Investigation of Biofuel as a Potential Renewable Energy Source

An accelerating global energy demand, paired with the harmful environmental effects of fossil fuels, has triggered the search for alternative, renewable energy sources. Biofuels are arguably a potential renewable energy source in the transportation industry as they can be used within current infrastructures and require less technological advances than other renewable alternatives, such as electric vehicles and nuclear power. The literature suggests biofuels can negatively impact food security and production; however, this is dependent on the type of feedstock used in biofuel production. Advanced biofuels, derived from inedible biomass, are heavily favoured but require further research and development to reach their full commercial potential. Replacing fossil fuels by biofuels can substantially reduce particulate matter (PM), carbon monoxide (CO) emissions, but simultaneously increase emissions of nitrogen oxides (NOx), acetaldehyde (CH3CHO) and peroxyacetyl nitrate (PAN), resulting in debates concerning the way biofuels should be implemented. The potential biofuel blends (FT-SPK, HEFA-SPK, ATJ-SPK and HFS-SIP) and their use as an alternative to kerosene-type fuels in the aviation industry have also been assessed. Although these fuels are currently more costly than conventional aviation fuels, possible reduction in production costs has been reported as a potential solution. A preliminary study shows that i-butanol emissions (1.8 Tg/year) as a biofuel can increase ozone levels by up to 6% in the upper troposphere, highlighting a potential climate impact. However, a larger number of studies will be needed to assess the practicalities and associated cost of using the biofuel in existing vehicles, particularly in terms of identifying any modifications to existing engine infrastructure, the impact of biofuel emissions, and their chemistry on the climate and human health, to fully determine their suitability as a potential renewable energy source.

Simulation of Turbulent Mixing Effects on Essential NOx–O3–Hydrocarbon Photochemistry in Convective Boundary Layer

The turbulence kinetics model (TKM) describes an overall reaction rate for microscopic mass transfer phenomenon expressed as separation intensity, Is, in a turbulent reacting flow. This study examines the effects of turbulent mixing in the convective boundary layer (CBL) on essential NOx–O3–Hydrocarbon photochemistry containing sources of NO and a surrogate reactive hydrocarbon. The modeling approach applies for all species except OH with an assumption of a photostationary steady state. The TKM results reveal principal findings as follows: (1) effects of turbulence on reaction rates lead to significant segregations throughout most of the CBL in reaction pairs NO + O3, RH + OH and NO + HO2; (2) segregations permit significantly higher concentrations of NO and RH to build up and endure in the CBL than would occur for a non-turbulent atmosphere; (3) turbulent segregation influences limit and shift the ranges of NO and O3 concentrations compared to the non-turbulent case; (4) while there are differences between the TKM results and those for a published Large Eddy simulation (LES) of the same chemical system, there are also strong similarities. Therefore, a future study remains to compare model results to observations if and when appropriately time-resolved measurements of reacting species are obtained.

Tropospheric ozone in CCMI models and Gaussian process emulation to understand biases in the SOCOLv3 chemistry-climate model

Previous multi-model intercomparisons have shown that chemistry-climate models exhibit significant biases in tropospheric ozone compared with observations. We investigate annual-mean tropospheric column ozone in 15 models participating in the SPARC/IGAC (Stratosphere-troposphere Processes and their Role in Climate/International Global Atmospheric Chemistry) Chemistry-Climate Model Initiative (CCMI). These models exhibit a positive bias, on average, of up to 40-50% in the Northern Hemisphere compared with observations derived from the Ozone Monitoring Instrument and Microwave Limb Sounder (OMI/MLS), and a negative bias of up to ~30% in the Southern Hemisphere. SOCOLv3.0 (version 3 of the Solar-Climate Ozone Links CCM), which participated in CCMI, simulates global-mean tropospheric ozone columns of 40.2 DU - approximately 33% larger than the CCMI multi-model mean. Here we introduce an updated version of SOCOLv3.0, "SOCOLv3.1", which includes an improved treatment of ozone sink processes, and results in a reduction in the tropospheric column ozone bias of up to 8 DU, mostly due to the inclusion of N₂O₅ hydrolysis on tropospheric aerosols. As a result of these developments, tropospheric column ozone amounts simulated by SOCOLv3.1 are comparable with several other CCMI models. We apply Gaussian process emulation and sensitivity analysis to understand the remaining ozone bias in SOCOLv3.1. This shows that ozone precursors (nitrogen oxides (NO_x), carbon monoxide, methane and other volatile organic compounds) are responsible for more than 90% of the variance in tropospheric ozone. However, it may not be the emissions inventories themselves that result in the bias, but how the emissions are handled in SOCOLv3.1, and we discuss this in the wider context of the other CCMI models. Given that the emissions data set to be used for phase ₆ of the Coupled Model Intercomparison Project includes approximately 20% more NO_x than the data set used for CCMI, further work is urgently needed to address the challenges of simulating sub-grid processes of importance to tropospheric ozone in the current generation of chemistry-climate models.

