### AucusT 1995 

### BIGLER-ENGLER AND BROWN 

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## Analysis of an Ozone Episode during the San I)iego Air Quality Study:

'I'he Significance of 'Transport Aloft

VIRGINIA BIGLER-ENGLER AND I

- IAL W. BROWN
San Diego Air Pollution Control District, San Diego, California 

### (Manuscript received 16 

### March 1994, 

### in final form 8 

### December 1994)



### ABSTRACT San Diego is subject to transport of 

### ozone and precursors from the Los 

### Angeles area, 170 

### km to the northwest, as well as to high ozone concentrations from local emissions. The San Diego Air Quality Study was conducted during the summer of 1989. 

### Air quality and meteorological data were obtained at the surface and aloft to provide a high quality database for photochemical modeling and control strategy development for both local and transport-influenced ozone episodes. Six 

### high-ozone episodes were potentially suitable for photochemical modeling, including several from 21 

### to 29 

### September 1989; 

### maximum 1-h ozone concentrations exceeded the federal ambient standard on six of 

### the nine days and reached 0.17 

### ppm on two days. From review of 

### preliminary surface and routine meteorological data and surface trajectory analysis, 25-26 

### September 1989 

### appeared to be a local episode with high ozone concentrations downwind from local (i.e., San Diego) emissions sources. This paper examines the candidate episode and finds that transport aloft from the Los 

### Angeles area played a key role.



### 1. Introduction The San Diego Air Basin exceeds both California and federal ambient ozone standards, of 0.09 and 0.12 ppm, respectively. In 1993, the most recent year of data, the California ambient ozone standard was exceeded on 90 days; the federal standard on 14 days, with a peak hour of 0.19 ppm. Both California and Federal Clean Air Acts require that attainment of their respective standards be demonstrated, generally by photochemical modeling. San Diego's highest concentrations of ozone and precursors result from transport from the greater Los Angeles area, with 14 million residents, 170 km to the northwest, as well as from San Diego County emissions. Controls placed on San Diego sources may achieve little airquality benefit for San Diego under conditions conducive to transport; thus, identifying an episode not contaminated by transport is essential to model and control strategy development. The boundaries of the San Diego Air Basin ( 

### SDAB ) are the borders of San Diego County, an area roughly the size of the state of Connecticut.SDAB is bounded on the north by Orange and Riverside Counties and Greater Los Angeles [ South Coast Air Basin ( SoCAB )], on the east by Imperial County, on the south by Mexico, and on the west by the Pacific Ocean (Fig. 1). Mean terrain increases

Corresponding author address: 

### Virginia Bigler-Engler, San Diego Air Pollution Control District, 9150 

### Chesapeake Drive, San Diego, CA 92123-1096. 

### from sea level at the coast to more than 1200 m above mean sea level (MSL) inland. Isolated peaks rise to more than 2100 m. Elevations fall sharply east of the mountain crests, to near sea level at the Imperial County line, and 60 m below sea level at the desert floor 10-20 km farther east. Meteorology and air quality in southern California and San Diego are dominated by the semipermanentPacific high and the effects of a coastal marine environment. The coastal marine layer is known to intrude more than 160 km over most of California. The marine layer extends over San Diego County as far inland as the mountain crests. The marine effects are modified by intense inland heating that producesa thermal low over the southern deserts and by terrain. The result is a mild marine climate at the coast, alpine climates 50 km inland, and desert conditions east of the mountains.A number of studies have documented the structure of the marine layer off the California coast. Mesoscale conditions, with particular attention to description of the inversion wind and temperature structure, were described by Bridger et al. ( 1993 ), based on the MABLES WC ( Marine Atmospheric Boundary Layer Experiments, West Coast) fieldstudy (1993). CEWCOM-76 (Cooperative Experiment in West Coast Oceanography and Meteorology ) (Davidson et al. 1979) and CEWCOM-78 (Fairall et al. 1979; Leipper 1979; Niziol et al. 1979; Rosenthal et al. 1979 ) provided insight into the structure and meteorology of the marine layer over coastal waters of southern California, the latter near San Nicolas

© 1995 

### American Meteorological Society

### 1864 JOURNAL OF APPLIED METEOROLOGY VOLUME 34

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### ,0

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### 1829
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(b) Profile of San Diego County.



### Island. Understanding of transport and diffusion inthe California shoreline environment has also benefited from research performed in other regions; Lyons ( 1975 ) summarized current knowledge and the complexity of the shoreline environment in a monograph for the American Meteorological Society. Lyons discussed plume behavior in the shoreline atlength, with particular attention to fumigation processes. More recent studies, for example, the Southern California Air Quality Study, the Lake Michigan Ozone Study, and the Gulf of Mexico Air Quality Study, continue to advance the understanding ofcoastal meteorology, as well as provide data for photochemical modeling of their respective regions, yet modeling the meteorology of coastal regions remains daunting.Meteorological conditions associated with air pollution episodes over southern California received research attention in the 1950s (Bell 1960; Blake 1960); meteorological and climatological analyses implied theexistence of long-range transport processes soon thereafter ( DeMarrais et al. 1965). Nevertheless, field studies to study transport processes and monitor pollutants and precursor pollutants did not follow for a decade (Schacher et al. 1978; Kauper 1977; Sklarew et al. 1975). CEWCOM-78 included aerosol measurements, as did a 19831idar experiment, the San Diego Oxidant Transport Study (McElroy et al. 1983; Smith andLehrman 1984), but gaseous data was liinited or nonexistent. While these studies confirmed ! the transport of ozone and precursors from the Los Ahgeles area toSan Diego County, few specific studies including pollutant measurements over coastal waters have occurred due to the extreme expense and logistical problems of monitoring a large, uninstrumented, sometimes hostilemarine region. The result is that data gathering is confined to short temporal and geographical zones, which may miss peak episodes and concentrations. It is the purpose of this paper to bring these topics to knowledge gained from the San Diego Air Quality Study. We examine the episode selection portion ofthe study and examine a candidate local episode, using routine regulatory classification and trajectory analysis techniques. Finally, we examine intensivestudy data at the surface and aloft to,form the hypothesis that best satisfies the observations. Conclusions are reached regarding the source of contaminants on the 26 September 1989 study day and the suitability of the episode for photochemical modeling. ;


