About the statistics
To be consistent with U.S. State Department measurements of air pollution in Beijing, the numbers reported for Los Angeles in this article and graphics use the Federal Equivalent Method (FEM).
For various technical reasons, this can make PM2.5 concentrations in the Los Angeles Basin appear significantly higher than those reported to the U.S. federal government using the Federal Reference Method (FRM).
The annual average reading of 12 PM 2.5 for Los Angeles cited in the story is the FRM measurement. FRM measurements are the official gauge of the region’s air quality compared with federal health-based standards.
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