**4. Methodology, study area and data**

#### **4.1. Method**

The overall methodology is described below (see Fig. 7):

**1. Satellite data products from the MODIS sensor:** Aerosol optical thickness (AOT) and aerosol size/type data were collected for the years 2002-2012 over Cyprus.

**Figure 7 :** Overall Methodology of the Airspace project **Figure 7.** Overall Methodology of the Airspace project

The overall methodology is described in the following (see Fig. 7):

**4.1 Method** 

Aerosol products are reported at 10 km resolution (at nadir). Details of file specification of

MODIS L2 aerosol products can be found at the website http://modis.gsfc.nasa.gov/.

188 Remote Sensing of Environment: Integrated Approaches

**Figure 6.** MODIS image for Eastern Mediterranean region

**4. Methodology, study area and data**

The overall methodology is described below (see Fig. 7):

**1. Satellite data products from the MODIS sensor:** Aerosol optical thickness (AOT) and

aerosol size/type data were collected for the years 2002-2012 over Cyprus.

**4.1. Method**


simultaneous prediction of air quality (in terms of PM aerosol mass) and weather for 72 hours. The model forecasts have been statistically evaluated against surface observations.

affected by frequent small depressions traversing the Mediterranean Sea from west to east between the continental anticyclone of Eurasia and the generally low pressure belt of North Africa. These depressions result in disturbed weather usually lasting no more than a few days and producing most of the annual precipitation (the average rainfall from December to February is typically about 60% of the average annual total precipitation). Relative humidity averages between 60% and 80% during the winter period and between 40% and 60% during the summer period. Fog is infrequent and visibility is generally very good. Sunshine is abundant all year round, particularly from April to September when the average duration of bright sunshine exceeds 11 hours per day. Winds are generally light to moderate with high variability when it comes to direction. Gales are infrequent over Cyprus and are mainly

Air Pollution from Space http://dx.doi.org/10.5772/39310 191

Aerosol sources: Two main types of air pollutant sources can be identified: anthropogenic and natural. Notable natural sources include dust from inland wind erosion, transboundary sources and sea salt. Cyprus' arid climate results in large portions of surface area having very low index of vegetative cover. This, combined with very low levels of moisture for a substantial part of the year, results in the overall vulnerability to wind erosion. Furthermore, Cyprus presents a high ratio of shoreline when compared to surface area, with maximum distances inland from the shore being in the order of 30-40 km and three of the four urban centres located on the coast. Therefore, sea salt can have a significant effect on the concentrations of particu‐ lates in the majority of the island's area. Finally, the transportation of dust from the surround‐ ing eastern Mediterranean and African areas (most notably from northern Africa) significantly

Local anthropogenic sources also contribute to PM concentrations on the island. The main anthropogenic PM sources include traffic (both highways and inner city traffic), industrial zones, urban agglomerations, agriculture, mines and quarries and localized emissions from a

For the purposes of the project, Limassol was selected as the main ground based site for the development and the application of the AIRSPACE methodology. The main instrumentation used for the aerosol observation in a daily basis was a backscatter-depolarization LIDAR system for the study of the vertical aerosol distribution as well as the sunphotometer for the columnar aerosol information, both located at the premises of CUT, in Limassol (see Figure 9) (34.675ºN, 33.043ºE, 10m above sea level), since 2010. The LIDAR records daily measure‐ ments between 08:00 UTC and 09:00 UTC (consistent with the MODIS overpass) and performs continuous measurements for the retrieval of the aerosol optical properties such as depolari‐ zation ratio and backscatter coefficient over Limassol, inside the Planetary Boundary Layer (PBL) and the lower free troposphere. Additionally, the AERONET sun-photometer provides

confined to exposed coastal areas as well as areas at high elevation.

series of activities such as power stations and cement factories.

daily aerosol information including AOT and aerosol size distribution.

affects air quality (Nisantzi et al, 2012).

*4.2.1. Ground based measurements*

**4.2. The dataset**

#### *4.1.1. Study areas in Cyprus and general characteristics*

An overview of the available instrumentations at the selected sites is given in Figure 8.

**Figure 8.** Overview of the available instrumentations at the selected sites within AIRSPACE project. Limassol was the main site (LIDAR, AERONET, PM), Nicosia validation site (MicrotopsII, PM); 15-day campaigns were conducted at Larnaca and Paphos.

