Project at a Glance

Title: Nighttime chemistry: observations of NO3 and N2O5.

Principal Investigator / Author(s): Ronald C. Cohen

Contractor: UC Berkeley

Contract Number: 04-335

Research Program Area: Atmospheric Processes

Topic Areas: Chemistry & Reactivity, Modeling


Ammonium nitrate is a key component of the composite particulate matter of aerodynamic size 2.5 micrometers and less (PM2.5). Nighttime chemical reactions between nitrates (from ozone and NO_2 photochemistry) and nitrogen dioxide (from direct emissions and NO photochemistry) form N_2 O_5 and further reactions produce nitric acid. Nitric acid combined with ammonia to form ammonium nitrate that essentially removes emitted nitrogen oxides (NO_X meaning NO and NO_2 ) species from the troposphere. However, N_2 O_5 may also dissociate forming NO_2 , and NO_2 would continue to participate in nighttime aerosol reactions. At the start of this project, there were no current field measurements for nighttime N_2 O_5 and nitric acid (HNO_3 ) that would reliably support Californiaís PM2.5 simulations. These simulations are the regulatory tools for compliance demonstration required for PM2.5 and other PM California (state) implementation plans (SIP). As part of this project UC Berkeley staff upgraded the prototype laser induced fluorescence (LIF) instrument that has successfully measured ambient concentrations of nitric acid and N_2 O_5 to reach 15 to 25 parts per trillion volume (pptV) sensitivity required for a robust simulation validation data set. UC Berkeley staff conducted two biweekly measurement campaigns at Blodgett Forest station and at a farm near Bakersfield. The data produced as a result of this project can serve as inputs and as validation tools for PM simulations. These measurements improve ARBís PM modeling efforts and thus improve the SIPs based on PM modeling.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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