Comparison between Sentinel 5P and WRF-CHEM long-term simulations: An analysis based on TROPOMI HCHO data over São Paulo, Brazil within the BIOMASP+ project

BIOMASP+: Biogenic Volatile Organic Compounds in the Metropolitan Area of São Paulo (MASP) is a collaboration project among different French and Brazilian institutions to investigate the critical role of the biosphere-atmosphere interactions on urban pollution conditions and to evaluate how the biogenic volatile organic compounds (BVOC) affect the secondary pollutant formation.

Formaldehyde (HCHO) is the most abundant atmospheric carbonyl compound and a photochemical oxidation product of VOCs from several anthropogenic and natural sources [1]. Over São Paulo state (SP), HCHO arises from complex atmospheric interactions between a large urban area with 15 million of vehicles using four different fuel types, several industries, an extensive Atlantic Rainforest (3.9 10⁴ km²), biomass burning and thousands of farms that cover 40% (2.5 10⁵ km²) of the SP area [2]. The Metropolitan Area of São Paulo (MASP) is a highly polluted megacity [3], with concentrations that often exceed the World Health Organization guidelines, particularly for ozone and PM_2.5, which are produced by photochemical reactions, such as the formaldehyde.

Vertical formaldehyde columns data (mol/m²) were obtained from the TROPOspheric Monitoring Instrument (TROPOMI) spectrometer onboard the Sentinel-5P satellite [2], and used in the WRF-CHEM model performance evaluation. Both, the long-term simulation and the Sentinel-5P data, covered the full 2022-year.

Satellite data confirmed the spatial distribution of HCHO simulated by WRF-CHEM, indicating MASP as the main formaldehyde hotspot in the state of São Paulo [2]. For the HCHO monthly averages, the normalized cross-correlation (i.e., spatial distribution) between model and satellite remains inside the range of: 0.3 < r < 0.6.

Using the satellite time series, it was possible to identify a bias in the HCHO simulated concentrations, that reached up to 80% in 1-year of simulation. This reduced the model's ozone production by up to 60% in the end of simulation. Comparing the simulation results with ozone data from air quality monitoring stations of the state of São Paulo [4], the linear correlation was within the range of 0.4 < r² < 0.7, while the error was high (RMSE < 46.5).

A long-term (1-year) simulation with WRF-CHEM is quite challenging task [3], however, the TROPOMI data was crucial to identify modeling problems in areas with absence of air quality data, indicating possible adjustments and corrections in the emissions inventories.

 

[1]        Gao, S., et al., 2021, Atmospheric formaldehyde, glyoxal and their relations to ozone pollution under low- and high-NOx regimes in summertime Shanghai, China, Atmospheric Research, https://doi.org/10.1016/j.atmosres.2021.105635

[2]        Freitas & Fornaro, 2022, Atmospheric Formaldehyde Monitored by TROPOMI Satellite Instrument throughout 2020 over São Paulo State, Brazil, Remote Sensing, https://doi.org/10.3390/rs14133032

[3]        Peralta, A., et al., 2023, Future Ozone Levels Responses to Changes in Meteorological Conditions under RCP 4.5 and RCP 8.5 Scenarios over São Paulo, Brazil., Atmosphere, https://doi.org/10.3390/atmos14040626

[4] CETESB < https://cetesb.sp.gov.br/ar/wp-content/uploads/sites/28/2023/07/Relatorio-de-Qualidade-do-Ar-no-Estado-de-Sao-Paulo-2022.pdf>

 

 

Keywords:  BIOMASP; Formaldehyde; TROPOMI; WRF-CHEM