Mobile Platforms for Continuous Spatial Measurements of Urban Trace Gases and Criteria Pollutants
Surface-based observations of atmospheric trace gases and criteria pollutants provide critical data on how emissions and pollutant concentrations vary over time. However, traditional stationary measurement sites only quantify concentrations at a single point in space, limiting our ability to understand spatial patterns. Using trace gas instrumentation capable of making continuous high-frequency (~1s) measurements, we have developed mobile platforms to complement stationary observation sites in order to better constrain the heterogeneity and complexities of urban emissions. These compact trace gas and criteria pollutant measurement systems are capable of precisely measuring CO2, CH4 PM2.5, O3, NOx, and several meteorological parameters on TRAX, Salt Lake City’s light-rail system (TRAX), and in a van-based mobile laboratory. Using case study observations, we discuss mobile measurement methodologies and the practical applications of mobile trace gas sampling platforms.
High-frequency trace gas and criteria pollutant measurements take place continuously on TRAX and semi-continuously during research campaigns using the Nerdmobile. TRAX houses a Los Gatos Research (LGR) Ultraportable GGA (CO2, CH4), a 2B Technologies 205 (O3), Met One E-Sampler (PM2.5), a suite of meteorological measurements including temperature, pressure, and relative humidity, and a GRIMM 1.109 during relevant studies (PM2.5, particle size distributions). These instruments are interfaced via RS232 to a Raspberry Pi, which serves as a central brain by controlling instruments and calibration systems as well as acting as a datalogger for over 70 simultaneously measured variables. The LGR, known to be exceptionally linear in both CO2 and CH4 space, is calibrated hourly against a single reference gas. Other measurements are calibrated on a seasonal basis.
The Nerdmobile houses two Picarro CRDS (CO2/CO, CO2/CH4), a 2B Technologies 205 (O3), a 2B Technologies 410/401 (NOx), a GRIMM 1.109 (PM2.5, particle size distributions), and a system for filling flasks for isotopic analysis. Similarly to TRAX, these instruments are interfaced via RS232 to an Intel NUC which logs over 60 simultaneously measured variables. Due to the importance of feedback for technicians operating the Nerdmobile, the Intel NUC wirelessly hosts a wireless real-time dashboard to a provided iPad as an app or most other internet-capable devices as a webpage. The wireless dashboard allows the operator to control onboard valves and pumps, take geolocated notes and flask observations, access in-depth documentation for diagnosing problems with instruments or control systems, and monitor any of the incoming variables from the six instruments in real-time.
A Spatial and Temporal Comparison of Highly-resolved Modeled Emissions of Carbon Dioxide, and Criteria Pollutants in Salt Lake City, Utah
Hestia 0.002deg Carbon Emissons
This study addresses the need for robust highly-resolved emissions and concentration data required for planning purposes and policy development aimed at managing pollutant sources. Adverse health effects resulting from urban pollution exposure are dependent on proximity to emission sources and atmospheric mixing, necessitating models with high spatial and temporal resolution. As urban emission sources co-emit carbon dioxide (CO2) and criteria pollutants (CAPs), efforts to reduce specific pollutants would synergistically reduce others. We present emissions inventories and modeled concentrations for CO2 and CAPs: carbon monoxide (CO), lead (Pb), nitrogen oxides (NOx), particulate matter (PM2.5 and PM10), and sulfur oxides (SOx) for Salt Lake County, Utah. We compare the resulting concentrations against stationary and mobile measurement data and present a systematic quantification of uncertainties.
The emissions inventory for CO2 is based on the Hestia emissions data inventory that resolves emissions at an hourly, building and road link resolution as well as hourly gridded emissions with a 0.002 x 0.002 deg spatial resolution. Two methods for deriving criteria pollutant emission inventories were compared. One was constructed using methods similar to Hestia but downscales total emissions based on the 2011 National Emissions Inventory (NEI). The other used Emission Modeling Clearinghouse spatial and temporal surrogates to downscale the NEI data from annual and county-level resolution to hourly and 0.002 x 0.002 deg grid cells. The gridded emissions from both criteria pollutant methods were compared against the Hestia CO2 gridded data to characterize spatial similarities and differences between them. Correlations were calculated at multiple scales of aggregation.
The CALPUFF dispersion model was used to transport emissions and estimate air pollutant concentrations at an hourly 0.002 x 0.002 deg resolution. The resulting concentrations were spatially compared in the same manner as the emissions. Modeled results were compared against stationary measurements and from equipment mounted atop a light rail car in the Salt Lake City area. The comparison between both approaches to emissions estimation and resulting concentrations highlights spatial locations and hours of high variability and uncertainty.