## I 2. The San Diego Air Quality Study I
The San Diego Air Quality Study ( SDAQS ) consists of a field study, episode selection,

~ 

### modei; development and application, model performance evaluation, and future-year control strategy design. The field portion of this study was conducted through tlie summer of1989, with the objective of acquiring high quality databases for photochemical modeling. Specifically, the goal was to obtain extensive mefeorological and air quality data for multiple episodes meeting two sets of meteorological criteria for the Carbon Bond IV version of the Urban Airshed Model (Tesche et al. 1991). Three-day intensive data-gathering periods were launched on the basis of forecasts by San Diego Air Pollution Control District ( SDAPCD ) meteorologists from July through October 1989. On iritensive studydays, two aircraft from North American Weather Consultants (NAWC), a Cessna 340-A and an Aero Commander 680, sampled temperature, ozone, NO x , hydrocarbons, and carbonyl from near-surface elevations to roughly 1500 m MSL. These data supplemented a28-station aerometric and air quality surface monitoring network, 5 upper-air sites, and a Doppler acoustic sounder located midcounty at Kearny! Mesa, 3 kmsouth of the National Weather Service (NWS ) rawinsonde site at Miramar Naval Air Station ,( NKX ). Surface sites included NWS airport observations, the 10- site SDAPCD moniioring network, and additional contract sites operated by Aerovironment. Technical & Business Systems, Inc. provided upper-air data via balloon soundings four times daily lat five sites ( SDAPCD 1990a,b ). Two island sites; were instru-AuGUST 1995 BIGLER-ENGLER AND BROWN 

### 1865

TABLE l. SDAQS data collection.

Abbr. Station Source

ALP Alpine SDAPCD CAT Catalina Island ERCE b CVA Chula Vista SDAPCD DES Descanso ERCE e DMR Del Mar SDAPCD DTN Downtown SDAPCD DUL Dulzura ERCE b ECA El Cajon SDAPCD ESC Escondido SDAPCD FLN Flinn Springs ERCE ° JAM Jamacha AERO ° KMA Kearny Mesa SDAPCD LAK Lakeside AERO ° MRA Mira Mesa AERO ° MTS Mount Soledad SDAPCD MYF Montgomery Field NCDC`• r NFG Camp Pendleton NCDC` NIM 

### Nimue ERCE b NKX Miramar NCDC` ,f NRS Imperial Beach NCDC` NUC San Clemente Island ERCE b NZY North Island NCDC` OSA Oceanside SDAPCD OTM Otay Mesa SDAPCD RAM Ramona SDAPCD SAN Lindbergh Field NCDC` SCR Scripps Pier SDAPCD SEE Gillespie Field ERCE b SNO San Onofre SDAPCD Comments

0 3 , NO x a, winds, temperature 0 3 , NO x a, winds 0 3 , NO x a, ROG`, winds 0 3 , winds, temperature 0 3 , ROG`, winds 0 3 , NO x a, carbonyl, winds 0 3 , winds, temperature 0 3 , NO x a, carbonyl, winds, temperature 0 3 , NOx , ROG`, carbonyl, winds, four soundings daily, temperature ROG` carbonyl, winds aloft—four balloons daily 0 3 , NO x a, winds, temperature 0 3 , NO x a, winds, temperature, winds aloft—Doppler sodar

03, NO x a, winds, temperature 0 3 , NO x e, winds, temperature 0 3 , NO x a, winds, temperature Airport sfc obs, winds aloft—NWS rawinsonde Airport sfc obs 0 3 , ROG`, carbonyl, winds aloft—four soundings Airport sfc obs, winds aloft—NWS rawinsonde Airport sfc obs 0 3 , NO x a, ROG`, airport sfc obs Airport sfc obs 0 3 , NO x e, ROG`, carbonyl, winds, four soundings daily, temperature 0 3 , NO a, ROG`, four soundings daily 0 3 , ROG`, winds Airport sfc obs 0 3 Airport sfc obs; ROG` 0 3 , NO x e, winds

a NO z = NO x

, NO, NO Z

. b Data collection under subcontract to project management, ERC Environmental and Energy Services Company. ` Reactive organic gases.

d Aerovironment. ` Standard surface data; winds, etc. reported to National Climatic Data Center.


### r National Weather Service upper-air site moved from MYF to NKX 14 September 1989.



### mented, San Clemente Island (120 km west of San Diego ) and Santa Catalina Island ( 80 km west of San Onofre), as well as the NAWC ketch 

## Nimue, approximately 20 km west of Del Mar ( Table I and Figure 2).

3. Episode selection methodology 

## a. Synoptic classification
Regulatory guidance for application of photochemical models recommends modeling episodes for all meteorological scenarios that lead to high ozone concentrations in an air basin. SDAB ozone episodes are associated with two distinctive meteorological signatures. The first, a"local episode," is marked by a strong marine inversion based around 400-800 m above ground level (AGL), moderate onshore pressure gradients, and a well-developed sea breeze. Morning precursor emissions in the urbanized coastal plain chemically react as they are carried inland toward the foothills. Trapped by the marine inversion, peak hour concentrations exceed the 0.09-ppm state standard and may edge above the federal standard at foothill sites, typified by Alpine ( ALP ). On the other hand, extreme values, above 0.20 ppm, are observed with a"transport episode" signature. High pressure builds over the Great Basin and southwestern deserts, producing northerly mesoscale flow and weak offshore pressure gradients. The marine layer may be shallow due to subsidence aloft, or the base of the inversion may be depressed to the surface along the coast. Ozone and precursors from SoCAB are carried offshore, southward over coastal waters, and back onshore into San Diego. Any part of SDAB may experience high ozone concentrations due to transport. ( Bigler-lEngler and Brown 1993).



