From Aerosols to Greenhouse Gases: evaluating the concentrations

Since the 1980s, the atmospheric aerosol in Sao Paulo, the most populous and economically active region of Southeast Brazil, has been extensively studied to determine its composition, concentration, and health impacts. The city of São Paulo is characterized by a multi-centric urban landscape, with people usually commuting from the periphery to downtown where there are most of the jobs and opportunities. This results in congestion, large emissions from the transport sector and as a consequence, more pollutant exposure. The transport sector is responsible for 60% of the CO₂ emission. PM_2.5, an important climate pollutant is composed mainly of carbonaceous compounds, associated with the emissions by the vehicular fleet which uses biofuels (gasohol and bio-diesel). Starting in 2020, the aerosol network in Sao Paulo underwent updates to include measurements of greenhouse gases (GHGs) at five sites as part of the METROCLIMA project (www.metroclima.iag.usp.br). The primary objectives of this project are to determine the megacity's contribution to CO₂ and CH₄ emissions. Measurements of stable carbon isotopes (¹²C and ¹³C) of CO₂ and CH₄ in the atmosphere provide valuable information for identifying and quantifying the predominant sources and sinks of these gases. Continuous monitoring of d¹³C-CO in Sao Paulo has revealed changes in the contributions of significant CO₂ sources, including fossil fuels (including biofuels) and wildfires. CO₂ background concentrations were estimated for the period from 2019 to 2021, resulting in an annual increase rate of 2.5 ppm/year, which is consistent with the estimated values provided by NOAA-USA. The concentrations in the background station varied from 416.94 (9.25) to 421.82 (7.47), from 2019 to 2022. The highest concentrations were found in the morning and evening hours associated with vehicular emissions, but during the day it was possible to observe the effect of local vegetation photosynthesis in the reduction of the CO₂ concentrations.