South Coast Air Quality Management Research Articles

Temporal shifts in sources and composition of particulate metals in an environmental justice community: Impacts of continued emission reductions, COVID-19, and wildfires

In this study, we evaluated trends in the composition and source contributions of ambient particulate metals, many of which are toxic air contaminants, in Paramount, California. Paramount is an environmental justice community disproportionately impacted by air pollution from multiple emission sources near sensitive receptors. Concentrations of ambient metals bound to total suspended particulates (TSP) were measured hourly using a Xact 625 ambient metal monitor between 2017 and 2020. The Positive Matrix Factorization (PMF) model identified traffic, industry, and soil dust as major contributors. Results showed that contributions of traffic and soil dust noticeably declined during the COVID-19 lockdown period (March–April 2020) due to reduced human activities but reverted to normal levels within a few months. Industry-related factors, however, dropped significantly during this period and remained low throughout the year. Contributions from industry-related sources in Paramount began declining even before 2020, despite no similar trend in regional levels, implying local emission reductions. These reductions resulted from tariffs, decreased demand, regulatory actions by the South Coast Air Quality Management District, and voluntary controls by local facilities. Consequently, Paramount is experiencing drastically lower levels of metals (up to 80%, depending on the metal and source) from metal-processing facilities and related sources. Moreover, we observed markedly elevated concentrations of several metals (e.g., Ba, Ca, Mn, K, etc.) during the unprecedented September 2020 wildfires that engulfed much of the western US, adding to the limited body of studies on this phenomenon and emphasizing the considerable impact of massive wildfires on ambient levels of particulate metals.

Trends in air toxics cancer risk in Southern California, 1998-2018

Air toxics are an important category of air pollutants that are known to cause adverse health effects, including increased cancer risk. Regulatory efforts at federal, state, and local levels have aimed to decrease air toxics emissions over the past several decades. This study evaluated trends in air toxics cancer risks in Southern California using data from 1998 to 2018. We estimated air toxics cancer risk for each of four iterations of the South Coast Air Quality Management District’s Multiple Air Toxics Exposure Study, which included at least one year of measurements at 10 stations and air toxics modeling for each iteration. Cancer risks were calculated using the measured and modeled air toxics concentrations averaged over a one to two year period and multiplied by the corresponding cancer potency factor and combined exposure factor that accounted for multiple exposure pathways and children’s increased sensitivity to the health effects of air pollution. We examined temporal trends in overall air toxics cancer risks and evaluated changes in the air toxics species that contributed most to cancer risk in the region. Both measurement and modeling results show that air toxics cancer risk in Southern California decreased by more than 80% between 1998 and 2018, including a decrease of about 50% from 2012 to 2018. Diesel particulate matter was the main risk driver, followed by benzene, 1,3-butadiene, and formaldehyde. We found that more densely populated communities showed larger decreases than sparsely populated areas. The substantial decrease in air toxics levels over this 20-year period points to the success of air pollution policies aimed at addressing air toxics emissions and can inform future policy efforts to further reduce air toxics health impacts.

Improved Spatial Resolution in Modeling of Nitrogen Oxide Concentrations in the Los Angeles Basin.

The extent to which emission control technologies and policies have reduced anthropogenic NOx emissions from motor vehicles is large but uncertain. We evaluate a fuel-based emission inventory for southern California during the June 2021 period, coinciding with the Re-Evaluating the Chemistry of Air Pollutants in CAlifornia (RECAP-CA) field campaign. A modified version of the Fuel-based Inventory of Vehicle Emissions (FIVE) is presented, incorporating 1.3 km resolution gridding and a new light-/medium-duty diesel vehicle category. NOx concentrations and weekday-weekend differences were predicted using the WRF-Chem model and evaluated using satellite and aircraft observations. Model performance was similar on weekdays and weekends, indicating appropriate day-of-week scaling of NOx emissions and a reasonable distribution of emissions by sector. Large observed weekend decreases in NOx are mainly due to changes in on-road vehicle emissions. The inventory presented in this study suggests that on-road vehicles were responsible for 55-72% of the NOx emissions in the South Coast Air Basin, compared to the corresponding fraction (43%) in the planning inventory from the South Coast Air Quality Management District. This fuel-based inventory suggests on-road NOx emissions that are 1.5 ± 0.4, 2.8 ± 0.6, and 1.3 ± 0.7 times the reference EMFAC model estimates for on-road gasoline, light- and medium-duty diesel, and heavy-duty diesel, respectively.

149 Keynote: Air Sensor Performance Testing in the AQ-Spec Program

Abstract The Air Quality Sensor Performance Evaluation Center (AQ-SPEC) at the South Coast Air Quality Management District in Southern California was initiated in 2014 as a leading-edge program to gauge the capabilities of low-cost, commercially-available air sensors against reference air monitors. AQ-SPEC is in the unique position of having evaluated over 210 sensors to date, allowing us to provide independent commentary on the overall state of performance of sensors available on the market. The array of testing resources available within AQ-SPEC, as well as the various sensor evaluation methods the program can execute will be covered, including the program’s long-standing field and laboratory evaluation protocols for sensors measuring criteria pollutants. New tools and increased interest in diverse sensor applications have motivated AQ-SPEC’s involvement in, and development of, many innovative sensor testing approaches, including mobile measurement protocols, indoor PM2.5 and CO2 sensor testing protocols, and laboratory evaluation of VOC sensors. The AQ-SPEC program is poised to transition to the latest sensor testing techniques and provide services that enable the comparison of sensors against performance targets.