## b. Source-receptor analysis
Identification of the synoptic type suggests thesource of an episode but may not be considered conclusive. Analysis of the flow fields through the duration of an episode and calculation of forward and backward air parcel trajectories are commonly used means to reveal source-receptor relationships. The most common practice is the calculation of surface

## 1866 JOURNAL OF APPLIED METEOROLOGY VOLUME 34



### MG. 2. SDAQS photochemical modeling domain and aerometric monitoring locations.



### wind trajectories, due to availability of data. The observed surface wind is assumed to represent theboundary layer mean wind. Forward trajectories follow a parcel from a potential source region for a specified time period. Backward trajectories track aparcel to its region of origin. Theoretically, trajectories can be determined accurately if wind fields are highly resolved spatially and temporally;

. they maybe developed from observed data or numerical simulation. In practice, they are subject to significant

error. Many studies have explored the uncertainty oftrajectories, generally in the context of multiday trajectories and long-range transport of pollutants. Differing meteorological regimes have been examined, from synoptic-scale cyclones ( Kuo et al. 1985; Dotyand Perkey 1993 ) to generally persistent flow conditions (Kahl and Samson 1986). Although verification is difficult, several researchers, notably Rolph and Draxler (1990 ) and Doty and Perkey (1993), have attempted to quantify errors in vertical as wellas horizontal components. In a paper exploring numerical error, Seibert ( 1993 ) also recommended use of an ensemble of trajectories offset 50-100 km to reduce error from uncertainty in the wind field.These studies agree that the existing NWS rawinsonde network is inadequate for long-range computations and suggest finer temporal and spatial resolution of the meteorological database would im
## prove accuracy.

c. SDAQS episode selection
The SDAQS field study yielded six potential modeling episodes with high ozone levels; all were evaluated for photochemical modeling (Tesche et al. 1991). Each episode was first classified by its synoptic signature. Each was subjected to a further series of tests, including trajectory and time series analyses, to identify a source—receptor relationship for the monitored concentrations at each site that exceeded the 0.12-ppm federal standard. Hourly analyses of surface observations were prepared for episodes of particufar interest, as were wind flow',fields, hourly at the surface and at 4-h and 300-m ihtervals aloft, on intensive days. Trajectories were calculated inhourly increments from surface streainlines. Backward trajectories were prepared for all sites exceedingthe federal ambient ozone standard; forward trajectories were determined for San Diego urban emissions and for SoCAB. Even in smaller-scale analyses, the simplifying assumption that the surface wind isequivalent to the transport wind can introduce substantial error, so streamlines were reviewed for consistency with winds within the marine layer. The ensemble of source- and receptor-based tr,ajectories anduse of a streamline field, rather than individual observations, were also designed to reduce error due to uncertainty in the wind field, somewhat along the lines suggested by Seibert (1993). Each candidate modeling episode was required to fulfill additional criteria. A high-ozorie event, with extreme ozone concentrations with respect to the federal ambient standard, would be pieferred to anepisode marginally exceeding the fedeial or California standards, as does the typical local SDAB localepisode. For each 2-day ( minimum) inodeling episode, a robust database with at least one day of intensive data was a prerequisite, preferably on the peak day. i

4. September 1989 episode selection and analysis

Federal and state ambient ozone standardswere violated on nine consecutive days in September 1989 (Table 2). Highest concentrations were monitored on the first six days I of this siege, with a maximum of 0.17 ppm. Concentrations on the final three days, 27-29 September, exceeded only the more stringent California standard and at fewer sites. 

# ~

a. Synoptic summary and classificationl
The period 21-24 September was maiked by strong ridging over the western United States, subsidence, andnortherly flow. Triggered by SDAPCD's forecast of potential transport conditions, 3-day intensive data sampling began; significant subsidence was evident in thefirst soundings early on the first intensive day, 21 September. Figure 3 displays the characterist ic features of the transport meteorological signature at the surface and 500 mb on 22 September 1989, when the pattern was well established. As the broad ridg'e moved into the western states, surface pressure gradients becameAuGusT 1995 BIGLER-ENGLER AND BROWN 

### 1867

TABLE 2. Daily maximum 1-h average ozone concentration in parts per million for 21-29 September 1989. Bold values are basin maximum.

Site

Day ALP CVA DMR DTN ECA ESC KMA MTS OSA RAM

21 0.11 0.12 0.13 0.14 0.11 0.16 0.14 0.13 0.09 0.12 22 0.15 0.07 0.07 0.07 0.12 0.10 0.09 0.07 0.06 0.11 23 0.14 0.08 0.10 0.09 0.11 0.09 0.08 0.10 0.08 0.10 24 0.16 0.13 0.14 0.14 0.13 0.17 0.16 0.16 0.12 0.12 25 0.15 0.07 0.07 0.08 0.10 0.10 0.10 0.08 0.06 0.12 26 0.17 0.05 0.04 0.06 0.10 0.12 0.08 0.09 0.05 0.12 27 0.12 0.06 0.07 0.07 0.08 0.08 0.07 0.06 0.06 0.09 28 0.10 0.09 0.07 0.09 0.10 0.08 0.09 0.08 0.06 0.09 29 0.10 0.07 0.07 0.07 0.07 0.08 0.12 0.06 0.06 0.09



### offshore. The thermal trough was pushed off the California coast; its southern section, into northern Mexico. Maximum ozone concentrations were associated with this phase. A transition to a local episodic signature began 25 September. By 26 September (Figs. 3c,d), a long-wave trough approached the West Coast, and the upper ridge moved on to the Rocky Mountains. At the surface, the thermal low became established once again over the southern California desert. The meteorology of 26 September shows a return to the more typical mesoscale conditions described by Bridger et al. (1993). This pattern resembles their 9 August 1978 example day, with a strong marine inversion and an inland thermal trough over most of California.All three high-ozone events, 21, 24, and 26 September, were evaluated for photochemical modeling. The 2-day period 20-21 September was developed as a transport episode; 23-24 September was rejected for lack of intensive data and its weekend occurrence ( for which there is no emissions inventory, the catalog of hourly emissions basinwide). Although 26 September 1989 was the sixth of the nine days of ozone violations, it was one of the two dates on which the extreme 0.17ppm was monitored, at Alpine, and the first day apparently with a local synoptic signature. Because of this, 25-26 September received further attention as a candidate for photochemical modeling, possibly as a local episode.



