Fig. 3: Relationships between sulfate and nitrogen oxide concentrations.
From: Fast sulfate formation from oxidation of SO2 by NO2 and HONO observed in Beijing haze
Data are shown for Stages I and II of the December 16–22, 2016 haze event. Concentrations of sulfate and nitrogen oxides are expressed in common parts per billion (ppb) units (1 μg m−3 sulfate = 0.23 ppb at T = 273.15 K). Individual points are hourly mean values from Fig. 1 during nighttime hours (19:00–6:00 local time). The figure shows scatterplots of PM1 sulfate versus a nitrous oxide (N2O); b nitrous acid (HONO); c nitrogen dioxide (NO2); d PM1 nitrate. Pearson correlation coefficients (r) and reduced-major-axis regression lines are shown separately for Stages I and II.
