Table 3. Molar Ratio of Oxalate Relative to Sulfate, Nitrate, and Ammoniuma Atmospheric Condition Type and Inlet (Number of Vials With Oxalate Above Detection Limits/Total Number of Vials) SO42- Slope (R2) NO3- Slope (R2) NH4+ Slope (R2) Clouds uninfluenced by local pollution sources CVI (34/131) 0.014 (0.37) 0.010 (0.15) 0.006 (0.24) Main (54/92) 0.024 (0.75) -0.007 (0.01) 0.015 (0.59) Cumulative (88/223) 0.023 (0.71) 0.000 (0.00) 0.013 (0.55) Power plant plume in cloud CVI (11/32) 0.083 (0.97) -0.009 (0.00) 0.073 (0.45) Main (44/79) 0.028 (0.77) -0.110 (0.03) 0.026 (0.81) Cumulative (55/111) 0.028 (0.82) -0.031 (0.04) 0.026 (0.84) Cloud-free air Main (24/196) 0.000 (0.00) 0.010 (0.08) 0.002 (0.17) Power plant plume in cloud-free air Main (10/24) 0.015 (0.21) 0.011 (0.10) 0.011 (0.28) Power plant plume in cloud-free air with precipitation from scattered clouds overhead Main (18/21) 0.051 (0.56) 0.031 (0.09) 0.024 (0.52) aCVI samples correspond to cloud droplet residual particles; main inlet samples correspond to total aerosol, which includes a mixture of interstitial aerosol and droplet residuals in clouds.