[1] During the field campaign of the Study of Houston Atmospheric Radical Precursors/ Surface-Induced Oxidation of Organics in the Troposphere (SHARP/SOOT) in Houston, Texas, a suite of aerosol instruments was deployed to directly measure a comprehensive set of aerosol properties, including the particle size distribution, effective density, hygroscopicity, and light extinction and scattering coefficients. Those aerosol properties are employed to quantify the mixing state and composition of ambient particles and to gain a better understanding of the formation and transformation of fine particulate matter in this region. During the measurement period, aerosols are often internally mixed, with one peak in the effective density distribution at 1.55 ± 0.07 g cm À3 , consistent with a population composed largely of sulfates and organics. Episodically, a second mode below 1.0 g cm À3 is identified in the effective density distributions, reflecting the presence of freshly emitted black carbon (BC) particles. The measured effective density demonstrates a clear diurnal cycle associated with primary emissions from transportation and photochemical aging, with a minimum during the morning rush hour, increasing from 1.4 to 1.5 g cm À3 on average over 5 h, and remaining nearly constant throughout the afternoon. The average BC concentration derived from light-absorption measurements is 0.31 ± 0.22 μg m À3 , and the average measured particle single scattering albedo is 0.94 ± 0.04. When elevated BC concentrations are observed, typically during the morning rush hours, single scattering albedo decreases, with a smallest measured value of about 0.7. Aerosol hygroscopicity measurements indicate that larger particles (e.g., 400 nm) are more hygroscopic than smaller particles (e.g., 100 nm). The measurements also reveal discernable meteorological impacts on the aerosol properties. After a frontal passage, the average particle effective density decreases, the average BC concentration increases, and the aerosol size distribution is dominated by new particle formation.

A new parameterization for quantifying the mixing state of aerosol populations has been applied for the first time to samples of ambient particles analyzed using spectro‐microscopy techniques. Scanning transmission X‐ray microscopy/near edge X‐ray absorption fine structure (STXM/NEXAFS) and computer‐controlled scanning electron microscopy/energy dispersive X‐ray spectroscopy (CCSEM/EDX) were used to probe the composition of the organic and inorganic fraction of individual particles collected on 27 and 28 June during the 2010 Carbonaceous Aerosols and Radiative Effects study in the Central Valley, California. The first field site, T0, was located in downtown Sacramento, while T1 was located near the Sierra Nevada Mountains. Mass estimates of the aerosol particle components were used to calculate mixing state metrics, such as the particle‐specific diversity, bulk population diversity, and mixing state index, for each sample. The STXM data showed evidence of changes in the mixing state associated with a buildup of organic matter confirmed by collocated measurements, and the largest impact on the mixing state was due to an increase in soot dominant particles during this buildup. The mixing state from STXM was similar between T0 and T1, indicating that the increased organic fraction at T1 had a small effect on the mixing state of the population. The CCSEM/EDX analysis showed the presence of two types of particle populations: the first was dominated by aged sea‐salt particles and had a higher mixing state index (indicating a more homogeneous population); the second was dominated by carbonaceous particles and had a lower mixing state index.

Papers based biosensors such as lateral flow test strips and paper‐based microfluidic devices are inexpensive, rapid, flexible, and easy‐to‐use analytical tools for point‐of‐care diagnosis. An apparent trend in their detection is to interpret sensing results from qualitative assessment to quantitative determination. Electrochemical (EC) detection plays an important role in quantifying test results. This review focuses on paper‐based biosensors with EC detection. The first part provides detailed examples in lateral flow test strips while the second part gives an overview of paper microfluidics. The outlook and recommendation of future directions of papers based EC biosensors are discussed in the end.

A novel microfluidic reactor for biofilm growth and in situ characterization using time-of-flight secondary ion mass spectrometry (ToF-SIMS) was constructed to enable two-dimensional chemical imaging of hydrated biofilms. We demonstrate the detection of characteristic fatty acid fragments from microfluidic reactor-grown biofilms and illustrate advantages of hydrated-state ToF-SIMS imaging.