ALBERT

Description: A high-ozone (O3) pollution episode was observed on 22 July 2014 during the concurrent “Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality” (DISCOVER-AQ) and “Front Range Air Pollution and Photochemistry Experiment” (FRAPPE) campaigns in northern Colorado. Surface O3 monitors at three regulatory sites exceeded the Environmental Protection Agency (EPA) 2008 National Ambient Air Quality Standard (NAAQS) daily maximum 8-hr average (MDA8) of 75 ppbv. To further characterize the polluted air mass and assess transport throughout the event, measurements are presented from O3 and wind profilers, O3-sondes, aircraft, and surface monitoring sites. Observations indicate thermally-driven upslope flow was established throughout the Colorado Front Range during the pollution episode. As the thermally-driven flow persisted throughout the day, O3 concentrations increased and affected high-elevation Rocky Mountain sites. These observations, coupled with modeling analyses, demonstrate a westerly return flow of polluted air aloft, indicating the mountain-plains solenoid circulation was established and impacted surface conditions within the Front Range.

Description: Aerosol hygroscopicity was investigated using a novel dryer-humidifier system, coupled to a TSI-3563 nephelometer, to obtain the light scattering coefficient ( scat ) as a function of relative humidity (RH) in hydration and dehydration modes. The measurements were performed in Porterville, CA (Jan 10-Feb 6, 2013), Baltimore, MD (Jul 3-30, 2013), and Golden, CO (Jul 12 - Aug 10, 2014). Observations in Porterville and Golden were part of the NASA-sponsored DISCOVER-AQ project. The measured  scat under varying RH in the three sites was combined with ground aerosol extinction, PM 2.5 mass concentrations, particle composition measurements, and compared with airborne observations performed during campaigns. The enhancement factor, f(RH), defined as the ratio of  scat (RH) at a certain RH divided by  scat at a dry value, was used to evaluate the aerosol hygroscopicity. Particles in Porterville showed low average f(RH = 80%) (1.42) which was attributed to the high carbonaceous loading in the region where residential biomass burning and traffic emissions contribute heavily to air pollution. In Baltimore, the high average f(RH = 80%) (2.06) was attributed to the large contribution of SO 4 2- in the region. The lowest water uptake was observed in Golden, with an average f(RH = 80%) = 1.24 where organic carbon dominated the particle loading. Different empirical fits were evaluated using the f(RH) data. The widely used Kasten (gamma) model was found least satisfactory, as it overestimates f(RH) for RH 〈 75%. A better empirical fit with two power-law curve-fitting parameters c and k was found to replicate f(RH) accurately from the three sites. The relationship between the organic carbon mass (OMC) and the species that are affected by RH and f(RH) was also studied and categorized.

Description: The evolution of a Stratospheric-Tropospheric Exchange (STE) event from 04-08 August 2014 at Ft. Collins, Colorado is described. The event is characterized with observations from the Goddard Space Flight Center TROPospheric OZone DIfferential Absorption Lidar (GSFC TROPOZ DIAL), the University of Wisconsin High Spectral Resolution Lidar (HSRL) and multiple ozonesondes during NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER AQ) campaign. Based on the extended TROPOZ observations throughout the entire campaign, it was found that STE events have largely contributed to an additional 10-30 ppbv of ozone at Ft Collins. Additional measurements of ozone and relative humidity from the Atmospheric Infrared Sounder (AIRS) are characterize the transport of the intrusion. The Real-time Air Quality Modeling System (RAQMS) simulated ozone agrees well with the TROPOZ ozone concentrations and altitude during the STE event. To extend the analysis into other seasons and years, the modeled ozone to potential vorticity ratio is used as a tracer for stratospheric air residing below the tropopause. It is found that at Ft. Collins, CO and depending on season from 2012-2014, between 18-31% of tropospheric ozone corresponds to stratospheric air. A relationship to determine the lifetime of stratospheric air below the tropopause is derived using the simulated ratio tracer. Results indicate that throughout Summer 2014, 43% of stratospheric air resided below the tropopause for less than 12 hours. However, nearly 39% persisted below the tropopause for 12 - 48 hours and likely penetrated deeper in the troposphere.

Description: Measurements of PM 2.5 chemical composition were carried out in Golden, CO during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field study. Chemical composition was dominated by organic compounds, which comprised an average of 75% of the PM 2.5 mass throughout the study. Most of the organic matter was secondary (i.e., secondary organic aerosol, SOA), and appears to derive predominantly from regional sources, rather than the Denver metropolitan area. The concentration and composition of PM 2.5 in Golden were strongly influenced by highly regular wind patterns and the site's close proximity to the mountains (~5 km). This second factor may be the cause of distinct differences between observations in Golden and those in downtown Denver, despite a distance between the sites of only ~15 km. Concentrations of aerosol nitrate, ammonium and elemental carbon increased significantly during the daytime when the winds were from the northeast, indicating a strong local source for these compounds. Local sources of dust appeared to minimally impact the Golden site, although this was not likely representative of other conditions in the Colorado Front Range. Conversely, dust that had undergone long-range transport from the southwestern U.S. likely impacted the entire Colorado Front Range, including Golden. During this event, water-soluble Ca 2+ concentrations exceeded 1 µg m -3 , and the PM 2.5 /PM 10 ratio reached its lowest level throughout the study. The long-range transport of wildfire emissions also impacted the Colorado Front Range for 1-2 days during DISCOVER-AQ. The smoke event was characterized by high concentrations of organics and water-soluble K + . The results show a complex array of sources and atmospheric processes influence summertime PM in the Colorado Front Range.