Appendix B: District and ARB Comment Letters on Proposed EPA Plan Disapproval Appendix B- 1 

# Appendix B: District and ARB Comment Letters on Proposed EPA Plan Disapproval

On November 30, 2010 (75 Federal Register 74518-74543), The U.S. Environmental Protection Agency (EPA) propos ed a limited approval and lim ited disapproval of the

2008 PM2.5 Plan . The San Joaquin Valley Air Distric t (District) and the California Air Resources Board (ARB) submitted ext ensive documentation and comments to EPA regarding the disapproval issues raised. The District believes that the collective

comments from the District and the State of California fully address the issues EPA identified in its proposed dis approval. This Appendix presents the District’s and ARB’s

written comments to EPA.Attachment 1



### Enforceable Commitment Level

U.S. EPA’s proposed partial disapproval of the Plan is primarily based upon U.S. EPA’s position that the Plan’s attainment demo nstration relies too heavily on enforceable commitments rather than on fully adopte d measures. Specifically, U.S. EPA is proposing to disapprove the Plan becaus e the percentage of emission reductions arising from enforceable commitments (i. e., 30%) is “too high and do[es] not represent a limited portion of the State ’s current estimate of total emissions reductions needed . . . .” (75 Fed.Reg. 7 4536 (Nov. 30, 2010).) U.S. EPA does not identify the maximum percentage t hat would be acceptable, but implies that it might be 10% by stating:

Historically, EPA has approved SIPs with enforceabl e commitments in the range of 10 percent or less of the total needed for attainment. ( Id

. at p. 74535.)

The Federal Register notice does not contain any re al analysis to justify the conclusion that 30% is “too high.” Instead, U.S. E PA merely makes the above statement about its historical actions in approving other nonattainment area SIPs. There is in fact no firm rule dictating what percen tage of emission reductions may be from enforceable commitments; the principal lega l requirement regarding the allowable proportion of enforceable commitments is simply that it be “limited.”

The language of the Clean Air Act (CAA) does not di rectly provide for the inclusion of enforceable commitments within a SIP. However, the CAA does state that a SIP may contain “means,” “techniques,” and/or “sche dules and timetables for compliance.” (42 U.S.C. § 7410(a)(2)(A).) The U.S . EPA and courts have interpreted this language to allow U.S. EPA to appr ove a SIP that relies on

enforceable commitments if the commitments meet a t hree part test:

(1) whether the commitment addresses a limited port ion of the statutorily-required implementation plan; (2) wheth er the state is capable of fulfilling its commitment; and (3) wh ether the commitment is for a reasonable and appropriate peri od of time. ( BCCA Appeal Group v. U.S. EPA (2003) 355 F.3d 817, 840.)

Here, the San Joaquin Valley Plan relies on enforce able commitments for approximately 30% of its required reductions. (75 Fed.Reg. 74536.) In applying the test set out above, U.S. EPA found that the Pla n satisfied the second prong, i.e. that the state would be capable of fulfilling its commitments, but did not meet the first and third prongs. ( Id . at pp. 74535-74536.)

Regarding the first prong, while 30% may be a large r portion of enforceable commitments than U.S. EPA has approved in the past, it is less than a third of theAttachment 1

overall commitment. Moreover, U.S. EPA’s brief men tion of what percentage has been approved in the past for different SIPs, under different circumstances, avoids any substantive analysis of why 30% is excessive in the context of this particular SIP revision. The failure to explain why 30% is “t oo high” is at odds with U.S. EPA’s past practice in analyzing other SIPS th at contain enforceable

commitments.

Furthermore, we believe that there are unique circu mstances that justify approving a higher percentage of enforceable commitments in t his Plan. In this comment letter, we have explained the situation regarding A RB’s in-use off-road equipment rule and in-use truck rule, which together account for a significant proportion of the

emission reductions needed to demonstrate attainmen t. These rules do not represent vague future commitments; they have alrea dy been adopted and are in effect today. The only reason ARB has not already s ubmitted them to U.S. EPA is that we are in the process of amending the rules to address the unique circumstances caused by the most serious recession to hit this country since the Great Depression. We have explained why ARB’s prop osed amendments to these rules continue to meet aggregate emission tar gets for these combined categories. Under these circumstances, we believe it is reasonable for U.S. EPA to accept a higher percentage of enforceable commit ments than has been accepted in other SIPs where the circumstances were very different.

