Loading...
HomeMy WebLinkAboutSP 144B; SDG&E Wastewater Facility; Specific Plan (SP) (8)AIR POLLUTION CONTROL DISTRICT County of San Diego I I I I STUDY OF SAN DIEGO COUNTY OZONE TRANSPORT I I I I I I I Environmental Studies I Xonics, Inc. 6862 Hayvenhurst Avenue Van Nuys, California 91405 ™ James G. Edinger, Ph.D. • Consultant Meteorology Department University of California • Los Angeles, California _ Raymond E. Kerr ™ Consultant 2021 Garden Street • Santa Barbara, California 93105 Prepared by Ralph C. Sklarew, Ph.D., John C. Wilson, Jeff H. Woolf for County of San Diego • Air Pollution Control District • 9150 Chesapeake Drive San Diego, California 92123 I June 1975 I I I I I I I • Uniform procedures are now followed throughout California for calibration of ozone monitoring instruments. Ozone levels in this report should I be corrected by a factor of 0.85 to be compatible with current data. I I I I I I I I I I 1 t 1 I ^I J I I I 1 1 «r I —t I J I I ^-sI I CONTENTS Section Page ACKNOWLEDGEMENTS iii ABSTRACT ' iv 1. INTRODUCTION 1 2. ANALYSIS TECHNIQUES . 2 2.1 Hand Drawn Surface Trajectories 2 2.2 Computer Generated Surface Trajectories 3 2. 3 Additional Meteorological Insights 3 2.4 Chemical Insights 4 3. CASE STUDIES 5 3.1 'January 25, 1975 Escondido 33 pphm at 1600 5 3.2 October 15 to 17, 1974 Oceanside 33 pphm 6 3.3 May 25, 1974 Escondido 27 pphm at 4 PM 8: San Ysidro 27 pphm at 3 PM 3.4 September 20 to 22, 1974 Kearny Mesa 27 pphm 8 at 4 PM on 9/21/74 3.5 March 17> 1974 Escondi.do 24 pphm at 2 PM 9 "3.6 April 5, 1974 Kearny Mesa 20 pphm at 4 PM 10 3.7 April 14, 1974 Oceanside 20 pphm at 5 PM 11 3.8 June 26, 1974 Escondido 20 pphm at 6 PM 11 3. 9 September 1, 1974 Escondido 20 pphm at 3 PM 12 3.10 June 13 to 15, 1974 Escondido 17 pphm at 11 AM 12 San Diego 17 pphm at 5 PM" 3.11 December 21, 1974 Kearny Mesa 19 pphm at 13 ^ 3 Section Page 4. RESULTS 15 5. SYNOPTIC OVERVIEW 17 6. CONCLUSIONS • 19 FIGURE & TABLE CAPTIONS 20 ii I I I I I I I I I I I 1 t 1 I «*/I I I I I 1 I 1 I «•*I J I ACKNOWLEDGEMENTS This study would not have been possible without the continual efforts of many people in the meteorology and air quality fields who diligently compile and archive the reams of data taken daily. Specifically, the efforts of the staffs of the San Diego Air Pollution Control District, the National Weather Service at Los Angeles, the Los Angeles Air Pollution Control District, the Orange County Air Pollution Control District and the U. S. Navy at Point Mugu are gratefully acknowledged. Meteorologists Donald Lust, NOAA and Hal Brown, SDAPCD, contributed many helpful suggestions and useful insights throughout this study and deserve special acknowledgement. - iii ABSTRACT Seventeen high ozone and related days in San Diego County from 1974 and January 1975 are analyzed to determine precursor source areas. Knowledge of these source areas is necessary to develop effective plans for meeting the air quality standards and for proper land use and transportation planning consistent with the standards. Three mechanisms for high ozone levels are identified: interbasin transport over the ocean, interbasin transport aloft and local generation. The highest ozone levels in San Diego County (33 pphm) are associated with a precursor source area in the Los Angeles basin and transport over the ocean. The highest ozone identified with a precursor source area in San Diego County was 19 to 20 pphm. These conclusions should be further substantiated by continuing analysis of future high ozone days and a interbasin transport study using a tracer for unique source area identification. •iv 1 I 1 I I J I I I 1 I I I I J I iifi i. INTRODUCTION This study was undertaken by the staff of Xonics, Inc. and their consultants for the San Diego County Air Pollution Control District to pro- vide insight and understanding of the sources and transport of ozone impact- ing San Diego County. County agencies are charged with developing plans for reducing ozone to meet the air quality standards and with assuring that land use and transportation plans are consistent with maintaining the standards. These agencies need to know the source and transport of the ozone they are attempting to control. The sources are actually emissions of reactive hydro- carbons and oxides of nitrogen, the precursors of ozone. Only sources within the County come under the jurisdiction of these agencies. Thus, the agencies are faced with distinguishing between high ozone levels caused by San Diego County sources and those caused by ozone or its precursors transported into the County. This study is primarily an investigation aimed at providing this needed information using case studies of seventeen days. The days chosen included all days with ozone reported over 20 pphm in 1974 and January 1975, and a few moderate ozone days for contrast. For each day, all available relevant meteorological and air quality data from the Southern California mainland and islands were compiled as a computerized data base for detailed analysis. The network of monitoring stations used in this study is illustrated in Figure 1-1 and an example of the data base is shown in Table 1-1. The data analyses included both hand drawn and computer generated surface trajectories, and meteorological and chemical insights. These are detailed and illustrated in Section 2. The analyses were applied to individual case studies as described in Section 3. The results of the case studies are summarized in Section 4. Additional general insight is offered by the discussion or synoptic analysis, in Section 5. The final section presents the study conclusions on major source areas and recommendations for future studies. -1- AKTAT trorn rrn-* and illustrated in this section. The techniques include hand drawn and computer generated surface trajectories, and meteorological and chemical insights. 