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Liquid water in cloud droplets and aqueous aerosols serves as an important reaction medium for the formation of secondary aerosol through aqueous-phase reactions (aqSA). Large uncertainties remain in estimates of the production and chemical evolution of aqSA in the dilute solutions found in cloud droplets and the concentrated solutions found in aerosol liquid water, which is partly due to the lack of available measurement tools and techniques. A new oxidation flow reactor (OFR), the Accelerated Production and Processing of Aerosols (APPA) reactor, was developed to measure secondary aerosol formed through gas- and aqueous-phase reactions, both for laboratory gas mixtures containing one or more precursors and for ambient air. For simulating in-cloud processes, ∼ 3.3 µ m diameter droplets formed on monodisperse seed particles are introduced into the top of the reactor, and the relative humidity (RH) inside it is controlled to 100 %. Similar measurements made with the RH in the reactor < 100 % provide contrasts for aerosol formation with no liquid water and with varying amounts of aerosol liquid water. The reactor was characterized through a series of experiments and used to form secondary aerosol from known concentrations of an organic precursor and from ambient air. The residence time distributions of both gases and particles are narrow relative to other OFRs and lack the tails at long residence time expected with laminar flow. Initial cloud processing experiments focused on the well-studied oxidation of dissolved SO 2 by O 3 , with the observed growth of seed particles resulting from the added sulfuric acid agreeing well with estimates based on the relevant set of aqueous-phase reactions. The OH exposure (OH exp⁡) for low RH, high RH, and in-cloud conditions was determined experimentally from the loss of SO 2 and benzene and simulated from the KinSim chemical kinetics solver with inputs of the measured 254 nm UV intensity profile through the reactor and loss of O 3 due to photolysis. The aerosol yield for toluene at high OH exp⁡ ranged from 21.4 % at low RH with dry seed particles present in the reactor to 78.1 % with cloud droplets present. Measurement of the composition of the secondary aerosol formed from ambient air using an aerosol mass spectrometer showed that the oxygen-to-carbon ratio (O : C) of the organic component increased with increasing RH (and liquid water content). [ABSTRACT FROM AUTHOR]

This paper evaluates the performance of a multirotor uncrewed aircraft and AirCore system (UAAS) for measuring vertical profiles of wind velocity (speed and direction) and the mole fractions of methane (CH 4) and carbon dioxide (CO 2) , and it presents a use case that combines UAAS measurements and dispersion modeling to quantify CH 4 emissions from a dairy farm. To evaluate the atmospheric sensing performance of the UAAS, four field deployments were performed at three locations in the San Joaquin Valley of California where CH 4 hotspots were observed downwind of dairy farms. A comparison of the observations collected on board the UAAS and an 11 m meteorological tower show that the UAAS can measure wind velocity trends with a root mean squared error varying between 0.4 and 1.1 m s -1 when the wind magnitude is less than 3.5 m s -1. Findings from UAAS flight deployments and a calibration experiment also show that the UAAS can reliably resolve temporal variations in the mole fractions of CH 4 and CO 2 occurring over periods of 10 s or longer. Results from the UAAS and dispersion modeling use case further demonstrate that UAASs have great potential as low-cost tools for detecting and quantifying CH 4 emissions in near real time. [ABSTRACT FROM AUTHOR]

Particle size dependent wall-loss rates vary widely between Teflon environmental chambers. For instance, the UCR/CE-CERT dual-90 m3 collapsible Teflon chambers (UCR collapsible chamber) measured particle wall-loss rates are relatively insensitive to particle size, while other chambers (e.g., Caltech, GaTech, UC Davis) exhibit a strong dependence of wall loss rates on particle size. Particle wall loss rates in the larger UCR collapsible chambers exceed those reported for some smaller volume chambers. The size-dependent particle wall-loss patterns in the absence of coagulation within the UCR collapsible chambers were experimentally characterized in this work using a monodisperse particle injection method. Electrostatic charges on chamber surfaces were found to dominate the particle deposition in the UCR collapsible chamber. Charged particles ∼50 nm in diameter decay much faster than charged 200 nm particles, but the overall decay enhancement by electrostatics was determined to be smaller for 50 nm particles due to kinetic charging limitations. Particles in the chamber, regardless of initial charge state, approached a chamber-specific charge steady-state, where the charge steady-state for smaller particles was driven by preferential loss of charged particles while the charge steady-state for larger particles was driven by bidirectional diffusion charging. Coagulation was found to be significant when high particle number loadings are present (e.g., 5 × 104 cm−3). Mitigation strategies are needed for environmental chambers susceptible to surface charging (e.g., UCR collapsible chambers) in order to lower the influence from electrostatics. The shape of the particle wall-loss pattern can be used to identify chambers driven by significant electrostatic particle wall-loss. [ABSTRACT FROM AUTHOR]