Finally, it is illogical for U.S. EPA to determine that California is capable of fulfilling its commitments (i.e. satisfying the second prong), while simultaneously finding that the size of those commitments is “too high” to approve the Plan. It is also incongruous that U.S. EPA commends California’s “am bitious rule development, adoption, and implementation schedules” ( id . at p. 74536) and states “we believe the State and District have provided reasonable and appropriate schedules for achieving their commitments” ( ibid .) but then goes on to conclude that those schedules do not satisfy the third prong of the tes t.

We believe that the Plan should be fully approved f or the reasons stated above.Attachment 2



### Implementation of State 2007 SIP Commitments

State Actions

• Smog Check Improvements (BAR) - Low Pressure Evaporative Test

- Add Visible Smoke Test - More Stringent Cutpoints - Inspection of Light- and Medium-Duty Diesels

• Expanded Light Duty Vehicle Retirement

• Cleaner In-Use Heavy-Duty Trucks regulation, inclu ding Port Truck

Modernization

• Modifications to Reformulated Gasoline Program

• Ocean Going Vessels Cleaner Main Ship Engines and Fuel Rule

• Ship Auxiliary Engine Cold Ironing & Clean Technol ogy

• Harborcraft Engine Replacement Requirements

• In-Use Off-Road Equipment Fleet Rule

• Pesticides Regulation (DPR)

• Portable Outboard Marine Tanks Standards

• Vapor Recovery for Above Ground Storage Tanks

• Consumer Products Regulation Revisions

Ongoing Programs

• Accelerated Introduction of Cleaner Line-Haul Loco motive

• Mobile Source Incentive Programs, including SB 118 and MoyerAttachment 3



### 2007 State Strategy In-Use Heavy Duty Truck and Off-Road Equipment

Emission Reduction Commitment

THE ADOPTED 2007 STATE STRATEGY COMMITS TO ACHIEVE

AGGREGATE EMISSIONS REDUCTIONS CONSISTENT WITH THE

ATTAINMENT TARGET

The 2007 State Strategy describes ARB’s aggregate e mission reduction

commitment as follows:

“The total emission reductions from the new measure s necessary to attain

the federal standards are an enforceable State comm itment in the SIP. While the State Strategy includes estimates of the emission reductions from each of the individual new measures, it is importan t to note that the commitment of the State Strategy is to achieve the aggregate emission reductions identified from the existing strategy an d the adopted State Strategy. Therefore, if a particular measure does not get its expected emission reductions, the State still commits to ach ieving the total aggregate emission reductions, whether this is realized throu gh additional reductions from the new measures, or from alternative control measures or incentive programs. If actual emission decreases occur that exceed the projections

reflected in the emission inventories and the State Strategy, the actual emission decreases may be counted toward meeting AR B’s total emission

reduction commitments.”

April 2009 Revision to 2007 State Strategy, p.13

The Board-adopted 2007 State Strategy identifies em issions targets on a regional basis by source categories, with each regional targ et equal to the emissions levels

needed to demonstrate attainment.

The South Coast Air Quality Management District app lied the same emissions target approach (defined as “remaining emissions” o r “carrying capacity”) to the 1997/1999 Air Quality Management Plan for ozone whi ch U.S. EPA approved as

the air basin’s attainment demonstration.Attachment 3

BOTH THE SOUTH COAST AND SAN JOAQUIN VALLEY PORTION S OF THE

STATE STRATEGY WILL MEET THE 2014 EMISSIONS TARGETS FOR IN-USE
HEAVY DUTY TRUCKS AND OFF-ROAD EQUIPMENT

In December 2010, the Board adopted amendments to A RB’s in-use heavy duty truck and off-road equipment rules which, taken tog ether, achieve the expected emissions targets identified in the 2007 State Stra tegy for these categories.

