# First Lidar Campaign in the Industrial Sites of Volta Redonda-RJ and Lorena-SP, Brazil
## 4 Data Retrieval and Results
### CALIPSO Satellite Retrieval  
The CALIPSO satellite data were used for two main purposes, to obtain the complete overview of the aerosol optical properties in this axis connecting region between two major capitals, Sao Paulo and Rio de Janeiro, and also to cover the absence of a second remote sensing instrument, such as a sunphotometer, which can be used to tune the first guess of  
Figure 2: Time series distribution of the monthly mean particulate matter concentration for the period of March of 2015 to December of 2020 for all four CETESB air quality stations over Paraiba valley. lidar ratio values and AOD retrievals. The 5 km aerosol layer data from CALIPSO version 4 were employed to retrieve the AOD and lidar ratio values at 532 nm for Volta Redonda and Lorena sites, where monitoring campaigns were carried out with the MSP-LIDAR II system. We calculated the mean and standard deviation of AOD values for the period from 2006 to 2020 retrieved by CALIPSO satellite at 532 nm in order to quantify aerosol optical properties for both campaign sites. In order to reduce the dependence with horizontal distances and increase the correlation between CALIPSO retrievals and the ground-based measurements, only cloud-free measurements were considered with CALIPSO overpasses inside a horizontal spatial range of 120 km centered at the closest distance between the ground-based station and satellite ground-track [58; 59; 60]. It is important to note that AOD values retrieved from the CALIPSO satellite can present large uncertainties considering thin or undetected layers. Poor extinction retrievals from layers within the column can impact the quality of the column optical depths. For instance, [PERSON] et al. [61] uses two years of CALIOP and Moderate Resolution Imaging Spectroradiometer (MODIS) data to quantify the aerosol optical depth of undetected layers of aerosol (ULA), showing the fraction of undetected backscattering layers are higher during daytime when compared to nighttime, mostly because a large amount of solar background noise lowers the signal-to-noise ratio. However, ULA is larger in the northern hemisphere and relatively larger at high latitudes, which is an important point for our results over South America. By analyzing aerosol optical depth values at 532 nm for both locations, we can see similar AOD annual patterns. Volta Redonda presents AOD mean values of \(0.15\pm 0.22\), with the lowest mean value in June, \(0.10\pm 0.15\), and the upper mean AOD in October \(0.21\pm 0.29\). The whisker plot results present high variation in the interquartile range values in the months of September and October, where 50% of the total AOD values span from 0.06 to 0.25, as can be seen in Figure 3. Likewise, Lorena presents the same pattern of AOD values at 532 nm, with a mean AOD value of \(0.14\pm 0.20\), with the lowest mean AOD of \(0.10\pm 0.13\) in July and the upper mean value of \(0.20\pm 0.25\) in October, as shown in Figure 4. The whisker plot results also present high variation in the interquartile range values in the months of September and October, where 50% of the total AOD values are allocated between values of 0.05 and 0.24, which agreed with the increase of the particulate matter concentration measured by the air quality stations of the Paraiba valley region, as presented in Figure 2. The analyses present the same rationale for CALIOP lidar ratio at 532 nm product for both locations. Lidar ratio products for Volta Redonda span from 44 sr to 70 sr most of the year, with a mean value of 55 sr for all months. In the case of the Lorena site campaign, the lidar ratio values span from 53 sr to 70 sr during most of the year, with mean values of 55 sr for all months, as can be seen in Figures 3 and 4. Figure 3: \(Cont.\)  
CALIOP's aerosol subtype plays a critical role for the aerosol optical properties retrieval, more specifically, for extinction profiles of level 2 CALIPSO data. In the context of the aerosol, the aerosol is not directly affected by the aerosol.