Land Use Change Impacts on Aerosols International Aerosol Modeling Algorithms Meeting December 10, 2015 Colette L. Heald Jeff Geddes, Sam Silva, Ashley Berg, Dom Spracklen

Land Use Change is A Key Element of Global Change Currently Neglected in IPCC Aerosol Forcing Estimates

Land Use Change Impacts on Aerosols & Radiation via Biosphere-Atmosphere Exchange NH 3 Soil NO x Bioaerosol Dust Smoke BVOC ↓ Deforestation Agricultural expansion Biome shifts Herbivory / Disease CO 2 fertilization ↑ Agricultural Expansion ↑ Desertification ↓↑ Deforestation Agricultural residue burning Human suppression + secondary impacts via changes in transport/meteorology, deposition, climate change

Historical land use change has likely led to a global mean aerosol cooling equivalent to 30% of the radiative forcing driven by anthropogenic emissions. Likely to continue through the 21 st century. Large Estimated Cooling Associated With Historical LUC [Heald and Spracklen, 2015]

Impact of the Western US Bark Beetle Infestation on SOA [Berg et al., 2013] Mortality Effect + Attack Effect Bark beetle infestation leads to a regional increase in organic aerosol of 20-40%, but the impacts are VERY uncertain & depend on vegetation species. Important Implications for EPA’s Regional Haze Rule (natural visibility conditions)

Land Use Harmonization in GEOS-Chem Model Land Cover & Plant Functional Type (from CLM v4) BVOC Emission Factors Dominant Soil Biomes Deposition Surface Type Leaf Area Index Developed independently and based on different (and inconsistent!) land maps + (inconsistent) MODIS LAI [Geddes et al., ACPD, 2015] BVOC Emissions (MEGAN) (Guenther et al., 2012) Deposition (Wesely et al., 1989) Soil NOx Emissions (Hudman et al., 2012) New GEOS-Chem land module

The Impact of Projected Tree Mortality in the US on SOA Fractional Tree Cover Surface BSOA Concentrations (μg/m 3 ) Baseline Change due to Tree Mortality USDA Forest Service National Insect and Disease Risk Assessment projects extensive risk of forest loss in the US due to insect and disease through BSOA decreases by 5-10% across many regions (up to 2 μgm -3 locally) [Geddes et al., ACPD, 2015]

The Impact of Oil Palm Expansion in SE Asia on SOA [Silva et al., in prep] Palm Production in SE Asia [% land palm] Production (MT) Indonesia Malaysia Isoprene emissions have increased by 13% in the region (+ 11% increase predicted for 2020). BSOA concentrations have increased by up to 60% in the region, with an average increase of 5% over all of SE Asia, with implications for AQ and visibility. (concurrent ↑ in O 3 ) Surface SOA Concentrations (2010) [μg/m 3 ]

Global Historical Anthropogenic LUC Impacts on SOA Land Use Change: 1850 to 2000 ↓ 11% ↓13% BVOC emissions SOA burden DRF SOA via LUC ~ W/m W/m 2 ↓ 35% ? GEOS-Chem [Heald et al, in prep] GISS [Unger, 2014]

Global Historical LUC Impacts on Nitrate [Heald et al., in prep] See 82% increase in nitrate concentrations; leading to DRF of W/m 2. However, this rise depends on both the supply of agricultural NH 3 and anthropogenic NO x. So cannot attribute this directly to LUC. Sensitivity experiment: zero out agricultural NH 3 emissions in 1850

Back of the envelope estimate: historical land use change impacts on aerosols equivalent to ~30% of emissions-driven direct radiative forcing. Also sporadic events (e.g. insects) can temporarily impact visibility/AQ In an era of decreasing anthropogenic emissions, land use change will become an increasingly important driver of aerosol-climate impacts. Our understanding of land use change impacts on air quality is limited, more studies needed! Need better representations of biosphere-atmosphere exchange in models. Also more observations to test models! Back of the envelope estimate: historical land use change impacts on aerosols equivalent to ~30% of emissions-driven direct radiative forcing. Also sporadic events (e.g. insects) can temporarily impact visibility/AQ In an era of decreasing anthropogenic emissions, land use change will become an increasingly important driver of aerosol-climate impacts. Our understanding of land use change impacts on air quality is limited, more studies needed! Need better representations of biosphere-atmosphere exchange in models. Also more observations to test models!