With the increasing number of electric vehicles taking to the roads, the impact of tailpipe emissions on air quality will decrease, while resuspended road dust and brake/tire wear will become more significant. This study quantified PM10 emissions from tire wear under a range of real highway conditions with measurements across different seasons and roadway surface types in Phoenix, Arizona. Tire wear was quantified in the sampled PM10 using benzothiazoles (vulcanization accelerators) as tire markers. The measured emission factors had a range of 0.005–0.22 mg km−1 veh−1 and are consistent with an earlier experimental study conducted in Phoenix. However, these results are lower than values typically found in the literature and values calculated from emissions models, such as MOVES (MOtor Vehicle Emission Simulator). We found no significant difference in tire wear PM10 emission factors for different surface types (asphalt vs. diamond grind concrete) but saw a significant decrease in the winter compared to the summer.

An oxidizing and harmful pollutant gas, tropospheric ozone is a product of a complex set of photochemical reactions that can make it difficult to enact effective control measures. A better understanding of its precursors including volatile organic compounds (VOCs) and nitrogen oxides (NOx) and their spatial distribution can enable policymakers to focus their control efforts. In this study we used low-cost sensors (LCSs) to increase the spatial resolution of an existing NO2 monitoring network in addition to VOC sampling to better understand summer ozone formation in Maricopa County, Arizona, and observed that afternoon O3 values at the downwind sites were significantly correlated, ~0.27, to the morning NO2 × rate values at the urban sites. Additionally, we looked at the impact of wildfire smoke on ozone exceedances and compared non-smoke days to smoke days. The average O3 on smoke days was approximately 20% higher than on non-smoke days, however, the average NO2 concentration multiplied by estimated photolysis rate (NO2 × rate) values were only 2% higher on smoke days. Finally, we evaluated the ozone sensitivity of the region by calculating HCHO/NO2 ratios using three different datasets: ground, satellite, and model. Although the satellite dataset produced higher HCHO/NO2 ratios than the other datasets, when the proper regime thresholds are applied the three datasets consistently show transition and VOC-limited O3 production regimes over the Phoenix metro area. This suggests a need to implement more VOC emission controls in order to reach O3 attainment in the county.

Frequent collocation and calibration paired with temperature, relative humidity, and ozone correction factors improved the performance of a low-cost NO2 sensor network in Maricopa County, Arizona.

Air quality is a key factor in the development and persistence of asthma. Our knowledge is limited to understand how air pollutants affect the immunogenicity of airborne particles. Ragweed (Ambrosia artemisifolia) pollens were chemically aged under controlled atmospheric conditions with ozone (O3) or nitrogen oxide (NO). BALB/c mice were exposed intranasally to non-treated ragweed pollen (RWP), O3-treated (RWPO), or NO-treated (RWPN) ragweed pollen grains and challenged with either respective pollen grains or ragweed pollen extract. Bronchoalveolar lavage fluids were analyzed for total cellularity, cell differentials, and cytokine levels. Pulmonary inflammation was assessed by histological staining. Lung function was assessed by measuring airway resistance and elastance with flexiVent®. Ragweed-specific plasma levels of IgG1 and IgG2a antibodies were quantified by ELISA. Mice exposed to RWPO and challenged with ragweed extract (RWE) had higher BAL cellularity and eosinophilia compared to animals exposed to RWP or RWPN. Bronchoalveolar lavage and lung homogenates from mice exposed to RWPO contained higher levels of IL-4, IL-5, and IL-13. In contrast, RWPO-exposed groups had the lowest levels in ragweed-specific IgG1. Assessment of lung function showed higher respiratory system resistance and elastance in mice exposed to RWPN compared to RWP treated mice. Exposure to O3 and NO enhances the immunogenicity and/or biological impact of ragweed pollens in an in vivo mouse model of allergic asthma.

Due to the global response to the COVID-19 pandemic, there have been a variety of policy responses that have produced a range of expected and unexpected effects on society and our surrounding environment. One widely reported result of the pandemic response is that travel restrictions have resulted in improvements in regional air quality. This study aims to determine the effect of COVID-19 related Stay at Home precautions on air quality in a metropolitan area. We specifically focus on CO, NO2, and PM10 in Maricopa County (Phoenix), Arizona, as these all contribute to local air quality concerns. The role of meteorological parameters on ambient concentrations for these pollutants was investigated by using the local planetary boundary layer height (PBH) to account for vertical mixing. Across all three sites studied, there was no uniform decrease in either CO or NO2, even when freeway traffic volume was down by ~35%. For PM10, there was a significant decrease of ~45% seen at all the sites for the period most directly impacted by local Stay at Home restrictions compared to the past two years. This indicates that different pollutants have fundamentally different behavior in the local environment and suggests that these pollutants originate from different sources.

Low-cost air quality sensors (LCSs) have become more widespread due to their low cost and increased capabilities; however, to supplement more traditional air quality networks, the performance of these LCSs needs to be validated. This study focused on NO2 measurements from eight Clarity Node-S sensors and used various environmental factors to calibrate the LCSs. To validate the calibration performance, we calculated the root-mean-square error (RMSE), mean absolute error (MAE), R2, and slope compared to reference measurements. Raw results from six of these sensors were comparable to those reported for other NO2 LCSs; however, two of the evaluated LCSs had RMSE values ~20 ppb higher than the other six LCSs. By applying a sensor-specific calibration that corrects for relative humidity, temperature, and ozone, this discrepancy was mitigated. In addition, this calibration improved the RMSE, MAE, R2, and slope of all eight LCS compared to the raw data. It should be noted that relatively stable environmental conditions over the course of the LCS deployment period benefited calibration performance over time. These results demonstrate the importance of developing LCS calibration models for individual sensors that consider pertinent environmental factors.

DNA aptamers previously selected as calcium phosphate mineralization templates were modified and analyzed to better understand structure-function relationships and to explore the mechanism of templated mineralization. Aptamers were created to strengthen or remove a prevalent G-quadruplex structure and were analyzed for structural stability, affinity to calcium phosphate, influence on homogeneous and heterogeneous calcium phosphate mineralization, and influence on mineral crystallinity and morphology. Aptamers were found to modulate mineralization kinetics in a concentration-dependent manner. Changes to the G-quadruplex structure affected affinity to hydroxyapatite (Ca10(PO4)6(OH)2, HAP) and had a substantial impact on the mineral crystallinity. We propose a model for aptamer-directed mineralization and anticipate the usefulness of these aptamer sequences in future biomimetic and biomedical applications.

Mineralization of calcium phosphate and other materials in vivo and in natural water sources occurs in solutions that are not stagnant, but are flowing. Flow conditions could influence solution mixing and, therefore, mineralization kinetics or mechanism. This work describes the design and characterization of a multi-stream parallel flow microfluidic device that allows for controlled solution mixing and indirect control of laminar flow by altering the microfluidic device width, shape, length, flow rate, and flow velocity. Measurement of solution mixing was accomplished using the protonation of quinine to produce a fluorescent molecule and the rate of calcium phosphate mineralization was monitored by optical microscopy and analysis with Image J software. Experiments were designed to hold the flow rate constant, allowing the solution velocity to vary and to hold the velocity constant, allowing the flow rate to vary. It was found that small changes in laminar flow conditions do not correlate to mineral growth, but solution velocity and flow rate have a substantial effect on calcium phosphate mineralization. AFM and SEM characterization of the mineral produced shows an amorphous material and varying degrees of mineralization possibly due to variation in supersaturation conditions across the solution mixing area. This microfluidic device and analysis procedure allows for improved study of mineralization and the effect of flow conditions relevant to those seen in biological settings.