Micro- and nanoplastic particles (MNPPs) are emerging pollutants with significant environmental impacts due to their persistence, increasing concentrations, and potential health risks. Most MNPP studies have focused on identifying, quantifying, and assessing their ecotoxicological impacts in water or soil. However, the atmosphere is crucial in transporting and chemically transforming MNPPs. Further, well-established aerosol particle characterization techniques are underutilized and inconsistently applied in existing atmospheric MNPP studies. This perspective synthesizes the existing literature and addresses future research needs unique to atmospheric MNPPs, highlighting the need to bridge the microplastics and atmospheric aerosol communities to better understand their sources, chemical transformations, transport mechanisms, as well as their health effects and ecological impacts, which differ from those in soil and water. Advancing research in these areas requires standardized methods and a multidisciplinary approach to comprehensively assess MNPP interactions across environmental compartments, providing essential insights into their environmental fate and risks.

Biogenic volatile organic compounds (BVOCs) emitted by plants represent the largest source of non-methane hydrocarbon emissions on Earth. Photochemical oxidation of BVOCs represents a significant pathway in the production of secondary organic aerosol (SOA), affecting Earth's radiative balance. Organic nitrates (RONO₂), formed from the oxidation of BVOCs in the presence of NO_x, represent important aerosol precursors and affect the oxidative capacity of the atmosphere, in part by sequestering NO_x. In the aerosol phase, RONO₂ hydrolyze to form nitric acid and numerous water-soluble products, thus contributing to an increase in aerosol mass. However, only a small number of studies have investigated the production of RONO₂ from OH oxidation of terpenes, and among those, few have studied their hydrolysis. Here, we report a laboratory study of OH-initiated oxidation of β-ocimene, an acyclic, tri-olefinic monoterpene released during the daytime from vegetation, including forests, agricultural landscapes, and grasslands. We conducted studies of the OH oxidation of β-ocimene in the presence of NO_x using a 5.5 m³ all-Teflon photochemical reaction chamber, during which we quantified the total (gas- and particle-phase) RONO₂ yield and the SOA yields. We sampled the organic nitrates produced and measured their hydrolysis rate constants across a range of atmospherically relevant pH. The total organic nitrate yield was determined to be 38(±9) %, consistent with the available literature regarding the dependence of organic nitrate production (from RO₂ + NO) on carbon number. We found the hydrolysis rate constants to be highly pH dependent, with a hydrolysis lifetime of 51(±13) min at pH = 4 and 24(±3) min at pH = 2.5, a typical pH for deliquesced aerosols. We also employed high-resolution mass spectrometry for preliminary product identification. The results indicate that the ocimene SOA yield (< 1 %) under relevant aerosol mass loadings in the atmosphere is significantly lower than reported yields from cyclic terpenes, such as α-pinene, likely due to alkoxy radical decomposition and formation of smaller, higher-volatility products. This is also consistent with the observed lower particle-phase organic nitrate yields of β-ocimene – i.e., 1.5(±0.5) % – under dry conditions. We observed the expected hydroxy nitrates by chemical ionization mass spectrometry (CIMS) and some secondary production of the dihydroxy dinitrates, likely produced by oxidation of the first-generation hydroxy nitrates. Lower RONO₂ yields were observed under high relative humidity (RH) conditions, indicating the importance of aerosol-phase RONO₂ hydrolysis under ambient RH. This study provides insight into the formation and fate of organic nitrates, β-ocimene SOA yields, and NO_x cycling in forested environments from daytime monoterpenes not currently included in atmospheric models.

The use of vibrational spectroscopy to probe environmental samples is increasing with the development of new methods, including microspectroscopic probes. In this study, we compare different vibrational methods to interrogate lipids and other compounds found in environmental samples. In particular, we compare the vibrational spectra for different lipids that include fatty acids (protonated and deprotonated forms), fatty alcohols, and fatty esters by utilizing attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, optical photothermal infrared (O-PTIR) spectroscopy, micro-Raman spectroscopy, and atomic force microscopy infrared (AFM-IR) spectroscopy. We show the utility of infrared methods to clearly delineate the structure of the lipid, i.e., whether it is an acid, alcohol, or ester. In contrast, it is difficult to differentiate these from micro-Raman spectroscopy. Furthermore, in the case of fatty acids, the protonation state can also be determined by infrared methods. In most cases, there is a high correlation between the three different infrared techniques as seen for ATR-FTIR and O-PTIR spectroscopy; however, this is not always true with AFM-IR spectroscopy for samples with low signal-to-noise or in a liquid phase state. Additionally, substrate-deposited aerosols were collected from the Scripps Ocean-Atmosphere Research Simulator (SOARS) and examined with both the O-PTIR and micro-Raman spectroscopy to show how these two vibrational probes together can provide essential chemical insights into environmental samples that are difficult to achieve otherwise.