Wintertime particulate pollution episodes in an urban valley of the Western US: a case study

Abstract

This study investigates the causes of elevated PM<sub>2.5</sub> episodes and potential exceedences of the US National Ambient Air Quality Standards (NAAQS) in Truckee Meadows, Nevada, an urban valley of the Western US, during winter 2009/2010, an unusually cold and snowy winter. Continuous PM<sub>2.5</sub> mass and time-integrated chemical speciation data were acquired from a central valley monitoring site, along with meteorological measurements from nearby sites. All nine days with PM<sub>2.5</sub> > 35 μg m<sup>−3</sup> showed 24-h average temperature inversion of 1.5–4.5 °C and snow cover of 8–18 cm. Stagnant atmospheric conditions limited wind ventilation while highly reflective snow cover reduced daytime surface heating creating persistent inversion. Elevated ammonium nitrate (NH<sub>4</sub>NO<sub>3</sub>) and water associated with it are found to be main reasons for the PM<sub>2.5</sub> exceedances. An effective-variance chemical mass balance (EV-CMB) receptor model using locally-derived geological profiles and inorganic/organic markers confirmed secondary NH<sub>4</sub>NO<sub>3</sub> (27–37%), residential wood combustion (RWC; 11–51%), and diesel engine exhaust (7–22%) as the dominant PM<sub>2.5</sub> contributors. Paved road dust and de-icing materials were minor, but detectable contributors. RWC is a more important source than diesel for organic carbon (OC), but vice versa for elemental carbon (EC). A majority of secondary NH<sub>4</sub>NO<sub>3</sub> is also attributed to RWC and diesel engines (including snow removal equipment) through oxides of nitrogen (NO<sub>x</sub>) emissions from these sources. Findings from this study may apply to similar situations experienced by other urban valleys

Airborne and ground-based observations of ammonium-nitrate-dominated aerosols in a shallow boundary layer during intense winter pollution episodes in northern Utah

“…Previous studies carried out in wintertime in San Joaquin Valley (CA) highlighted the critical role of nocturnal chemical production of nitrate aloft in the residual layer (i.e., that region decoupled from the stable nocturnal boundary layer influenced by previous-day surface emissions). Those studies suggested that nighttime nitrate formation within the residual layer was a major contributor to surface-level PM 2.5 concentrations (Watson et al, 2002;Chow et al, 2006;Lurmann et al, 2006;Prabhakar et al, 2017). Studies in other regions of the US have reached similar conclusions regarding the role of nighttime processing aloft as a source of winter soluble nitrate (Stanier et al, 2012;Kim et al, 2014).…”

“…A simulated 50 % decrease in total ammonium leads to a 36 ± 17 % µg m −3 decrease in total PM 1 mass, over the entire area of the study. Despite some differences among locations, our results showed a higher sensitivity to decreasing nitric acid concentrations and the importance of ammonia at the lowest total 1 Introduction Intense wintertime air pollution from particulate matter affects numerous locations in the United States (Chen et al, 2012;Lurmann et al, 2006) and around the world (Bessagnet et al, 2005;Gwaze et al, 2007;Petetin et al, 2016, Ricciardelli et al, 2017Wang et al, 2014). In the US, pollution from fine particles (PM 2.5 ) has been decreasing in the past decades.…”

Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT): Overview of a wintertime air chemistry field study in the front range urban corridor of Colorado

“…Although a number of important issues are specific to polluted wintertime environments, detailed wintertime intensive field studies are less common. Accumulation of aerosol mass in excess of National Ambient Air Quality Standards (NAAQS, currently 35 µg m –3 for PM 2.5, particulate matter (PM) less than 2.5 µm diameter, 24 h average), particularly ammonium nitrate aerosols, tends to be a winter phenomenon due to the temperature‐dependent phase partitioning of nitric acid and ammonia [ Chen et al ., ; Chen et al ., ; Fischer and Talbot , ; Katzman et al ., ; Mathur et al ., ; Schaap et al ., ; Stanier et al ., ; Tolocka et al ., ; Yu et al ., ]. Air quality models often fail to accurately predict nitrate aerosol, due to the complexity of both the chemistry and the shallow boundary layers typically associated with these episodes.…”

Estimation of the direct and indirect impacts of fireworks on the physicochemical characteristics of atmospheric PM<sub>10</sub> and PM<sub>2.5</sub>

“…Chemical mass balance is also a widely used receptor model for cases in which the number and profiles of sources are available (Watson et al, 1984;Chen et al, 2012). Similar to PMF, the CMB can be described as…”