2. 1 HAND DRAWN SURFACE TRAJECTORIES I The analysis techniques used in the case studies are described • ™ _ I Professor Edinger of the UCLA Meteorology Department prepared hand drawn trajectories for days of highest San Diego County recorded ozone • levels. Each trajectory traces the high ozone air parcel backwards from the monitoring station and hour of high ozone to the early morning hours, ex. see • Figure 2-1. This trajectory was developed from maps of surface winds, such * as those shown in Figure 2-2. For each hour, a subjective interpolation in • space and time was made based on the surface wind maps. The use of the . m trajectories is shown by Figure 2-1 illustrating a case where an air parcel _ with 13 pphm ozone in San Diego at 4 PM (1600) came off the ocean after a | twelve hour transit from the Los Angeles basin. Thus, the source of pre- cursors for the ozone measured in San Diego at 4 PM on April 5, 1974 is suggested to be the southern portion of the Los Angeles basin. The accuracy of this technique is difficult to evaluate. On a specific day, the accuracy will depend on the available wind data, its consistency, wind shear and atmospheric stratification. Transport by winds aloft can present considerable difficulty if they differ from the surface winds. The channeling of the local winds by terrain is another source of possible inaccuracies. Each of these are subjectively accounted for by the skilled meteorologist. Typical accuracies in trajectory position and timing may be at a minimum on the order of ten miles and one hour respectively. -2- I II I I I I I I I I I I I 1 I w I I 2. 2 COMPUTER GENERATED SURFACE TRAJECTORIES Computer generated surface trajectories were used in this study to supplement the hand drawn ones as well as to provide a second and objective methodology. The large number of days to be studied, seventeen, necessitated an automated methodology. Computer generation permitted the examination of trajectories from many more stations and hours than was possible using only hand drawn methods. Most important trajectories were developed by both methods. In the development of the computer interpolation algorithm, a sensitivity analysis was performed that quantifies some of the variabilities in trajectory generation. The algorithm specifies the stations to be used and their weighting for interpolation, the power law interpolation (IL and 1/r,^K K were tried), and a wind speed increase factor for winds aloft (1. 2 to 1.4). Best agreement with Professor Edinger's trajectories (compare Figures 2-1 and 2-3) was obtained with six stations (San Clemente Island, LAX, LGB, Long Beach, Oceanside and San Diego), weighting San Clemente Island by 5 and all other by 1, spatial interpolation by !/„, linear temporal interpolation, and an wind speed aloft factor of 1. 2 for San Clemente Island data and 1. 3 for data from the mainland (Edinger used 1. 2 and 1. 4, respectively). The greatest trajectory variability is shown in Figure 2-4 for trajectory generation by the extremes of (1) mainland stations only and (2) San Clemente Island only. 2. 3 - ADDITIONAL METEOROLOGICAL INSIGHTS Additional meteorological data was complied to provide further insight in cases where surface trajectories are not meaningful. Specifically, winds aloft and inversion height and depth were obtained from soundings at Montgomery Field, LAX, El Monte and San Nicolas Island. Local maximum temperatures were also compiled for San Diego County. These additional data were used to show why inland stations can reach much higher ozone levels than the coastal stations up wind (based on surface winds). -3- I I The higher temperatures inland can result in much of the air in a previously elevated inversion to be mixed downward bringing possibly high ozone • concentrations to ground level. This is called fumigation. To determine the source of the precursors of fumigated ozone, winds aloft must be traced backwards. The only data on winds aloft is • entirely too sparse for any more than suggestions of the direction and distance ™ of source areas. _ 2.4 CHEMICAL INSIGHTS I Since ozone is produced through photochemical reactions using oxides of nitrogen and hydrocarbons, the ozone observations are causally • related to these precursors and other primary pollutant emissions. A number of techniques based on the chemistry were utilized to further doc- • ument the ozone source areas. However, local sources and the lack of data over a significant portion of the travel path (the ocean) severely limits <• the usefulness of these insights. Some conclusions can be drawn from the • NO2/NO ratio as a measure of completeness of the photochemical reactions. 1 1 I I I I I I 1 I I I I I I I i I I I I I I I I \-SI I The case by case analyses of the seventeen days are described in this section. The days will be discussed in order starting with the highest ozone levels. 