Analysis of alternative pathways for reducing nitrogen oxide emissions

Abstract

Strategies for reducing tropospheric ozone (O 3 ) typically include modifying combustion processes to reduce the formation of nitrogen oxides (NO x ) and applying control devices that remove NO x from the exhaust gases of power plants, industrial sources and vehicles. For portions of the U.S., these traditional controls may not be sufficient to achieve the National Ambient Air Quality Standard for ozone. We apply the MARKet ALlocation (MARKAL) energy system model in a sensitivity analysis to explore whether additional NO x reductions can be achieved through extensive electrification of passenger vehicles, adoption of energy efficiency and conservation measures within buildings, and deployment of wind and solar power in the electric sector. Nationally and for each region of the country, we estimate the NO x implications of these measures. Energy efficiency and renewable electricity are shown to reduce NO x beyond traditional controls. Wide-spread light duty vehicle electrification produces varied results, with NO x increasing in some regions and decreasing in others. However, combining vehicle electrification with renewable electricity reduces NO x in all regions.Implications: State governments are charged with developing plans that demonstrate how air quality standards will be met and maintained. The results presented here provide an indication of the national and regional NO x reductions available beyond traditional controls via extensive adoption of energy efficiency, renewable electricity, and vehicle electrification. IntroductionNational Ambient Air Quality Standards (NAAQS) specify maximum allowable air pollutant concentrations in the United States. The 8-hr NAAQS for tropospheric ozone (O 3 ), a principal component of photochemical smog, was set at 75 ppb in (Federal Register, 2008. State air quality agencies are charged with developing State Implementation Plans (SIPs) to bring nonattainment areas into attainment with the standard. Since O 3 is formed through a photochemical reaction involving nitrogen oxides (NO x ) and volatile organic compounds (VOCs), and since this reaction is limited by NO x in most parts of the country, O 3 SIPs typically focus on reducing NO x .State actions related to SIPs, combined with a range of federal regulations, have reduced U.S. NO x emissions by 51% from 1990 to 2014 (U.S. Environmental Protection Agency [EPA], 2015a). Over that period, electric sector NO x was reduced by 73% and onroad vehicle NO x by 53%. The majority of these reductions have been achieved by modifying combustion processes and placing control devices on the exhaust systems of stationary and mobile sources. For example, many coal-fired electric utilities reduce emissions via low-NO x burners (LNB) and selective catalytic reduction (SCR) systems, and modern passenger cars and trucks are fitted with catalytic converters.One approach for developing an O 3 SIP is to estimate the NO x reductions that could be achieved through greater application of traditional controls, such as LNB and SCR. The state's emis...

Evolution of the United States Energy System and Related Emissions under Varying Social and Technological Development Paradigms: Plausible Scenarios for Use in Robust Decision Making

“…This time horizon is reasonable for strategies that focus on end-of-pipe controls or episodic behavioral changes. Analysis timelines are being extended, however, as decision-makers begin to explore nontraditional measures such as switching to cleaner fuels and introducing renewable electricity and energy-efficiency targets . Modeling out several decades into the future can more fully represent turnover from existing stock and capture additional impacts, such as climate co-benefits of policies directed at local emissions or air pollution co-benefits of programs to reduce carbon emissions.…”

Emission Impacts of Electric Vehicles in the US Transportation Sector Following Optimistic Cost and Efficiency Projections

“…We use an integrated energy system model to evaluate how the US energy system might respond to increased EV penetration. Although EVs, both plug-in hybrid (PHEV) and all-electric (BEV), have low or no tailpipe emissions, they may lead to indirect emissions, depending on the technology used to generate electricity for battery charging. − Moreover, increased penetration of EVs could shift emissions in sectors beyond electricity generation . For example, increased EV penetration could draw natural gas from the industrial sector to the electricity sector and push the industrial sector to use more carbon-intensive fuels.…”

“…Prior studies have examined potential reductions in fuel use and GHG emissions from the LDV sector, including through introducing EVs. − ,− Some of these studies examined how to reduce emissions to a set target level; ,,, others examined reductions achievable under specified policies. ,,− The prior studies examined specific pathways such as demand reductions or use of alternative fuels and technologies; some investigate electrification in particular. − ,− However, recent advances in EV technology have outpaced vehicle cost and performance assumptions used in earlier assessments, so consideration of more optimistic projections is needed. Furthermore, most prior studies of implications of EV introduction have focused on the transportation and electricity sectors alone without considering implications for energy use in other parts of the economy. − ,− Although some studies have accounted for “life cycle” emissions upstream of the electric sector, ,− they still lack the intersectoral connections of an integrated model and a feasibility check for their exogenous assumptions such as the assumed penetration rates of EVs.…”

“…Their study suggests that a tight economy-wide cap is required to be able to sharply reduce CO 2 emissions from the transportation sector . Loughlin et al included deploying PHEVs and BEVs among the pathways they investigated for reducing NO x emissions, using the 2014 EPA US9R database. They find the EV pathway to be complicated due to offsetting emissions from intersectoral shifts .…”

“…Loughlin et al included deploying PHEVs and BEVs among the pathways they investigated for reducing NO x emissions, using the 2014 EPA US9R database. They find the EV pathway to be complicated due to offsetting emissions from intersectoral shifts . Rudokas et al used MARKAL with the 2012 US9R database and examined the influence of system-wide CO 2 emissions fees or a 70% CO 2 emissions cap on the transportation sector, looking out to the year 2050.…”