To illustrate how the emissions targets are being m et for the on-road truck and offroad equipment categories, ARB staff developed a th ree-step approach. First, staff aggregated the categories to determine the co mbined emission reduction benefits; then a conversion factor was applied to n ormalize NOx and PM2.5 emissions from these categories into a NOx equivale nt emissions metric; in the third and final step, the SIP emissions target for these categories were compared with the emissions resulting from the regulations u sing the same NOx equivalent

metric.

Applying this approach to the 2007 South Coast and San Joaquin Valley SIPs,

ARB staff first converted the NOx and PM2.5 invento ries for the 2014 baseline for on-road trucks and off-road equipment into NOx equi valents. In the South Coast, this resulted in a NOx equivalent baseline of 329 t ons per day (tpd). In the San Joaquin Valley, the NOx equivalent baseline was 246 tpd.

Staff also converted into NOx equivalents the expec ted emission reductions in 2014 for the South Coast and San Joaquin Valley por tions of the State Strategy, and subtracted the results from their respective SI P baselines. This calculation provides the NOx equivalent emissions target for bo th categories to support the attainment demonstration: 187 tpd in the South Coas t and 141 tpd in the San Joaquin Valley.

Using the same NOx equivalent metric, staff then co mpared the amended truck and off-road equipment regulations (including inven tory improvements) with their applicable emissions targets. In each case, the re maining emissions are lower than or identical to the aggregate emissions target : 182 tpd in the South Coast and 141 tpd in the San Joaquin Valley.

The chart below illustrates this comparison, and sh ows that in the aggregate the proposed regulations will meet the SIP commitments.Attachment 3

Comparison of 2014 Remaining Emissions On-Road Truck and Off-Road Equipment Source Categor ies

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340

San Joaquin Valley South CoastNOx Equivalent Emissions (tpd)

2007 SIP

Emissions
Target 2007 SIP

Emissions
Target

Adopted
Regs (Dec 2010) Adopted
Regs
(Dec 2010) 2007 SIP

Baseline

Emissions 2007 SIP

Baseline

EmissionsAttachment 4

1 Air Resources Board comments on U.S. EPA’s November 30, 2010 proposal that VOC be considered a significant PM2.5 precurso r for the San Joaquin

Valley 2008 PM2.5 State Implementation Plan (SIP)

In its November 30, 2010 Federal Register notice on the San Joaquin Valley’s 2008 PM2.5 SIP, U.S. EPA has proposed to make a fin ding that volatile organic compounds (VOCs) are a significant PM2.5 precursor, which if made final, would impede California’s ability to implement the most c ost-effective regulations for attaining PM2.5 standards in this region. The Cali fornia Air Resources Board (ARB) is providing comments which document the scie ntific weight of evidence showing that VOC emission reductions are ineffectiv e in reducing PM2.5 at current ambient concentrations in the San Joaquin V alley. A review of the full set of peer reviewed studies of particulate matter in t he San Joaquin Valley, the current ambient air monitoring data, the emissions anticipated in the attainment year from enforceable SIP measures, and the complet e set of SIP modeling results all support the conclusion that VOC should not be considered a significant PM2.5 precursor in this instance.

U.S EPA’s PM2.5 Implementation Rule (Rule) establis hes a presumption that VOC is not an attainment plan precursor (40 CFR 51. 1002 (c )(3)). The federal Rule also provides that either a state or U.S. EPA can provide an appropriate technical demonstration for a specific area showing that VOC emissions significantly contribute to PM2.5 concentrations. In the case of the San Joaquin Valley PM2.5 SIP, U.S. EPA has proposed such a demo nstration suggesting that it is supported by the administrative record. Howe ver, U.S. EPA’s proposal also

indicates that the State of California should submi t a demonstration to either support or reverse the presumption under the PM2.5 implementation rule that VOC is not an attainment precursor.