There are two predominant methods for understanding and studying bioaerosol aging: capture on microfibers, and Goldberg rotating drums. There are advantages and disadvantages to each approach depending on the experimental needs, cost, and timeline, but they have rarely been compared in parallel to determine the similarity of results. Experiments that use Goldberg drums have the advantage of studying aerosol particles in suspension, but due time resolution of aging processes is limited by chamber volume, sample volumes, and aerosol loss mechanisms. For microfiber experiments, particles are adhered to the fiber, and so only simulate natural aerosols, but there are significant advantages since particles are not lost during aging and the time resolution is not limited by sampling. In this study, we compared outdoor UV-transmitting Goldberg rotating drums with polymethyl methacrylate (PMMA) synthetic spider web material in a complex real-world environment during a summer near Houston, Texas. Bacillus thuringiensis al hakam spores were aerosolized into UV-transmitting, gas-permeable chambers that allowed relevant exposure to real-world atmospheric conditions while isolating particles of interest. Aging was compared for up to 4 h in both sunlight exposed and protected environments to compare and quantify relative degradation rates. The two disparate methodologies yielded similar results, with no statistical difference found in three out of four combinations of carbon-filtered air vs. ambient air, and protection from sunlight vs. exposure to sunlight, but this could vary for other particle sizes or organisms. Copyright © 2023 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Liquid water in cloud droplets and aqueous aerosols serves as an important reaction medium for the formation of secondary aerosol through aqueous-phase reactions (aqSA). Large uncertainties remain in estimates of the production and chemical evolution of aqSA in the dilute solutions found in cloud droplets and the concentrated solutions found in aerosol liquid water, which is partly due to the lack of available measurement tools and techniques. A new oxidation flow reactor (OFR), the Accelerated Production and Processing of Aerosols (APPA) reactor, was developed to measure secondary aerosol formed through gas- and aqueous-phase reactions, both for laboratory gas mixtures containing one or more precursors and for ambient air. For simulating in-cloud processes, droplets formed on monodisperse seed particles are introduced into the top of the reactor and the relative humidity (RH) inside it is controlled to 100 %. Similar measurements made with the RH in the reactor <100 % provide contrasts for aerosol formation with no liquid water and with varying amounts of aerosol liquid water. The reactor was characterized through a series of experiments and used to form secondary aerosol from known concentrations of an organic precursor and from ambient air. The transmission efficiency of O3 and CO2 for all RH and of SO2 for low RH exceeds 90 %, while it falls to about 70 % for SO2 at 100 % RH. Particle transmission efficiency increases with increasing particle diameter from 0.67 for 0.050 µm particles to 0.98 at 0.20 µm, while that of the ~3.3 µm droplets formed on seed particles is greater than 80 %. The residence time distributions of both gases and particles are narrow relative to other OFRs and lack the tails at long residence time expected with laminar flow. Initial cloud processing experiments focused on the well-studied oxidation of dissolved SO2 by O3, with observed growth of seed particles resulting from the added sulfuric acid agreeing well with estimates based on the relevant set of aqueous phase reactions. The OH exposure (OHexp) for low RH, high RH, and in-cloud conditions was determined experimentally from the loss of SO2 and benzene, and simulated from the KinSim chemical kinetics solver with inputs of measured 254 nm UV intensity profile through the reactor and loss of O3 due to photolysis. The aerosol yield for benzene at high OHexp ranged from 18 % at low RH with dry seed particles present in the reactor to 59 % with cloud droplets present. Measurement of the composition of the secondary aerosol formed from ambient air using an aerosol mass spectrometer showed that the oxygen to carbon ratio (O:C) of the organic component increased with increasing RH (and liquid water content). [ABSTRACT FROM AUTHOR]