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2 Committee's Review of the Study
Pages 13-44

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From page 13...
... The Study also needed an inventory of emissions in Mexico, both at the 4-km level for part of the Gulf Coast that is included in the 4km modeling domain and at the 12- and 36-km levels. All of this work appears to have been done carefully and with attention to detail, and the Study authors deserve credit for this effort.
From page 14...
... . The Study authors should review that paper and the NRC (2007)
From page 15...
... Their study concludes that the impact on ozone due to drought related biogenic emission change is likely small in most areas and has little impact on the overall model performance of ozone. The driving force that caused the differences in biogenic emissions between 2011 and 2012 is the temperature difference.
From page 16...
... Even for the single location being examined here, there are significant correlations between peak ozone levels and peak temperatures, as well as year (due to controls) , as expected.a The averaging time for ozone is the annual fourth-highest daily maximum 8-hour concentration.
From page 17...
... Specific details about the committee's assessment of the Study's Air Quality Model Performance Evaluation can be found below in the review of Chapter 4. The Study uses a meteorologically average year (2012)
From page 18...
... Recommendation: The Study should also conduct the photochemical modeling for 2011, given that warm years are more conducive to ozone, PM2.5, and PM10 formation and are projected to become more prevalent in the future. Having results from two different years with different meteorological conditions would allow the Study authors to more comprehensively assess impacts of emissions now and in the future under climate change.
From page 19...
... REVIEW OF CHAPTER 2: WRF MODEL PERFORMANCE EVALUATION Meteorology in the Gulf of Mexico Region and Its Impact on Air Quality Meteorology in the GOMR is very complex. It is characterized by land-sea interactions, sea breeze circulation, surface temperature contrasts, and a complex coastline, which result in a warm, humid, subtropical climate with moderate rainfall.
From page 20...
... is particularly relevant to the Study as it found that ozone exceedances in the Houston region were largely due to recirculation processes within the land-sea breeze system. In general, meteorological errors can contribute significantly to bias in the air quality models (Cheng et al., 2007; Heidorn and Yap, 1986; Robeson and Steyn, 1990)
From page 21...
... Based on the results from their evaluation of the existing WRF datasets, the Study authors decided to develop a new 5-year high-resolution WRF dataset. The evaluation of the existing datasets presents errors and biases of wind speed, wind direction, and temperature as WRF performance benchmarks categorized for simple and complex domain conditions.6 The Study authors conclude that the errors and biases are outside the "acceptable conditions" for a few of the months in the dataset and that the datasets would not accurately represent the overwater portions of the Study area.
From page 22...
... contrasts. A more comprehensive review of the literature of WRF model performance in similar situations to the Study would be informative as to how well the model should capture the observed meteorologies and the potential impacts of the biases.
From page 23...
... The time series analysis of error/bias for stability regime and model evaluation of a combination of metrics, including PBL height, is more suitable for the GOMR.  An instantaneous hourly output is stored for analysis instead of using an hourly averaged output.
From page 24...
... Finding: The Study does not fully evaluate the meteorological and air quality models for the various meteorological conditions that would favor outer continental shelf sources having the greatest air quality impact on vulnerable areas onshore in the Gulf of Mexico region. Meteorological conditions that would be expected to have the greatest impact on onshore air quality include:  predominantly onshore flows,  inter-season variations,  cold air outbreaks, and  periods of high temperatures, stagnation, and recirculation of pollutants due to time varying sea breeze circulation and stationary fronts.
From page 25...
... Scenarios of Lease Sales The authors specifically analyze two future emissions scenarios in which a single lease or nine additional leases for new oil and gas development are sold in the 2017-2022 period. The committee notes that emissions in the single-lease scenario rose sharply in a few years (Figure 37 of the Study)
From page 26...
... Finding: The Study uses an overly specific and perhaps biased scenario of lease sales; in particular, the scenario does not include emission-generating activities associated with potential future sales after 2022. Recommendation: A future update to the Study should evaluate the impacts from other scenarios for continued exploration, development, and production of oil and gas reserves on the outer continental shelf beyond the 2017-2022 lease-sale scenarios.
From page 27...
... Model performance evaluation for criteria pollutants is conducted using the photochemical modeling results for 2012 based on the base case emission inventory. The chapter moves on to assess the future year air quality impacts with respect to the NAAQS criteria pollutants as well as sulfur and nitrogen deposition and visibility using the source apportionment modeling results.
From page 28...
