Abstract
Spectroscopic methods have played an important role in the study of chemical and physical processes related to the composition of the atmosphere and the differential optical absorption spectroscopy (DOAS) has been one of the most powerful methods to measure a wide range of trace gases. The pollutants are identified by their respective ranges of wavelengths that must be previously known. A Passive Differential Optical Absorption Spectroscopy system that uses the ultraviolet region from 400 to 480 nm of the solar radiation is presented. In this research diurnal variation of NO2 was remotely measured by means of MAX-DOAS system which uses multiple viewing angles to monitor pollutant concentrations in urban area at the city of Rio de Janeiro. The instrument was placed on the roof of a building oriented to the center of the city. Tropospheric NO2 amounts are retrieved from the measured spectra using the DOAS technique. In this paper we give a general description of the procedure and present the results from measurements during four days in winter 2017 associated with the prevailing meteorological aspects. These days were characterized by mostly sunny and dry conditions, no convection, periods of medium clouds and clear sky. The tropospheric NO2 slant column densities values are presented and the results are consistent for all three used elevation angles (5º, 10º, and 15º). The results demonstrate the capability and the potential of the MAX-DOAS technique to derive information on spatial distribution of NO2 in an urban environment.
Highlights
Air pollution is associated mainly to the processes of growth, industrialization and urbanization, which has been increasing since the first half of the twentieth century
The area of interest is the center of Rio de Janeiro, as well as, the nearby environment, where emissions from mobile and stationary sources play an important role in the deterioration of air quality in this urban center due to various means of transportation that circulate throughout the city
The MAX-differential optical absorption spectroscopy (DOAS) station is located on the urban areas boundary of the Guanabara Bay (GB), where several industries operate in the industrial area north-west of the metropolitan region of Rio de Janeiro (MRRJ)
Summary
Air pollution is associated mainly to the processes of growth, industrialization and urbanization, which has been increasing since the first half of the twentieth century. In the last sixty years, the indiscriminate use of natural resources, increased automotive fleet and poor or non-existent planning played an important role in the deterioration of air quality in major world urban centers. Emissions from mobile and stationary sources together industrial activities are somehow responsible for the presence of pollutants in the atmosphere (Fernandes, 2017). It is very important to understand better the temporal and spatial presence of NO2, especially in urban area over both the source and surrounding area with a high population density which is certainly not an easy task (Lee, Gu, Kim, Hwang, & Jung, 2012; Psiloglou et al, 2013)
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