Characterization of Air Toxics and Greenhouse Gas Emission Sources and Their Impacts on Community-Scale Air Quality Levels in Disadvantaged Communities

Rapport, 2021

Methane (CH4) is an important short-lived climate pollutant and contributes roughly 9 percent to California's statewide GHG emissions. California has passed several climate legislations, including AB 1383 (Lara, 2015-16) and AB 1496 (Thurmond, 2015-16), which require CARB to use the best available scientific and technical methods to monitor and measure high-emission CH4 hotspots within the State, to use the information to update relevant programs and policies, and to implement a climate mitigation program to reduce statewide CH4 emissions by 40 percent below the 2013 levels. Furthermore, certain industrial emissions sources of CH4, such as oil and gas facilities, are known to co-emit air toxics that have adverse health effects, and their impacts are more pronounced in communities near those sources than they are regionally. Therefore, it is important to understand these emissions, and conduct enhanced community-scale monitoring for air toxics in near-source communities, many of which may be disadvantaged. Additionally, scientific studies have suggested that national and statewide CH4 emissions inventories may be underestimated, and real-world emissions measurements may be useful to evaluate source-level emission estimates and understand emission behaviors.

The objectives of this research study are to characterize air toxics and GHG emission behavior from a variety of complex emission sources, and to study the impact of these sources on air quality levels in disadvantaged communities. The project utilized a state-of-the-art research-grade mobile monitoring laboratory equipped with advanced monitoring instruments to characterize and quantify the air toxics and GHG emission behavior from complex air pollution sources, as well as their air pollution impacts on nearby communities. Through four regional campaigns across California, the project measured facility-level emissions of CH4, alkanes, benzene, BTEX (benzene, toluene, ethylbenzene and xylene), ammonia (NH3), and sulfur and nitrogen oxides (SOX and NOX) from a variety of sources, including refineries, petrochemical facilities, oil storage, port activities, landfills, oil and gas production and dairy farms, and tracked the air pollution impact of the emission plumes in neighboring communities.

This study found that the observed emissions, which are representative of emissions at a single point in time, were greater than inventory factors and models, representative of overall averages, for many of the volatile organic compounds (VOC). Alkane emissions from five large refinery areas in the Bay Area were on average 2.5 times the reported emission, and CH4 emissions were roughly 3 times the reported emissions, while total NOX emissions were comparable to the inventory estimates. Similarly, alkane and CH4 emissions from oil and gas fields in the San Joaquin Valley, which accounts for more than 70 percent of California's oil and gas production capacity, were 10 and 2 times higher than production-based emission factors, respectively. On the other hand, CH4 and NH3 emissions from roughly 20 dairy farms were 50 percent and 100 percent higher than annual emission factor, respectively, some of which were due to diurnal variations. These discrepancies suggest more work is needed to ascertain whether these point-in-time measurements are representative of annual averages, and if emissions are indeed higher than standard methods suggest. The measurements in the Richmond community showed VOC concentrations dominated by alkanes from the port area. Community-scale ground-level concentrations of BTEX were on average low in all studies.

The research study demonstrated the use of advanced techniques for facility-wide emission measurements and community monitoring of air toxics, and suggests that a combination of mobile and fixed continuous measurements may provide useful information to understand source emissions, and their impacts on communities. The source-level emission data may be useful to understand emissions from complex emission sources (including large point sources, distributed emission sources, area sources). The community-scale measurement effort will provide the ability to conduct community-scale air toxics measurements in real-time, with information on air pollution hotspots in various disadvantaged communities and useful screening information to identify potential sources for prioritizing air pollution mitigation efforts. 

https://ww3.arb.ca.gov/research/single-project.php?row_id=67028