ARB appreciates the opportunity to provide technic al information which supports the presumption in the federal Rule that VOC is not a significant PM2.5 precursor. While the 2008 SIP relies on a very com prehensive set of peer reviewed studies, modeling, and air monitoring data , ARB staff agrees that additional documentation of the scientific findings will better inform U.S. EPA and the public.

On September 16, 2010, ARB provided U.S. EPA with i nformation on the California Regional Particulate Matter Air Quality Study (CRPAQS) and the role it has played in the development of the 2008 PM2.5 SIP for the San Joaquin Valley. To date, over 60 papers have been publishe d in peer-reviewed journals such as Atmospheric Environment, Environmental Scie nce and Technology, and the Journal of Air and Waste Management. Over 50 p resentations of CRPAQS results have been given at national and internation al conferences. Data collected at over 100 monitoring sites has resulted in a publically available database containing over 180,000,000 records and a comprehensive website provides study documentation and reports. A full s tudy bibliography wasAttachment 4

2 provided to U.S. EPA. CRPAQS study results have be en previously been relied upon in U.S. EPA rulemakings for PM10, which in ter ms of the annual standard in the San Joaquin Valley is dominated by PM2.5.

On January 28, 2011 ARB sent to U.S. EPA the full m odeling documentation

and results used in the 2008 PM2.5 SIP. All of thi s information is part of the record for U.S. EPA’s consideration of the San Joaq uin Valley PM2.5 SIP. When the full weight of scientific evidence in the recor d is considered, U.S. EPA should reach the same conclusion about the efficacy of VOC controls as the Air Resources Board and San Joaquin Valley Air Pollutio n Control District.

U.S. EPA itself found that the state of the science on secondary organic aerosols does not support a finding of significant contribut ion to PM2.5. ARB agrees with U.S. EPA’s finding on secondary organic aerosols. The other potential chemical mechanism by which VOC may contribute indirectly to PM2.5, is a series of reactions ultimately resulting in formation of ammo nium nitrate. This is the chemical pathway that U.S. EPA cites as a basis for its proposal to overturn the negative presumption for VOC contained in its PM2.5 rule.

While ARB agrees that this chemical pathway exists, the weight of scientific evidence shows that it is not significant for PM2.5 attainment in the San Joaquin Valley. U.S. EPA states that with respect to nitra te formation the monitoring studies are not conclusive, and that early box mode ling differed on whether VOC controls would significantly affect PM2.5. This le aves the more sophisticated photochemical grid based modeling as U.S. EPA’s pri mary technical basis for its proposed finding that VOC controls are significant for reducing PM2.5 in the San Joaquin Valley.

ARB scientists have consulted with U.S. EPA’s model ing staff in the Office of Air Quality Planning and Standards to better understand the basis for the agency’s interpretation of the published photochemical model ing studies with respect to

the contribution of VOC to nitrate formation. ARB staff agrees with U.S. EPA that the cited PM2.5 modeling study (Kleeman et. al 200 5), shows a benefit of 50 percent VOC reductions at the higher emissions l evels at the time of the 2000 field study. However, that same modeling study sho ws a very different result when attainment year emission levels are taken into account. Using this data, the modeling study cited by U.S. EPA does not show a significant benefit of further VOC reductions. In fact, once the regional reductions in NOx (oxides of nitrogen) emissions are taken into consideration, V OC emission reductions produce essentially no benefit and in some instance s, may actually lead to an increase in PM2.5 nitrate concentrations (see page 7 of Technical Demonstration).

Additional PM2.5 modeling studies also reviewed by U.S. EPA show similar responsiveness to the 50 percent VOC reduction scen ario done by Kleeman. However, the SIP submitted to U.S. EPA for approval reflects actual NOx andAttachment 4

3 VOC reductions in the San Joaquin Valley, rather th an the theoretical scenario of an additional 50 percent reduction in VOC explored as part of the SIP development process. Such modeling sensitivity run s can be a preliminary step in the SIP process, but the actual emissions and re ductions in the attainment year are the basis for the required attainment demo nstration. U.S. EPA should reconsider its proposed VOC finding in light of the more refined analysis

discussed below.

