Environmental plastics in the context of UV radiation, climate change, and the Montreal Protocol.

There are close links between solar UV radiation, climate change, and plastic pollution. UV-driven weathering is a key process leading to the degradation of plastics in the environment but also the formation of potentially harmful plastic fragments such as micro- and nanoplastic particles. Estimates of the environmental persistence of plastic pollution, and the formation of fragments, will need to take in account plastic dispersal around the globe, as well as projected UV radiation levels and climate change factors.

Plastics in the environment in the context of UV radiation, climate change and the Montreal Protocol: UNEP Environmental Effects Assessment Panel, Update 2023.

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) considers the interactive effects of solar UV radiation, global warming, and other weathering factors on plastics. The Assessment illustrates the significance of solar UV radiation in decreasing the durability of plastic materials, degradation of plastic debris, formation of micro- and nanoplastic particles and accompanying leaching of potential toxic compounds. Micro- and nanoplastics have been found in all ecosystems, the atmosphere, and in humans. While the potential biological risks are not yet well-established, the widespread and increasing occurrence of plastic pollution is reason for continuing research and monitoring. Plastic debris persists after its intended life in soils, water bodies and the atmosphere as well as in living organisms. To counteract accumulation of plastics in the environment, the lifetime of novel plastics or plastic alternatives should better match the functional life of products, with eventual breakdown releasing harmless substances to the environment.

Updated analysis of data from Palmer Station, Antarctica (64° S), and San Diego, California (32° N), confirms large effect of the Antarctic ozone hole on UV radiation.

The status of the stratospheric ozone layer is assessed by a panel of experts every 4 years. Reports prepared by this panel include a section with common questions and answers (Q&A) about ozone depletion and related matters. Since 2002, this Q&A supplement has featured a plot comparing historical and current ultraviolet (UV) Index data from Palmer Station, Antarctica (64° S), with measurements at San Diego, California (32° N), and Barrow, Alaska (79° N). The assumptions in generating these plots are discussed and an updated version is presented. The revised plot uses additional data up to the year 2020 and the methods used to create it are better defined and substantiated compared to those used for the legacy plot. Differences between the old and new UV Index values are small (typically < 5%). Both versions illustrate that the ozone hole has led to a large increase in the UV Index at Palmer Station. Between mid-September and mid-November, the maximum UV Index at this site has more than doubled compared to the pre-ozone-hole era (i.e., prior to 1980). When Palmer Station was below the ozone hole in December 1998, an "extreme" UV Index of 14 was observed, exceeding the highest UV Index of 12 ever measured at San Diego despite the city's subtropical latitude. Increases in the UV Index at Barrow and San Diego remain below 40% and 3%, respectively.

The success of the Montreal Protocol in mitigating interactive effects of stratospheric ozone depletion and climate change on the environment.

The Montreal Protocol and its Amendments have been highly effective in protecting the stratospheric ozone layer, preventing global increases in solar ultraviolet-B radiation (UV-B; 280-315 nm) at Earth's surface, and reducing global warming. While ongoing and projected changes in UV-B radiation and climate still pose a threat to human health, food security, air and water quality, terrestrial and aquatic ecosystems, and construction materials and fabrics, the Montreal Protocol continues to play a critical role in protecting Earth's inhabitants and ecosystems by addressing many of the United Nations Sustainable Development Goals.

Floral bullseyes and stratospheric ozone.

As well as guiding pollinators to the centre of flowers, areas of the corolla that absorb UV radiation may help to protect floral reproductive parts from solar UV radiation that would otherwise be reflected onto them. In their recent article, 'Floral pigmentation has responded rapidly to global change in ozone and temperature', Koski et al.1 compared herbarium specimens collected between 1941 and 2017 to investigate whether the size of the UV-absorbing area in the centre of flowers (called 'bullseyes', UV proportion, or UVP) has changed relative to the size of the flower over this period. The article, and a subsequent feature2, describe an increase in UVP of ∼2% per year across all taxa examined. However, the study's main conclusion that this trend can be partially related to changes in ozone and temperature does not withstand close examination.

