The Camp Fire was one of California\'s deadliest and most destructive wildfires, and its widespread smoke threatened human health over a large area in Northern California in November 2018. To analyze the Camp Fire influence on air quality on a 200 km distant site in Berkeley, highly time-resolved total carbon (TC), black carbon (BC), and organic carbon (OC) were measured using the Carbonaceous Aerosol Speciation System (CASS, Aerosol Magee Scientific), comprising two instruments, a Total Carbon Analyzer TCA08 in tandem with an Aethalometer AE33. During the period when the air quality was affected by wildfire smoke, the BC concentrations increased four times above the typical air pollution level presented in Berkeley before and after the event, and the OC increased approximately ten times. High-time-resolution measurements allow us to study the aging of OC and investigate how the characteristics of carbonaceous aerosols evolve over the course of the fire event. A higher fraction of secondary carbonaceous aerosols was observed in the later phase of the fire. At the same time, the amount of light-absorbing organic aerosol (brown carbon) declined with time.

Brown carbon (BrC), a significant wavelength-dependent atmospheric absorber of solar radiation, plays a key role in photochemistry and long-lasting haze episodes. Herein, two types of BrC extracted from one-year PM2.5 samples (June 2017-May 2018 in Nanjing), i.e. methanol-extracted organic carbon (MSOC) and ultrapure water-extracted organic carbon (WSOC), were obtained to investigate distinct optical properties of atmospheric BrC. The extraction efficiency of BrC was as high as 91% in methanol solution, and the corresponding light absorption coefficient (Abs) of MSOC at 365 nm (Abs365-MSOC, 7.75 ± 3.95 Mm-1) was approximately 1.6 times that of WSOC (Abs365-WSOC, 4.84 ± 2.97 Mm-1), indicating that the water-insoluble compounds mostly affected the light absorption of BrC. The seasonal variations of Abs365-WSOC and Abs365-MSOC were followed the sequence of winter > spring > autumn > summer, due to the dominated emissions from fossil fuel combustion and biomass burning in the cooling seasons. Additionally, four fluorescent chromophores in WSOC and MSOC, containing three humic-like chromophores and one protein-like chromophore, exhibited the highest fluorescent intensities in winter but weakest in summer. The lower humification index (HIX) in MSOC reflects that humic-like chromophores were preferentially water-soluble, in coordination with high degree of photo-oxidation and aromaticity. Fluorescence index (FI) of BrC was also higher in winter because of the effects of photo-bleaching, whereas biological index (BIX) remained stable throughout a year. Considering the correlation between primary organic carbon (POC) and secondary organic carbon (SOC), aside from the contribution of primary emissions, secondary formation has become another major source to atmospheric BrC in Nanjing.