U.S. EPA’s PM2.5 implementation rule appropriately directs SIP planning efforts and regulation to those pollutants generally known to significantly contribute to PM2.5 concentrations. In the implementation rule p reamble U.S. EPA defines “significantly contribute” to mean a significant em ission reduction in precursors which would result in a significant change in the P M2.5 concentration. The CRPAQS modeling shows that in the attainment year e ven a 30 to 50 percent further reduction in VOC would not significantly af fect PM2.5 concentrations.

Therefore it is essential that California has the a bility to focus on the pollutants of most significance to attainment of air quality stan dards. States need the discretion to develop the best approach for a meeti ng an air quality standard in each nonattainment area taking into account the sup porting science, technical feasibility of regulations, and the costs.

TECHNICAL DEMONSTRATION:

VOC emissions have the potential to contribute to t he formation of two different components of PM2.5, secondary organic aerosols (SO A) and ammonium nitrate. While these components contribute to obse rved PM2.5 concentrations in the San Joaquin Valley to a small degree, the weigh t of evidence indicates that anthropogenic VOC is not a significant contributor to PM2.5.

Secondary Organic Aerosols (SOA)

On an annual average basis, secondary organic aeros ols derived from anthropogenic VOC emissions account for only 1 perc ent to 2 percent of the annual total PM2.5 concentrations throughout the Va lley. SOA form when intermediate molecular weight VOCs emitted by anthr opogenic and biogenic sources react and condense in the atmosphere to bec ome aerosols. In addition, lighter VOCs participate in the formation of atmosp heric oxidants which then participate in the formation of SOA. As noted by U .S. EPA in the November 30, 2010 proposal, the processes of SOA formation are c omplex and have not been fully characterized.

ARB air quality modeling exercises conducted as par t of the San Joaquin Valley 2008 PM2.5 SIP attainment demonstration analysis us ing the Community Multiscale Air Quality (CMAQ) model showed that primary PM2.5 emissions are the main contributor to organic aerosols and SOA co ntribute to only a small extent. Furthermore, as illustrated in Figure 1, S OA are mostly formed during theAttachment 4

4 summertime, when total PM2.5 concentrations are low , and are mainly derived from biogenic emission sources. On an annual aver age basis, SOA derived from anthropogenic VOC emissions are a small part o f the organic aerosol concentrations (3 percent to 5 percent).

BAC

0 2 4 6 8 10 12 141163146617691106121136151166181196211226241256271286301316331346361 SB

SA

PA

Figure 1. Daily contributions to organic aerosol c oncentrations in Bakersfield in 2000 modeled with CMAQ: Primary organic aerosols (PA), secondar y aerosols formed from biogenic VOC emissions (SB) and secondary aerosols formed from a nthropogenic source VOC emissions (SA). Units are μg/m 3

.

As part of the CRPAQS study, simulations of a winte rtime episode conducted using CMAQ-Madrid, a model with an enhanced seconda ry organic aerosol formation mechanism, also found that organic aeroso l concentrations were dominated by directly emitted (“primary”) emissions . The study found that, because of the dominance of primary PM2.5 organic m atter, overall, a 50 percent reduction in anthropogenic VOC emissions has limited effects on the modeled PM2.5 organic matter (Pun, et al., 2009).

These study results show that for secondary organic aerosols, further VOC reductions would have very limited effectiveness in reducing PM2.5 concentrations. U.S. EPA’s proposal acknowledges th e state of the science on secondary organic aerosols, and indicates that the overall considerations presented in the 2008 PM2.5 SIP are not enough to f ind VOC as a significant PM2.5 SIP precursor for SOA in the San Joaquin Vall ey.

