Fig. 4.
Schematic illustrating how NOx emissions from Manaus greatly enhance formation of biogenic SOA within the urban plume. NOx emitted by Manaus greatly increases oxidants (OH and ozone; brown arrows), which promote reaction of forest carbon (emitted as isoprene and terpenes; green arrows). In the absence of the urban plume, background soil NOx emissions (purple arrows) drive the oxidant cycling but are much smaller than the NOx emitted from Manaus. Lower background NOx causes smaller OH and ozone production, thus decreasing reacted biogenic VOCs and SOA formation. The pie charts indicate WRF-Chem simulated domain-averaged components of a Mass emissions fluxes of biogenic VOCs, b Background biogenic SOA and c In-plume biogenic SOA at 500 m altitude during the afternoon (16–20 UTC) of 13 March 2014. Biogenic SOA consists of two parts: gas-phase chemistry of isoprene, monoterpenes, and sesquiterpenes represented by VBS approach (~70% of total SOA), and multiphase chemistry that is driven by IEPOX uptake into SOA, as described in the text