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Modeling NH 4 NO 3 Over the San Joaquin Valley During the 2013 DISCOVER‐AQ Campaign
Author(s) -
Kelly James T.,
Parworth Caroline L.,
Zhang Qi,
Miller David J.,
Sun Kang,
Zondlo Mark A.,
Baker Kirk R.,
Wisthaler Armin,
Nowak John B.,
Pusede Sally E.,
Cohen Ronald C.,
Weinheimer Andrew J.,
Beyersdorf Andreas J.,
Tonnesen Gail S.,
Bash Jesse O.,
Valin Luke C.,
Crawford James H.,
Fried Alan,
Walega James G.
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd028290
Subject(s) - san joaquin , cmaq , environmental science , air quality index , atmospheric sciences , relative humidity , particulates , nitrate , aerosol , meteorology , climatology , chemistry , geography , soil science , organic chemistry , geology
The San Joaquin Valley (SJV) of California experiences high concentrations of particulate matter NH 4 NO 3 during episodes of meteorological stagnation in winter. A rich data set of observations related to NH 4 NO 3 formation was acquired during multiple periods of elevated NH 4 NO 3 during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER‐AQ) field campaign in SJV in January and February 2013. Here NH 4 NO 3 is simulated during the SJV DISCOVER‐AQ study period with the Community Multiscale Air Quality (CMAQ) model, diagnostic model evaluation is performed using the DISCOVER‐AQ data set, and integrated reaction rate analysis is used to quantify HNO 3 production rates. Simulated NO 3 − generally agrees well with routine monitoring of 24‐hr average NO 3 − , but comparisons with hourly average NO 3 − measurements in Fresno revealed differences at higher time resolution. Predictions of gas‐particle partitioning of total nitrate (HNO 3 + NO 3 − ) and NHx (NH 3 + NH 4 + ) generally agree well with measurements in Fresno, although partitioning of total nitrate to HNO 3 is sometimes overestimated at low relative humidity in afternoon. Gas‐particle partitioning results indicate that NH 4 NO 3 formation is limited by HNO 3 availability in both the model and ambient. NH 3 mixing ratios are underestimated, particularly in areas with large agricultural activity, and additional work on the spatial allocation of NH 3 emissions is warranted. During a period of elevated NH 4 NO 3 , the model predicted that the OH + NO 2 pathway contributed 46% to total HNO 3 production in SJV and the N 2 O 5 heterogeneous hydrolysis pathway contributed 54%. The relative importance of the OH + NO 2 pathway for HNO 3 production is predicted to increase as NOx emissions decrease.