Transport and mixing patterns over Central California during the carbonaceous aerosol and radiative effects study (CARES)

Abstract

Abstract. We describe the synoptic and regional-scale meteorological conditions that affected the transport and mixing of trace gases and aerosols in the vicinity of Sacramento, California during June 2010 when the Carbonaceous Aerosol and Radiative Effects Study (CARES) was conducted. The meteorological measurements collected by various instruments deployed during the campaign and the performance of the chemistry version of the Weather Research and Forecasting model (WRF-Chem) are both discussed. WRF-Chem was run daily during the campaign to forecast the spatial and temporal variation of carbon monoxide emitted from 20 anthropogenic source regions in California to guide aircraft sampling. The model is shown to reproduce the overall circulations and boundary-layer characteristics in the region, although errors in the upslope wind speed and boundary-layer depth contribute to differences in the observed and simulated carbon monoxide. Thermally-driven upslope flows that transported pollutants from Sacramento over the foothills of the Sierra Nevada occurred every afternoon, except during three periods when the passage of mid-tropospheric troughs disrupted the regional-scale flow patterns. The meteorological conditions after the passage of the third trough were the most favorable for photochemistry and likely formation of secondary organic aerosols. Meteorological measurements and model forecasts indicate that the Sacramento pollutant plume was likely transported over a downwind site that collected trace gas and aerosol measurements during 23 time periods; however, direct transport occurred during only eight of these periods. The model also showed that emissions from the San Francisco Bay area transported by intrusions of marine air contributed a large fraction of the carbon monoxide in the vicinity of Sacramento, suggesting that this source likely affects local chemistry. Contributions from other sources of pollutants, such as those in the Sacramento Valley and San Joaquin Valley, were relatively low. Aerosol layering in the free troposphere was observed during the morning by an airborne Lidar. WRF-Chem forecasts showed that mountain venting processes contributed to aged pollutants aloft in the valley atmosphere that are then entrained into the growing boundary layer the subsequent day.

Characterization of submicron particles influenced by mixed biogenic and anthropogenic emissions using high-resolution aerosol mass spectrometry: results from CARES

“…During summer, Cool is influenced by highly consistent winds bringing urban outflow from Sacramento during the afternoon (Dillon et al, 2002). A complete description of the meteorological conditions during the CARES is given by Fast et al (2012). In summary, the meteorological conditions were spring like, with high temperatures on average 27 • C during the day and 14 • C in the night (Fig.…”

“…Finally, another air mass was brought to the T1 site during the night, when the decrease of the temperature reversed the wind direction and favored downslope flows from the western Sierra Nevada back to the Sacramento Valley. These different periods determined by model predictions and given by Fast et al (2012) were slightly refined in the present study using wind data recorded at T1 and the results of the PMF analysis, which identified among others an oxygenated organic aerosol (OOA) component resulting from urban transport (see Sect. 3.2).…”

“…The aim of this field campaign was to better understand the evolution and ageing of carbonaceous aerosols in a region influenced by mixed anthropogenic and biogenic precursors, and to integrate this knowledge into models used for simulating their direct and indirect radiative effects on climate Fast et al, 2012). Measurements were conducted at two ground-based sites: one within the Sacramento urban area (denoted T0 to represent the urban emission origin of the project) and one at Cool, CA (denoted T1 to represent a rural receptor site located ∼40 km northeast of Sacramento, i.e., downwind from T0).…”

Impact of natural and anthropogenic aerosols on stratocumulus and precipitation in the Southeast Pacific: a regional modelling study using WRF-Chem

“…WRF-Chem has been used in a wide range of applications including air quality, aerosol-cloud-precipitation studies, and regional climate (e.g., Fast et al, 2012;Gao et al, 2011;Qian et al, 2009;Zhang et al, 2010). Q. and Saide et al (2012) evaluated WRF-Chem simulations of aerosols, clouds, precipitation, and their interactions over the SEP during VOCALS-REx using extensive measurements from the field campaign and satellite retrievals.…”

Using spectral methods to obtain particle size information from optical data: applications to measurements from CARES 2010

“…In this work, measurements of aerosol optical properties (extinction, scattering and absorption coefficients) made at multiple wavelengths during the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES; Fast et al, 2012;Zaveri et al, 2012) are reported and analyzed using the O'Neill et al (2003O'Neill et al ( , 2008b methods. The measurements were made at two locations near Sacramento: a more urban site in Granite Bay, CA (T0), and a more rural site in Cool, CA (T1), that were often linked by direct atmospheric transport.…”