3.1 JANUARY 25, 1975 ESCONDIDO 33 pphm at 1600 Moderate drainage winds were observed through the morning hours. In the Los Angeles basin, the sea breeze was not established until after 10 AM. During the period 6-10 AM, strong NW winds transported air approximately 40 miles parallel to the coast. This resulted in the trajectories shown in Figure 3-1. The air over inland San Diego County at 4 PM came from the LA coastal region around 2 AM. This early in the morning, the oxidant precursor, NO , was extremely high at 53 to 74 pphm in the LA basin. X NMHC (non-methane hydrocarbons) were moderately high at 5.4 ppm while CO was 14 to 25 ppm and ozone was of course low (only 0 to 2 pphm). The NOVNO ratio varied around 0.4.£ X Following the 1600 Escondido trajectory, this air parcel should have passed the coast near Oceanside about 2 PM. No ozone data was avail- able from Oceanside this day. However, at 2 PM NO was 16 pphm, NO9 = 9 X <w pphm and CO = 3 ppm. All were very high for a 6 mph wind off the ocean. NMHC = 1.4 ppm for this hour. The NO9/NO ratio was . 6. These are *• A. appropriate for the longer reaction times with less sunlight in January. Two hours later in Escondido: O3 = 33 pphm, NO = 15 pphm, NO0 = 14 pphm, is X A NMHC = . 7 ppm and CO = 2 ppm. The NO0/NOV ratio was . 9. This ratioj£ X shows further photochemical conversion has taken place during the trans- port from the coast. However, there is no evidence of significant additional pollutant emissions in the NO and CO levels on the journey from the coast.X Another high ozone concentration (23 pphm) was recorded at Kearny Mesa for 3 and 4 PM (see Figure 3-1). This air parcel's trajectory was similar to the one discussed above and had similar pollutant concentrations: -5- I I NO -16 jjplim, NG9 - 16 ppinu, NIvIHC - i. 0 ppm and CO = 3 ppm. Due tox A the complex interrelationships between precursors, sunlight, local emissions I and time, the other stations did not record such high ozone levels. However NO and NMHC did increase even after 4 PM to levels of 33 to 55 pphm NOx x and 2. 0 to 2. 9 ppm NMHC. At these late times, both the lack of sunlight and scavaging by NO limited ozone production. I I Thus, the surface winds and pollutant measurements support a LA basin source area and transport over the ocean into San Diego County. | The winds aloft are also consistent with this picture. The inversion was below one thousand feet (limiting any dilution of the high pollutants monitored I at night in the LA basin), with NW winds of 3-6 mph (transport lines on the order of ten hours). B 3. 2 OCTOBER 15 to 17, 1974 OCEANSIDE 33 pphm at 1300 on 10/15/74 This three day period exhibited the 1974 highest ozone level and subsequent decay of high ozone levels over the next two days. On 10/15/74, the early morning winds were offshore, with the islands reporting offshore or NW winds. The reversal came after 10 AM with the southern-most and inland stations persisting easterly throughout the day. . This set up a convergence zone in surface winds throughout the afternoon, ex. at 1 PM Oceanside reported 11 mph at 280° while Escondido had 15 mph at 40°. Pollution observed at Oceanside could be expected to be entirely different than that at Escondido. That these were different air masses was further shown by the maximum temperatures: 82°F at Oceanside and 96°F at Escondido. The soundings showed an inversion well below a thousand feet with a break temperature of 88° F. Thus Oceanside was trapped under a low inversion while Escondido had good vertical mixing. Oceanside was over 30 pphm ozone from 1 to 3 PM on 10/15/74. A typical trajectory for this ozone laden air is shown in Figure 3-2. The 3 PM air over Oceanside left the Long Beach coast in the early morning and traveled over water thereafter. -6- I I I I I ^ I I i* I I I I^^- I I between 2 and 6 AM, the Lennox and (Josta Mesa (Long Beach NO and A. NMHC were not available) stations recorded a maximum of 48 pphm NOA (the only available NMHC look very'suspect). On arrival at Oceanside, the pollutant levels were 7 to 13. pphm NO and . 7 to 1. 3 ppm NMHC. ComputerX generated (CG) trajectories shown in Figure 3-3 differ by about the expected inaccuracies but show the same Orange. County source area. San Diego County stations farther inland being in a different air mass do not observe the high ozone. Kearny Mesa is too far south' for the limited along-shore transport and only reaches 18 pphm at 4 PM. By the next day, 10/16/75, the along-shore transport had dis- appeared. The islands only recorded an onshore flow in the late afternoon. The inversion raised to about a thousand feet. The maximum ozone in San Diego County was a 24 pphm in Oceanside at 1 PM. A possible trajectory for this is shown in Figure 3-4. To draw this trajectory, the recorded winds were subjectively channeled by the terrain in the early morning. Source area assignment is not definitive but large regions of "left overs" probably existed from the previous day. Near the assigned area, Costa Mesa had 46 ppm NOV at 5 AM. The explanation of why* X Escbndido failed to record high ozone is the over 10 mph winds and good vertical mixing due to the maximum temperature of 100° F (it is surprising that Escondido even reached 9 pphm). On the last of this three day series, 10/17/74, 14 pphm at San Ysidro for noon was the highest ozone recorded. The daytime winds had a slight southerly component which effectively blocked any transport from north of the county and the inversion height was over a thousand feet. Any ozone recorded in the county was probably due to county sources as shown by the CG trajectories in Figure 3-5. -7- This series of three days illustrates the effect of high emissions source areas north of the County. With good transport southward along the coast and a very low inversion, very high ozone was recorded on October 15, 1974. On the second day when the low inversion and winds along the coast dissipated, the ozone dropped appreciably. By the third day, the winds are more from the south and ozone levels are more representative of San Diego County alone. 