Assessing emission and power tradeoffs of biodiesel and n-Butanol in diesel blends for fuel sustainability.

The use of renewable biodiesel and additives diversifies transportation fuel supply. Combustion tests on neat ultra-low sulfur No.2 diesel (D100) and its blends with biodiesel and the n-butanol additive were conducted to investigate environmental impacts and tradeoffs in engine emission and power output. The testing results show measurable changes in power output and engine emission, particularly in diesel particulate matter (DPM) size distribution and black carbon compositions. The binary diesel-biodiesel blend D80B20 (80% D100 and 20%B100 by volume) offers reduced PM and black carbon emission, but higher NOx in engine exhaust. Comparatively the tertiary diesel-biodiesel-butanol blend B15Bu5 (80% D100, 15% B100, and 5% Bu100 by volume) shows superior environmental tradeoff in the black carbon and NOx emission than D80B20. Both fuel blends suffer a 3.0-5.6% increase in brake-specific fuel consumption. At higher combustion temperature, the butanol-oxygenated diesel fuel produces DPMs of smaller size, higher number concentrations, greater OC fractions, and more amorphous black carbon particles. The peak DPM aerodynamic size dp max for D80B20 and B15Bu5 blends is 0.20-0.32 µm, smaller than > 0.40 µm dp max for D100 and the 0.30 µm cut-off size of regular DPM filters. For an internal combustion engine capable of accommodating biodiesel and water fraction in the fuel mixture, the B15Bu5 blend offers a viable fuel alternative according to the comparative testing results. The use of biodiesel and butanol additive in petroleum diesel can decrease the DPM emission, while the undesired NOx formation in tradeoff can be managed through optimizing the tertiary composition of petroleum diesel, biodiesel, and fuel additives.

Assessing and managing design storm variability and projection uncertainty in a changing coastal environment.

Coastal urban infrastructure and water management programs are vulnerable to the impacts of long-term hydroclimatic changes and to the flooding and physical destruction of disruptive hurricanes and storm surge. Water resilience or, inversely, vulnerability depends on design specifications of the storm and inundation, against which water infrastructure and environmental assets are planned and operated. These design attributes are commonly derived from statistical modeling of historical measurements. Here we argue for the need to carefully examine the approach and associated design vulnerability in coastal areas because of the future hydroclimatic changes and large variability at local coastal watersheds. This study first shows significant spatiotemporal variations of design storm in the Chesapeake Bay of the eastern U.S. Atlantic coast, where the low-frequency high-intensity precipitations vary differently to the tropical cyclones and local orographic effects. Average and gust wind speed exhibited much greater spatial but far less temporal variability than the precipitation. It is noteworthy that these local variabilities are not fully described by the regional gridded precipitation used in CMIP5 climate downscaling and by NOAA's regional design guide Atlas-14. Up to 46.4% error in the gridded precipitation for the calibration period 1950-1999 is further exacerbated in the future design values by the ensemble of 132 CMIP5 projections. The total model projection error (δM) up to -61.8% primarily comes from the precipitation regionalization (δ1), climate downscaling (δ2), and a fraction from empirical data modeling (δE). Thus, a post-bias correction technique is necessary. The bias-corrected design wind speed for 10-yr to 30-yr storms has small changes <20% by the year 2100, but contains large spatial variations even for stations of close proximity. Bias-corrected design precipitations are characteristic of large spatial variability and a notable increase of 2-5 year precipitation in the future along western shores of the Lower and Middle Chesapeake Bay. All these accounts point to the potential vulnerability of water infrastructure and water program in coastal areas, when the hydrological design basis using regional values fails to account for significant spatiotemporal precipitation variations in local coastal watersheds.

Atmospheric Feedback of Urban Boundary Layer with Implications for Climate Adaptation.

Atmospheric structure changes in response to the urban form, land use, and the type of land cover (LULC). This interaction controls thermal and air pollutant transport and distribution. The interrelationships among LULC, ambient temperature, and air quality were analyzed and found to be significant in a case study in Cincinnati, Ohio, U.S.A. Within the urban canopy layer (UCL), traffic-origin PM2.5 and black carbon followed Gaussian dispersion in the near road area in the daytime, while higher concentrations, over 1 order of magnitude, were correlated to the lapse rate under nocturnal inversions. In the overlying urban boundary layer (UBL), ambient temperature and PM2.5 variations were correlated among urban-wide locations indicating effective thermal and mass communications. Beyond the spatial correlation, LULC-related local urban heat island effects are noteworthy. The high-density urbanized zone along a narrow highway-following corridor is marked by higher nighttime temperature by ∼1.6 °C with a long-term increase by 2.0 °C/decade, and by a higher PM2.5 concentration, than in the low-density residential LULC. These results indicate that the urban LULC may have contributed to the nocturnal thermal inversion affecting urban air circulation and air quality in UCL and UBL. Such relationships point to the potentials of climate adaptation through urban planning.

Low-wind and other microclimatic factors in near-road black carbon variability: A case study and assessment implications.

Airborne black carbon from urban traffic is a climate forcing agent and has been associated with health risks to near-road populations. In this paper, we describe a case study of black carbon concentration and compositional variability at and near a traffic-laden multi-lane highway in Cincinnati, Ohio, using an onsite aethalometer and filter-based NIOSH Method 5040 measurements; the former measured 1-min average black carbon concentrations and the latter determined the levels of organic and elemental carbon (OC and EC) averaged over an approximately 2-h time interval. The results show significant wind and temperature effects on black carbon concentration and composition in a way more complex than predicted by Gaussian dispersion models. Under oblique low winds, namely ux [= u × sin(g=q)]~ (0,-0.5 m s-1), which mostly occurred during morning hours, black carbon concentrations per unit traffic flow were highest and had large variation. The variability did not always follow Gaussian dispersion but was characteristic of a uniform distribution at a near-road distance. Under all other wind conditions, the near-road black carbon variation met Gaussian dispersion characteristics. Significant differences in roadside dispersion are observed between OC and EC fractions, between PM2.5 and PM10-2.5, and between the morning period and rest of the day. In a general case, the overall black carbon variability at the multi-lane highway can be stated as bimodal consisting of Gaussian dispersion and non-Gaussian uniform distribution. Transition between the two types depends on wind velocity and wind angle to the traffic flow. In the order of decreasing importance, the microclimatic controlling factors over the black carbon variability are: 1) wind velocity and the angle with traffic; 2) diurnal temperature variations due to thermal buoyancy; and 3) downwind Gaussian dispersion. Combinations of these factors may have created various traffic-microclimate interactions that have significant impact on near-road black carbon transport.