## b. Source-receptor analysis 1 ) SURFACE TRAJECTORY ANALYSIS 

### A surface wind trajectory was used to trace the plume back to a precursor source region at sunrise. One-hour increments were calculated from flow fields generated by means of surface streamlines. Figure 4 exhibits thebackward surface trajectory for ALP. The urban emissions of the populous coastal plain are represented by a density plot of emissions of oxides of nitrogen; two freeway corridors from the less-populated North County can be discerned, as can the large urbanized core region. A forward trajectory was also calculated for morning emissions downtown. This trajectory was consistent, moving morning emissions toward the foothills on the sea breeze. Use of the 1-h average winds of the SDAQS database, as well as the relatively high resolution of the data in the coastal plain, and the shorttransit period would, presumably, minimize uncertainty in the surface trajectory; thus, there is a strong suggestion that the surface trajectory originates in the San Diego Air Basin in the urbanized coastal region. There is, however, significant uncertainty attached to the assumption that the surface wind and, accordingly, the surface trajectory are representative of the mean boundary layer wind, in this case, the marine layeroverlying the basin throughout the episode. The assumption must be valid from early morning when conditions may be stable through midday when they may be unstable inland, at least. NWS rawinsonde data were inconclusive. Shown in Fig. 5, the 1200 UTC (0400 PST) NKX sounding of 26 September showed southerly winds above 800 mbunder the influence of the approaching trough; nevertheless, the marine inversion was still surface based, winds at and below 850 mb remained northerly, and low-level winds were missing. By 0000 UTC, 4 h after the ozone peak at Alpine, winds had backed to thesouthwest at all levels, and the base of the marine inversion had risen to 500 m.
2) DIURNAL PATTERNS OF OZONE GENERATION 

### Emissions moving downwind from a local source region after sunrise should display an expected pattern of ozone generation that reflects the flow field and rate of chemical reaction. Figure 6 presents Alpine and Oceanside ( OSA ) hourly ozone, monitored against the monthly mean hour. Upwind of San Diego's core emissions area and 30 km southwest of the Orange County line, OSA is a receptor for transport from SoCAB, while ALP lies downwind of San Diego urban emissions. Mean September concentrations for both sites rise after sunrise to an afternoon peak, then decline during the night to a background level. On 26 Septem-

### lti

H

FiG. 3. Synoptic maps for (a) 500 mb 0400 PST 22 Septe

(c) 500 mb 0400 PST 26 September 1989, 

### i 

### 1868 JOURNAL OF APPLIED METEOROLOGY VOLUME 34



### ber, OSA ozone remained low, generally following theexpected profile. In contrast, ozone at ALP rose gradually after sunrise but nearly doubled in I h before reaching its 0.17-ppm maximum in the next. Rather than evidence of a local episode, this is an anomaly that hints of a sudden event: the arrival of some ozone "front" or fumigation of pollutants aloft. Alpine ozone reached 0.17 ppm at 1200 PST (1-h average, 1200-1300 PST ). This site is 42km east of the downtown San Diego urban corridor, at 604 m MSL. Hourly ozone concentrations at the 10 SDAB network sites are presented in Table 3. No other site exceeded the federal 'standard, although Escondido (ESC) (0.12 

## ppm), El Cajon ( ECA )( 0.10 ppm), and Ramona ( RAM )( 0.12 ppm) exceeded the state ozone standard. These are all ininland areas known for high afternoon temperatures. Like Alpine, Ramona is in the foothills at 424 m MSL. jStation data were reviewed with regard to site location, hourly temperature, and behavior of the sea breeze. Alpine ozone nearly doubled 

## iri the hour in which the maximum temperature w'a s observed, 33.3°C, while the mean stood at 32°C for 2 h. Maxi-AUGUST 1995 BIGLER-ENGLER AND BROWN 

### 1869

FiG. 4. Surface trajectory for a parcel of air that moves from urbanemissions sources to Alpine on 26 September 1989. The surface trajectory assumes observed surface winds are representative of the mean boundary layer wind.



### mum temperatures of 32°-35°C were observed in the same hour at ESC, ECA, and RAM. Unfortunately, ozone data are missing for El Cajon for this hour. At Alpine, concentrations exceeded the state standard for an extraordinary 7 h, four of them 0.14 or more. At Escondido, ozone fell in the 1100-1200 PST hour as the sea breeze arrived and the temperature dropped more than I°C. Ambient temperature began to recover in the next hour, and ozone nearly doubled to 0.11ppm. At ESC and RAM, the episode lasted 5 h; concentrations finally declined to moderate levels in the evening, as temperatures dropped below 27° or 28°C. In contrast, ozone remained low at coastal sites near sea level [ OSA, Del Mar ( DMR ), Downtown ( DTN ), Chula Vista (CVA)], where the maximum was near 24°C. At 219 m MSL on the windward side of the mountain, the 0.09 ppm recorded at Mount Soledad was twice the peak hour monitored at the other coastal sites, 200 m below. In the coastal plain with moderate temperatures less than 30°C, the ICMA ( 13 5 m MSL) peak was 0.08 ppm. Ozone transported from SoCAB at low levels will cause high concentrations at one or more SDABcoastal sites, most frequently OSA and DMR, impacting additional sites successively as the "cloud"or "front" advances southward and inland. Concentrations on 24 September 1989 ( Table 2) exhibit thispattern. The dramatic increase in ozone concentrations and duration at inland sites during intense surface heating, the low concentrations near sea level at coastal sites, and an increase in concentration at higher elevations on 26 September, however, suggest an episode in which vertical processes and pollutants aloft are significant.



