Dataset: Western Pacific Cruise Data

For the aerosol samples, we measured the concentrations of aerosol particulate OC (POC), total nitrogen (TN), and carbon isotope (13C and 14C) compositions of aerosol OC. All measurements were conducted at the Center for Isotope Geochemistry and Geochronology (CIGG) at the Qingdao National Laboratory for Marine Science and
Technology (QNLM) in Qingdao, China. For atmospheric POC measurements, a cut piece of filter containing particles was acidified first with 10% high-purity HCl to remove inorganic carbon and then dried at 50 °C. Concentrations of POC and TN were measured using an elemental analyzer (Elementar vario Isotope select) with analytical standard deviations of ±0.03% for OC, and ±0.04% for TN (n = 6). The δ13C values of POC were measured using a Thermo Delta V advantage isotope ratio mass spectrometer coupled with an Elemental Analyzer-IsoLink CN. Values of δ13C were reported in ‰ relative to 13C standards (IAEA-CH-3, cellulose, and IAEA-600 caffeine), and the analytic precision was ≤0.2‰ (n = 10). For POC 14C measurements, the pretreated flters were placed separately in double quartz tubes (precombusted at 850 °C for 2 h) with CuO and Ag wires added. The tubes were then evacuated on a vacuum line, flame sealed, and combusted at 850 °C for 2 h (Druffel et al., 1992). CO2 resulting from POC oxidation was collected cryogenically and quantifed monometrically on a vacuum line. The purified CO2 was converted to graphite using the closed tube iron reduction method (Xu et al., 2007; Walker et al., 2019) and 14C was measured by accelerator mass spectrometry (AMS, NEC 0.5MV XCAMS). Δ14C results were reported, and conventional radiocarbon ages [years before present (BP)] were calculated based on the study by Stuiver and Polach (1977).

Nitrogen (15N /14N) and oxygen (18O /16O) isotope analyses of nitrate were conducted at the Department of Earth, Environmental, and Planetary Sciences at Brown University in Providence, RI (USA). After the frozen samples were received at Brown University, a 5 × 5 cm square was cut from the center of the filter at room temperature and extracted in a pre-cleaned bottle with ~100 mL of MQ water (exact amounts were recorded via weight) and then sonicated for 1 h. After sonication, the filters were removed, and the samples were frozen at -20 ◦C until further analyses.

The denitrifier method (Casciotti et al., 2002; Sigman et al., 2001) was used to complete nitrate (15N /14N) and oxygen (18O /16O) isotope analyses via nitrous oxide on a continuous flow isotope ratio mass spectrometer. Values were reported in ‰ relative to standards.

Instruments:

Portable aerosol particle samplers: aerosol samples were collected with portable aerosol particle samplers (model 2030, Qingdao Laoying Environmental Technology Co.) with a filter size of 9 cm O.D.

Elemental analyzer: the concentrations of POC and TN were measured using an elemental analyzer (Elementar vario Isotope select).

Thermo Delta V mass spectrometer: the δ13C values of POC were measured using a Therm Delta V advantage isotope ratio mass spectrometer coupled with an Elemental Analyzer-IsoLink CN.

Thermo Delta V Plus Isotope Ratio Mass Spectrometer: used in continuous flow mode for ammonium, nitrate, and oxygen isotope analyses.

Accelerator mass spectrometry: the Δ14C values of POC were measured by accelerator mass spectrometry (AMS, NEC 0.5MV XCAMS).