Top-Down Model-Free Computed Emissions, Size, Mixing State, and Radiative Forcing of BC, CO, and NOx: Increased Emissions and Less Negative Radiative Forcing in Rural Areas Coupled with Reduced Emissions and More Variable Radiative Forcing in Urban Areas

Studies have demonstrated that black carbon (BC) tends to be underestimated by models in general, while NO₂ and CO columns are also underestimated, although surface measurements are reasonable. These findings are at odds with increased regulations and incentives to improve air quality and address climate altering species.

Recent advances in analyzing large datasets allows new analytical methods to detect signals and quantify patterns among different in-situ species, which were not previously realized. This work adopts one such approach merging mass conservation, number conservation, first order thermodynamics and chemistry, single-particle MIE modeling, and remotely sensed measurements across the UV, VIS, and NIR in tandem. Using basic thermodynamical relationships of combustion under different energy use conditions to constrain the ratios between co-emitted species, first order in-situ chemistry, and advective and pressure-based transport, emissions and uncertainties of BC, CO, and NO₂ are quantified. The total errors are explored in depth based on boundaries established from the first order physical laws and mathematical bootstrapping, with the overall error generally observed to be smaller than the day-to-day variability.

The significance of day-to-day, week-to-week, and grid-to-grid variation are quantified. This is especially true in the regions undergoing the most change. The impacts of dynamical transport, chemical-decay, thermodynamic initiation, and in-situ interactions with UV radiation are attributed using additional measurements not used to fit the mass-conserving model free approach used in this work. This work relies on AERONET, SONET, OMI, TROPOMI, GEMS, MOPITT, MISR, CEMS, and other ground-based platforms.

A few conclusions are discussed. First, regulations are working in urban centers and at large sources including powerplants, steel plants, and concrete plants, with overall emissions being reduced for at least one and in many cases two species. Second, there are large increases in suburban and rural areas, including in regions previously unidentified as being emission s free. Third, the effects of biomass burning are clearly identified and attributed, even in regions which were previously thought to be nearly completely controlled by urban sources, such as the megacities of Hong Kong, New Delhi, and Shanghai. Fourth, attribution has determined that emissions, UV radiation, and long-range transport are all significant. Fifth, there are biases in the observed TOA radiative forcing, in which a small but significant percentage of the total BC outcomes have a positive radiative forcing, and the median values are far less negative than current models can capture. Sixth, the concept of TOA and ABS radiative forcing per unit of AOD is found to not be reasonable, and a new framework is demonstrated that accounts for more than 90% of the possible cases computed.