Houston's rapid ozone increases: preconditions and geographic origins

Many of Houston’s highest 8-h ozone (O3) peaks are characterised by increases in concentrations of at least 40 ppb in 1 h, or 60 ppb in 2 h. These rapid increases are called non-typical O3 changes (NTOCs). In 2004, the Texas Commission on Environmental Quality (TCEQ) developed a novel emissions control strategy aimed at eliminating NTOCs. The strategy limited routine and short-term emissions of ethene, propene, 1,3-butadiene and butene isomers, collectively called highly reactive volatile organic compounds (HRVOCs), which are released from petrochemical facilities. HRVOCs have been associated with NTOCs through field campaigns and modelling studies. This study analysed wind measurements and O3, formaldehyde (HCHO) and sulfur dioxide (SO2) concentrations from 2000 to 2011 at 25 ground monitors in Houston. NTOCs almost always occurred when monitors were downwind of petrochemical facilities. Rapid O3 increases were associated with low wind speeds; 75 % of NTOCs occurred when the 3-h average wind speed preceding the event was less than 6.5 km h−1. Statistically significant differences in HCHO concentrations were seen between days with and without NTOCs. Early afternoon HCHO concentrations were greater on NTOC days. In the morning before an observed NTOC event, however, there were no significant differences in HCHO concentrations between days with and without NTOCs. Hourly SO2 concentrations also increased rapidly, exhibiting behaviour similar to NTOCs. Oftentimes, the SO2 increases preceded a NTOC. These findings show that, despite the apparent success of targeted HRVOC emission controls, further restrictions may be needed to eliminate the remaining O3 events

Scenarios of Global Change: Integrated Assessment of Climate Impacts

Using the MIT Integrated Global System Modeling (IGSM) framework, we assess the climate impacts of emission scenarios exhibiting global mean surface temperatures ranging between 2.4°C and 4.3°C above pre-industrial by 2100. We compare the outcomes from these forward-looking scenarios against the common goal described by the target-driven scenario of 2°C. Without further policy measures, the agreement at COP-21 in Paris is projected to result in a 3.5°C increase in global temperature in 2100 relative to pre-industrial levels. Scenarios developed by Shell International (called Mountains and Oceans) exhibit a substantial movement towards temperature stabilization, as they result in increases of only 2.4–2.7°C by 2100. Valuable components of these scenarios include a substantial shift to renewable energy and deployment of carbon capture and storage (CCS). These scenarios are successful in mitigating a large portion of water stress impacts and air pollution damages. They also significantly mitigate increases in ocean acidity. These projections show the significant value of policies that do not quite reach 2°C stabilization, but fall substantially close to that target by the end of the century. The challenge of meeting the Paris Agreement’s aspiration to limit warming to 1.5°C is monumental, yet may be desirable if societies see the 2°C impacts, described here, as running too much risk.The MIT Joint Program on the Science and Policy of Global Change is supported by the U.S. Department of Energy, Office of Science under grants DEFG02-94ER61937, DE-FG02-08ER64597, DE-FG02-93ER61677, DE-SC0003906, DE-SC0007114, XEU-0-9920-01; the U.S. Department of Energy, Oak Ridge National Laboratory under Subcontract 4000109855; the U.S. Environmental Protection Agency under grants XA-83240101, PIv83412601-0, RD-83427901-0, XA-83505101-0, XA-83600001-1, and subcontract UTA12-000624; the U.S. National Science Foundation under grants AGS-0944121, EFRI-0835414, IIS-1028163, ECCSv1128147, ARC- 1203526, EF-1137306, AGS-1216707, and SES-0825915; the U.S. National Aeronautics and Space Administration under grants NNX06AC30A, NNX07AI49G, NNX11AN72G and Sub Agreement No. 08-SFWS-209365.MIT; the U.S. Federal Aviation Administration under grants 06-C-NE-MIT, 09-C-NEMIT, Agmt. No. 4103-30368; the U.S. Department of Transportation under grant DTRT57-10-C-10015; the Electric Power Research Institute under grant EP-P32616/C15124, EP-P8154/C4106; the U.S. Department of Agriculture under grant 58-6000-2-0099, 58-0111-9-001; and a consortium of industrial and foundation sponsors (for the complete list see: globalchange.mit.edu/sponsors/all). Shell participated actively in this study, supplying all the background data behind their scenarios. MIT remain responsible for 32 all analysis and conclusions. Shell provided a gift of USD 250,000 to the MIT Joint Program, to defray costs related to this research. Martin Haigh represents the Scenarios Team at Shell International Ltd. The paper also benefited from comments from David Hone