3. 3 MAY 25, 1974 ESCONDIDO 27 pphm at 4 PM SAN YSIDRO 27 pphm at 3 PM This was a day of wide-spread high ozone. In addition to Escondido and San Ysidro at 27 pphm, El Cajon and Kearny Mesa measured 20 pphm at 1 PM. Transport southward along the coast was well established with 8 to 12 mph winds. However, this is not sufficient data to establish a source region north of San Diego County due to the offsetting southerly flow- component in afternoon surface winds, coupled with the lack of drainage winds in the LA basins, see Figure 3-6. These trajectories shoot far out over the g ocean reducing possible association with a source area. With analysis of multiple day data, the 1600 Escondido trajectory may reach the LA basin, • but this is only conjecture. During the day, the inversion height sank to 1200 feet, but few high concentrations of primary pollutants were observed • due to the high wind speeds. The winds aloft present the only possible explanation of all these observations. During the afternoon of May 24th and • at the next sounding (4 AM, May 25th), the winds aloft were consistently from ™ the northwest at 5 to 10 mph. Thus, the source area could have been to the ^ northwest but it can not be established to be outside San Diego County (though £ this is highly probable). 3. 4 SEPTEMBER 20 to 22, 1974 KEARNY MESA 27 pphm at 4 PM on 9/21/74 • This three day period began with 9/20/74, a day with a maximum _ ozone reading of 8 ppm. Strong southerly flow along the coast persisted in | the afternoon but with a strong sea breeze near the coastline. -8-I I I I I I I I I I I I / I *I I I I X.x' I I Thus, only air parcels that went far off the LA shore during the night could move southward. At 10 AM, the sounding at San Nicolas Island shows an inversion base height of over 1500 feet and winds in the inversion from the northeast at 10-12 mph. The same pattern was true at the 1:30 PM sounding. Thus, transport aloft out of the basin is well established. The surface trajectory for a possible high ozone air parcel is shown in Figure 3-7. Trans- port down the coast proceeded until the wind decreased around midnight and the air parcel was near San Clemente Island. Westerly winds prevailed on 9/21 and brought the day old pollution into the County around noon. On the twenty-first, the inversion subsided to 1200 feet with a break temperature of 95°F. Thus inland stations, El Cajon and Escondido with ground temperatures of 101° F and 96° F, respectively, had reduced pollution due to good vertical mixing. This illustrates why El Cajon only reached 12 pphm at 4 PM when nearby stations were 19 and 27 pphm. Similarly, Escondido peaked at 17 pphm; unfortunately for further corroboration, Oceanside ozone data was missing. On the twenty-second, the winds turned and came out of the south and maximum ozone dropped to 14 pphm in Kearny Mesa and Chula Vista at 10 AM. This early peak was perhaps due to residuals from the previous day. 3. 5 MARCH 17, 1974 ESCONDIDO 24 pphm at 2 PM This day had a very low inversion base (under 500 feet at Montgomery field). The two highest stations were both inland (in addition to Escondido, El Cajon peaked with 19 pphm at noon) while only low ozone was recorded at coastal stations (primarily Oceanside). This pattern is typical of fumigation (an opposite case to September 21, 1974 discussed above). The elevated inland temperatures mixed downward a portion of the air that had been trapped in the inversion. The morning (4 AM) Montgomery field sounding showed a northeast flow at 5 mph as did the island stations for hours 8 to 10 AM. Thus inversion trapped pollutants could have been trans- ported aloft down the coast and mixed downward over the hotter San Diego County inland stations. Of course, this is not evident in the surface tra- jectory shown in Figure 3-8. .9. A npTT C in'?/* VP APMV MT?Q A OH ™-»u^» *>+ 4 mxJLj.VJ.XJ *^> JL. ./ / -JL »^.---A*J.** i A J.*X*_*^AA 4-w ^J^tilJ.1 Cic "0; J. 1VA This is a case of "text book" transport of Los Angeles basin precursors into San Diego County producing widespread elevated ozone levels. The 4 PM CG trajectories shown in Figure 3-9 illustrate that air from the LA basin in the early morning reaches as far south as San Diego by 4 PM. This is seen more graphically in the outlined air parcels shown in Figures 3-10 to 12 for San Diego arrival times of 4, 6 and 8 PM. Elevated NO wasX. measured in the coastal LA basin from 4 to 8 AM. This air then proceeded out over the ocean and southeast into San Diego County. The high winds of the sea breeze in the afternoon brought this air onto land between 4 and 8 PM, after a twelve hour transit time. Aloft the winds had the same pattern with northeast in the morn- ing and north to west rotation during the day at Montgomery field, LAX, El Monte and San Nicolas Island. The inversion base at the coast began around five hundred feet and increased to about twelve hundred. The inver- sion break temperature of just under 80° F was almost met along the coast and was exceeded inland. To illustrate these effects, consider the Escondido maximum of 18 pphm at 4 PM. The CG trajectory in Figure 3-9 indicates that this air passed near Oceanside between 2 and 3 PM. Oceanside recorded 12-14 pphm ozone, 6-8 pphm NO and . 