Apportioned primary and secondary organic aerosol during pollution events of DISCOVER-AQ Houston.

Understanding the drivers for high ozone (O3) and atmospheric particulate matter (PM) concentrations is a pressing issue in urban air quality, as this understanding informs decisions for control and mitigation of these key pollutants. The Houston, TX metropolitan area is an ideal location for studying the intersection between O3 and atmospheric secondary organic carbon (SOC) production due to the diversity of source types (urban, industrial, and biogenic) and the on- and off-shore cycling of air masses over Galveston Bay, TX. Detailed characterization of filter-based samples collected during Deriving Information on Surface Conditions from Column and VERtically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) Houston field experiment in September 2013 were used to investigate sources and composition of organic carbon (OC) and potential relationships between daily maximum 8 h average O3 and PM. The current study employed a novel combination of chemical mass balance modeling defining primary (i.e. POC) versus secondary (i.e. SOC) organic carbon and radiocarbon (14C) for apportionment of contemporary and fossil carbon. The apportioned sources include contemporary POC (biomass burning [BB], vegetative detritus), fossil POC (motor vehicle exhaust), biogenic SOC and fossil SOC. The filter-based results were then compared with real-time measurements by aerosol mass spectrometry. With these methods, a consistent urban background of contemporary carbon and motor vehicle exhaust was observed in the Houston metropolitan area. Real-time and filter-based characterization both showed that carbonaceous aerosols in Houston was highly impacted by SOC or oxidized OC, with much higher contributions from biogenic than fossil sources. However, fossil SOC concentration and fractional contribution had a stronger correlation with daily maximum 8 h average O3, peaking during high PM and O3 events. The results indicate that point source emissions processed by on- and off-shore wind cycles likely contribute to peak events for both PM and O3 in the greater Houston metropolitan area.

Formation of Particulate Matter from the Oxidation of Evaporated Hydraulic Fracturing Wastewater.

The use of hydraulic fracturing for production of petroleum and natural gas has increased dramatically in the past decade, but the environmental impacts of this technology remain unclear. Experiments were conducted to quantify airborne emissions from 12 samples of hydraulic fracturing flowback wastewater collected in the Permian Basin, as well as the photochemical processing of these emissions leading to the formation of particulate matter (PM). The concentration of total volatile carbon (hydrocarbons evaporating at room temperature) averaged 29 mg of carbon per liter. After photochemical oxidation under high NO x conditions, the amount of organic PM formed per milliliter of wastewater evaporated averaged 24 µg; the amount of ammonium nitrate formed averaged 262 µg. Based on the mean PM formation observed in these experiments, the estimated formation of PM from evaporated flowback wastewater in the state of Texas is in the range of estimated PM emissions from diesel engines used in oil rigs. Evaporation of flowback wastewater, a hitherto unrecognized source of secondary pollutants, could significantly contribute to ambient PM concentrations.

Biomechanical abnormalities and ulcers of the great toe in patients with diabetes.

A prospective analysis was conducted to identify structural and biomechanical first ray abnormalities in consecutive diabetic patients presenting with their first great toe ulcer. Twenty-six patients (33 feet) met the inclusion criteria, with seven patients having bilateral hallux ulcers. There was no other history of ulcer, trauma, or surgery on the respective limb. Data were obtained during the patients' initial presentation with a great toe ulcer and included verbal history, standardized weight bearing radiographs, and standardized objective clinical measurements. Four patients (four feet) with subungual ulcers were included because of mechanical etiology. Twenty-four of the remaining 29 involved limbs exhibited gastrocnemius/soleus equinus and two other limbs had gastrocnemius equinus. Twenty-eight of 29 had structural hallux limitus. Twenty-four had hallux interphalangeal abductus. Twenty of the 33 ulcers were located plantar-medially at the interphalangeal joint area. Other frequent findings were first ray elevatus or dorsiflexion deformity (18 of 29), functional hallux limitus (14 of 29), interphalangeal joint sesamoid bone (13 of 29), hyperextended interphalangeal joint (13 of 29), and a prominent plantar-medial condyle of the proximalaspect of the distalphalanx (7 of 29). Halluxmalleus was less common (4 of 29), but consistently associated with plantar-distal tip ulceration. Metatarsus primus adductus was also infrequent (6 of 29). This study identifies and illustrates the importance of several biomechanical and structural factors present on initial presentation of great toe ulcers. Addressing these factors may improve the success of treatment and lessen the occurrence of this common and complex problem.