## c. SDAQS data analysis
The second 3-day intensive sampling program of the extended episode began Monday, 25 September. Early morning aircraft sampling began shortly after 0500, ending about 0830 PST. Afternoon takeoffwas at 1400 and landing at about 1700 PST. Data are available for both aircraft early on 26 September but only for theAero Commander on the evenings of 25 and 26 September. Sampling included ambient temperature as well as continuous ozone and reactive organic gases ( ROG ) to permit additional ozone sampling and ROG grab samples, for example, near the base and within the marine inversion. Logistical and technical problems (e.g., limited number and location of samples, lack of reproducibility in laboratory analysis, etc.) precluded use of most of the ROG data, and they will not bediscussed further. Soundings were taken at approximately 0500, 1000, 1400, and 2100 PST at 

## Nimue, ( NIM )( offshore ), Oceanside, Otay Mesa ( OTM ) (known also as Brown Field), Escondido, and Flinn Springs ( FLN ) .

1) SDAQS UPPER-AIR DATA, 25-26 SEPTEMBER 

### 1989


### (i) Evening, 25 September 1989
The soundings taken 25 September show a strong marine inversion and northerly flow. Each of the five

700


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750 2500f 

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1500 850 

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900 1000M

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## ~ 500
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20- 30 am Wind pm 04PST - - - 16PST_ Temp,°C

FIG. 5. Miramar (NKX) sounding 26 September 1989.

### 1870 JOURNAL OF APPLIED METEOROLOGY , VoLUME34

a ❑ ALP'observed ALP mo. mean 0.18
0.16-n
0.14
0.12 ppm 0.1
0.08
0.06
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### J R 00 Ot 02 03 04 05 06 07 08 09 10 1112 13 14 15 16 17 18 19 20 2122 23 0

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### FIG. 6. Comparison of hourly observed ozone versus monthly mean hour ozone for 26 September 1989 for (a) Alpine and (b) Oceanside



## evening soundings taken between 2030 ( ESC) and 2127 PST ( NIM ) shows a shallow surface layer 1-200 m deep. The surface temperature range from 20 ° (OSA) to 24 ° C (FLN) reflects surface influences ranging fromcool sea surface temperatures to radiative cooling inland; otherwise, the Nimue sounding is representative of all five, showing a consistent structure for the marinelayer overlying the basin from coastal waters to mountain crests 90 km east of the coastline. Figure 7 presents two soundings at Nimue, 20 km west of Del Mar. The Nimue sounding at 2127 PST 25 September shows continued northerly flow from the surface to more than 1500 m aloft and moderate winds of 5-7 m s

- ' within the inversion. Winds above the stable layer drop off to 1-2 m s

- '; they increase and become southeasterly above 2300 m AGL.

(ii) Early morning, 26 September 1989
Near dawn at 0502 PST, the inversion is surface based at all sites, the surface temperature near 18 ° C. At Nimue, the top of the strong inversion is found at about 500 m; it slopes gradually upward to near 700 m AGL inland. Whether at Nimue at sea level or 30 km inland at Flinn Springs at an elevation of 202 m MSL, the profile is remarkably similar, with a stable layer that continues to around 1200-1300 m AGL. Surface winds at several inland sites show light (1 m s

- ' ) easterly or southeasterly components due to nighttimedrainage, but northerly winds continue within the inversion to 4.0 m s

- ' . Winds peak at 4.6 m s

- ' near the top of the stable layer, which is nearly isothermal
at Nimue, a suggestion of the California coastal jet described by Bridger et al. (1993).

( iii ) Midmorning, 26 September 1989The marine layer dominates the San Diego Air Basin. The soundings taken about 1000 PST and 1400 PST are presented as cross sections of the basin. This means of presentation discloses the essential structureof the marine layer, which maintains its integrity despite terrain effects and intense heating, even 50 km east of the ocean. Figure 8 demonstrates the plane ofprojection, roughly perpendicular to the;coastline. Interestingly enough, this plane also approximates a crosssection through the northerly nighttime flow field previously discussed. Figure 9 presents soundings taken between 0930 and 1004 PST for Nimue, Oceanside (37 m MSL), Escondido (197 m), and Flinn Springs (202 m MSL) from the surface to 1200 'm MSL. The surface at Oceanside has been slow 6 warm, even compared to the boat; the inversion rexnains surface based. A shallow sea breeze can be seen and there is a northerly component within the inversion and deep stable layer to at least 900 m MSL. The top of the inversion, at 500-600 m MSL for both the offshore NIM and coastal OSA, is near 28 ° C. It retains its character as a deep, nearly isothermal layei of 28°C to nearly 1300 m MSL, despite the higher mixing heights due to surface temperatures of 32 ° -35' ° C (versus a temperature of 18°C at OSA). The inversion slopesupward gradually with increasing terrairi until the intense heating of the more arid inland aieas produces a dramatic gradient in mixing heights pa'st Escondido. It is in or near this hour that maximum !temperatures were observed through most of the suiface network and, soon after, that ozone rose dramatically.

