Regime shift in secondary inorganic aerosol formation and nitrogen deposition in the rural US

Secondary inorganic aerosols (SIA) play an important role in air pollution and climate change, and their formation modulates atmospheric deposition of reactive nitrogen (Nr; including oxidized and reduced nitrogen), impacting the nitrogen cycle. Large-scale and long-term analyses of SIA formation based on model simulations have significant uncertainties. Here, we improve constraints on SIA formation using decade-long in-situ observations of aerosol composition and gaseous precursors from multiple monitoring networks across the US. We reveal a shift in the formation regime of SIA in the rural US between 2011 – 2020, making rural areas less sensitive to changes in ammonia (NH3) concentrations and shortening the effective atmospheric lifetime of reduced forms of Nr. This leads to potential increases in Nr deposition near NH3 emission hotspots, with ecosystem impacts warranting further investigation. NH3, a critical but not directly regulated precursor of fine particulate matter (PM2.5) in ..., This dataset contains the following data:
1. Integrated observations from several aerosol composition and gaseous precursor monitoring networks and meteorological stations between 2011 and 2020. Observations of the chemical composition and gaseous precursors of aerosols are from: 1) the Clean Air Status and Trends Network (CASTNET), the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, the US Environmental Protection Agency’s (EPA’s) PM2.5 Chemical Speciation Monitoring Network (CSN), and the Ammonia Monitoring Network (AMoN). Meteorological observations are from the NOAA Integrated Surface Database (ISD).

To integrate the monitoring networks, we first identify the spatial window for collocation determination by comparing observations from CASTNET, IMPROVE, and EPA CSN sites as well as temperature (T) and relative humidity (RH) observations from CASTNET and ISD located within 10, 25, 50, and 100 km of each other. For aerosol observations, no significant differe..., , # Regime Shift in Atmospheric Secondary Inorganic Aerosol Formation in the Rural United States

[https://doi.org/10.5061/dryad.zpc866tg3](https://doi.org/10.5061/dryad.zpc866tg3)

## Versioning

* Version 2 (19 Mar 2024) contains additional files, 12 & 13.

## Data files and description

This dataset contains the following data:

1\. Integrated observations from several aerosol composition and gaseous precursor monitoring networks and meteorological stations between 2011 and 2020. Observations of the chemical composition and gaseous precursors of aerosols are from: 1) the Clean Air Status and Trends Network (CASTNET), the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, the US Environmental Protection Agency’s (EPA’s) PM2.5 Chemical Speciation Monitoring Network (CSN), and the Ammonia Monitoring Network (AMoN). Meteorological observations are from the NOAA Integrated Surface Database (ISD) and North American Regional Reanalysis (NARR) data.

To integrate ...