Science Talks Lecture 139: Secondary Organic Aerosols from Biogenic and Biomass Burning Emissions

[Music]

The introduction of Professor Sali, detailing her background and research focus.

Introduction of Professor Sali

• Professor Sali holds the Love Family Professor position at Georgia Institute of Technology in chemical and biomolecular engineering and Earth and atmospheric sciences.

• Her research centers on aerosol formation, composition, health effects, using advanced mass spectrometry techniques.

• Recognized with various awards for research contributions in aerosol science.

Secondary Organic Aerosols: Chemistry to Climate and Health

Exploring secondary organic aerosols from biogenic and biomass burning emissions in relation to climate, human health, and chemistry.

Understanding Aerosols

• Aerosols are fine particulate matter with diverse sources like vehicle exhaust, wildfires, cooking emissions, trees, impacting indoor and outdoor environments.

• Significance of studying aerosols due to their severe health impacts globally leading to millions of deaths attributed to PM2.5 pollution.

Impact on Health and Climate

• Air pollution ranks high in global disease burden affecting human health significantly.

• Aerosols play a crucial role in climate change by either cooling or warming the Earth through radiation absorption or reflection processes.

Formation of Secondary Organic Aerosols

• Primary organic aerosols emitted as particles while volatile organic compounds (VOCs) can be biogenic (from trees) or anthropogenic (human activities).

Chemistry in the Atmosphere

In this section, the speaker discusses their group's systematic approach to studying organic aerosols through laboratory experiments and ambient measurements to understand aerosol formation and composition.

Understanding Organic Aerosols

• Trees emit compounds like monoterpenes, such as α-pinene and β-pinene, which interact with vehicle emissions like nitrogen oxides (NOx) in urban areas.

• Monoterpenes are C10H16 compounds responsible for the distinct smell of pine forests.

• Interaction between tree emissions and car emissions can lead to intriguing atmospheric chemistry processes.

Analyzing Aerosols

• The speaker uses advanced mass spectrometry instruments like the aerosol mass spectrometer for real-time analysis of submicron non-refractory aerosols.

• Nitrate measurements reveal the presence of organic nitrates alongside inorganic nitrates in aerosols.

Global Presence of Organic Nitrates

• Research in the Southeast US shows significant organic nitrate levels from interactions between tree and car emissions.

• Organic nitrates are prevalent worldwide, contributing substantially to organic aerosol composition.

Formation and Fate of Organic Nitrates

This part delves into how organic nitrates form, their impact on atmospheric processes like ozone formation, and their fate within aerosols.

Formation Mechanisms

• Ozone formation from NOx photochemical cycles leads to the creation of nitrate radicals that react with volatile organic compounds (VOCs), forming organic nitrates.

• Organic nitrates contribute to secondary organic aerosol formation through gas-to-particle conversion.

Transformation Processes

• Hydrolysis and release of NOx back into the atmosphere by organic nitrates influence atmospheric chemistry cycles.

Experimental Study

Measurement of Gas and Particle Phase Organics

The discussion revolves around the measurement of gas and particle phase organics at a molecular level using different techniques to understand the composition and behavior of organic nitrates.

Analyzing Organic Nitrates Composition

• Organic nitrates, crucial for research, are synthesized from compounds like alpha pinene, B pinene, and loline to study primary, secondary, and tertiary functionalities.

• These synthetic organic nitrates contain alcohol groups, carbonyl groups, nitro groups that aid in understanding their reactivity upon formation.

Experimental Procedures for Understanding Photolysis

• Experiments involve injecting compounds like loline hydroxy nitrate into a chamber to observe various reactions such as loss to chamber walls or reaction with ozone.

• Different pathways contribute to compound loss including wall losses, reaction with hydroxyl radicals or ozone; focus on studying photolysis impact on compound stability.

Teasing Out Photolysis Rate

• Detailed experiment steps include injecting compounds into the chamber followed by observing changes during light exposure indicating processes like vapor wall loss or consumption by ozone.

• By comparing compound decay during light and dark periods, researchers calculate photolysis rates crucial for understanding the rapid degradation of organic nitrates.

Impact of Organic Nitrates on Ozone Formation

The conversation delves into how the short photolysis lifetime of organic nitrates due to specific chemical structures can lead to NOx release impacting ozone formation.

Understanding Photolysis Lifetime

• Research reveals that organic nitrates have a short photolysis lifetime attributed to chemical features like Nitro group and double bonds facilitating rapid degradation upon formation.

Implications on Ozone Formation

• Photolysis of organic nitrates releases NOx which can participate in ozone formation; simulations show significant release of NOx leading to increased ozone levels over time.

Role of Organic Nitrates in Ozone Formation

Exploring how organic nitrate photolysis can release NOx impacting ozone levels necessitates understanding the composition and behavior of these compounds in atmospheric chemistry.

Simulation Insights

Climate Impact of Wildfires and Biomass Burning

In this section, the speaker discusses the impact of wildfires and biomass burning on climate through the emission of particles and volatile organic compounds.

Wildfires Emissions

• Wildfires, including Canadian wildfires, emit particles that can travel long distances, impacting regions like Atlanta.

• "Wildfires emit a lot of particles which are primary particles."

Volatile Organic Compounds (VOCs)

• VOCs emitted by wildfires include furans, different from terpenes found in trees.