( iv ) Afternoon, 26 September 1989 ;

i 

## Figure 10 displays the afternoon profiles along with ozone measured by aircraft. By 1400 PST, the marine inversion has lifted and weakened in response to the approaching trough; winds have backed to the west within the inversion, cutting off any poteritial for ozoneand precursor transport. The peak heating and temperatures of the day are past. Cooling of about 2°C can be discerned in the inversion andl above in all soundings. Over the ocean and along the coast, the inversion is elevated and a little weaker in response to the cooling of the air mass. Inland, surface; temperatures are still very warm, and the structure and slope of the inversion are still indicative of the intense heating that has occurred; nevertheless, the strength of the marine layer is such that the inversion is already becomingro

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### reestablished. Winds have become westerly aloft. ( In both 1000 and 1400 PST soundings, the temperature lapse becomes nearly adiabatic, and winds above 1200- 1300 m are southerly to the end of the release, about 3000 m MSL.)

2) SDAQS AIRCRAFI' DATA, 25-26 SEPTEMBER 

### 1989



### The Aero Commander 680 aircraft collected ozone data by means of a Dasibi 1003-AAS sampler. This aircraft flew spirals to 1500 m MSL over each of the SDAQS sites (in order: CVA, OTM, ECA, ALP, RAM,ESC, OSA ) to locate the inversion and gather temperature, precursor, and ozone data over the basin. Equipped with a Scintrex LOZ-3 ozone sampler, the Cessna 340-A established boundary values of ozoneand precursors for the boundaries of the modeling domain: offshore (west), SoCAB (northwest), ridgeline( east ), and Mexican border ( south ). Flying in a terminal control area prevented sampling much below 1400 m over land. Descent to low levels could only beaccomplished where the aircraft could make an approach to an airport. Offshore, continuous ozone samples were taken to 1-200 m MSL.



## ( i) Afternoon, 25 September 1989 The Aero Commander made the only flight. Between takeoff at 1403 and landing at 1648 PST, the aircraft reported relatively uniform concentrations of 0.05-0.08 ppm, except a layer of 0.10 ppm (1615 PST) foundover Escondido at 788 m MSL, the lowest altitude allowed before the aircraft was required to climb out.

(ii) 

## Morning, 26 September 1989
From takeoff at Montgomery Field (MYF) at 0507 PST, the Cessna climbed to the southwest boundary of the domain. A spiral from 1300 m down to 229 m MSL found ozone concentrations of 0.06-0.07 ppm. At 0600, the plane turned eastward, climbed from 250 m MSL over the ocean to about 1400 m MSL along the Mexican border, then turned northward along the mountain ridgeline. At 0630, at 1484 m, 0.09-ppm ozone was monitored north of Alpine. The plane turned westward, to 

## Nimue, and descended over the water to 90 m(0.05 ppm) and the western boundary. The next leg climbed northeastward back to Oceanside. In level flight over Oceanside at 0734 PST, a band of ozone 5-10 km wide was found (0.10 ppm, 1294 m MSL); concentrations around 0.08 ppm continued to the Riverside County line. High concentrations (0.11 ppm) were again encountered on the descent back to OSA and for 15 km over nearby waters at 506 m(0748 PST). Finally, the aircraft retraced its path, first to the western boundary then back to the coast, this time at an altitude of about 200 m MSL. Ozone on the order of 0.06 ppm was seen enroute over the water until ~ 10 Vl
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### 7. Ntmue sounding for (a) 2127 PST 25 September and (b) 0502 PST 26 September 1989.



### landing at MYF at 0831 PST. Surface stations monitored low ozone concentrations of 0.02-0.03 ppm at this time. Expected "clean" background ozone is 0.04-0.05 ppm; ozone aloft of 0.10-0.11 ppm is a significant finding given that, just 2 h after sunrise, photochemicalreactions have just begun and will continue for a number of hours.

(iii) 

## Afternoon, 26 September 1989
The Aero Commander took off from Montgomery Field at 1412 PST. Spirals were flown over SDAQS sites beginning at Chula Vista for periods of 2( ESC ) to 12 (CVA, ECA) min. Longer, more detailed spirals were possible near airport sites (OSA, MYF, OTM, ECA, RAM ) than over Escondido, where the planewas required to remain above 800 m MSL. Where possible, additional ozone data were collected at the baseand within the inversion as identified by airborne temperature observations. Spirals were flown over SDAQS sites (start time, PST:altitude, m MSL) as follows: CVA (1439:1461-529 m); OTM (1455:165-922 m); ECA (1519:222-941 m); ALP (1536:1488-769 m); RAM (1548:368-1056 m); ESC (1608:1269-870 m); OSA 

### (1618:1289-37 m). At 1633 PST, the plane climbed to 750 m to head back to MYF, encountering the most concentrated ozone a few minutes later (0.22 ppm at 450 m MSL) just north of the airport. In Fig. 10, the afternoon spiral data are presented with the sounding data for 1400 PST. Mean terrain increases from left to right from 

## Nimue at sea level, eastward, and inland; elevation increases more rapidly past Alpine, which at 604 m is above the level of the mean terrain. Ozone is plotted at the station over which 

## I the spiral was flown. The aircraft sampling time is 1 ( OTM ) to 3 h( OSA ) after the 1400 sounding. While little ozone is seen in the south ( 0.04-0.08 ppm above CVA and OTM), high concentrations are found nearthe base and witfiin the inversion over all of the remaining sites from mid- to north county' OSA, MYF, ECA, and ALP. Southward from Oceanside (0.11-0.15 ppm, 300-400 m MSL), (0.19-0.22 pprri, 350-500 m MSL ) to MYF, and eastward to ECA ( 0.1' 1-0.14 ppm, 400-800 m MSL), there is evidence of a large pool of ozone over the basin. The layer of significant ozoneclearly slopes upward with terrain, following the upward trend of the inversion base showri in the four afternoon temperature soundings. The he I ight at which

i

FiG. 8. Projected cross section for SDAQS stations.

