Relationships between electrical activity, nitrogen oxides and ultrafine particles in Central Amazonia during the rainy season

Author(s)

Carolina de Aguiar Monteiro

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto Astronômico e Geofísico (IAG/SBD)
• Defense date: 2022-10-14

Examining board members

Rachel Ifanger Albrecht; Luiz Augusto Toledo Machado; Luciana Varanda Rizzo

• Advisor: Rachel Ifanger Albrecht

Abstract

Central Amazônia has been the focus of studies of aerosol-cloud-precipitation interactions because it is a region with little anthropogenic influence and significant electrical activity. The electrical activity forms nitrogen oxides (Lightning Nox - LNOx), which are precursors to the main oxidants in the atmosphere, the hydroxyl radical (OH) and ozone (O3), being the main natural source of NOx in the atmosphere. These oxidants attack the double bonds of biogenic volatile organic compounds emitted from the forest, and produce organic side products that can serve as components of ultrafine particles (UAPs). This process can occur within deep convective systems that are capable of bringing these components to the surface. This work investigates the transport of NOx and UAPs to the surface during deep convective systems in the Amazon region. It was used data from the two wet seasons of GoAmazon2014/15 project. Out of the 362 days analyzed, 42 days (11.6%) presented electrical activity with NOx peaks, and without contamination of the Manaus plume. Of these days, 19 days were classified into 3 classes based on particle size: events with an increase of ultrafine particles concentration only (<50 nm), events with no increase in UAPs concentrations, and events with an increase in concentration of all particle sizes studied here (<50 nm - ND50, between 50 and 100 nm ND50-100, and >100 nm ND100). It was observed that an increase in particle concentration was related to NOx peaks and vertical downward transport from precipitating systems. It was found a significative correlation (0.61 to 0.69) between the amount of lightning and the highest NOx peaks in each case, and NOx concentrations are comparable to concentrations observed in large urban areas in previous studies. The relationship between NOx peaks and UAPs concentration in the three sizes classes studied suggests three hypotheses. The first (Hypothesis A) says that events with an increase only in the concentration ND50 particles are related to the formation of particles by the oxidation of biogenic volatile organic compounds (BVOCs) within convective and transported to the surface by downdrafts, in time scale of hours, as proposed by other authors. The second (Hypothesis B) says that events that do not have a significant increase in the concentration of particles of any sizes (less than 100nm), may be associated with very recent convection, or convection with weak previous updrafts, which are not capable of carrying high concentrations of BVOCs for significant nucleation of ultrafine particles. And the third (Hypothesis C) says that an event with a considerable increase in the concentration of particles of all sizes, ultrafine and fine, may be evidence of the transport of ultrafine particles nucleated and grown in the upper troposphere to the surface by the downdraft of the convective system. (AU)

• FAPESP's process: 20/11000-5 - Relationships between electrical activity, precipitation and aerosol life cycle in the Amazon
• Grantee: Carolina de Aguiar Monteiro
• Support Opportunities: Scholarships in Brazil - Master