Satellite-derived constraints on the effect of drought stress on biogenic isoprene emissions in the southeastern US

Abstract. While substantial progress has been made to improve our understanding of biogenic isoprene emissions under unstressed conditions, large uncertainties remain with respect stressed conditions. Here, we use the US Drought Monitor (USDM) as a weekly drought severity index and tropospheric columns formaldehyde (HCHO), key product oxidation, retrieved from Ozone Monitoring Instrument (OMI) derive top-down constraints on response summertime stress in southeastern United States (SE US), region high that is also prone drought. OMI HCHO column density found be 6.7 % (mild drought) 23.3 (severe higher than non-drought A global chemical transport model, GEOS-Chem, version 2.1 Model Emissions Gases Aerosols Nature (MEGAN2.1) emission algorithm can simulate this direction change, but simulated increases at corresponding levels are 1.1–1.5 times HCHO, suggesting need for drought-stress model. By minimizing model–OMI differences temperature sensitivity different levels, derived factor (γd_OMI) GEOS-Chem parameterizes using water temperature. The led an 8.6 20.7 reduction SE relative simulation without it. With γd_OMI model predicts nonlinear increasing trend consistent single site's flux measurements. Compared previous latter, satellite-based performs better capturing regional-scale drought–isoprene responses, indicated by near-zero mean bias between reduces model's organic aerosol (OA) simulations 6.60 11.71 over compared no-stress simulation. ozone displays spatial disparity due isoprene-suppressing effect oxidants, <1 ppb increase O3 high-isoprene regions 1–3 ppbv decrease low-isoprene regions. This study demonstrates unique value exploiting long-term satellite observations develop empirical algorithms where situ measurements limited.