Meteorological conditions: Cyprus is characterized by a subtropical - Mediterranean climate with very mild winters (mainly in the coastal areas) and hot summers. Snowfall occurs mainly in the Troodos Mountains in the centre of the island. Rain occurs mostly during the winter period, with summer being generally dry. Temperature and rainfall are both correlated with altitude and, to a lesser extent, distance from the coast. The prevailing weather conditions on the island are hot, dry summers (from mid-May to mid-September) and rainy, rather change‐ able winters (from November to mid-March). These are separated by short autumn and spring seasons.

During the summer period (a season of high temperatures with almost cloudless skies), the island is often under the influence of a shallow trough of low pressure extending from the great continental depression centred over Western Asia. During winter, Cyprus is mainly affected by frequent small depressions traversing the Mediterranean Sea from west to east between the continental anticyclone of Eurasia and the generally low pressure belt of North Africa. These depressions result in disturbed weather usually lasting no more than a few days and producing most of the annual precipitation (the average rainfall from December to February is typically about 60% of the average annual total precipitation). Relative humidity averages between 60% and 80% during the winter period and between 40% and 60% during the summer period. Fog is infrequent and visibility is generally very good. Sunshine is abundant all year round, particularly from April to September when the average duration of bright sunshine exceeds 11 hours per day. Winds are generally light to moderate with high variability when it comes to direction. Gales are infrequent over Cyprus and are mainly confined to exposed coastal areas as well as areas at high elevation.

Aerosol sources: Two main types of air pollutant sources can be identified: anthropogenic and natural. Notable natural sources include dust from inland wind erosion, transboundary sources and sea salt. Cyprus' arid climate results in large portions of surface area having very low index of vegetative cover. This, combined with very low levels of moisture for a substantial part of the year, results in the overall vulnerability to wind erosion. Furthermore, Cyprus presents a high ratio of shoreline when compared to surface area, with maximum distances inland from the shore being in the order of 30-40 km and three of the four urban centres located on the coast. Therefore, sea salt can have a significant effect on the concentrations of particu‐ lates in the majority of the island's area. Finally, the transportation of dust from the surround‐ ing eastern Mediterranean and African areas (most notably from northern Africa) significantly affects air quality (Nisantzi et al, 2012).

Local anthropogenic sources also contribute to PM concentrations on the island. The main anthropogenic PM sources include traffic (both highways and inner city traffic), industrial zones, urban agglomerations, agriculture, mines and quarries and localized emissions from a series of activities such as power stations and cement factories.

#### **4.2. The dataset**

simultaneous prediction of air quality (in terms of PM aerosol mass) and weather for 72 hours. The model forecasts have been statistically evaluated against surface observations.

An overview of the available instrumentations at the selected sites is given in Figure 8.

**Figure 8.** Overview of the available instrumentations at the selected sites within AIRSPACE project. Limassol was the main site (LIDAR, AERONET, PM), Nicosia validation site (MicrotopsII, PM); 15-day campaigns were conducted at Larna-

Meteorological conditions: Cyprus is characterized by a subtropical - Mediterranean climate with very mild winters (mainly in the coastal areas) and hot summers. Snowfall occurs mainly in the Troodos Mountains in the centre of the island. Rain occurs mostly during the winter period, with summer being generally dry. Temperature and rainfall are both correlated with altitude and, to a lesser extent, distance from the coast. The prevailing weather conditions on the island are hot, dry summers (from mid-May to mid-September) and rainy, rather change‐ able winters (from November to mid-March). These are separated by short autumn and spring

During the summer period (a season of high temperatures with almost cloudless skies), the island is often under the influence of a shallow trough of low pressure extending from the great continental depression centred over Western Asia. During winter, Cyprus is mainly

*4.1.1. Study areas in Cyprus and general characteristics*

190 Remote Sensing of Environment: Integrated Approaches

ca and Paphos.

seasons.

#### *4.2.1. Ground based measurements*

For the purposes of the project, Limassol was selected as the main ground based site for the development and the application of the AIRSPACE methodology. The main instrumentation used for the aerosol observation in a daily basis was a backscatter-depolarization LIDAR system for the study of the vertical aerosol distribution as well as the sunphotometer for the columnar aerosol information, both located at the premises of CUT, in Limassol (see Figure 9) (34.675ºN, 33.043ºE, 10m above sea level), since 2010. The LIDAR records daily measure‐ ments between 08:00 UTC and 09:00 UTC (consistent with the MODIS overpass) and performs continuous measurements for the retrieval of the aerosol optical properties such as depolari‐ zation ratio and backscatter coefficient over Limassol, inside the Planetary Boundary Layer (PBL) and the lower free troposphere. Additionally, the AERONET sun-photometer provides daily aerosol information including AOT and aerosol size distribution.

