Fig. 1
Bulk elemental composition shows limited variability. Functionalized OA composition averaged across all samples shows limited variability in overall elemental ratios and compound class distributions (a) at the forested site, (b) near downtown Atlanta, and (c) in New York City. In (a-c), elemental ratios (points on upper scales) are displayed as daytime (red) and nighttime (blue) values for LC-ESI-Q-TOF data, and shown along with AMS ratios (black). Error bars represent one standard deviation (LC-ESI-Q-TOF data) and 28% error (AMS data, as determined by Canagaratna et al. for improved-ambient analysis17). Values presented here are unweighted. O/N and O/S are computed for compounds with one or more N or S atoms. Bar charts show the fraction of compounds in each compound class, denoted by the elements present in each class (daily compound class distributions are shown in Supplementary Figures 10–11). Oxygen and nitrogen-containing organic compounds are split into two classes depending on O/N: CHON with O/N < 3, and CHON with O/N ≥ 3 (includes organic nitrates). Error bars represent one standard deviation from the mean. In Atlanta, the LC-ESI-Q-TOF O/C agrees with the AMS O/C. However, there is a larger discrepancy between these values in the forest, which decreases slightly in the abundance-weighted results (see Supplementary Note 2, Supplementary Figure 3)
