Dataset: Aerosol composition data of ion concentrations (ammonium, nitrate, nitrite, sodium, chloride, magnesium, calcium, potassium, sulfate), and ammonium isotope (15N) of atmospheric particulates collected on Oahu, Hawaii from March 2021 to June 2022

Aerosol sampling was conducted from March 24, 2021 to June 30, 2022. A high-volume aerosol sampler operating at 1,200 L min^-1 with 25 × 20 cm filters was used. Aerosol samples were for seven days for each filter, with a total of 66 samples collected.

We measured for ammonium isotopes (¹⁵N), and a suite of ion concentrations (calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), and potassium (K⁺), Chloride (Cl^-) and sulfate (SO₄^2-)). All measurements were conducted at the Department of Earth, Environmental, and Planetary Sciences at Brown University in Providence, RI (USA).

The filter was extracted in a pre-cleaned bottle with ~30 mL of MQ water (exact amounts were recorded via weight) and sonicated for 1 h. After sonication, the solutions were filtered via a vacuum pumped. Samples were frozen then at -20 ◦C until further analyses.

 The concentration of ammonium, nitrate, and nitrite were determined colorimetrically (indophenol blue) using a discrete UV–Vis analyzer (Westco Smartchem 200). U.S. EPA Compliant Methods 350.1 (O’Dell, 1993), 353.2 (Revision 2.0), and 354.1 were followed for ammonium, nitrate, and nitrite, respectively. Standard lab protocols were followed, including calibration to standards as well as blanks and in-house quality control measurements.

The azide method (Zhang et al., 2007) was used to complete ammonium (¹⁵N /¹⁴N) isotope analyses on a continuous flow isotope ratio mass spectrometer. Values were reported in ‰ relative to standards (IAEA-N₂ and USGS-25).

Concentrations of calcium, magnesium, sodium, potassium, chloride, and sulfate were measured on an Ion Chromatography (IC) instrument (Dionex Integrion HPIC) using suppressed conductivity detection. Anions were determined using a Dionex AS19-4 μm guard (4 × 50 mm) and analytical column (4× 250 mm) with 20 mM KOH as eluent with a flow rate of 1 mL min^-1. Cations were analyzed using a Dionex CS-16 guard column (5 × 50 mm) analytical column (5 × 250 mm). Eluent of 30 mM methane sulfonic acid was used to detect cations with a pump flow rate of 1 mL min⁻¹. All samples were filtered with 0.20-μm filters before being analyzed. In-house quality control standards were run approximately every six samples.