8 ppm NMHC during thisX period. These values are consistent with further photochemical ozone gen- eration during the transit to Escondido. In the southern portion of the County, • San Diego and San Ysidro peak a little later as is consistent with Figures 3-11 • and 12 showing a later arrival time for LA basin air. This can be seen in ^ the 6 AM upwind streak lines shown in Figure 3-13. These streak lines show £ the position of 6 AM air that will later pass over the San Diego County stations. The numbers added indicate the ozone measured and time when the air reached I the station. For example, air that arrived in Escondido only during 3 to 8 PM was in the LA basin at 6 AM. The highest Escondido ozone was observed only I during this period. The ozone decrease towards 8 PM may be due to decreased sunlight and local evening emissions. -10- I I I I II I I I I 1 I I I I I I J I I I 1 3. 7 APRIL 14, 1974 OCEANSIDE 20 pphm at 5 PM The transport along shore was slightly weaker than in the above case. The inversion persisted below a thousand feet throughout the day at the coast. The Oceanside maximum ozone air trajectory is shown in Figure 3-14. The inversion was broken at El Cajon and Escondido and they did not record ozone above 10 pphm. This is another case of transport of the precursors of the maximum ozone from 'the LA basin over the ocean. 3. 8 JUNE 26, 1974 ESCONDIDO 20 pphm at 6 PM This is a "text book" case of fumigation with Escondido at 20 pphm, El Cajon at 12 pphm and all other stations below 10 pphm. The maximum ozone surface CG trajectory is shown in Figure 3-15. This surface air parcel passed near Oceanside about 3 PM when only 5 pphm ozone was recorded. The additional 15 pphm could not have been made during the one hour transit with only the .1 ppm NMHC and 2 pphm NO measured at Oceanside, norX could the Oceanside ozone be depressed due to local sources since no N©2 was measured. Thus the ozone came from another direction. The soundings showed an inversion at a thousand feet rising to over fifteen hundred feet in the afternoon at Montgomery field. Significant portions of the inversion were mixed downward at Escondido and El Cajon with maximum temperatures of 96°F and 93°F respectively. In the morning (4 AM), the wind below a thousand feet was from the south and those above from the northeast. In the afternoon (1600), the winds aloft were out of the west at 10 mph. Further out at sea, San Nicolas Island recorded high (15-25 mph) winds aloft at the two soundings (10 AM and 4 PM). These sounding data are consistent with a lengthly transit aloft and fumigation over Escondido of the precursors from the early morning in the LA basin. -11- I I3. 9 SiiPiJtiMB&R I, 1974 ttSCGiNUluO 20 pphm at 3 I'M This case is somewhat similar to the previous one. The ™ maximum ozone surface air trajectory was out of the west (see Figure 3-16) and the maximum temperatures in Escondido indicated significant portions I of the coastal inversion would have mixed to the surface. However, on 9/1/74, Oceanside did measure elevated ozone (as well as NO ) a few hours before J the Escondido peak. For example, at noon in Oceanside, 7 pphm ozone was measured with NO = 18 pphm and NO2 = 5 pphm which show considerable • potential for further photochemical ozone production (the next hour ozone increased to 12 pphm). • 3.10 JUNE 13 to 15, 1974 ESCONDIDO 17 pphm at 5 PM on 6/15/74 SAN DIEGO 17 pphm at 11 AM on 6/15/74 -12- IThe data aloft for this day are sparse. The inversion base at Montgomery field rose from 1200 feet at 4 AM to 1700 feet at 4 PM.. In the morning, winds were 5 mph out of the northwest below the base and southwest « above. Thus the transport south along the coast shown in Figure 3-16 may. V have been considerably longer. In the afternoon, the winds were 10 mph from the west. I Though some of the precursors were observed at Oceanside, the • winds were off the ocean at 6 and 7 mph. Any source area identification would be pure conjecture with sparse data showing possible transport both || up and down the coast. I IThe first day of this series had a maximum of 12 pphm in Escondido at 1 PM. GG noon trajectories are shown in Figure 3-17 and a 4 PM I outlined parcel in Figure 3-18. These two figures strongly suggest entirely different flow then on any of the days discussed previously. Aloft, the inver- • sion base was around 2000 feet which also contributed to low pollution levels. ™ I I I I I I I >I I 1 I I 1 I I I «^ I J I The next day, 6/14/74, the inversion lowered to about 1200 feet. The maximum ozone measured was 16 pphm at Escondido at 1 PM. In El Cajon, ozone peaked with 15 pphm at 11 AM. At Escondido, the ozone also reached 15 pphm by 11 AM. During and preceding the high ozone