Modeled response of ozone to electricity generation emissions in the northeastern United States using three sensitivity techniques

ABSTRACT: Electrical generation units (EGUs) are important sources of nitrogen oxides (NOx) that contribute to ozone air pollution. A dynamic management system can anticipate high ozone and dispatch EGU generation on a daily basis to attempt to avoid violations, temporarily scaling back or shutting down EGUs that most influence the high ozone while compensating for that generation elsewhere. Here we investigate the contributions of NOx from individual EGUs to high daily ozone, with the goal of informing the design of a dynamic management system. In particular, we illustrate the use of three sensitivity techniques in air quality models—brute force, decoupled direct method (DDM), and higher-order DDM—to quantify the sensitivity of high ozone to NOx emissions from 80 individual EGUs. We model two episodes with high ozone in the region around Pittsburgh, PA, on August 4 and 13, 2005, showing that the contribution of 80 EGUs to 8-hr daily maximum ozone ranges from 1 to >5 ppb at particular locations. At these locations and on the two high ozone days, shutting down power plants roughly 1.5 days before the 8-hr ozone violation causes greater ozone reductions than 1 full day before; however, the benefits of shutting down roughly 2 days before the high ozone are modest compared with 1.5 days. Using DDM, we find that six EGUs are responsible for >65% of the total EGU ozone contribution at locations of interest; in some locations, a single EGU is responsible for most of the contribution. Considering ozone sensitivities for all 80 EGUs, DDM performs well compared with a brute-force simulation with a small normalized mean bias (–0.20), while this bias is reduced when using the higher-order DDM (–0.10). Implications: Dynamic management of electrical generation has the potential to meet daily ozone air quality standards at low cost. We show that dynamic management can be effective at reducing ozone, as EGU contributions are important and as the number of EGUs that contribute to high ozone in a given location is small (<6). For two high ozone days and seven geographic regions, EGUs would best be shut down or their production scaled back roughly 1.5 days before the forecasted exceedance. Including online sensitivity techniques in an air quality forecasting model can provide timely and useful information on which EGUs would be most beneficial to shut down or scale back temporarily

Houston’s rapid ozone increases: preconditions and geographic origins

Many of Houston’s highest 8-h ozone (O(3)) peaks are characterised by increases in concentrations of at least 40 ppb in 1 h, or 60 ppb in 2 h. These rapid increases are called non-typical O(3) changes (NTOCs). In 2004, the Texas Commission on Environmental Quality (TCEQ) developed a novel emissions control strategy aimed at eliminating NTOCs. The strategy limited routine and short-term emissions of ethene, propene, 1,3-butadiene and butene isomers, collectively called highly reactive volatile organic compounds (HRVOCs), which are released from petrochemical facilities. HRVOCs have been associated with NTOCs through field campaigns and modelling studies. This study analysed wind measurements and O(3), formaldehyde (HCHO) and sulfur dioxide (SO(2)) concentrations from 2000 to 2011 at 25 ground monitors in Houston. NTOCs almost always occurred when monitors were downwind of petrochemical facilities. Rapid O(3) increases were associated with low wind speeds; 75 % of NTOCs occurred when the 3-h average wind speed preceding the event was less than 6.5 km h(−1). Statistically significant differences in HCHO concentrations were seen between days with and without NTOCs. Early afternoon HCHO concentrations were greater on NTOC days. In the morning before an observed NTOC event, however, there were no significant differences in HCHO concentrations between days with and without NTOCs. Hourly SO(2) concentrations also increased rapidly, exhibiting behaviour similar to NTOCs. Oftentimes, the SO(2) increases preceded a NTOC. These findings show that, despite the apparent success of targeted HRVOC emission controls, further restrictions may be needed to eliminate the remaining O(3) events