Interagency Monitoring of Protected Visual Environments

Visibility has improved dramatically in the US, due largely to the Clean Air Act and Regional Haze Rule.

Our National Parks and Wilderness Areas possess many stunning vistas and scenery. Unfortunately, these scenes are diminished by uniform haze causing discoloration and loss of texture and visual range. Layered hazes and plume blight also detract from the scene.  Recognizing the importance of visual air quality, congress included legislation in the 1977 Clean Air Act to prevent future and remedy existing visibility impairment in Class I areas.  To aid in the implementation of this legislation, the IMPROVE program was initiated in 1985.  This program implemented an extensive long term monitoring program to establish the current visibility conditions, track changes in visibility and determine causal mechanism for the visibility impairment in the National Parks and Wilderness Areas.

As the result of reduced emissions due to the Clean Air Act and Regional Haze Rule, as well as the ongoing efforts of IMPROVE and other state, regional and national programs, visibility has improved dramatically in the US.  However, new sources related to climate change and oil and gas development are expected to impact all aspects of air quality in the US, including visibility, and continued efforts are needed to ensure that impacts from new and existing sources are well understood and controlled.

News & Updates


Visibility impacts at Class I areas near the Bakken oil and gas development has been published.


 The 2016 RHR Summary Data have been posted.


The semi-annual Quality Assurance Report for the IMPROVE Network has been posted (March 2018).


The 2017 annual Quality Assurance Report for Ion Analysis has been posted.


The 2018 IMPROVE Field Maintenance Schedule is now available.  


The 2018 IMPROVE calendar is now available.  


A new Data Advisory has been posted regarding a calibration bias in reported V concentrations.


The 2017 Technical System Audit Summary is now available.


The semi-annual Quality Assurance Report for the IMPROVE Network has been posted (August 2017).


An assessment of wildfire smoke in Western U.S. National Parks using IMPROVE monitoring data has been posted in the Gray Literature.


A new Data Advisory has been posted regarding over-reporting of sodium in salt-rich samples.


A new tool (beta version) for Estimating PM2.5 Mass in near-real time at 11 National Parks is now available.


A new Data Advisory has been posted regarding negative chloride concentrations at salt-poor sites.


An online version of WinHaze is now available.


Resources for Technical Systems Audits have been posted.


 The 2016 IMPROVE Steering Committee Meeting Presentations have been posted.


The Regional Haze Rule Summary Data are now available for 1988 - 2015.