... Since source apportionment simulations have been carried out, the Study authors could also select the days based on the source apportionment results -- the days with higher contributions to modeled concentrations can be selected for model performance analysis. Different sets of days might be identified at different receptor locations.
From page 29...
... In most off-line air quality modeling studies, the WRF model is configured for two-way nesting while the air quality model is configured for one-way nesting. The Study needs to further explain this uncommon choice in the configuration of the models.
From page 30...
... Such a treatment is included in the CMAQ post-processing procedure and should be applied in the PM2.5 model performance analysis.  In 2012, high ozone concentrations were simulated over the Gulf of Mexico and significant contributions were found to be due to new offshore emissions.
From page 31...
... These discrepancies are especially pronounced for the Carpinteria and Pismo Beach overwater dispersion experiments, and should be investigated by the Study authors. The Study conducted a synthetic source modeling study for offshore distances of 20 and 40 km and found that: "Overall, there is better agreement between AERMOD and OCD concentrations than between CALPUFF and OCD, especially for the highest concentrations, which carry the most weight for regulatory purposes" (EPA, 2014)
From page 32...
... This should be investigated by the Study authors. Emission Exemption Thresholds The emission exemption thresholds (EETs)
From page 33...
... A third area of concern is the degree to which the new EET approaches continue to generate false negatives (i.e., instances where more refined air quality modeling or emission controls are needed, but the EET does not call for it)
From page 34...
... The existing EET methods do not generate false negatives for the annual-average NAAQS for NO2, PM10, or SO2 when compared to the new modeling conducted under the Study, and only 1.2% false negatives for PM2.5. This implies that the existing EETs are generally protective of the long-term NAAQS onshore, although with many false positives for NO2 (41%)
From page 35...
... This is why the Study recommends a minimum and balanced number of false positives and false negatives. -- -- -- -- -- -- -- -- -- -- -- -- a False positives are situations in which the EET limit is exceeded although refined modeling shows no significant air quality impact as defined by EPA's SILs.
From page 36...
... The Study proposes the CART approach to balance false positives and false negatives, but it is more appropriate to eliminate false negatives, based on EPA guidance and the objective of protecting air quality and public health. The CART analysis results in abrupt patterns that are physically unrealistic in comparison to the smooth curves generated from a series of EETs proposed in a still open rulemaking by BOEM (2016)
From page 37...
... should be noted on each CART result, in consistent emission rate units. An important concern of the committee is that limitations of the EET methods should be clearly stated in the main body of the report and the summary, not just in an appendix.
From page 38...
... The Study authors should use caution in relying on decision trees that lack atmospheric physics- and chemistry-based insights, and scrutinize the use of branches in the decision tree that are not reflective of a specific physically and chemically realistic relationship between estimated maximum impact, the emissions level, and distance. The Study suggests a potential alternative approach to the EET formulas that "estimate impacts based on comparable modeled sources.
From page 39...
... The resulting scatter plot of ESER versus distance, D would potentially be very crowded with data points; however, a line drawn below all of the data would represent a curve that had no false negatives. One could then fit this curve to an appropriate function of D, so that one ended up with a true EET formula with no false negatives rather than end up with a CART decision tree.
From page 40...
... Based on this analysis the Study concludes that the existing EETs are generally protective of annual NAAQS, but are not sufficiently protective of the short-term NAAQS for any pollutant. The committee agrees with this assessment and supports the choice of the Study authors to develop new exemption level thresholds for all NAAQS and their precursors.
From page 41...
... The EETs may also not be as accurate when used as a screening tool for deep-water operations farther offshore. Recommendation: The Study should develop EET formulas and methods based on meteorological conditions that are most conducive to elevated levels of ozone, PM2.5, and PM10 and the EET methods developed for the criteria pollutants should eliminate false negatives15.
From page 42...
... Specifically,  the meteorological analyses and photochemical modeling have not been evaluated for their performance of conditions typical of when offshore emissions would have the largest impact on air quality on land and during the most critical times,  the choice of base year does not account for increasing temperatures resulting from climate change,  future emissions are only included through 2022, meaning that potential emissions from 2023-2036 are not considered in the future case, and  the CART approach for the EETs allows for false negatives and, in some cases, has physically unrealistic results. As such, the Study's current results have the potential to underestimate the current and future impacts of OCS emissions on air quality, visibility, and deposition.
From page 43...
... COMMITTEE'S REVIEW OF THE STUDY 43 The Study authors are in a unique position to further advance our understanding of how OCS sources impact air quality in the GOMR and develop robust and protective EET approaches.


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