Ozone and Secondary Organic Aerosol Formation Potential from Native Tree Species in Atlantic Forest Remnants of Southeastern Brazil under Anthropogenic Influence

Biogenic volatile organic compounds (BVOCs) play a crucial role in urban air quality by contributing to ground-level ozone (O₃) and secondary organic aerosol (SOA) formation. While forests help mitigate air pollution, BVOC emissions can interact with anthropogenic pollutants, exacerbating air pollution. These emissions are influenced by seasonality and urbanization, affecting both their rates and chemical compositions [1]. In the Metropolitan Area of São Paulo (MASP), the Atlantic Forest provides a valuable opportunity to study these interactions, but current research is limited [2].

This study assessed BVOC emissions from four native Atlantic Forest species —Alchornea sidifolia (AS), Casearia sylvestris (CS), Guarea macrophylla (GM), and Machaerium nyctitans (MN) —across two forest reserves exposed to different pollution levels. Sampling was conducted at the less polluted Morro Grande Forest Reserve (RMG) and the more urbanized Matão-IAG Forest during the dry (August–September 2023) and rainy (January–February 2024) seasons.

Six replicates per species were analyzed. Branches were cut and placed in water to prevent embolism, and BVOCs were collected using a dynamic enclosure system for 1h. Volatiles were trapped on Tenax cartridges, desorbed using thermal desorption, and analyzed via gas chromatography-mass spectrometry. Ozone formation potential (OFP) and SOA formation potential (SOAP) were calculated using emission rates (ER, µg g⁻¹ h⁻¹), Maximum Incremental Reactivity (MIR), and Fractional Aerosol Coefficients (FACs).

Among the species studied, no isoprene emitters were identified. Sesquiterpenes (SQTs) dominated the emissions. During the dry season at RMG, CS presented the highest OFP (23.44 µg g⁻¹ h⁻¹), driven by elevated SQT emissions. MN ranked second (4.89 µg g⁻¹ h⁻¹) due to high 3-hexen-1-ol emissions, followed by GM (2.91 µg g⁻¹ h⁻¹) and AS (1.96 µg g⁻¹ h⁻¹). At Matão-IAG, CS remained the top contributor but with reduced OFP. AS rose to second place (2.40 µg g⁻¹ h⁻¹), surpassing GM (2.05 µg g⁻¹ h⁻¹). During the rainy season, CS still led (3.26 µg g⁻¹ h⁻¹) at RMG, followed by GM (2.10 µg g⁻¹ h⁻¹), AS (1.65 µg g⁻¹ h⁻¹), and MN (1.50 µg g⁻¹ h⁻¹). Similar trends were observed at Matão-IAG, with CS (2.74 µg g⁻¹ h⁻¹) leading, followed by AS (2.23 µg g⁻¹ h⁻¹), GM (1.99 µg g⁻¹h⁻¹), and MN (0.51 µg g⁻¹ h⁻¹). SOAP trends mirrored OFP. CS consistently had the highest SOAP, particularly at RMG during the dry season (213.30 µg g⁻¹ h⁻¹). GM (19.98 µg g⁻¹ h⁻¹) and AS (17.93 µg g⁻¹ h⁻¹) followed while MN had minimal contributions (1.89 µg g⁻¹ h⁻¹). At Matão-IAG, AS surpassed GM during the rainy season (18.93 vs. 15.63 µg g⁻¹ h⁻¹). Overall, OFP and SOAP exhibited site- and season-dependent variations, declining during the rainy season. CS, as the highest emitter, warrants careful consideration in reforestation planning.

Keywords: BVOCs, São Paulo, Atlantic Forest

Acknowledgements: Funded by Biomasp+ Project - FAPESP (20/07141-2) and, conducted at the Laboratory of Plant-Atmosphere Interaction (LABIAP), Environmental Research Institute of São Paulo.

References
[1] dos Santos et al. 2022. Science of the Total Environment, 824, 153728.
[2] Anselmo-Moreira et al. 2025. Urban Forestry & Urban Greening, 104, 128645.