Bay breeze influence on surface ozone at Edgewood, MD during July 2011

Surface ozone (O₃) was analyzed to investigate the role of the bay breeze on air quality at two locations in Edgewood, Maryland (lat: 39.4°, lon: -76.3°) for the month of July 2011. Measurements were taken as part of the first year of NASA's "Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality" (DISCOVER-AQ) Earth Venture campaign and as part of NASA's Geostationary for Coastal and Air Pollution Events Chesapeake Bay Oceanographic campaign with DISCOVER-AQ (Geo-CAPE CBODAQ). Geo-CAPE CBODAQ complements DISCOVER-AQ by providing ship-based observations over the Chesapeake Bay. A major goal of DISCOVER-AQ is determining the relative roles of sources, photochemistry and local meteorology during air quality events in the Mid-Atlantic region of the U.S. Surface characteristics, transport and vertical structures of O₃ during bay breezes were identified using in-situ surface, balloon and aircraft data, along with remote sensing equipment. Localized late day peaks in O₃ were observed during bay breeze days, maximizing an average of 3 h later compared to days without bay breezes. Of the 10 days of July 2011 that violated the U.S. Environmental Protection Agency (EPA) 8 h O₃ standard of 75 parts per billion by volume (ppbv) at Edgewood, eight exhibited evidence of a bay breeze circulation. The results indicate that while bay breezes and the processes associated with them are not necessary to cause exceedances in this area, bay breezes exacerbate poor air quality that sustains into the late evening hours at Edgewood. The vertical and horizontal distributions of O₃ from the coastal Edgewood area to the bay also show large gradients that are often determined by boundary layer stability. Thus, developing air quality models that can sufficiently resolve these dynamics and associated chemistry, along with more consistent monitoring of O₃ and meteorology on and along the complex coastline of Chesapeake Bay must be a high priority.

Bay breeze climatology at two sites along the Chesapeake bay from 1986-2010: Implications for surface ozone

Hourly surface meteorological measurements were coupled with surface ozone (O₃) mixing ratio measurements at Hampton, Virginia and Baltimore, Maryland, two sites along the Chesapeake Bay in the Mid-Atlantic United States, to examine the behavior of surface O₃ during bay breeze events and quantify the impact of the bay breeze on local O₃ pollution. Analyses were performed for the months of May through September for the years 1986 to 2010. The years were split into three groups to account for increasingly stringent environmental regulations that reduced regional emissions of nitrogen oxides (NO_x): 1986-1994, 1995-2002, and 2003-2010. Each day in the 25-year record was marked either as a bay breeze day, a non-bay breeze day, or a rainy/cloudy day based on the meteorological data. Mean eight hour (8-h) averaged surface O₃ values during bay breeze events were 3 to 5 parts per billion by volume (ppbv) higher at Hampton and Baltimore than on non-bay breeze days in all year periods. Anomalies from mean surface O₃ were highest in the afternoon at both sites during bay breeze days in the 2003-2010 study period. In conjunction with an overall lowering of baseline O₃ after the 1995-2002 period, the percentage of total exceedances of the Environmental Protection Agency (EPA) 75 ppbv 8-h O₃ standard that occurred on bay breeze days increased at Hampton for 2003-2010, while remaining steady at Baltimore. These results suggest that bay breeze circulations are becoming more important to causing exceedance events at particular sites in the region, and support the hypothesis of Martins et al. (2012) that highly localized meteorology increasingly drives air quality events at Hampton.

Global change: state of the science

Only recently, within a few decades, have we realized that humanity significantly influences the global environment. In the early 1980s, atmospheric measurements confirmed basic concepts developed a decade earlier. These basic concepts showed that human activities were affecting the ozone layer. Later measurements and theoretical analyses have clearly connected observed changes in ozone to human-related increases of chlorine and bromine in the stratosphere. As a result of prompt international policy agreements, the combined abundances of ozone-depleting compounds peaked in 1994 and ozone is already beginning a slow path to recovery. A much more difficult problem confronting humanity is the impact of increasing levels of carbon dioxide and other greenhouse gases on global climate. The processes that connect greenhouse gas emissions to climate are very complex. This complexity has limited our ability to make a definitive projection of future climate change. Nevertheless, the range of projected climate change shows that global warming has the potential to severely impact human welfare and our planet as a whole. This paper evaluates the state of the scientific understanding of the global change issues, their potential impacts, and the relationships of scientific understanding to policy considerations.

Direct estimate of methane radiative forcing by use of nadir spectral radiances

Direct determination of the radiative forcing of trace gases will be made possible by use of the next generation of nadir-looking spaceborne instruments that provide measurements of atmospheric radiances in the infrared spectral range with improved spectral and spatial resolution. An inversion statistical method has thus been developed and applied to the direct determination of the radiative forcing of methane, based on such instruments as the Fourier-transform Interferometric Monitor for Greenhouse Gases launched onboard the Japanese Advanced Earth Observing Satellite in 1996 and the Infrared Atmospheric Sounding Interferometer planned for the European polar platform Meteorological Operational Satellite in 2000. The method is based on simple statistical laws that directly relate the measured radiances to the radiative forcing by use of an a priori selection of appropriate spectral intervals and global modeling of methane spatial variations. This procedure avoids the use of an indirect determination based on an inversion process that requires precise knowledge of the methane vertical profiles throughout the troposphere. The overall accuracy and precision of this new algorithm are studied, and interfering gases and instrumental characteristics are taken into account. It is shown that radiative forcing can be determined at high horizontal spatial resolution with a precision better than 7% in cloud-free conditions and with well-known surface properties.