## 1873

AuGUST 1995 BIGLER-ENGLER AND BROWN

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### the high concentrations reside is directly related to the location of the inversion. Extreme concentrations remain over the coastal zone from north to midcounty (0.15 ppm at OSA to 0.22 ppm near MYF) an hour before sunset. Mixing heights were, at most, a few hundred meters in this region.Due to further cooling during the evening and the already strong marine inversion, no mechanism exists to bring these pollutants to the surface. As shown in Table 3, surface ozone maxima were 0.06 ppm or less at all coastal sites: DTN, OSA, DMR, and CVA. It is important to note that coastal mixing heights remained low throughout the day; thus, flow within the extremelystable marine layer aloft (500 m MSL) remained decoupled from processes near the surface. Hot inland temperatures led to higher mixing heights and erosion of the base of the inversion. Concentrations of ozone aloft at.Ramona and Alpine continue aboveambient standards but are less than the extremes sampled aloft near the coast within the next hour. Interestingly, they are comparable to the concurrent surfaceobservations. At RAM and ESC, surface ozone has declined little from the day's maximum at this hour, and surface temperature has fallen only 1°C. The Alpine spiral, flown 3 h after the 0.17-ppm surface peak, still shows 0.13 ppm aloft. At the same time, 1500 PST, surface temperature has fallen 3°C from the day's high, and ALP surface ozone at 0.13 ppm is in the fifth hour of a 7-h episode. Concentrations fall from 0.11 to 0.06ppm in the 1800-1900 PST hour as the surface temperature finally cools to 25°C (approximately, the diurnal maximum in the coastal area).

S. Conclusions
The uniformity of observed concentrations between the surface and reestablished inversion at Alpine andRamona, and ECA ( aloft ) and ESC ( surface ) observations, is suggestive of mixing of elevated pollutants into an expanding surface boundary layer. This mixing continues so long as surface sensible heat is sufficient. The near-doubling of surface ozone in 1 h at Alpineand at Escondido, are anomalous, as is the 5-7-h duration of high concentrations. This leads to the conclusion that fumigation of pollutants from aloft begins when the threshold temperature of the polluted stable layer is reached. High concentrations are brought to the surface at inland sites with high temperatures and mixing heights; dilution of concentrated ozone aloft occurs in the process. Low surface concentrations in the cool coastal zone with extreme coastal ozone levels aloft are consistent with a hypothesis of fumigation into the surface layer of pollutants transported from SoCAB in the stable layer aloft. Lyons' (1975 ) obser-1874 JOURNAL OF APPLIED METEOROLOGY VOLUME 34

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### vations of shoreline fumigation in southern Wisconsin, of individual power plant emissions (p. 156) as well as photochemical pollutants transported aloft from Chicago, are pertinent. Although the depth, strength,and geographical scale of the marine layer cause fumigation much farther inland than Lyons observed (1- 5 km), processes in the shallow surface layer and aloft are decoupled. Photochemical smog fumigation was found at similar levels above the shallow lake breeze, and high concentrations from continuous fumigation can continue for hours. Intensive data have shown that northerly flow continued through the night and into the morningof 26 September. The northerly wind flow field, persistent until midmorning on 26 September precludes any possibility that San Diego was the 'source of elevated ozone and precursors. The northerly flow andobservations of concentrated ozone within the inversion, seen as high concentrations from 0.13 to 0.22 ppm over the air basin, give evidence of a broad pool of ozone transported southward from SoCAB in the stable layer aloft into San Diego County. The 25-26 September 1989 episode is actually a complex transport episode unsuitable for photochemical modeling. Trajectory analysis is routinely usedl to establish accountability for source emissions in regulatory programs. Use of finely resolved data of observations in a single diurnal cycle of transport should minimize uncertainty but may give false confidence in re-AUGUST 1995 BIGLER-ENGLER AND BROWN 

## 1875

FIG. 11. Trajectory analyses for air parcels at the surface and aloft. The surface trajectory is as in Fig. 4. The trajectory aloft is based on SDAQS intensive winds aloft. It represents the path of a parcel trapped within the base of the marine inversion.



### sults. Reliance on the surface trajectory in Fig. 4 would improperly attribute the 

## 25-26 September episode solely to San Diego emissions sources. Figure 11 presents a new trajectory along with the original. Prepared using the SDAQS soundings, it represents flow within the base of the inversion on 

## 26 September 

## 1989. This trajectory, for a parcel reaching Alpine at the maximum hour, originates off the southern coast of Orange County ( part of SoCAB, a source region of 

## 6000 km -2 early on 

## 26 September). Sincethe Los Angeles source region is several hundred kilometers long, there are many possible regional-scale trajectories, but no two-dimensional trajectory canadequately describe the episode. The example trajectories serve to demonstrate that flow within the marine layer aloft may be independent and verydifferent than that determined by surface analysis. Routine wind and air quality network data sampling inadequate to satisfy needs for source attribution. Evenaircraft data provides limited temporal and spacial resolution data, at best, and is prohibitively expensive.Inferences can be made about the presence of transported species, but neither extent nor magnitude can be quantified. Acquisition of both continuous wind andair quality information aloft by remote sensing techniques is needed.Inaccurate attribution resulting from oversimplification and erroneous assumptions can have serious consequences on air quality programs and communities in downwind air basins. Control programs can force expensive regulatory burdens on local communities without accompanying air quality benefit.


## Acknowledgments. SDAQS was supported by a grant from the California Secretary of Environmental Affairs,as part of the Coastal County Offshore Energy Assistance Program. Field study project management was provided by ERC Environmental and Energy ServicesCompany. Project manager for SDAPCD was Mahmood Hossain. Many thanks are due Barry Speer for his many hours of assistance. The authors also wish to express their appreciation to the reviewers whose comments greatly improved this paper.