hours, the winds were very low (1-3 mph). This together with the lower inversion resulted in reduced ventilation and the clear indication of local source areas for the observed ozone. When the winds picked up in El Cajon, the ozone dropped. The final day of this series, 6/15/74, had a morning peak at San Diego and afternoon at Escondido. Aloft LAX showed the land breeze, sea breeze diurnal variation but in San Diego winds from the northwest were observed by both soundings. The inversion base was 1000 to 1500 feet and the maximum temperatures inland were adequate for considerable fumigation. The morning peak at San Diego of one hour duration started and ended with 12 pphm. Winds were off the ocean at 10 mph so the only tentative explanation is precursors from the previous evening and probably a source area within San Diego County. At Escondido, a morning peak of 15 pphm was observed by 10 AM and the afternoon peak reached 17 pphm at 5 PM. The morning peak was similar to one observed on the previous day and may have been of local origin. In the afternoon, it is likely that fumigation was the cause with an indefinite source area. 3.11 DECEMBER 21, 1974 KEARNY MESA 19 pphm at 3 PM The final day to be discussed is the "text book" case for local pollution. A low inversion base and low winds led to very high precursor build up in San Diego County during the night and morning. The sea breeze the next day brought this air to inland stations with photochemically produced ozone. The possibility of an early maximum was eliminated by the over- abundance of unconverted NC- (ex. 20 pphm in San Diego at 11 AM withX -13- NO0/NO = . b) and the reduced sunlight in December. The inland stations/ x peaked at 3 - 4 PM. New NO emissions quickly eliminated the productionX of yet higher ozone levels, (ex. 54 pphm in El Cajon at 6 PM with NO9/NO = . 4).^ X -14- I I I I I I I I I I I 1 I I 1 I I I I I I I I I I I I I I I I I I I I I0 I I 4. RESULTS These case studies have shown three mechanisms resulting in elevated ozone in San Diego County: interbasin transport over the ocean, inter- basin transport aloft and local generation. The surface wind transport of precursor over the ocean from the Los Angeles basin accounts for the highest observed ozone levels. This route requires a 10 - 36 hour transit over the ocean. During this time, dispersion is limited by the increased stability over the usually colder water. There are no known chemical sinks for the ozone pro- duced in route and trapped in the inversion so it may arrive in San Diego County at high concentrations. The case studies fitting this pattern include: Date: Maximum Observed Ozone: 1/25/75 33 pphm 10/15/74 33 pphm 9/21/74 27 pphm 10/16/74 24 pphm 4/5/74 20 pphm 4/14/74 20 pphm The second route is aloft with fumigation over inland stations. Identification of the source area is more tenuous due primarily to the scarcity of data, but the northwest flow aloft in these cases suggest the Los Angeles basin. Case studies following this route are: 3/17 24 6/26 20 A local source area is the third possibility. The days studied that demonstrated San Diego County sources include: 6/15 17 12/21 19 -15- Tiit; results fur Lwu uaya were ambiguous. The ox,one peak on May 25, 1974 may have been due to transport aloft of air from the Los Angeles basin but the critical data needed to establish this were not avail- able. The ozone maximum observed September 1, 1974 could be interpreted to result from a source area either in Los Angeles basin or in San Diego County, but any single conclusion is very tenuous. -16- I I I I I I I I I I I I I I I I I I *r I 1 I 1 I 1 I wI I I 5. SYNOPTIC OVERVIEW In this section, the comments by meteorologist Raymond E. Kerr are p. sented on the synoptic weather patterns associated with the high ozone days studied. The scope of this work was simply to examine the weather maps associated with a number of cases of recent high ozone episodes in San Diego County to see what these patterns had in common. Specifically, it was desired to test the generality of the weather pattern described by Bell (1960) for the two Fall episodes that he examined. In brief, he found that a relative high pressure area dominated the Great Basin area, favor- ing off shore flow during the night and early morning hours. Upper air conditions favored strong subsidence leading to low inversion heights over San Diego. These conditions can result in the surface transport of precursors from the LA basin into San Diego County. The dates chosen for this study were all cases in 1974 and January 1975 where ozone reached 20 pphm or more in San Diego County. Maps used were the Daily Weather Maps, Weekly Series, published by the Environmental Data Service, NOAA. The following Table shows a thumbnail characterization of the patterns for the days selected. The specific Indicators are; (1) the reduced sea level pressure for Needles (BED), (2) Pressure difference SAN - BED, and (3) relevant features of the 500 mb. flow pattern. The data on Table 5-1 suggest, and inspection of the weather maps verify, that the March, April, October and January episodes generally followed the pattern postulated by Bell. A weak to moderate intensity high pressure area was located inland over the Great Basin, which favored nighttime offshore flow with late development of the sea breeze. The 0400 PST map usually showed