Ammonium Nitrate

While VOCs can influence the formation of ammonium nitrate, in the San Joaquin Valley this effect is minor. U.S. EPA cited ten re ferences as part of their technical demonstration. Four were monitoring stud ies conducted as part of CRPAQS that suggested that VOCs could under some co nditions be important inAttachment 4

5 the formation of secondary ammonium nitrate. Howev er, as U.S. EPA noted, the

studies differed in their assessment of the overall role of VOCs, and they cannot

be used to evaluate whether VOC controls would redu ce ammonium nitrate concentrations. The six remaining studies used dif fering types of air quality modeling to quantitatively assess the expected chan ge in ammonium nitrate to hypothetical VOC reductions. The two earliest stud ies used photochemical box modeling. This simplified type of modeling approac h does not fully capture atmospheric dynamics and reflect older chemical mec hanisms and levels of emissions. Thus these studies provide limited usef ulness in assessing VOC responsiveness under current conditions. ARB focus ed the SIP evaluation on the more recent modeling studies which used more ro bust photochemical grid modeling. These studies provide a more appropriate basis for evaluating the complex NOx and VOC interactions that occur in the atmosphere under realworld emissions control scenarios.

There are two primary pathways through which ammoni um nitrate can form. During the day, NO 2 is oxidized to nitric acid. Nitric acid then reac ts with ammonia to form ammonium nitrate. This daytime pat hway involves sunlight, VOCs, and background ozone. During the night, nitr ic acid is formed through

oxidation of NO 2 (via N 2 O 5 ) by background ozone, which then also reacts with ammonia to form ammonium nitrate. Studies by Pun e t al. (1998, 2004) suggested that the daytime pathway may be important and therefore the

formation of ammonium nitrate would be sensitive to changes in VOC emissions. However, other studies (Lurmann et al., 2006), sugg est that on average, daytime production of nitric acid in the San Joaquin Valley is relatively slow and that nighttime production of ammonium nitrate aloft, whi ch then mixes to the surface after sunrise could explain the observed homogeneou s patterns of ammonium nitrate in the Valley. Ying et al. (2009) also th eorized that the ozone concentration aloft in the San Joaquin Valley is pr edominantly due to the regional background and does not vary significantly with sur face-level VOC emissions. Therefore, nighttime ammonium nitrate formation in the San Joaquin Valley

would not be sensitive to VOC reductions.

ARB agrees with U.S. EPA that while the monitoring studies cited above provide evidence that the VOC pathway may be important at t imes, these studies do not provide quantitative information about the overall role and cannot be used to evaluate the benefits of VOC controls. Rather, mod eling studies are more appropriate to assess the overall impact of precurs or controls.

Staff reviewed the results of seven modeling studie s containing information on the significance of VOC controls in reducing ammoni um nitrate in the SJV. While the results of the earliest studies were mixed, lat er studies provide generally consistent results regarding the role of VOCs. In assessing the potential benefits of VOC controls it is important that significance b e interpreted in the context of California’s overall control program with its stron g focus on NOx control to

achieve benefits for both PM2.5 and ozone. ARB sta ff’s review of whether VOCsAttachment 4

6 should be considered a significant precursor was ex amined in the context of two key considerations:

1) Whether further VOC reductions would provide sig nificant benefits to expedite attainment beyond the existing NOx control program; and 2) The feasible magnitude of any potential VOC redu ctions beyond ARB’s already rigorous VOC control program.

Two early studies used simplified box modeling to e xplore the sensitivity of

ammonium nitrate to VOC and NOx reductions. One of the two studies simulated a typical winter episode (Stockwell et al ., 2000) and found that

decreases in VOC emissions had little effect. The second study (Pun and Seigneur, 2001) simulated winter conditions during the 1996 CRPAQS pilot study around the Fresno area. The study found that ammon ium nitrate formation decreased with VOC emission reductions, but increas ed with NOx reductions. Pun and Seigneur (2001) theorized that reducing NOx could lead to higher

concentrations of OH and increase the overall rate of nitrate production, despite the reductions in NOx. However, the box modeling a pproach has a number of limitations, including lack of transport into/out o f the box, robust vertical transport,

and use of an older chemical mechanism. In additio n, the VOC emissions were increased by a factor of two to improve model perfo rmance. As such, the box modeling did not fully represent the complete scope of atmospheric variations and has limited usefulness in assessing the respons iveness to VOC controls.