REFERENCES
Bell, G., 1960: Meteorological conditions during oxidant episodes in coastal San Diego County in October and November, 1959. California Dept. of Public Health, 19 pp. Bigler-Engler, V. J., and H. W. Brown, 1993: Episode classification for the San Diego air basin. 

### Proc., Regional Photochemical Measurement & Modeling Studies Int. Conf. San Diego, CA, Air & Waste Manage. Assoc., in press. Blake, D., 1960: Notes on meteorological conditions affecting air pollution in San Diego County. San Diego APCD, 19 pp. Bridger, A. F. C., W. C. Brick, and P. F. Lester, 1993: The structure of the marine inversion layer off the central California coast: Mesoscale conditions. 

### Mon. Wea. Rev., 121, 335-351. Davidson, K. L., G. E. Schacher, C. W. Fairall, and T. M. Houlihan, 1979: Observations of atmospheric mixed-layer changes off the California coast (CEWCOM-76). Preprints, 

### Second Conf. on Coastal Meteorology, Los Angeles, CA, Amer. Meteor. Soc., 63-70.DeMarrais, G. A., G. C. Holzworth, and C. R. Hosler, 1965: Meteorological summaries pertinent to atmospheric transport and dispersion over southern California. Tech. Paper 54. U.S. Weather Bureau, Department of Commerce, 86 pp.Doty, K. G., and D. J. Perkey, 1993: Sensitivity of trajectory calculations to the temporal frequency of wind data. 

### Mon. Wea. Rev., 121, 387-401. Fairall, C. W., G. E. Schacher, K. L. Davidson, and T. M. Houlihan, 1979: Atmospheric marine boundary layer measurements inthe vicinity of San Nicholas Island during CEWCOM-78. Preprints, 

### Second Conf. on Coastal Meteorology, Los Angeles, CA, Amer. Meteor. Soc., 71-75.Kahl, J. D., and P. J. Samson, 1986: Uncertainty in trajectory calculations due to low resolution meteorological data. 

### J. Climate Appl. Meteor., 25, 1816-1831. Kauper, E. K., 1977: San Diego trajectory study. Contract 11394E. Prepared for San Diego Air Pollution Control District by Metro Monitoring Services, Covina, CA, 36 pp. Kuo, Y-H., M. Skumanich, P. L. Haagenson, and J. S. Chang, 1985: The accuracy of trajectory models as revealed by the observing system simulation experiments. 

### Mon. Wea. Rev., 113, 1852- 1867. Leipper, D. F., 1979: Day to day and place to place changes in low level atmospheric temperature structure off southern California. Preprints, 

### Second Conf. on Coastal Meteorology, Los Angeles, CA, Amer. Meteor. Soc., 58-62. Lyons, W., 1975: Turbulent Diffusion and Pollutant Transport in Shoreline Environments. 

### Lectures on Air Pollution and Environmentallmpact Analyses, A. Venkatram and J. C. Wyngaard, Eds., Amer. Meteor. Soc., 136-208. McElroy, J. L., D. H. Bundy, C. E. Edmonds, M. J. Pearson, E. L. Richardson, and W. H. Hankins, 1983: Airborne downward-

## 1876 JOURNAL OF APPLIED METEOROLOGY VOLUME 34

looking LIDAR measurements during the San Diego oxidant transport study—Operations/data report. TS-AMD-83612. U.S. Environmental Protection Agency, Las Vegas, NV, 48 pp. Niziol, T. A., C. W. Rogers, E. J. Mack, and C. K. Akers, 1979: Characteristics of the marine boundary layer in the vicinity of San Nicolas Island during CEWCOM-78. Preprints, 

### Second Conf. on Coastal Meteorology, Los Angeles, CA, Amer. Meteor. Soc., 101-104.Rolph, G. D., and R. R. Draxler, 1990: Sensitivity of three-dimensional trajectories to the spacial and temporal densities of the wind field. J. Appl. 

### Meteor., 29, 1043-1054. Rosenthal, J., T. E. Battalino, H. Hendon, and V. R. Noonkester, 1979: Marine/continental history of aerosols at San Nicolas Island during CEWCOM-78 and OSP III. Preprints, 

### Second Conf. on Coastal Meteorology, Los Angeles, CA, Amer. Meteor. Soc., 84-93. Schacher, G. E., C. W. Fairall, K. L. Davidson, and T. M. Houlihan, 1978: Experimental investigation of the marine boundary layer in support of air pollution studies in the Los Angeles Air Basin. NPS61-78-002. Prepared for California Air Resources Board by Naval Postgraduate School, Monterey, CA, 257 pp. SDAPCD, 1990a: Air quality and meteorological monitoring for theperiod l July 1989-8 October 1989. Final submission. AV-DM90/005. Prepared for the San Diego Air Pollution Control District by Aerovironment, Inc., Monrovia, CA. , —, 1990b: Final data report for the period July I through October6, 1989. Prepared for the San Diego Air Pollution Control District by ERC Environmental and Energy Services Co., San Diego, CA. { Seibert, P., 1993: Convergence and accuracy of numerical methods for trajectory calculations. J. Appl. 

### Meteor., 

## 32, 558-566. Sklarew, R. C., J. C. Wilson, J. H. Woolf, J. G. Edinger, R. E. Kerr, 1975: Study of San Diego County ozone transport. Prepared for San Diego Air Pollution Control District by Xonics, Inc., Van Nuys, CA, 47 pp. Smith, T. B., and D. Lehrman, 1984: Analysis of lidar data. P.O.No. RS 2379. Prepared for Lockheed Engineering and Management Services Co., Inc., Environmental Piograms Offices, by Ted B. Smith and Associates, Inc., Pasadena, CA, 125 pp. Tesche, T. W., H. Ballentine, and E. Fosdick, 1991: Ozone modeling protocol for the San Diego Air Quality Study (revised). DCN:91-264-104-04. Prepared for San Diego APCD; by Radian Corporation, Sacramento, CA, 162 pp.