Multi-functional Organic Nitrogen in the Los Angeles Air Basin

We report an inventory of nitrogen-containing organic compounds in the Los Angeles Air Basin in late August, 2021. Gas-phase multifunctional nitrogen-containing compounds are measured by chemical ionization mass spectrometry (CIMS) using the CF₃O^– reagent ion both with and without gas chromatography (GC) separation. We use a time-of-flight aerosol mass spectrometer (ToF-AMS) to quantify the abundance of nitrogen-containing organic compounds present on submicron particles. These nitrogen-containing organic compounds comprise a substantial fraction of non-NO_x reactive nitrogen during the day and, together with nitrous acid (HONO), a larger fraction during nighttime. Alkylnitrates produced in the oxidation of biogenically- and anthropogenically derived alkenes dominate the budget, but nitroaromatics also make a significant contribution. The GC–CIMS observations illustrate that the nighttime alkylnitrates are generated via reaction of alkenes with the nitrate radical and that the resulting nitrooxy-peroxy radicals react with both HO₂ to form hydroperoxides and other RO₂ to form primarily nitrooxy carbonyls. Aerosol organic nitrates on PM1.0 make up approximately a quarter of the total organic nitrates during daytime and nearly half at night.