03 May 2023
 | 03 May 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Development and evaluation of processes affecting simulation of diel fine particulate matter variation in the GEOS-Chem model

Yanshun Li, Randall V. Martin, Chi Li, Brian L. Boys, Aaron van Donkelaar, Jun Meng, and Jeffrey R. Pierce

Abstract. The capability of chemical transport models to represent fine particulate matter (PM2.5) over the course of a day is of vital importance for air quality simulation and assessment. In this work, we used the nested GEOS-Chem model at 0.25° × 0.3125° resolution to simulate the diel (24 h) variation in PM2.5 mass concentrations over the United States (US) in 2016. We evaluate the simulations with in situ measurements from a national monitoring network. Our base case simulation broadly reproduces the observed morning peak, afternoon dip and evening peak of PM2.5, matching the timings of these features within 1–3 hours. However, the simulated PM2.5 diel amplitude in our base case was 105 % biased high relative to observations. We find that temporal resolution of emissions, differences in vertical representativeness between model and observations, as well as boundary layer mixing are the major causes for this inconsistency. We applied an hourly anthropogenic emission inventory and converted the PM2.5 masses from model level center to the height of surface measurements by correcting for aerodynamic resistance. The biases in the PM2.5 diel amplitude were reduced to 25 % in the improved simulation and the timing of diel variations were better captured. In addition, notable sensitivity of the simulated diel amplitude of PM2.5 (8 %) on the boundary layer height in the driving met fields were identified. Based on the improved model, we find that the diel variation in PM2.5 is driven by 1) building up of PM2.5 in early morning due to increasing anthropogenic emissions into a shallow mixed layer, 2) decreasing PM2.5 from mid-morning through afternoon associated with mixed layer growth, 3) increasing PM2.5 from mid-afternoon though evening as emissions persist into a collapsing mixed layer, and 4) decreasing PM2.5 overnight as emissions diminish.

Yanshun Li et al.

Status: open (until 14 Jun 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-704', Anonymous Referee #1, 01 Jun 2023 reply
  • RC2: 'Comment on egusphere-2023-704', Anonymous Referee #2, 06 Jun 2023 reply

Yanshun Li et al.


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Short summary
We developed and evaluated processes affecting within-day (diel) variability in fine particulate matter (PM2.5) concentrations in a chemical transport model (GEOS-Chem) over the US. We find that diel variability in PM2.5 is driven by 1) early morning accumulation into a shallow mixed layer, 2) decreases from mid-morning through afternoon with mixed-layer growth, 3) increases from mid-afternoon through evening as the mixed-layer collapses, and 4) decreases overnight as emissions decrease.