Centre building (N35.181°, 33.379° E) during the period February 2012 to June 2012 and the period October 2012 to January 2012. The Strovolos area is mainly commercial with heavy

Air Pollution from Space http://dx.doi.org/10.5772/39310 193

For both sites, a TSI Dust Trak model 8520 was used for measuring the mass concentration of particulate matter of diameter less than 10 micrometers (PM10). The Dust Trak is a light scattering laser photometer which determines PM10 concentrations by measuring the amount of scattering light, which is proportional to the volume concentration of aerosols, in order to determine the mass concentration of aerosols (Nisantzi et al., 2012). The Dust Track features an integrated pump, internal memory and data-logger for automatic storage of measured values at programmable intervals. The device was programmed to begin PM10 recordings every morning at 08:00 UTC for a 5-hour period to coincide with the satellite MODIS TERRA

Adjacent to the Dust Trak, a Microtops II model 540 sunphotometer was set up to measure the AOT. This is a 5-channel hand-held sunphotometer which measures and stores data at 5 different wavelengths. In addition to the Dust Track and the sunphotometer which were set up originally at the Strovolos site and then moved to the Pallouriotissa site, the Harvard Impactors were operated at the Pallouriotissa site only (next to the other two devices) for

The in-situ data were collected in conjunction with satellite data (MODIS) to validate a novel statistical model developed within AIRSPACE using AOT retrievals to estimate air particulate

For Larnaka, two sets of measurements took place: one using the Dust Track along with the Sun photometer for a period of three weeks in August of 2011 (8th-26th) on a site at the centre of Larnaka city (34.916° N, 33.630° E), for the first set of measurements: PM10 recordings every morning at 08:00 UTC for a 5-hour period and subsequent measurements using the MICRO‐ TOPS sun photometer at 08:00 UTC and at 11:00 UTC to coincide with the MODIS TERRA and AQUA overpasses. A second set of measurements was provided by the Harvard Impactor situated on top of the tax agency building (34.919° N, 33.631° E) in Larnaka. This station provided measurements of PM10, PM2.5, EC-OC (elemental & organic carbon) and nitrate

For air pollution ground level measurements, the Harvard Impactor stations were established by HSPH and CII: Limassol, Nicosia, Larnaca and Paphos. The sampling commenced on 12 January 2012 and ended on 12 January 2013. Samples were collected every six days, on 24-hr basis from 08:00 to 08:00 next day (UTC), at all sites except Limassol, where the sample collection was done every three days. Samples were collected for PM2.5, PM10, EC-OC and nitrates using the Harvard Impactors. For quality assurance and control, collocated and blank samples were collected for each sample at the Limassol site, according to a predetermined schedule. Standard Operating Procedure (SOP) was followed for each measurement at each site. Filters were collected and sent to HSPH for chemical analysis. The parameters measured included fine particles (PM2.5): mass, reflectance, nitrate, trace elements and EC-OC; and inhalable particle (PM10): mass, reflectance and trace elements. Chemical analysis included

traffic at peak hours while the Pallouriotissa site is residential.

chemical analysis of PM10, PM2.5, EC-OC and nitrate concentrations.

and AQUA overpass except at weekends.

pollution.

concentrations.

**Figure 9.** Satellite image of Limassol

For the purposes of the AIRSPACE project, Nicosia was selected as a validation site (in addition to the Limassol main site), for ground based measurements of PM10 and AOT. Two locations in Nicosia were used as test sites: Strovolos municipality building (N35.144°, 33.343° E) during the period September 2011 to December 2011 and Pallouriotissa Frederick University Research Centre building (N35.181°, 33.379° E) during the period February 2012 to June 2012 and the period October 2012 to January 2012. The Strovolos area is mainly commercial with heavy traffic at peak hours while the Pallouriotissa site is residential.

For both sites, a TSI Dust Trak model 8520 was used for measuring the mass concentration of particulate matter of diameter less than 10 micrometers (PM10). The Dust Trak is a light scattering laser photometer which determines PM10 concentrations by measuring the amount of scattering light, which is proportional to the volume concentration of aerosols, in order to determine the mass concentration of aerosols (Nisantzi et al., 2012). The Dust Track features an integrated pump, internal memory and data-logger for automatic storage of measured values at programmable intervals. The device was programmed to begin PM10 recordings every morning at 08:00 UTC for a 5-hour period to coincide with the satellite MODIS TERRA and AQUA overpass except at weekends.

