Multi-decadal aerosol variations from 1980 to 2009: a perspective from observations and a global model

Abstract

Abstract. Aerosol variations and trends over different land and ocean regions from 1980 to 2009 are analyzed with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model and observations from multiple satellite sensors and available ground-based networks. Excluding time periods with large volcanic influence, aerosol optical depth (AOD) and surface concentration over polluted land regions generally vary with anthropogenic emissions, but the magnitude of this association can be dampened by the presence of natural aerosols, especially dust. Over the 30-year period in this study, the largest reduction in aerosol levels occurs over Europe, where AOD has decreased by 40–60% on average and surface sulfate concentrations have declined by a factor of up to 3–4. In contrast, East Asia and South Asia show AOD increases, but the relatively high level of dust aerosols in Asia reduces the correlation between AOD and pollutant emission trends. Over major dust source regions, model analysis indicates that the change of dust emissions over the Sahara and Sahel has been predominantly driven by the change of near-surface wind speed, but over Central Asia it has been largely influenced by the change of the surface wetness. The decreasing dust trend in the North African dust outflow region of the tropical North Atlantic and the receptor sites of Barbados and Miami is closely associated with an increase of the sea surface temperature in the North Atlantic. This temperature increase may drive the decrease of the wind velocity over North Africa, which reduces the dust emission, and the increase of precipitation over the tropical North Atlantic, which enhances dust removal during transport. Despite significant trends over some major continental source regions, the model-calculated global annual average AOD shows little change over land and ocean in the past three decades, because opposite trends in different land regions cancel each other out in the global average, and changes over large open oceans are negligible. This highlights the necessity for regional-scale assessment of aerosols and their climate impacts, as global-scale average values can obscure important regional changes.

The version 3 OMI NO<sub>2</sub> standard product

“…The SPv3 AMF calculation uses the GMI threedimensional CTM simulation in the troposphere and stratosphere (Duncan et al, 2007;Strahan et al, 2013). The GMI CTM uses a stratosphere-troposphere chemical mechanism, natural and anthropogenic emissions, and aerosol fields from the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model (Chin et al, 2014). It simulates tropospheric processes such as NO x production by lightning, scavenging, and wet and dry deposition.…”

Climate Feedback on Aerosol Emission and Atmospheric Concentrations

“…Anthropogenic aerosol emissions are changing in response to economic developments and environmental policies. In the past decades, anthropogenic aerosol concentrations have strongly increased in eastern Asia, but decreased in Europe and North America since the mid-1980s [7]. Not only fossil fuels but also changes in land use and agricultural emissions contribute to aerosol trends.…”

“…While those reviews were mainly motivated by surveying the role of climate variability on air quality changes and concentrations of cloud condensation nuclei (CCN), variability and trends in aerosol optical depth (AOD) ( [5], Fig. 1a) are also an important factor for studies of the role of aerosol articles in climate [7]. Aerosols consist of mixtures of different particle species from specific natural and anthropogenic sources (e.g., primary particles like sea salt, mineral dust, biological particles, and soot; particles secondarily formed from precursor gases like ammonium sulfate, ammonium nitrate, and secondary organic aerosols (SOA)) (e.g., [8]).…”

Climatology of the aerosol optical depth by components from the Multi-angle Imaging SpectroRadiometer (MISR) and chemistry transport models

“…Therefore, here we focus, in particular, on characterizing AOD distributions in regions near major aerosol emission sources: East Asia, the Sahara, and West Africa, with comparisons between MISR climatological observations and two model simulations. One is from the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model (Chin et al, 2002(Chin et al, , 2014, and the other is from the SPectral RadIatioNTrAnSport (SPRINTARS) model for Aerosol Species (Takemura et al, 2002(Takemura et al, , 2005 interactively coupled to the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) (Satoh et al, , 2014Suzuki et al, 2008). We also demonstrate why it is important to consider spatiotemporal distributions of AOD when comparing satellite observations and models rather than simply using spatially and temporally averaged AODs for model evaluation.…”