Smog In Fallbrook

This page exists because several people have written to ask why I didn't have an analysis of smog in Fallbrook. The reason is that there is essentially no major smog in Fallbrook, especially in comparison with the Los Angeles area, which is where most of the questions have originated.

Actually, there is no place in Southern California that has good air quality all the time, due to our relatively stagnant air in the summertime and our famous temperature inversions. Only places that have vigorous air movement, usually accompanied by storms, have such good air quality. However, the air quality in Fallbrook rarely gets worse than ~50-75 on the smog scale, which is typical of nearly every place in the U.S. in the summertime (see below).

A note about the smog scale. The smog scale is just 100 times the measured amount of a pollutant divided by the federal standard. Thus air which just meets the standard is assigned a value of 100. Above 100 is unhealthful air quality, since it violates the federal standard. The scale is linear, and for ease of understanding, the range 0-50 is said to be good air quality and 50-100 is moderate air quality. For ozone, the main pollutant in Southern California, the standard is a one hour average value of 0.12 parts per million (ppm), or an 8 hour average value of 0.08 ppm. See Air Quality Guide.)

Practically, this means that one can garden freely, or hike anytime, without worrying about the smog level. I used to severely limit my physical activities between 9 am and 5 pm when I lived in Altadena, and I still try to avoid hiking the San Gabriel Mountains during smoggy periods. Even then, I still get smogged every so often while hiking the San Gabriels. (The first indication of getting smogged is when you take a deep breath and then have to cough. It signifies that you have lost 5-10% of your lung capacity due to smog. Heavy exertion in smog can result in the loss of 10-20% of lung capacity, creating the need to lie down and gasp for breath, which happened to me before I learned that one was not supposed to play tennis in heavy smog!) I've never yet gotten smogged in 6 years in Fallbrook, despite much more physical activity than when I was in L.A.

However, people doing strenuous prolonged physical activity may get smogged even at an air quality of 50. The federal standard is for a resting person. If you breathe twice the amount of air per hour due to strenuous activity, and the air quality is 50, you have exposed yourself to twice the pollutant compared to a resting person, and hence it is equivalent to an air quality of 100 for you during that period.

Many people think that they can see air pollution. In fact, except at the times when nitrogen dioxides color the air in L.A. brown, you cannot see pollution. Ozone, the main pollutant by far in the summertime, is essentially invisible and colorless. See the discussion in Air Quality in the San Gabriel Mountains and for the inversion layer in High Temperatures in the San Diego County Mountains.

What people see is haze, which in Fallbrook, and most of the time in L.A.., is simply due to coastal haze, not pollution. Coastal haze can be seen in absolutely unpolluted Greek islands, the unpolluted Canary Islands, etc. I've seen far "worse apparent air quality" visually in those pristine places than even in L.A.! Coastal air is very often hazy air, caused by water droplets condensing on dust, sea salt, etc. in the air.

There is no smog monitoring station near Fallbrook. The closest ones are in Oceanside and Escondido. Thus the numbers quoted for the maximum level above come from comparisons to the readings of other stations in San Diego County, and from my personal observations. My personal observations come from having never been smogged in Fallbrook, whereas I have been smogged numerous times at a pollution index of ~75 while hiking in the San Gabriel Mountains.

You can check the air quality in San Diego County using the online forecast, the online latest observations or the L.A. Times Metro section every day for those two stations. The average of the forecast for those two stations is probably a pretty good prediction for Fallbrook. You'll quickly find that pollution isn't much of an issue in San Diego County compared with L.A.

The Oceanside and Escondido stations combined exceeded a level of 100 for ozone on only one day in 1994-1998, and exceeded a level of 75 on average on only 4 and 8 days, respectively, per year in 1994-1998. (See Ozone Violations By Year.) By comparison, in L.A. in 1998, the ozone level exceeded 100 someplace in the basin on 57 days, and on at least 10 days nearly every place in the basin except the extreme coastal areas (see 1998 L.A. Air Quality).

It is interesting that in north San Diego County about half of the few days with the highest smog levels are due to smog transported from L.A. This occurs when northeasterly strong Santa Ana winds blow the L.A. smog over the ocean, followed by northwesterly winds when the Santa Ana weakens that transport the smog to North County. (Source: San Diego: An Introduction to the Region, Philip R. Pryde, p. 261.) So you might be alert to those wind patterns for your physical exercise plans in North County.

The worst smog at any location usually occurs at the top of the inversion layer, which is typically at 2000' or above. Hence the worst smog in San Diego County is recorded at the Alpine station, simply because it is the only observing station at an elevation of 2000'. Other locations at 2000' would be expected to have similar smog levels. The greater Fallbrook area would be expected to have much lower smog levels than Alpine, since most of the area is well below 1000' in elevation. The extreme elevations in the Fallbrook area are ~140' in Bonsall at the San Luis Rey River to ~1500-1600' in the highest locations. Most of the Fallbrook area is below 1000'.

San Diego County is considered to have a serious air pollution problem (0.16-0.18 ppm of ozone; see Map of Ozone Nonattainment Areas), due to the areas of the worst smog in the county. In comparison, the greater L.A. area is classified as having an extreme and severe problem, with > 0.28 ppm of ozone. The value probably typical of Fallbrook, 0.06-0.09 ppm, or 60-90 ppb, is typical of that of urban areas in most of the country. In summer, essentially every place in the country has values above 45 ppb, with an average value of 60 ppb.

The above information was current as of the year 2000. Amazingly, since then the ozone levels in San Diego County, and in California in general, have been getting better steadily! Although our air still gets a grade of F from the American Lung Association in its State of the Air website, in 2014 San Diego County only had 11.3 "weighted average days" of high ozone, compared to 60 (SIXTY; 5.3 times HIGHER) in 1996! Click on the "change since 1996" link to see a plot of how the number of high ozone days has been steadily falling.

This is absolutely wonderful news; all the pain we've had to go through to clean up the air has been paying off in better health.


Go to Weather, Climate and Seasons of Fallbrook


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Last update: 29 January 2015.