• "Wildfires emit a lot of VOCs called furans."

Laboratory Experiments

• Chamber experiments involve injecting seed particles like ammonium sulfate and specific VOCs for oxidation to form secondary organic aerosols.

• "Inject seed particles like ammonium sulfate into the chamber."

Chemical Composition and Formation of Brown Carbon Aerosols

This section delves into the formation process and chemical composition of brown carbon aerosols resulting from biomass burning emissions.

Experimental Profile

• Typical experiment shows the reaction between furans with oxidants forming organics and organic nitrates.

• "Formation of organics and organic nitrate in a typical experimental profile."

Mass Absorption Efficiency (MAE)

• MAE is used to characterize light-absorbing aerosols with furan aerosol exhibiting the highest MAE among compounds studied.

• "Furan aerosol has the highest MAE followed by two methyl and three methyl furan."

Impact on Climate and Human Health

The discussion shifts towards exploring how biomass burning emissions impact both climate through light absorption and potentially human health.

Formation Mechanism

• Nitrogen-containing compounds formed during reactions enhance light absorption contributing to brown coloration observed in filters.

• "Nitrogen-containing compounds enhance light absorption leading to brown carbon aerosols."

Human Health Implications

• Investigation into toxicity of organic aerosols from biomass burning raises concerns about potential impacts on human health.

Environmental Toxicity Study Using Cellular Assay

In this section, the speaker discusses using a cellular assay to study the toxicity of different organic aerosols in Atlanta during summer and winter.

MacCrage Cell as First Line of Defense

• The MacCrage cells serve as the first line of defense against environmental insults.

Chemical Composition Analysis

• Mass spectrometers are deployed in summer and winter to analyze aerosol chemical composition.

• Instruments like AMS and FIGOS provide bulk and speciated composition data at molecular levels.

• Filters are collected for offline mass spectrometry analysis.

Health Analysis with MacCrage Essay

• The MacCrage essay involves exposing extracted filters to MacCrage cells to capture reactive oxygen species generated by cells.

• Understanding oxidative stress is crucial for comprehending adverse health effects from inhaling particles.

Organic Aerosol Composition Analysis

This part delves into characterizing organic aerosols in Atlanta, focusing on their sources and types.

Source Apportionment Analysis

• Organic aerosols are predominantly present in Atlanta, with up to 90% being organics.

• Source apportionment analysis categorizes organic aerosols into different types based on origins like biomass burning, cooking emissions, vehicle combustion, and isoprene emissions.

Oxygenated Organic Aerosol Types

• Two key oxygenated organic aerosol types (L and M OA) are highlighted due to their significance in total organic aerosol content.

• Secondary organic aerosols dominate the organic aerosol composition in Atlanta and globally.

Toxicity Assessment of Organic Aerosols

This segment focuses on linking different types of organic aerosols to cellular toxicity through multi-linear regression analysis.

Multi-linear Regression Analysis

• A comprehensive analysis links various types of organic aerosols to cellular toxicity measured by the cellular assay.

• More oxidized OA consistently emerges as a major predictor for cellular reactive oxygen species (ROS), indicating high toxicity levels.

Detailed Analysis of Organic Aerosols and Their Impact

In this section, the speaker discusses the correlation between highly unsaturated and aromatic compounds in organic aerosols, emphasizing their impact on toxicity and oxidation.

Correlation Between Unsaturated Compounds and Aromatics

• Highly unsaturated species in organic aerosols tend to be aromatic as well.

• The presence of a high degree of unsaturation correlates with high oxidation levels.

Formation of Toxic Compounds

• Conjugation of acids and carbonyls on an aromatic system leads to the formation of compounds with diverse functionalities.

• Compounds with many functionalities can be highly reactive and contribute to cellular ROS production.

Impact of Biogenic and Anthropogenic Sources on Aerosol Composition

This segment delves into the interaction between biogenic terpenes from trees and anthropogenic NOx emissions, highlighting their role in organic nitrate formation and ozone production.

Interaction Between Biogenic Terpenes and NOx Emissions

• Oxidation of terpenes in the presence of NOx results in the formation of organic nitrates.

• Organic nitrates have short photolysis lifetimes, impacting ozone formation.

Photooxidation Effects from Biomass Burning

• Oxidation of compounds from biomass burning generates brown carbon and secondary organic aerosols rich in nitrogen-containing compounds.

• These aerosols can influence climate by absorbing radiation and affecting health due to their transportability.

Future Implications: Increased Toxicity Potential in Organic Aerosols

The discussion shifts towards future scenarios where increased combustion activities may lead to heightened toxicity in secondary organic aerosols (SOA).

Combustion Impact on SOA Toxicity

• Combustion processes generate highly oxidized SOA containing unsaturated species that can enhance cellular toxicity.

• With rising combustion rates due to climate change, there is a potential for more toxic SOA production.

Work Presentation Acknowledgment

In this segment, the speaker acknowledges the contributions of postdoctoral and graduate students to the work presented.

Acknowledgment of Postdoctoral and Graduate Students

• The speaker highlights the talent and motivation of postdoctoral and graduate students who significantly contributed to the work.

• Three recent postdoctoral and graduate students are specifically mentioned for their substantial contributions.