U.S. Air Quality

Special Feature: California Fires in October 2004

Introduction

During Fall 2004, major fires started in California and lasted about a week. Even though these fires were not as intense as the October 2003 Californian fires (also see ASTER images), they, nevertheless, produced a fairly high amount of smoke particles and did contribute to the poor air quality in central California. While posting, we monitored the evolution of the smoke plumes and the air quality in California during these days. This special post is about the advection of the smoke plume from October 11th to 20th.

This true color MODIS picture is from the NOAA Climate of 2004 Wildfire Season Summary web page. It was taken on October the 12th 2004. Fires are represented in red and the smoke extending over the Pacific is in a grayish color.

How it started

On October 11th, there was a small fire in central California near Napa. The fire produced a thin plume of particles that extended south over the Pacific. On the 12th, the smoke thickened and more fires started in the same region. According to the MODIS Terra sensor, the plume had an optical depth close to 1. The same plume can be identified on the Hazard Mapping System (HMS) image (see help files for image explanation).

The October 13th MODIS AOD image shows another major plume in California. On the 14th, according to the EPA AirNow site, this region had "moderate" air quality. The smoke produced by the fires surely contributed to the conditions.

MODIS Aqua image from October 15 2004

This is a MODIS image showing the west coast. The color scale has been adjusted to roughly approximate the EPA AQI six-color scale. For description of AOD images see help files. The reddish color indicates the presence of higher particle concentrations. On this day, the smoke was advecting toward the ocean.

On October 15th, the smoke was still very thick. The AQ worsened to “unhealthy” near San Francisco. The visibility in Napa dropped as low as 4.0 miles around 11:00am. Even though particle concentration does affect visibility, in this case, the reduced visibility may have also been caused by fog and smog.

The model below from the Naval Research Laboratory (NRL) website, shows smoke particle production in California. According to the NAAPS model below, the particle concentration in central California was above 64 ug/m3 (last quadrant). The first quadrant shows the AOD values ranging from 0.8 to 1.6. See NRL map descriptions. This agrees with the EPA AirNow data. According to EPA, the particle concentration near Stockton was between 65.5 ug/m3 and 150.5 ug/m3. According to MODIS data, the AOD value in the same region was around 1 (see MODIS Aqua image above).

NAAPS model (Oct. 15th) and EPA AirNow map (Oct. 16th)

On October 16th, the fires were still intense. An image from the NOAA NESDIS GASP Viewer posted on the Smog blog shows moderate to highly elevated AOD. Some areas had an AOD reaching 1.2. According to the AirNow map showing the air quality (AQ) in the US, California had “moderate” AQ with concentrations ranging from 15.5 ug/m3 to 40.4 ug/m3, as well as “unhealthy for sensitive groups” (40.5 ug/m3 to 65.4 ug/m3) AQI on the 16th. These conditions were partially due to the burning fires. Also, because of the fact that central and southern California often experience atmospheric inversion (or see Ramp et al.), particles are often trapped and usually exit the continent westward toward the Pacific ocean.

How it ended

Unfortunately, during the following days, the sky was too cloudy over California to detect any smoke plume or Aerosol Optical Depth. A frontal system swept across the US bringing rain and cleaning the air. The Air quality in the West, more precisely in California, improved to “good” (0 to 15.4 ug/m3) on October 19th. By the end of October, the major fires had ceased.

Data sources

The data come from the MODIS instrument aboard the Terra and Aqua satellites. NASA DAAC provides several products. In this post, we used MYD04 level 2 to create Aerosol Optical Depth (AOD) images. Data was also sourced from GOES. Some of the images were generated using HDFLook.

Posted by Kamonayi Mubenga at April 25, 2005 12:00 PM