Record-Breaking Increases in Arctic Solar Ultraviolet Radiation Caused by Exceptionally Large Ozone Depletion in 2020.

Measurements of solar ultraviolet radiation (UVR) performed between January and June 2020 at 10 Arctic and subarctic locations are compared with historical observations. Differences between 2020 and prior years are also assessed with total ozone column and UVR data from satellites. Erythemal (sunburning) UVR is quantified with the UV Index (UVI) derived from these measurements. UVI data show unprecedently large anomalies, occurring mostly between early March and mid-April 2020. For several days, UVIs observed in 2020 exceeded measurements of previous years by up to 140%. Historical means were surpassed by more than six standard deviations at several locations in the Arctic. In northern Canada, the average UVI for March was about 75% larger than usual. UVIs in April 2020 were elevated on average by about 25% at all sites. However, absolute anomalies remained below 3.0 UVI units because the enhancements occurred during times when the solar elevation was still low.

Success of Montreal Protocol Demonstrated by Comparing High-Quality UV Measurements with "World Avoided" Calculations from Two Chemistry-Climate Models.

The Montreal Protocol on Substances that Deplete the Ozone Layer has been hailed as the most successful environmental treaty ever ( https://www.unenvironment.org/news-and-stories/story/montreal-protocol-triumph-treaty ). Yet, although our main concern about ozone depletion is the subsequent increase in harmful solar UV radiation at the Earth's surface, no studies to date have demonstrated its effectiveness in that regard. Here we use long-term UV Index (UVI) data derived from high-quality UV spectroradiometer measurements to demonstrate its success in curbing increases in UV radiation. Without this landmark agreement, UVI values would have increased at mid-latitude locations by approximately 20% between the early 1990s and today and would approximately quadruple at mid-latitudes by 2100. In contrast, an analysis of UVI data from multiple clean-air sites shows that maximum daily UVI values have remained essentially constant over the last ~20 years in all seasons, and may even have decreased slightly in the southern hemisphere, especially in Antarctica, where effects of ozone depletion were larger. Reconstructions of the UVI from total ozone data show evidence of increasing UVI levels in the 1980s, but unfortunately, there are no high-quality UV measurements available prior to the early 1990s to confirm these increases with direct observations.

The 1997 North American Interagency Intercomparison of Ultraviolet Spectroradiometers Including Narrowband Filter Radiometers.

The fourth North American Intercomparison of Ultraviolet Monitoring Spectroradiometers was held September 15 to 25, 1997 at Table Mountain outside of Boulder, Colorado, USA. Concern over stratospheric ozone depletion has prompted several government agencies in North America to establish networks of spectroradiometers for monitoring solar ultraviolet irradiance at the surface of the Earth. The main purpose of the Intercomparison was to assess the ability of spectroradiometers to accurately measure solar ultraviolet irradiance, and to compare the results between instruments of different monitoring networks. This Intercomparison was coordinated by NIST and NOAA, and included participants from the ASRC, EPA, NIST, NSF, SERC, USDA, and YES. The UV measuring instruments included scanning spectroradiometers, spectrographs, narrow band multi-filter radiometers, and broadband radiometers. Instruments were characterized for wavelength accuracy, bandwidth, stray-light rejection, and spectral irradiance responsivity. The spectral irradiance responsivity was determined two to three times outdoors to assess temporal stability. Synchronized spectral scans of the solar irradiance were performed over several days. Using the spectral irradiance responsivities determined with the NIST traceable standard lamp, and a simple convolution technique with a Gaussian slit-scattering function to account for the different bandwidths of the instruments, the measured solar irradiance from the spectroradiometers excluding the filter radiometers at 16.5 h UTC had a relative standard deviation of ±4 % for wavelengths greater than 305 nm. The relative standard deviation for the solar irradiance at 16.5 h UTC including the filter radiometer was ±4 % for filter functions above 300 nm.