Introduction to the A&WMA 2002 critical review visibility: Science and regulation

Judith C. Chow, Ron Berglund, Pratim Biswas, John Watson, Chang Yu Wu, John G. Watson

Research output: Contribution to journalReview articlepeer-review

24 Scopus citations


The 1999 Regional Haze Rule provides a context for this review of visibility, the science that describes it, and the use of that science in regulatory guidance. The scientific basis for the 1999 regulation is adequate. The deciview metric that tracks progress is an imperfect but objective measure of what people see near the prevailing visual range. The definition of natural visibility conditions is adequate for current planning, but it will need to be refined as visibility improves. Emissions from other countries will set achievable levels above those produced by natural sources. Some natural events, notably dust storms and wildfires, are episodic and cannot be represented by annual average background values or emission estimates. Sulfur dioxide (SO2) emission reductions correspond with lower sulfate (SO42-) concentrations and visibility improvements in the regions where these have occurred. Non-road emissions have been growing more rapidly than emissions from other sources, which have remained stable or decreased since 1970. Simpler models representing transport, limiting precursor pollutants, and gas-to-particle equilibrium should be used to understand where and when emission reductions will be effective, rather than large complex models that have insufficient input and validation measurements. Examples of model-based source attribution show large differences among estimates from various modeling systems and with ambient measurements.

Original languageEnglish (US)
Pages (from-to)626-627
Number of pages2
JournalJournal of the Air and Waste Management Association
Issue number6
StatePublished - 2002
Externally publishedYes

ASJC Scopus subject areas

  • Waste Management and Disposal
  • Management, Monitoring, Policy and Law


Dive into the research topics of 'Introduction to the A&WMA 2002 critical review visibility: Science and regulation'. Together they form a unique fingerprint.

Cite this