We investigate the effects of natural variability of meteorological fields on surface PM₂.₅ concentration changes in East Asia during El Niño periods for the past three decades (1980–2014) through GEOS-Chem 3D global chemical transport model simulations. First, our evaluation of the model with anthropogenic emissions for 2006 and a comparison against observations show that the simulated results accurately reproduced the observed spatial distribution of annual mean aerosol concentrations for 2006–2007 including inorganic (sulfate, ammonium, and nitrate) and carbonaceous (organic and black carbon) aerosols in the surface air. Based on the Oceanic Niño Index, the assimilated meteorological data used in the model simulations indicate that 10 El Niño events occurred for the past three decades (1980–2014). We further classified the 10 El Niño events into 6 central Pacific El Niño (C-type) and 4 eastern Pacific El Niño (E-type) to examine the different roles of two El Niño types in determining seasonal surface PM₂.₅ concentrations in East Asia. We find opposite impacts on the seasonal surface PM₂.₅ concentrations depending on two El Niño types, such that the surface PM₂.₅ concentrations during the E-type period are higher than the climatological mean value, especially in northern East Asia. The peak increase of as much as 20% occurs in winter and is sustained until the following spring. However, the C-type period shows a decrease in seasonal PM₂.₅ concentrations in northern East Asia compare to the climatological mean, and the peak decrease of as much as 10% occurs in the following spring. The different of two El Niño types also have dissimilar impacts on surface PM₂.₅ concentrations in southeastern China. Natural variation of aerosol concentrations driven by the different of two El Niño types appears to be significant and would be an important factor in determining the inter-annual variation of aerosol concentrations in East Asia.

In the 21st century, severe droughts associated with climate change will increase biomass burning (BB) in Brazil caused by the human activities. Recent droughts, especially in 2005, 2010, and 2015, caused strong socioeconomic and environmental impacts. The 2015 drought considered the most severe since 1901, surpassed the 2005 and 2010 events in respect to area and duration. Herein, based on satellite data, the 2005, 2010 and 2015 drought impacts on wildfire episodes and carbon monoxide (CO) variability during the dry and the dry-to-wet transition seasons were examined. The BB occurrences in the dry season were fewer during 2015 than during 2005 (−44%) and 2010 (−47%). Contrasting, the BB events in the dry-to-wet transition season, were higher during 2015 than during 2005 (+192%) and 2010 (+332%). The BB outbreaks were concentrated in the southern and southwestern Amazon during 2005, in the Cerrado region during 2010, and mainly in the central and northern Amazon during 2015, an area normally with few fires. The CO concentration showed positive variations (up to +30%) occurred in the southern Amazon and central Brazil during the 2005 and 2010 dry seasons, and north of 20 °S during the 2015–2016 dry-to-wet transition season. The BB outbreaks and the CO emissions showed a considerable spatiotemporal variability among the droughts of 2005, 2010, and 2016, first of them driven by local conditions in the tropical North Atlantic (TNA), characterized by warm than normal sea surface waters and the other two by the El Niño occurrences.