Adjacent to the Dust Trak, a Microtops II model 540 sunphotometer was set up to measure the AOT. This is a 5-channel hand-held sunphotometer which measures and stores data at 5 different wavelengths. In addition to the Dust Track and the sunphotometer which were set up originally at the Strovolos site and then moved to the Pallouriotissa site, the Harvard Impactors were operated at the Pallouriotissa site only (next to the other two devices) for chemical analysis of PM10, PM2.5, EC-OC and nitrate concentrations.

The in-situ data were collected in conjunction with satellite data (MODIS) to validate a novel statistical model developed within AIRSPACE using AOT retrievals to estimate air particulate pollution.

For Larnaka, two sets of measurements took place: one using the Dust Track along with the Sun photometer for a period of three weeks in August of 2011 (8th-26th) on a site at the centre of Larnaka city (34.916° N, 33.630° E), for the first set of measurements: PM10 recordings every morning at 08:00 UTC for a 5-hour period and subsequent measurements using the MICRO‐ TOPS sun photometer at 08:00 UTC and at 11:00 UTC to coincide with the MODIS TERRA and AQUA overpasses. A second set of measurements was provided by the Harvard Impactor situated on top of the tax agency building (34.919° N, 33.631° E) in Larnaka. This station provided measurements of PM10, PM2.5, EC-OC (elemental & organic carbon) and nitrate concentrations.

For air pollution ground level measurements, the Harvard Impactor stations were established by HSPH and CII: Limassol, Nicosia, Larnaca and Paphos. The sampling commenced on 12 January 2012 and ended on 12 January 2013. Samples were collected every six days, on 24-hr basis from 08:00 to 08:00 next day (UTC), at all sites except Limassol, where the sample collection was done every three days. Samples were collected for PM2.5, PM10, EC-OC and nitrates using the Harvard Impactors. For quality assurance and control, collocated and blank samples were collected for each sample at the Limassol site, according to a predetermined schedule. Standard Operating Procedure (SOP) was followed for each measurement at each site. Filters were collected and sent to HSPH for chemical analysis. The parameters measured included fine particles (PM2.5): mass, reflectance, nitrate, trace elements and EC-OC; and inhalable particle (PM10): mass, reflectance and trace elements. Chemical analysis included

**Figure 9.** Satellite image of Limassol

192 Remote Sensing of Environment: Integrated Approaches

For the purposes of the AIRSPACE project, Nicosia was selected as a validation site (in addition to the Limassol main site), for ground based measurements of PM10 and AOT. Two locations in Nicosia were used as test sites: Strovolos municipality building (N35.144°, 33.343° E) during the period September 2011 to December 2011 and Pallouriotissa Frederick University Research

Thermal Optical Transmitance (TOT) to measure EC-OC particle concentration, gravimetric mass determination and X-Ray fluorescence to determine trace elemental composition of PM2.5 and PM10. Samples up to 19 June 2012 have been completely analyzed. The remaining samples have undergone chemical process for analysis.

Figure 10 features the correlation of the MODIS AQUA and TERRA sensors and CUT\_TEPAK AERONET measurements. The slope of linear regression in the correlation plot between MODIS and AERONET provides an overview of possible differences. The correlation coeffi‐ cient value of the order of 0.62 for both TERRA and AQUA satellites is due to the coast line of the Limassol site. Limassol's CUT-TEPAK AERONET site is a coastal area, thus the surface inhomogeneity or sub-pixel water contamination has a larger effect than anticipated in continental coastal regions (Nisantzi et al., 2012). The systematic biases overestimations in MODIS retrievals are mainly due to aerosol model assumptions (deviation of 0–20%) andin‐

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

R2 =0.61

AOT MODIS=0.067+0.89\*AOT AERONET

Air Pollution from Space http://dx.doi.org/10.5772/39310 195

AOT CUT-TEPAK AERONET

**Figure 10.** Comparisons of MODIS and AERONET derived at 0.50 nm wavelength, encompassing 352 points from CUT-TEPAK AERONET coastal site. The solid line represents the slopes of linear regression both for AQUA and TERRA

Using the MICROTOPS II AOT, the procedure was duplicated for the validation of the satellite observations in Nicosia. The number of collocated and synchronized ground based and satellite measurements were statistically low in order to provide correlation factor which can

strument calibration (2–5%).

0.0

represent a reliable validation study.

MODIS sensors

0.1

0.2

0.3

0.4 0.5

AOT MODIS AQUA/TERRA

0.6

0.7

0.8

0.9

1.0
