Integrated Assessment of the Leading Paths to Mitigate CO2 Emissions from the Organic Chemical and Plastics Industry.

The chemical industry is a major and growing source of CO2 emissions. Here, we extend the principal U.S.-based integrated assessment model, GCAM, to include a representation of steam cracking, the dominant process in the organic chemical industry today, and a suite of emerging decarbonization strategies, including catalytic cracking, lower-carbon process heat, and feedstock switching. We find that emerging catalytic production technologies only have a small impact on midcentury emissions mitigation. In contrast, process heat generation could achieve strong mitigation, reducing associated CO2 emissions by ∼76% by 2050. Process heat generation is diversified to include carbon capture and storage (CCS), hydrogen, and electrification. A sensitivity analysis reveals that our results for future net CO2 emissions are most sensitive to the amount of CCS deployed globally. The system as defined cannot reach net-zero emissions if the share of incineration increases as projected without coupling incineration with CCS. Less organic chemicals are produced in a net-zero CO2 future than those in a no-policy scenario. Mitigation of feedstock emissions relies heavily on biogenic carbon used as an alternative feedstock and waste treatment of plastics. The only scenario that delivers net-negative CO2 emissions from the organic chemical sector (by 2070) combines greater use of biogenic feedstocks with a continued reliance on landfilling of waste plastic, versus recycling or incineration, which has trade-offs.

Nonstatistical Dissociation Dynamics of Nitroaromatic Chromophores.

Organic carbon in the atmosphere is emitted from biogenic and anthropogenic sources and plays a key role in atmospheric chemistry, air quality, and climate. Recent studies have identified several of the major nitroaromatic chromophores embedded in organic "brown carbon" (BrC) aerosols. Indeed, nitroaromatic chromophores are responsible for the enhanced solar absorption of BrC aerosols, extending into the near UV (300-400 nm) and visible regions. Furthermore, BrC chromophores serve as temporary reservoirs of important oxidizing intermediates including hydroxyl (OH) and nitric oxide (NO) radicals that are released upon electronic excitation. The present work represents the first study of the 355 nm photolysis of known BrC chromophores ortho-nitrophenol and 2-nitroresorcinol, as well as the prototypical nitroaromatic, nitrobenzene. Experiments are carried out in a pulsed supersonic jet expansion with velocity map imaging of NO X2Π (ν″ = 0, J″) fragments to report on the photodissociation dynamics. The total kinetic energy release (TKER) distributions and the NO X2Π (ν″ = 0, J″) product state distributions deviate significantly from Prior simulations, indicating that energy is partitioned nonstatistically following dissociation. Experiments are conducted in tandem with complementary calculations using multireference Møller-Plesset second-order perturbation theory (MRMPT2) for stationary points obtained by using multiconfiguration self-consistent field (MCSCF) with an aug-cc-pVDZ basis on the ground and lowest energy triplet electronic states. Furthermore, insights into the partitioning of energy upon photodissociation are achieved by using relaxed scans at the MCSCF/aug-cc-pVDZ level of theory. As a whole, the results suggest that upon excitation to S1, all three nitroaromatics share a common overall mechanism for NO production involving isomerization of the nitro group, nonradiative relaxation to S0, and dissociation to form rotationally hot NO.