an easterly wind and low dew point at LAX, although the general Bell, G. B. (1960) Meteorological conditions during oxidant episodes in coastal San Diego County, California Bureau of Air Sanitation I high at 500 mb. The most consistent change noted between the day before and the day of the episode was an increase of the height at 500 mb. over I liow pattern was a more reliable indicator than any point parameter. None of the episodes showed a very strong high in the Great Basin or strong north to northeast winds aloft. All of these episodes showed a ridge or contour I San Diego. These episodes all terminated when low pressure returned to the lower Colorado River Basin (Las Vegas to Yuma). The pattern noted by | Bell for the two Fall episodes may also occur in Winter and Spring and corresponds to each of the identified surface transport days. • I The "smog season" episodes in the sample (May through September) ft are quite different from those observed during the winter half year. None of the Summer types showed high pressure inland, but rather a weak trough in the lower Colorado. The day of the episode, all cases showed onshore flow with typical marine layer dew points at 0400 PST at LAX. If oxidant precursor _ were transported from Los Angeles to San Diego, it would require a compli- | cated, mostly over land trajectorj7. The common feature a.gain was a. ridge or contour high at 500 mb., with apparent intensification on the day of the • episode. Inspection of data for other years shows that the Winter type of high pressure in the Great Basin can also occur in September, so we can • apparently have either type during that month. Rapid inspection of a number of weather maps shows that days when a trough or closed low at 500 mb. prevailed over San Diego, high oxidant • values were never reported. The September 21, 1974 episode is an apparent • exception, but it appears that the ridge to the north rather than the closed low _ to the south was the determining factor. p -18- I I I I I I I•wI I I I I I I I I I I I I I I ***>I I 6. CONCLUSIONS As determined in the case studies, the major source area for the precursors causing San Diego County's highest ozone levels is the Los Angeles basin. The precursors react in transit, either over the ocean or aloft, to produce a significant portion of the observed ozone concentrations (up to 33 pphm). The highest ozone levels shown to be associated with source areas in San Diego County are 19 to 20 pphm. Further substantiation of these conclusions should be undertaken by continuing analyses of episodes and by a transport study. The techniques used in this study should be applied to new episodes of high ozone as they occur. Commencing the study of an episode with the minimum elapsed time will maximize the data availability and the social impact of the results. However, critical data will always be missing since most of the path is over the ocean or aloft. A unique identification of source area would be possible if the air . from the area were tagged with a tracer and the tracer were detected in San Diego coincident with elevated ozone. Such a transport or tracer study should be conducted in the Fall, Winter or Spring when conditions are as listed in Table 5.1. Synoptic analyses and regime delineation briefly described in Section 5 should be persued both to better understand and explain high ozone episodes and to provide the proper background for ozone forecasting in San Diego County. -19- FIGURE & TABLE CAPTIONS Fig 1-1 Network of monitoring stations used for air quality,©, and meteorology, X. data. Table 1-1 Example of compiled data base. Fig 2-1 Hand drawn surface trajectory 4/5/74 showing path taken by air parcel from 4 AM in southern Los Angeles basin to the 4 PM (1600) measurement of 13 pphm ozone in San Diego, Fig 2-2 Surface winds for 1400 on 4/5/74, The arrows point in the direction of the winds with length equal to one hour trans- | port. Fig 2-3 Computer generated surface trajectory for comparison with • Fig 2-1. ' Fig 2-4 Comparison of extremes of interpolation algorithms: — mainland • date. oaly» — San Clemente Island data only. — Fig 3-1 January 25, 1975 maximum ozone air trajectories: Escondido * 33 pphm at 1600, Kearny Mesa 23 pphm at 1600. m Fig 3-2 October 15, 1974 high ozone air trajectory: Oceanside 31 pphm at 1500. • Fig 3-3 October .15, 1974 CG (Computer Generated) air trajectories around maximum hour for Oceanside, • Fig 3-4 October 16, 1974 maximum ozone air trajectory: Oceanside 24 pphm at 1300. • I Fig 3-5 October 17, 1974 low ozone trajectories for 1300 air parcels. Fig 3-6 May 25, 1974 high ozone air trajectories: Escondido 27 pphm | at 1600,, San Ysidro 27 pphm at 1500 and Kearny Mesa 20 pphm at 1300. I Fig 3-7 September 20-21, 1974 possible multiple-day air trajectory: Kearny Mesa 27 pphm 1600 9/21/74. | -20- I I 1 I1 1 1^^v 1 1 1 1 1 B Im 1 - 1 1 I r i FIGURE & TABLE CAPTIONS (uon't) Fig 3-8 March 17, 1974 surface trajectory unrelated to observed ozone: Escondido 24 pphm at 1400. Fig 3-9 April 5, 1974 representative 1600 air trajectories for San Diego and Fig 3-10 April 5, 1974 at 1600. Fig 3-11 April 5, 1974 at 1800. Fig 3-12 April 5, 1974 at 2000. Fig 3-13 April 5, 1974 at arrival Fig 3-14 April 14, 1974 Oceanside. outlined air parcel arriving in San Diego County outlined air parcel arriving in San Diego County outlined air