Global distribution and 14-year changes in erythemal irradiance, UV atmospheric transmission, and total column ozone for2005–2018 estimated from OMI and EPIC observations
Authors: Herman Jay , Cede Alexander , Huang Liang , Ziemke Jerald , Torres Omar , Krotkov Nickolay , Kowalewski Matthew , Blank Karin 
Published: July 2020

Abstract. Satellite data from the Ozone Measuring Instrument (OMI) and Earth
Polychromatic Imaging Camera (EPIC) are used to study long-term changes and
global distribution of UV erythemal irradiance E(ζ,φ,z,t)
(mW m−2) and the dimensionless UV index E ∕ (25 m Wm−2) over major
cities as a function of latitude ζ, longitude φ, altitude z,
and time t. Extremely high amounts of erythemal irradiance (12 < UV
index <18) are found for many low-latitude and high-altitude sites (e.g., San Pedro, Chile, 2.45 km; La Paz, Bolivia, 3.78 km). Lower UV
indices at some equatorial or high-altitude sites (e.g., Quito, Ecuador)
occur because of persistent cloud effects. High UVI levels (UVI > 6) are also found at most mid-latitude sites during the summer months for
clear-sky days. OMI time-series data starting in January 2005 to December 2018 are used to estimate 14-year changes in erythemal irradiance ΔE, total column ozone ΔTCO3, cloud and haze transmission ΔCT derived from scene reflectivity LER, and reduced
transmission from absorbing aerosols ΔCA derived from absorbing
aerosol optical depth τA for 191 specific cities in the
Northern Hemisphere and Southern Hemisphere from 60∘ S to 60∘ N using publicly available OMI data. A list of the sites showing changes at the 1 standard deviation level 1σ is provided. For many specific sites there has
been little or no change in E(ζ,φ,z,t) for the period 2005–2018. When the sites are averaged over 15∘ of latitude, there are
strong correlation effects of both short- and long-term cloud and absorbing
aerosol change as well as anticorrelation with total column ozone change
ΔTCO3. Estimates of changes in atmospheric transmission ΔCT (ζ, φ, z, t) derived from OMI-measured cloud and haze reflectivity LER and averaged over 15∘ of latitude show an increase of 1.1±1.2 % per decade between 60 and 45∘ S, almost no average 14-year change of 0.03±0.5 % per decade from 55∘ S to 30∘ N, local increases and decreases from 20 to 30∘ N, and an
increase of 1±0.9 % per decade from 35 to 60∘ N. The largest changes in E(ζ,φ,z,t) are driven by changes in cloud transmission CT. Synoptic EPIC radiance data from the sunlit Earth are
used to derive ozone and reflectivity needed for global images of the
distribution of E(ζ,φ,z,t) from sunrise to sunset centered
on the Americas, Europe–Africa, and Asia. EPIC data are used to show the latitudinal distribution of E(ζ,φ,z,t) from the Equator to 75∘ for specific longitudes. EPIC UV erythemal images show the dominating effect of solar zenith angle (SZA), the strong increase in E with altitude, and the decreases
caused by cloud cover. The nearly cloud-free images of E(ζ,φ,z,t) over Australia during the summer (December) show regions of extremely
high UVI (14–16) covering large parts of the continent. Zonal averages
show a maximum of UVI = 14 in the equatorial region seasonally following
latitudes where SZA = 0∘. Dangerously high amounts of erythemal
irradiance (12 < UV index < 18) are found for many low-latitude and high-altitude sites. High levels of UVI are known to lead to
health problems (skin cancer and eye cataracts) with extended unprotected exposure, as shown in the extensive health statistics maintained by the Australian Institute of Health and Welfare and the United States National
Institute of Health National Cancer Institute.