1F: A Community Chemistry Initiative: “Quantifying atmospheric reactive carbon chemistry at the molecular level”

ACOM is developing, with community partners, an integrated research program to study transformations of tropospheric ‘reactive carbon’ (rC) species.  These ‘rC’ compounds are emitted in very large quantity (> 1000 Tg/year) into the atmosphere from both anthropogenic and natural (biogenic) sources. Their chemistry is central to the workings of the troposphere, providing the ‘fuel’ that drives oxidative processes, controls radical and NOx budgets, and ultimately controls the formation of critical secondary pollutants such as ozone and secondary organic aerosol (SOA).  Developing predictive capability regarding the formation of these secondary pollutants, in particular the impacts of the SOA on human health and Earth’s radiative balance, requires detailed multi-phase molecular level understanding of the processes involved.

Reactive carbon research at ACOM (in association with many University partners) involves a multi-pronged approach that includes laboratory chamber studies, development of structure-reactivity relationships and concomitant chemical mechanism development, process model development, instrumentation development, community field campaign development and leadership, and the development and implementation of community 3D air quality and chemistry-climate regional and global models.  Key activities at the moment include the following:

a) continued development of the TOGA-TOF (Trace Organic Gas Analyzer – Time of Flight) fast GC-MS instrument for in situ quantification of multiple rC species.
b) chamber studies aimed at quantifying organic nitrate formation, and understanding complex isoprene chemistry over ranges of NOx levels (see figures below).
c) inclusion of a more detailed rC chemical mechanism in community models (WRF-Chem and CAM-Chem / WACCM).
d) simulations of rC chemistry in the Amazon forest, both in pristine conditions and in those impacted by human activity (pollution from nearby Manaus, Brazil).
e) development of evaluated rate coefficient databases for community use, and for testing and development of structure-reactivity relationships.

NCAR 10 m3 Teflon reaction chamber.
Figure 1. Photo of the NCAR 10 m3 Teflon reaction chamber, used to study rC chemistry in relevant tropospheric conditions.
Yields of two major oxidation products.
Figure 2. Yields of two major oxidation products (methyl vinyl ketone, MVK, and methacrolein, MACR) from the OH-initiated oxidation of isoprene, color-coded by the amount of NO in the chamber.