higher PM_2.5 and PM₁₀ concentrations in the cold period (autumn and winter) compared to the warm period (spring and summer), with a seasonal variability of the chemical composition that allowed evaluating the variability of the contribution of the different sources using advanced statistical methods (Figure 1.2). The increase of concentrations in the cold period is largely due to greater anthropogenic emissions from vehicular traffic and biomass burning, the latter being an important source in the study area. The combustion of biomass includes different types of emissions such as domestic heating, agricultural practices and fires and is a source characterized by a very heterogeneous chemical profile that includes organic carbon compounds (including polycyclic aromatic hydrocarbons – PAHs), elemental carbon that is similar to black carbon, one of the components of the aerosol most influential on the climatic effects but which also has significant effects potentially harmful to human health, potassium and trace metals. The impact of biomass burning on the concentrations of atmospheric aerosol is lesser in the summer but not negligible and is therefore one of the most relevant sources at the measurement site. It is important to observe how the contribution of the different sources is divided into the fine (PM_2.5) and the coarse fraction (Figure 1.3). The contribution of biomass burning is mainly composed of fine particles with a distribution similar to industrial emissions and secondary-origin sulphates. The latter are not emitted directly from the sources but are formed in the atmosphere as a result of chemical reactions (more effective in the hot period) of SO₂ gas (mainly emitted in industrial processes, in maritime transport and in the combustion of heavy oils). The particles emitted by biomass burning therefore have a potential relevant impact on health as they can more easily penetrate the respiratory system than the coarse particles that represent an important part of the contribution of natural sources such as marine aerosol, the crustal matter and carbonates from the soil.

Fig. 1.2) Seasonal variability of sources contribution to PM₁₀ (up) and PM_2.5 (down).

Fig. 1.3) Average annual distribution of the sources contributions between fine (PM_2.5) and coarse fraction (diameter greater than 2.5 microns).

[1] ‘Seasonal variability of PM_2.5 and PM₁₀ composition and sources in an urban background site in Southern Italy’, D. Cesari, G.E. De Benedetto, P. Bonasoni, M. Busetto, A. Dinoi, E.Merico, D. Chirizzi, P. Cristofanelli, A. Donateo, F.M. Grasso, A. Marinoni, A. Pennetta, D. Contini, Science of the Total Environment 612, pp. 202–213, 2018,  http://dx.doi.org/10.1016/j.scitotenv.2017.08.230.

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AERONET collaboration provides globally distributed observations of spectral aerosol optical depth (AOD), inversion products, and precipitable water in diverse aerosol regimes. Version 3 AOD data are computed for three data quality levels: Level 1.0 (unscreened), Level 1.5 (cloud-screened and quality controlled), and Level 2.0 (quality-assured). Inversions, precipitable water, and other AOD-dependent products are derived from these levels and may implement additional quality checks.

The processing algorithms have evolved from Version 1.0 to Version 2.0 and now Version 3.0. The Version 3 databases are available from the AERONET and PHOTONS web sites. Version 2 data may be downloaded from the web site through 2018 and thereafter upon special request. New AERONET products will be released as new measurement techniques and algorithms are adopted and validated by the AERONET research community. The AERONET web site also provides AERONET-related news, a description of research and operational activities, related Earth Science links, and an AERONET staff directory (https://aeronet.gsfc.nasa.gov/).

The I-AMICA stations of Napoli, Lamezia Terme and Lecce are part of the AERONET and below are reported the AOD (level 1.5) behaviour for the year 2018 concerning these stations.

Napoli: AOD 2018, level 1.5

Lamezia Terme: AOD 2018, level 1.5

Lecce: AOD 2018, level 1.5

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