Sensitivity of Nitrate Aerosol Production to Vehicular Emissions in an Urban Street

Minjoong J Kim

doi:10.3390/atmos10040212

Abstract

This study investigated the sensitivity of nitrate aerosols to vehicular emissions in urban streets using a coupled computational fluid dynamics (CFD)–chemistry model. Nitrate concentrations were highest at the street surface level following NH3 emissions from vehicles, indicating that ammonium nitrate formation occurs under NH3-limited conditions in street canyons. Sensitivity simulations revealed that the nitrate concentration has no clear relationship with the NOx emission rate, showing nitrate changes of only 2% across among 16 time differences in NOx emissions. NOx emissions show a conflicting effect on nitrate production via decreasing O3 and increasing NO2 concentrations under a volatile organic compound (VOC)-limited regime for O3 production. The sensitivity simulations also show that nitrate aerosol is proportional to vehicular VOC and NH3 emissions in the street canyon. Changes of VOC emissions affect the nitrate aerosol and HNO3 concentrations through changes in the O3 concentration under a VOC-limited regime for O3 production. Nitrate aerosol concentration is influenced by vehicular NH3 emissions, which produce ammonium nitrate effectively under an NH3-limited regime for nitrate production. This research suggests that, when vehicular emissions are dominant in winter, the control of vehicular VOC and NH3 emissions might be a more effective way to degrade PM2.5 problems than the control of NOx.

Highlights

Nitrate aerosol is a fine particulate matter (PM2.5 ) component produced from the reaction of gas-phase nitrate and ammonia (NH3 )
HNO3 to nitrate aerosol (Figure 7b). These results suggest that the production of ammonium nitrate is proportional to NH3 emissions, indicating that higher NH3 emissions induce a higher conversion reduced by the low concentration of NH3 under an NH3 -limited regime for nitrate production
Studies rate of HNO3 to nitrate aerosol (Figure 7b). These results suggest that the production of ammonium based on both modeling and observed campaigns have reported that nitrate formation occurs under an nitrate is reduced by the low concentration of NH3 under an NH3-limited regime for nitrate regime based in Easton

Summary

Introduction

Nitrate aerosol is a fine particulate matter (PM2.5 ) component produced from the reaction of gas-phase nitrate (nitric acid; HNO3 ) and ammonia (NH3 ). The production of nitrate aerosol in urban areas is affected by vehicular emissions such as nitrogen oxides (NOx = NO + NO2 ) and NH3 [7,8,9]. These vehicular emissions are highly concentrated and are transported by turbulence from the complex geometry of buildings, causing steep gradients of pollutant concentrations [10,11,12,13]. The sensitivity simulation results reveal what significant factors lead to nitrate aerosol problems in urban streets

Model Description

Simulation Set-Up

Model Validation

Model Sensitivity to Geometry and Speciation of VOC Emissions

Findings

Conclusions