Quantifying the Role of the Relative Humidity-Dependent Physical State of Organic Particulate Matter in the Uptake of Semivolatile Organic Molecules.

The uptake of gas-phase dicarboxylic acids to organic particulate matter (PM) was investigated to probe the role of the PM physical state in exchange processes between gas-phase semivolatile organic molecules and organic PM. A homologous series of probe molecules, specifically isotopically labeled C-dicarboxylic acids, was used in conjunction with aerosol mass spectrometry to obtain a quantitative characterization of the uptake to organic PM for different relative humidities (RHs). The PM was produced by the dark ozonolysis of unlabeled α-pinene.

Intermediate-scale horizontal isoprene concentrations in the near-canopy forest atmosphere and implications for emission heterogeneity.

The emissions, deposition, and chemistry of volatile organic compounds (VOCs) are thought to be influenced by underlying landscape heterogeneity at intermediate horizontal scales of several hundred meters across different forest subtypes within a tropical forest. Quantitative observations and scientific understanding at these scales, however, remain lacking, in large part due to a historical absence of canopy access and suitable observational approaches. Herein, horizontal heterogeneity in VOC concentrations in the near-canopy atmosphere was examined by sampling from an unmanned aerial vehicle (UAV) flown horizontally several hundred meters over the plateau and slope forests in central Amazonia during the morning and early afternoon periods of the wet season of 2018.

Influence of Particle Surface Area Concentration on the Production of Organic Particulate Matter in a Continuously Mixed Flow Reactor.

Organic particulate matter (PM) was produced at different particle surface area concentrations S in a continuously mixed flow reactor (CMFR). The apparent PM yield from the dark ozonolysis of α-pinene increased from 24.5 ± 0.

Influence of Particle Physical State on the Uptake of Medium-Sized Organic Molecules.

The uptake of medium-sized levoglucosan and 2,4-dinitrophenol to organic particles produced by α-pinene ozonolysis and to ammonium sulfate particles was studied from 10% to >95% relative humidity (RH). For aqueous sulfate particles, the water-normalized gas-particle partitioning coefficient of levoglucosan decreased from (1.0 ± 0.

Isoprene photo-oxidation products quantify the effect of pollution on hydroxyl radicals over Amazonia.

Nitrogen oxides (NO ) emitted from human activities are believed to regulate the atmospheric oxidation capacity of the troposphere. However, observational evidence is limited for the low-to-median NO concentrations prevalent outside of polluted regions. Directly measuring oxidation capacity, represented primarily by hydroxyl radicals (OH), is challenging, and the span in NO concentrations at a single observation site is often not wide.

Regional Similarities and NO-related Increases in Biogenic Secondary Organic Aerosol in Summertime Southeastern U.S.

During the 2013 Southern Oxidant and Aerosol Study, Fourier Transform Infrared Spectroscopy (FTIR) and Aerosol Mass Spectrometer (AMS) measurements of submicron mass were collected at Look Rock (LRK), Tennessee, and Centreville (CTR), Alabama. Carbon monoxide and submicron sulfate and organic mass concentrations were 15-60% higher at CTR than at LRK but their time series had moderate correlations (r~0.5).

Isoprene photochemistry over the Amazon rainforest.

Isoprene photooxidation is a major driver of atmospheric chemistry over forested regions. Isoprene reacts with hydroxyl radicals (OH) and molecular oxygen to produce isoprene peroxy radicals (ISOPOO). These radicals can react with hydroperoxyl radicals (HO2) to dominantly produce hydroxyhydroperoxides (ISOPOOH).

Uptake of epoxydiol isomers accounts for half of the particle-phase material produced from isoprene photooxidation via the HO2 pathway.

The oxidation of isoprene is a globally significant source of secondary organic material (SOM) of atmospheric particles. The relative importance of different parallel pathways, however, remains inadequately understood and quantified. SOM production from isoprene photooxidation was studied under hydroperoxyl-dominant conditions for <5% relative humidity and at 20 °C in the presence of highly acidic to completely neutralized sulfate particles.

Measurement of gas-phase hydroperoxides by chemical ionization mass spectrometry.

A new method for the detection of gas-phase hydroperoxides is described. The clustering chemistry of CF3O- is exploited to produce speciated measurements of several hydroperoxides with high sensitivity and fast time response. Correspondence of airborne observations made with this technique and the established HPLC method is illustrated.