Abstract
Abstract. There are few multi-decadal observations of atmospheric aerosols worldwide. This study applies global hourly visibility (Vis) observations at more than 3000 stations to investigate historical trends in atmospheric haze over 1945–1996 for the US, and over 1973–2013 for Europe and eastern Asia. A comprehensive data screening and processing framework is developed and applied to minimize uncertainties and construct monthly statistics of inverse visibility (1/Vis). This data processing includes removal of relatively clean cases with high uncertainty, and change point detection to identify and separate methodological discontinuities such as the introduction of instrumentation. Although the relation between 1/Vis and atmospheric extinction coefficient (bext) varies across different stations, spatially coherent trends of the screened 1/Vis data exhibit consistency with the temporal evolution of collocated aerosol measurements, including the bext trend of −2.4 % yr−1 (95 % CI: −3.7, −1.1 % yr−1) vs. 1/Vis trend of −1.6 % yr−1 (95 % CI: −2.4, −0.8 % yr−1) over the US for 1989–1996, and the fine aerosol mass (PM2.5) trend of −5.8 % yr−1 (95 % CI: −7.8, −4.2 % yr−1) vs. 1/Vis trend of −3.4 % yr−1 (95 % CI: −4.4, −2.4 % yr−1) over Europe for 2006–2013. Regional 1/Vis and Emissions Database for Global Atmospheric Research (EDGAR) sulfur dioxide (SO2) emissions are significantly correlated over the eastern US for 1970–1995 (r = 0.73), over Europe for 1973–2008 (r ∼ 0.9) and over China for 1973–2008 (r ∼ 0.9). Consistent "reversal points" from increasing to decreasing in SO2 emission data are also captured by the regional 1/Vis time series (e.g., late 1970s for the eastern US, early 1980s for western Europe, late 1980s for eastern Europe, and mid 2000s for China). The consistency of 1/Vis trends with other in situ measurements and emission data demonstrates promise in applying these quality assured 1/Vis data for historical air quality studies.
Highlights
Atmospheric aerosols have broad implications for air quality and climate change
Collocations are considered between Interagency Monitoring of PROtected Visual Environments (IMPROVE) and ISD time series over 1988–2013 within the distance of less than 1◦ and altitude difference of less than 500 m
PM2.5 trends derived from satellite aerosol optical depth (AOD) over 1998–2012 have decreasing tendencies over North America and Europe, and increasing tendencies over eastern Asia (Boys et al, 2014; van Donkelaar et al, 2015), similar to the 1/Vis trends found here
Summary
Atmospheric aerosols have broad implications for air quality and climate change. The Global Burden of Disease (GBD) assessment attributed ambient exposure to aerosol particles with an aerodynamic diameter below 2.5 μm (PM2.5) as the sixth largest overall risk factor for premature mortality with 3.2 million premature deaths per year (Lim et al, 2012). Multidecadal Vis data might contain possible variation or even reversal in haze trends as expected from historical emission and surface solar radiation (SSR) data (Lu et al, 2010; Stern, 2006; Streets et al, 2006; Wild et al, 2005) It is of particular interest how these changes would associate with the trends of air quality, and would be captured by the Vis data. This study revisits the Vis observations to characterize historical trends of atmospheric haze by asserting two major efforts: a more comprehensive data quality assurance processing and a more detailed trend analysis for separate periods. This analysis provides multi-decadal information about air quality evolution and its connections to emission trends over major industrialized regions.
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