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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


A new paper has been published characterizing trends in seasonal mean speciated aerosol composition from IMPROVE data.


Photos and Presentations from the 2023 IMPROVE Steering Committee Meeting have been posted.


The 2022 RHR files have been posted.


A revised IMPROVE Data User Guide has been posted


A draft of the 6th IMPROVE Report has been posted.


A new video featuring Bill Malm has been released by the NPS: National Parks in the History of Science: Visibility


The IMPROVE Charter that was adopted by the Steering Committee in 2022 has been posted.


The 2021 RHR files have been posted.


The agenda and presentations and the meeting minutes have been posted from the 2022 IMPROVE Steering Committee Meeting.


A new paper has been published documenting wintertime haze in Dinosaur National Monument.


A History of the A&WMA Visibility Specialty Conferences has been posted in the Gray Literature.


A new paper has been published evaluating the PurpleAir sensor as a light scattering instrument.


The 2021 Technical System Audit Report has been posted.


The 2020 RHR files have been posted.


The IMPROVE Carbon Report has been posted to the Gray Literature.


The minutes have been posted from the 2021 IMPROVE Steering Committee Meeting.


The 2019 RHR files have been posted.


A new Quality Assurance Report for the IMPROVE Network covering January 2019-June 2020 has been posted.


Updates on IMPROVE data and Meetings are emailed periodically.  Please contact anthony_prenni@nps.gov if you wish to be included on these communications.


The agenda and presentations have been posted from the 2021 IMPROVE Steering Committee Meeting.


The meeting minutes from the 2020 IMPROVE Steering Committee Meeting have been posted.


Updated SOPs have been posted for IMPROVE Operations, filter absorption, and XRF analysis.


The 2020 Ions QA Report has been posted.


The agenda and presentations have been posted from the 2020 IMPROVE Steering Committee Meeting.


The minutes from the 2019 IMPROVE Steering Committee Meeting have been posted.


IMPROVE Operations during COVID-19

The COVID-19 pandemic disrupted the operation of the IMPROVE monitoring network.  Despite the many challenges, the IMPROVE network continued to operate, with 27 of the 160 sites shutting down between mid-March and mid-May, 2020.  Only 2 of these sites remain closed as of September 2, 2020.