Subsequent modeling sensitivity studies for the sam e winter episode were conducted with the UCD/CIT model, an advanced resea rch grade modeling system (Kleeman et al., 2005). The authors conclud ed that NOx emission controls are more effective in reducing PM2.5 nitra te concentrations in the San Joaquin Valley. Summary study results indicate that on average, large reductions in VOC emissions (on the order of 50 per cent) reduced PM2.5 nitrate concentrations by approximately 17 percent. Howe ver, to evaluate the significance and effectiveness of VOC controls in t he context of control strategy design, the study’s isopleths of PM2.5 nitrate resp onse to combined NOx/VOC emission reductions provide more in-depth informati on.

Figures 2(a) and 3(a) show that, based on the shape s of the graphs, NOx controls are the most effective approach to reduce PM2.5 nitrate concentrations at Fresno and at the location with the highest mode led PM2.5 nitrate concentration (grid location -85 km Northing, 90 km Easting) respectively. Once NOx controls are taken into consideration, VOC emis sion reductions produce essentially no benefit and in some instances, may a ctually lead to an increase in PM2.5 nitrate concentrations. For example, as ill ustrated in Figure 2(a) for Fresno, after considering an approximately 60 perce nt reduction in NOx emissions resulting from existing and proposed cont rols, reductions in VOC emissions to any level would not decrease PM2.5 nit rate concentrations. Furthermore, at grid location -85 km Northing, 90 k m Easting, any level of VOCAttachment 4

7 emission reductions would actually cause an increas e in nitrate concentrations. Nitrogen-containing molecules such as PAN can act a s temporary sinks for NO 2

. When VOCs are controlled, the reduced availability of certain radicals which are generated from VOCs reduces the amount of NO 2 that is sequestered, thereby increasing the availability of NO 2 and enhancing ammonium nitrate formation (Meng et al., 1997)

.

Figure 2. 24-h average NOx/VOC particulate nitrate isopleths at Fresno for (a) all sources, (b) diesel engines, (c) catalyst equipped gasoline engines, and (d) upwind sources of nitrate. Units are μg/m 3 . (Source: Kleeman et al., 2005, Figure 3 pg 5333 ).Attachment 4

8 Figure 3. 24-h average NOx/VOC particulate nitrate isopleths at grid location -85 km Northing, 90 km Easting for (a) all sources, (b) diesel engin es, (c) catalyst equipped gasoline engines, and (d) upwind sources of nitrate. Units are μg/m 3 . (Source: Kleeman et al., 2005, Figure 5 pg 5335 ).

Four additional modeling studies investigated the m ore recent two-week winter episode of 2000-2001 that occurred during the CRPAQ S field study.

In the first study, preliminary data from modeling of this CRPAQS winter episode conducted using the Lagrangian form of the UCD/CIT model qualitatively confirm

that NOx control is the most efficient method to re duce nitrate concentrations (Kleeman, M.J., personal communication, May 2008). Figure 4 illustrates the response of PM2.5 nitrate concentrations to NOx and VOC emission reductions at a rural (Angiola) and an urban (Fresno) site on December 31, 2000. Again, based on their shapes, these graphs show that NOx c ontrols are the most effective approach to reduce PM2.5 nitrate concentr ations. Once NOx controls are taken into consideration (approximately 60 perc ent reduction in NOx emissions), reductions in VOCs of up to 30 percent produce basically no benefitAttachment 4

9 (Fresno). Futhermore, at some locations (Angiola) any VOC emission reductions may actually lead to an increase in PM2.5 nitrate c oncentrations.

Figure 4. The isopleths plot of PM2.5 nitrate with emission control of NOx and VOC at Angiola (ANG) and Fresno (FEI) after a 5-day back trajector y simulation for December 31, 2000. Units are in μg/m 3 . (Source: Kleeman, M.J., personal communication, May 2008)

A second study conducted simulations of the two-wee k CRPAQS episode with the CMAQ photochemical model (Livingston, et al., 2 009). The study consisted

of two simulations. The first was a baseline scena rio using a preliminary emissions inventory. This simulation showed that 5 0 percent reductions in anthropogenic VOC and NOx emissions had similar eff ects in reducing ammonium nitrate (about 20 percent each). A secon d simulation was conducted using an updated emission inventory representing a more accurate spatial distribution of total ammonia emissions (referred t o as “Vehicle NH 3 ” scenario, per Livingston, P., personal communication, January 19, 2011). This second 50 percent VOC reduction simulation showed a much l ower response to VOC controls. The response was lowered to a 12 percent reduction in ammonium nitrate, with a corresponding increase in responsiv eness to NOx control of 38 percent. These results are consistent with thos e found by Kleeman et al.,

2005.

