PM10
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PM10 Information Page
 
PM10 (Particulate Matter):
A major air pollutant consisting of tiny solid or liquid particles of soot, dust, smoke, fumes, or mists.  The size of the particles (10 microns or smaller, about 0.0004 inches or less) allows them to enter the air sacs deep in the lungs where they may be deposited to result in adverse health effects.  PM10 also causes visibility reduction.  The PM10 data listed in these web pages are reported as 24-hour average concentrations in ug/m3 (weight of particles in micrograms per one cubic meter of air).
 
Sampling Schedule:
  Only PM10 data collected using a high volume sampler with a size selective inlet (SSI) are presented in this web site.  The SSI is typically used to measure a 24-hour average concentration once every six days.   Some monitoring sites measure PM10 more frequently throughout the year, others increase sampling frequency or sample only during high PM10 season.  Special terminology, like the number of complete months and the percent of samples above the standard, was used in the tables to help illustrate the extent and severity of the PM10 problem.
 
Max 24-Hr:
  Highest Annual 24-hour concentration in ug/m3.
 
AGM
  Annual Geometric Mean of all 24-hour average concentrations at a monitoring site in ug/m3.
 
Max AGM
  Highest Annual Geometric Mean at a monitoring site within the county, basin, or district.
 
AAM
Annual Arithmetic Mean of all 24-hour average concentrations at a monitoring site in ug/m3.
 
Max AAM
Highest Annual Arithmetic Mean at a monitoring site within the county, basin, or district.
 
EPDC (Expected Peak Day Concentration)
The PM10 concentration expected to recur once per year.  The EPDC is calculated for each monitoring site based on data for 3 successive years and is listed by the last year of the three year period.  The EPDC can be higher than the highest concentration measured at a monitoring site.
 
Max EPDC (Expected Peak Day Concentration)
Highest PM10 concentration expected to recur once per year within an area (e.g. county, basin, district).
 
99th Percentile
PM10 24-hour concentration out of a year of monitoring data below which 99 percent of all values in the group fall. This is the current form of the federal 24-hour PM10 standard.
 
Max 99th Percentile
Highest of the 99th percentiles of 24-hour PM10 concentrations taken from the monitoring sites within the county, basin, or district.
 
Complete Months
The number of complete months, quarters, and years represents completeness of the data.  The data that meet each level of representativeness criteria (month, quarter, and year) are sufficiently complete to reliably characterize air quality during the representative period.  The completeness criteria for PM10 are shown in the table below.

Criteria for Representativeness of PM10 Air Quality Data
Month Four or more 24-hour samples
Quarter Three representative months
Year Four representative calendar quarters
 
PM10 Ambient Air Quality Standards
The U.S. EPA and the ARB have adopted air quality standards to protect the public and the environment from adverse effects of air pollution.  The standards identify acceptable levels of pollutants that can be present in ambient air.  The current PM10 air quality standards are shown in the table below.  The 24-hour standards protect the public from the effects of short-term exposure to ambient PM10 concentrations and the annual standards protect the public and the environment from the effects of long term exposure.  The State 24-hour standard is exceeded when the 24-hour PM10 concentration is greater than or equal to 50.5 ug/m3.  The federal 24-hour PM10 standard is exceeded when the 24-hour PM10 concentration is greater than or equal to 155 ug/m3.  The State annual standard is exceeded when the annual geometric mean of all 24-hour concentrations at a site is greater than or equal to 30.5 ug/m3.  The national annual standard is exceeded when the annual arithmetic mean of all 24-hour concentrations at a site is greater than or equal to 50.5 ug/m3.

On July 18, 1997, the U.S. EPA announced the new PM10 standards.  The U.S. EPA retained the annual PM10 standard of 50 ug/m3 and adjusted the PM10 24-hour standard of 150 ug/m3 by changing the form of the standard.  The one-expected exceedance form was replaced by the 99th percentile of 24-hour concentrations at each monitor within an area averaged over 3 years.

PM10 Ambient Air Quality Standards
Averaging Time California Standards Concentration National Standards Concentration
24-hour 50ug/m3 150ug/m3
Annual Mean 30ug/m3
(Geometric Mean)
50ug/m3
(Arithmetic Mean)
 
% of samples above the standard
The % of samples above the standard is calculated based on the total number of samples and the number of samples with concentrations that exceeded the standard.  The percents are first calculated for calendar quarters.  Only quarters with 12 or more samples are included in the calculation.  The percents for all complete quarters are then averaged.  For a basin, county, or district, samples or exceedances measured at multiple monitoring sites on the same day are counted as one.
 
Highly Irregular or Infrequent Events
The ambient air quality data are used in determining an area's designation status with respect to the State standards.  The designation criteria provide for excluding exceedances affected by highly irregular or infrequent events because it is not reasonable to mitigate these exceedances through the regulatory process.
Three types of highly irregular or infrequent events may be identified:
Exceptional Event - specific, identifiable event beyond reasonable regulatory control which causes an exceedance of a state standard.  An exceptional event may be caused by an act of nature (for example, a severe wind storm or a forest fire) or it may be of human origin (for example, a chemical spill or industrial accident).
Extreme Concentration Event - an event that may not have a specific, identifiable cause, but is identified by a statistical procedure which calculates the concentration
(Expected Peak Day Concentration) that is not expected to recur more frequently than once per year.  One potential cause of an extreme concentration event is adverse meteorology.  Measured concentrations that are higher than the Expected Peak Day Concentration are identified as extreme concentrations and are excluded from the area designation process.  The highest concentration remaining after excluding extreme concentrations is referred to as the designation value.
Unusual Concentration Event - an event that causes an anomalous exceedance of a State standard.  To identify an exceedance as affected by an unusual concentration event, the ARB Executive Officer must find (based on the relevant information) that the impact of the affected exceedance is limited to the local area, the exceedance is not expected to recur, and the data do not support a nonattainment designation.
 
Nature and Sources of the Pollutant
Particulate matter can be directly emitted or can be formed in the atmosphere when gaseous pollutants such as SO2 and NO2 undergo chemical reaction in the atmosphere.
Major sources of PM10 include:
motor vehicles
wood burning stoves and fireplaces
dust from construction, landfills, and agriculture
wildfires and brush/waste burning
industrial sources
windblown dust from open lands
 
Measurements Methods
PM10 samples are collected over a 24-hour period on an 8 inch x 10 inch quartz fiber filter by using a high volume sampler equipped with a size selective inlet (SSI), and operated at 36 to 44 cubic feet per minute.  Each filter is weighed before and after sampling to determine the net weight gain (micrograms) of the sample. Samples are usually collected from midnight to midnight every sixth day. PM10 data collected using other measurements methods, including the dichotomous sampler, Tapered Element Oscillating Microbalance (TEOM), or Beta Attenuation Monitor, are not presented in this web site.
 
Elemental Analyses
Some PM10 filters are analyzed for chemical composition, including some or all of the following: five ionic species (nitrate, sulfate, ammonium, chloride, potassium) and total carbon.  This information is useful in identifying sources of particulate matter. The chemical composition data are reported as a 24-hour average concentration in ug/m3.
 
How to Request PM10 Air Quality Data?
To request PM10 data please contact Ron Rothacker:
  Address: Air Resources Board
    Technical Support Division
    Air Quality Data Review Section
    P.O. Box 2815, Sacramento, CA 95812
  Phone: (916)324-7672
  Fax: (916)327-8524
  e-mail:
aqdweb@arb.ca.gov
 
Please send questions or comments to:
aqdweb@arb.ca.gov
 
This page last revised on October 9, 1997
 
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