parcel arriving in San Diego County 0600 upwind streaklines with time and ozone (in []) indicated (trajectories are shown in Figure 3-9). high ozone air trajectories: Oceanside 20 pphm at 1700 and Costa Mesa 20 pphm at 1200. Fig 3-15 June 26, 1974 Escondido surface CG trajectory unrelated to observed ozone 20 pphm at 1800. Fig 3-16 September 1, 1974 surface CG trajectory with ambiguous relation to observed ozone: Escondido 20 ppm at 1500. Fig 3-17 June 13, 1974 Escondido Fig 3-18 June 13, 19/4 at 1600. surface CG trajectory on low pollution day: 12 pphm at 1300. outlined air parcel arriving in San Diego County Table 5-1 Synoptic Features for High Ozone Days -21- Nicolas Island Westwood—"V&T f LAX ^N^ Lennox— Long Beach—j LGB 77? Costa Mesa Laguna Beach San Juan Capistrano Temecula -Aval on San Onofre Palomar Field- Encinitas- San CLemente -f ^k^Escondldo 3^r~My/' r~:j.'l~ -"-^fr"<—-y'\ -', •< <f. i '•- ' ^ \ •OTM ; i •^•» 0 10 20 30 40 \ Coordinate Origin 2\ %v%OK^vrj^^> Explanation of Symbols O Air Quality Station / Wind Measuring Stationi \ V."\ ^'\ VMiraiuai NAo v«v MonLgoiiiery Field \ o/ Lindbergh Field , ^aj (o Sail Diego V^/ UliUllclb \y f Ream Field — V San Ysidro = % ^ j-3^ .-.*.-'fsr'- '^- •< N '' /./ .,^-V:,. .._.;.-.' > GiJlespie Field^;-v,^' ,- , ro^- Vi ^eV. '; ••?<-- 1*-' .'-g^ ;i , Alpine / fe Cajon '•**• ,-: } ' — J _,--/!X -^' '^; N-r; •-_^-^/r,: /oT •• "j .'•/ -•'"' '\_^./^•..^i.^.&%—-' —Brown Field (I TABLE 1-1 HOUR: STATION WEST *r. LAX LifJNUX LU-C- e.EA CSTA '-'SA LAC-!J'!£ S J CPfT "SAN t-.f-d SA?V C";f-P — ST MCC'L oosir,i"" E:CCNT to S AN C t • (•' K !-*>'.'< J LA EL CAjr,-.' " C! CLL.- SSAN Llr-C " CHO VIST S/SN YSJD 11 CC£.P.OINATCS , { ( ( { ( ( ( f ( •"( ( ( ( { f ( ( C.149- ~? 1 » 1 T —2 u.6 , —1 ? .? , 4.4, 1 3 . ? t T C;.V, ~"2?.0'," ii.it -65.2, ? 5 . ? t 1 • "•• • fc~ i - : 1 . 2 i ""51.4, 17.3, l-c'.V, A "i 0 14.3, 17.3, 66.3) 61.9} 6 C . \ ) 56.0) *i.r) 36. G)13 '-• . c 24.2 " 24.1- " i '» . 7 Ir . j " 8.'£ 0.0) -ilVF.r - ! 6 . 1 1 - i '.- . 2 ) — ? 0 t ) -26.1) -32.' ) CO NC2 NCX DX NMHC 11 ***11 t 7 """ 13 *** *** *** ***"7 *** *** 1 1 ***i -*** 1 *** ***" "15" =>** " 32 ***&** ***^•v** 6 2 *** 2 *.** * ** ***1 *** ***i? ***32 **.* ** V" "*** 14 A. ***t. 2 ***"X "7 * - ^** 2 o.e?3»** :>**' 5 2 15 ' 12 *** *** ***" *** 11 ~ IT ' *** 4 3 A* ** *- - 4- 3 ***-•> =><• 2 !»*# ***a*S: ******" ff-** *v* ~- 11 *** - ***ti 3 **w - ^*** " 1 NC2/NCX OX/CO 0.92 i A ** s~isr ******O.ft-2 ******1.00 *< **** ***:>** M-lj**** *JT*:<>\* 0 . «• r ' 0.75 ******~ I. 00 . i.r-o *Jr****,J. .*. j, -w rf. ^, ****** C.1.C- ****** ******0.45 " C.33" 2.14 C .^2 ****** **s **» ****** ******'• : .67 •— *#«.*»* ******"4". 00" ?..uO•****»>* * A-1--*-* -^ ******2<.00 CC/VCX NCR. CX NPRK3 W 0.19 ****** ****** »***-.^* ,:***** 0.83... 0^2 ^^ 4;^E^c^^i3fc 1 i> C^ 5- O.-l i.2£ ****** ****** :;***** ****** ****** ****<*• - # *** * * ******(; . / 1 0.61 -***-,*** 1.^2 ****** ******" 0.1->0- (:.4C o.5(» l.?7 **?>*** " ' 0.91 •*t*w**c** *^*v*Me ****** l.Cif *• f ! f "/ OV » . • \J l^ » / v. ****** i***-** 0.15o.sc 0.6° " '" C . >• 5 ********«*«.* ****** " :>***** ' O.40 ' ~ ' 1 . C ? ******0.2 ?" 0.9C ' "0.60 ^.jj 5^^ ,. ^ ' C.6° 0.51 DIR W SPO 22 27"" **2 27 1R ?2 29 31 35 "•"0 ft 35 ••29" 6 **^0 9 f 8 "13 ** 3 e; 5 5 3 3 H, IS 5 4 £ • «» c ;2 13 IN A 1C 20 30 40 Figure 2-1 •N A 10 20 30 40 ...[ N 10 0 10 20 30 40 Figure 2-3 0 San Clemente Island Alone: Only the Mainland Stations N 10 0 10 20 . 30 40 Figure 2-4 >J^*£s 0 c JUJpv^W?WK-:-)o,-V 20 30 40 Figure 3-1 (I N A 10 I nI v>40 Figu.re 3-2 <"V*X.--,V ^5::-"\ 10 0' 10 20 30 13- 40 Figure 3-3 N A ^evtV? ft^~^£>Jfl{ \tiJ.K<\*.»e-, 'r,r 10 20 30 Ficnire 3-4 f N 10 20 30 \ ,;V vX/v" I £ ^<y> _V " "V^ -'^ ^ ^^Mp 1^^ ^ ~^^^W7!,.,'"'-/r^ " // r-"^-} ft-.> ' fi.-/—v 'J ?(¥/?<* ?&((? A^" /C >^^-v-^-,SJ ,/^L. '-••-\\\ .Jj^fr. , /; X^ '-U t-, f \ •'. • I S~-S,sJ '- - • - /• . , : ->^^•^0^ ^:^',^~:r^.^%,-f =S ^3y^A.::- - x ,.^ - Fipure 3-5 G N _<•'. 10 10 20 30 Figure 3-6 N A I -°- 10 20 . 30 Figure 3-7 • "-'Xv -* 5C:"C*\ -"•^ • a tvyv/ry,:-..••••'•-... ~ir!// °s y^J>-') p^v^.i^ N ^•^:;-vi V ^^C''-'. • ^. -n •- 6 \ ^ ^5.--^:^ CO- -. '• ••'" . .-• \ « / '-^fji^^ >il y. " -_; '\- ..(S'i^r^ .:'-0>-»-^'•?" rv '^rv ••^*-~--j's ' x-~ >~fV[^'--> \S • -3 .' 20 30 40 Figure 3-8 \ N - , 10 10 20 30 Figure 3-9 TUSK i^iz- »j^ N 10 0 10 20 . 30 40 Fic-nrp .^-1 08 01 Cl —— . _ -v •„ - \ r j^--; ^ •>> ' "" / \ in • i ' - \ \ <-i <- .s ^--OAf -^ _ A,- V»._ >j .^.^.-/^y /•'^"aA^: i;,,- ^;rt-^ c. c 10 0 N- 10 ^5fic,, r^VrTx -£*<V ~-> ^c-r 5000-s N-)V'^r-l--^-, ^.c-^ 2Q . 30 40 Figure 3-12 0 10 20 . 30 40 Figure 3-13 N t k 10 20 30 40 «<£>«,e ^xP O^fe^-fes^-\^/>;J V -^CV.-. ~-"? v, -c,-Cf^ N 4 10 10 20 30 40 Figure 3-15 N. A 10 0 10 20 30 40 Figure 3-16 30 ^N_VV^-V> ^ . -r- '••',,\S.::'.^'- - P^ Figure 3-17 TABLE 5-1 SYNOPTIC FEATURES FOR HIGH OZONE DAYS PRESSURE PRESSURE DIFFERENCE DATE EED SAN - BED March 17 1016.4 +1.0 April 5 1021. 3 - 3. 2 April 14 1018.1 - 1.7 May 25 1011.7 +2.9 June 26 . 1005. 3 + 5. 0 Sept. 1 1006.3 +2.6 Sept. 21 1009. 7 + 0. 1 Oct. 15 1020.2 - 2.3 Oct. 16 1018.5 -2.9 Jan. 25 1019.8 - 1.2 1 1 1 1 500 MILLIBAR FEATURll Ridge over So. Cal. , Ar: 1 Ridge over Nevada Ridge moving onshore • Ridge moving onshore • High over Arizona Ridge over California I Ridge onshore, Lo So. C High over So. Cal. • High over So. Cal. • Ridge onshore 1 1 1 1 1 1 1