THE ANALYSIS OF A COMPLEX FIRE EVENT USING MULTI-SPACEBORNE OBSERVATIONS

This study documents a complex fire event that occurred on October 2016, in Middle East belligerent area. Two fire outbreaks were detected by different spacecraft monitoring instruments on board of TERRA, CALIPSO and AURA Earth Observation missions. Link with local weather conditions was examined using ERA Interim Reanalysis and CAMS datasets. The detection of the event by multiple sensors enabled a detailed characterization of fires and the comparison with different observational data.


INTRODUCTION
Oil and sulfur fires have a major deleterious impact on the environment and human health.Crude oil burns produce smoke containing carbon dioxide, carbon monoxide, sulfur dioxide, oxides of nitrogen, volatile organic hydrocarbons, ozone, acidic aerosols, soot, droplets of unburned oil and PM 10.Sulfur fires generate fumes of sulfur dioxide and sulfur trioxide, and when these react with moisture they produce sulfurous and sulfuric acids [1].Sulfur dioxide (SO2), in particular, is an important pollutant gas with significant impact on the environment.It is a precursor of sulfate aerosols that can affect air quality and climate.Although SO2 has a relatively short atmospheric lifetime, sizable transient SO2 plumes can travel into remote oceanic areas [2].
Sulfur fires were documented as some of the largest sources of SO2 fumes released into the atmosphere.In June 2003, a fire at a sulfur mine and processing facility near Mosul, Iraq, released about 600 kilotons of SO2, making it the largest non-volcanic release of SO2 that has ever been observed with satellites [3].
Major oil fires were reported in the 1990s, in the Persian Gulf War, when Iraqi troops ignited over 700 oils well in Kuwait and consumed roughly 4.6 million barrels of oil a day.Similar events occurred over several months in 2016, periodic oil fires being recorded by satellite imagery.These events produced a thick, dark smoke [4].
On October 2016, a complex fire event was registered, combining fires at the Al-Mishraq sulfur plant (the same that produced the event in 2003) and at the nearby Qayyarah oil field, when ISIS forces that retreated from Mosul torched the plants.The complex event lasted for 6 days and spread a sulfur plume across northern Iraq, Syria and Turkey [5], [6] exposing the local population to substantial risks [7].
Taking into consideration the negative effects of oil and sulfur fires it is highly important to study the events using state of the art satellite data.The present study is focused on the analysis of a prolonged fire event occurred during 20 th and 25 th of October, 2016 over the belligerent area of Mosul-Iraq (35.99°N, 43.34°E).Using different spacecraft monitoring instruments onboard of TERRA satellite, two distinct fire outbreaks have been spotted: one with dark plume due to oil wells burning and one with white plume coming from a burning sulfur plant (Fig. 1).The analysis has implied the use of multiple data from the following instruments: Multi-angle Imaging SpectroRadiometer (MISR), Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), Ozone Monitoring Instrument (OMI).The link with the local weather conditions has been examined by the use of Copernicus Atmosphere Monitoring Service (CAMS) datasets.
Onboard of TERRA, the Multi-angle Imaging SpectroRadiometer instrument uses 9 push-broom cameras, which allow the system to image every scene at 9 viewing zenith angles in line with the ground track of the satellite in 7 minutes.[8].The instrument has been used to access the magnitude and variability of smoke plume heights.
The retrievals from MISR have been validated by/compared with the spaceborne lidar retrievals coming from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations).
CALIPSO carries the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), which provides vertical resolved aerosol and cloud observations.CALIOP measures the backscatter signal at 532 nm and 1064 nm, and polarization at 532 nm.Cloud and aerosol layers are identified using the level 2 retrievals and through the cloud aerosol discrimination algorithm, based on the probability distribution functions of altitude-and-latitude dependent parameters (integrated colour ratio, layer-integrated volume depolarization ratio, mean attenuated backscatter coefficient) [9].
The Ozone Monitoring Instrument (OMI) has been used to detect the concentration of SO 2 over the plume.OMI, onboard NASA Earth Observing System Aura satellite, observes aerosols and trace gases, including SO2.Data from the first and last 10 cross-track positions were excluded from the analysis to limit the across-track pixel width to about 40 km [10], [11].
Weather conditions during the event were examined using ERA Interim Reanalysis and Copernicus Atmosphere Monitoring Service (CAMS) datasets [12], [13].Boundary layer height, obtained from the European Centre for Medium-Range Weather Forecast (ECMWF), was compared with the injection height measured & computed by MISR [8].Concentration of SO2 from OMI was compared/validated using SO2 from CAMS.The corresponding plumes height generated by MINX are shown in Figure 2 c, d.Red points represent zero-wind heights, blue points windcorrected heights, and the green line represents the terrain heights with sea level as references.CALIOP is rarely able to detect specific targets such as aerosol source due to its narrow field-ofview [14].However, by the time of the event CALIPSO overpass the area of Mosul and an aerosol layer can be seen in the PBL, using the CALIOP Vertical Feature Mask on October 21 st 2016, 23:15 UTC (Fig. 4).The layer is localized between near surface and 2.5 km altitude and is classified as a mix of dust and pollution, (2= dust, 5=polluted dust) with traces of smoke (6 = smoke) [15].

CONCLUSIONS
The detection of smoke by multiple instruments has enabled the detailed characterization of the fire event and the comparison between different observational datasets.CALIOP was able to detect the vertical details of the aerosol layers highlighting both the dust and smoke pollution.Complementary data from the OMI quantitatively estimated the SO2 released in the atmospheric column.
the fire event on October 21 st , 2016.Digitized plumes (Figure 2 a, b) indicate the dispersion along W-NW air circulation within the troposphere.

Figure 2
Figure 2 Digitized plumes of SO2 (a), and oil well (b) in nadir view, height profile of SO2 plume (c), and height profile of oil plume (d) detected with MISR, on October 21 st , 2016

Figure 3
Figure 3 Time series of PBL height from ECMWF during the fire event Time series of planetary boundary layer (PBL) height from ECMWF (Figure 3) shows that the maximum value of PBL on October 21 st has

Figure 4
Figure 4 Vertical Feature Mask of aerosol layers detected with CALIOP over Mosul, Iraq OMI was used to detect the column integrated SO2 over the dispersion area.The data measured by OMI from 20 to 25 Oct 2016 reveals an average maximum value of 7 DU (Figure 5 a).CAMS analysis (Figure 5 b) emphasizes the initiation of the fire event, showing an injection of SO2 throughout the atmospheric column.