AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Role of Emissions Controls on Aerosol pH over a Decade (2001-2011) in the United States
PETROS VASILAKOS, Armistead G. Russell, Athanasios Nenes, Georgia Institute of Technology
Abstract Number: 176 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Emission controls, particularly on SO2, have long been thought to lead to an increase in the aerosol pH (West et al. 1999). However, despite these controls, recent studies have highlighted the highly acidic nature of aerosol in the present day Southeast United States (Guo et al. 2015), which, in spite the reduction in sulfate, has maintained a relatively constant, acidic pH over time (Weber et al. 2016). The constant pH has been attributed to the buffering effect of ammonia that retains the pH in the SE US between 0 and 2 (Weber et al. 2016). In contrast to SO2 emissions which are projected to be reduced even further, ammonia emissions from livestock and fertilizers are expected to remain constant or even increase in the future.
In this work, we use a version of CMAQ with extended isoprene chemistry (Pye et al. 2013) and updated model parameters (Vasilakos et al. 2016), to simulate pH over the entire US for the years 2001 and 2011. Simulations will be carried out on a 36x36 km grid covering the entire US, using meteorology from the Weather Research and Forecasting (WRF) model. Biogenic emissions and land use will be provided from the Biogenic Emissions Inventory System version 3.6 (BEIS3.6) using Biogenic Emissions Landuse Database (BELD 4) inputs. Sensitivity studies quantify the importance of pH prediction errors for fine mode ammonium, nitrate and gas-phase counterparts ammonia and nitric acid. Predicted pH fields are evaluated against observations collected from ground-based and airborne field studies, to establish whether simulations are predisposed for under/overpredict of semi-volatile acidic inorganic species. The role of nonvolatile alkaline cations from dust and seasalt and their (potentially) disproportionately strong impact on nitrate partitioning, is presented. We conclude by presenting the importance of pH modulations for reactive N deposition fluxes.