In a third analysis, the San Joaquin Valley Air Dis trict (District) in a PM2.5 SIP appendix included a bounding sensitivity analysis o n the responsiveness to VOC controls. Based on this hypothetical scenario the appendix included a finding

that VOC reduction is effective for the annual stan dard and the winter episode for reduction of total carbon secondary particulates. This analysis used preliminary results from CMAQ modeling, namely that a 50 percen t reduction in VOC emissions led to a 10 percent reduction in particul ate nitrate. This is basically the same level of responsiveness reported from the studies by Livingston et al.,Attachment 4

10 2009 and Pun et al., 2009. However, as previously discussed, a hypothetical scenario of 50 percent reduction should not replace an analysis using actual

emissions and SIP reductions. Overall 2008 PM2.5 S IP concluded that VOC is not a significant precursor to PM2.5.

A fourth study modeled one-week of the CRPAQS episo de using a version of CMAQ with a more advanced chemical mechanism (CMAQ- Madrid) (Pun et al, 2009). In contrast to the earlier Pun study using a simplified box modeling approach, this later work found that on av erage, nitrate was most

sensitive to reductions in NOx emissions. While is opleths were not provided, the

time evolution of nitrate and PM2.5 mass to VOC res ponse illustrated in Figure 5 provides further detail regarding the efficacy of V OC control. The response of nitrate to a 50 percent reduction in VOC emissions increased as PM2.5 levels rose during the episode. In urban areas, a 50 perc ent reduction in anthropogenic VOC emissions caused small reductions in nitrate, o n the order of 10 percent on the modeled days when 24-hour PM2.5 concentrations measured over 100 μg/m 3 at urban sites and above 65 μg/m 3 in rural areas.

The difference in the VOC response on the days with the higher PM2.5 concentrations as compared to those days with lower concentrations may be due to a difference in the chemical formation regime fo r nitrate. In general, there is sufficient background ozone to generate enough free radicals to initiate and propagate the chemistry of nitrate formation (Ying et. al, 2009). However, on days with high PM2.5 concentrations, the daytime ph otochemistry may have contributed to a rapid increase in nitrate, resulti ng in higher VOC and NOx sensitivity. It does not appear that VOCs contribu ted significantly to the free radical budget on the simulated days mainly because rapid increases in ozone

were not observed. The effect of VOC levels on nit rate formation may also have a diurnal pattern since the hydroxyl and hydroperox yl radical levels are high during the daytime and negligible at night. In add ition, more reactive VOCs react quickly during the day and there is a minimal carry over to the next day. Therefore, it is reasonable to assume that the high er response to VOC and NOx at higher PM2.5 concentrations may be due the nitra te formation mechanism rather than to PM2.5 accumulation due to the length of the episode.

Overall, nitrate was only responsive to a 50 percen t reduction in VOCs at PM2.5 concentration levels that are no longer reached in the San Joaquin Valley. Currently, the 24-hour PM2.5 design value in the Va lley is 70 μg/m 3 recorded at Bakersfield and the rest of the Valley records 24-h our design values between 50 μg/m 3 and 60 μg/m 3 . Given the current levels of PM2.5, we believe th e Valley is now in a nitrate chemical formation regime that is less responsive to VOC

controls.Attachment 4

11 Figure 5. Time series with daily observations, bas e case simulation results and results from the sensitivity cases of (a) nitrate and (b) PM2.5 at A ngiola (left) and Bakersfield (right). (Source: Pun et al., 2009, excerpt from Figure 2, pg 406)Attachment 4

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