Towards the Development of a Sensor Educational Toolkit to Support Community and Citizen Science.

As air quality sensors increasingly become commercially available, a deeper consideration of their usability and usefulness is needed to ensure effective application by the public. Much of the research related to sensors has focused on data quality and potential applications. While this information is important, a greater understanding of users’ experience with sensors would provide complementary information. Under a U.S. EPA-funded Science to Achieve Results grant awarded to the South Coast Air Quality Management District in California, titled “Engage, Educate, and Empower California Communities on the Use and Applications of Low-Cost Air Monitoring Sensors”, approximately 400 air quality sensors were deployed with 14 California communities. These communities received sensors and training, and they participated in workshops. Widely varying levels of sensor installation and engagement were observed across the 14 communities. However, despite differences between communities (in terms of participation, demographics, and socioeconomic factors), many participants offered similar feedback on the barriers to sensor use and strategies leading to successful sensor use. Here, we assess sensor use and participant feedback, as well as discuss the development of an educational toolkit titled “Community in Action: A Comprehensive Toolkit on Air Quality Sensors”. This toolkit can be leveraged by future community and citizen science projects to develop networks designed to collect air quality information that can help reduce exposure to and the emissions of pollutants, leading to improved environmental and public health.

Development of a Performance Evaluation Protocol for Air Sensors Deployed on a Google Street View Car

Performance evaluation studies of low-cost sensors (LCS) measuring air pollutants have been conducted by academic and governmental groups for stationary applications. In contrast, evaluation protocols are nonexistent for LCS used in mobile deployments, though LCS are used in this manner by research groups and may be employed to complement regulatory directives for community monitoring. Mobile measurements with LCS are a nascent but growing use-case, and questions of data quality will become increasingly important. The South Coast Air Quality Management District's Air Quality Sensor Performance Evaluation Center has developed the first evaluation protocol in which LCS are compared to reference- or research-grade instruments while deployed on a ground-based mobile platform. LCS are assessed in test scenarios of various degrees of environmental control, ranging from placement in a controlled flow sampling duct to unsheltered mounting on a vehicle rooftop. The testing procedures aim to quantify the performance of LCS and the effects of sensor siting, orientation, and vehicle velocity, the results of which can guide users on appropriate LCS and configurations for their applications. Unexpected performance effects have been revealed through pilot-testing of this evaluation protocol that would likely have not been known from stationary field and laboratory testing.

Responsive high-resolution air quality index mapping using model, regulatory monitor, and sensor data in real-time

Interpolated regulatory monitor measurements that are used to calculate the Air Quality Index (AQI) have low spatial resolution and are less accurate where regulatory monitors are sparsely distributed, especially during episodic events such as wildfires and dust storms. In this paper, an AQI map that is more responsive and accurate than current formulations with 5 km spatial and hourly temporal resolution is constructed for Southern California using interpolated concentration fields. The fine particle mass (PM2.5) fields are calculated by combining regulatory-grade monitored concentrations, low-cost sensor measurements, and Community Multiscale Air Quality Model forecasts, using Residual Kriging (RK) interpolation to account for the uncertainty of each input component. The Ozone fields are calculated by combining regulatory monitor and model forecasted concentrations using RK. The interpolated concentration fields have root mean square interpolation errors (RMSE) of 5.59 µg m−3 (PM2.5) and 6.66 ppb (Ozone), smaller than corresponding RMSE of current inverse distance weighting methods used by the U.S. Environmental Protection Agency AirNOW system, and a previous interpolation method used by the South Coast Air Quality Management District. The inclusion of low-cost sensor measurements makes the AQI more responsive to wildfire events, with a PM2.5 RMSE of 7.73 µg m–3, a significant improvement from the other interpolation methods. The mass of particles with an aerodynamic diameter smaller than 10 micrometers (PM10) calculated using natural neighbor interpolation of the difference, PM10—PM2.5, and carbon monoxide and nitrogen dioxide fields calculated using natural neighbor interpolation, have small but usually not statistically significant reductions of RMSE relative to the other interpolation methods. Quality control and correction procedures applied to the low-cost sensor measurements are described. Display of the blended AQI data on an interactive map in real time provides an important tool for the public to minimize their exposure to poor air quality in one of the most polluted regions in the United States.

Early adopters, firm survival, and environmental policy: dry cleaners in the South Coast Basin of California

This paper examines the relationship between the early adoption of new technologies, the probability of firm survival, and environmental regulations through a case study of dry cleaners in the South Coast Basin of California (SC Basin). Most dry cleaners use machines that use the toxic chemical perchloroethylene (PERC) to clean garments. PERC vapors are emitted into the ambient air during the dry cleaning process and can cause cancer in people who live and work nearby. In 2002, the South Coast Air Quality Management District (AQMD) required all dry cleaners in the region to purchase a costly alternative machine that used a non-toxic cleaning solvent by the year 2020. Using bivariate and multivariate analysis, we found that the timing of the early adoption of non-PERC machines among dry cleaners was optimal, ceteris paribus, and adopting early did not have a negative effect on the probability of surviving.

High time-resolution and time-integrated measurements of particulate metals and elements in an environmental justice community within the Los Angeles Basin: Spatio-temporal trends and source apportionment

Abstract The Los Angeles Basin is home to several environmental justice communities that are disproportionately impacted by localized sources of air pollution. City of Paramount, CA, is one of these communities that encompasses several industrial facilities, including metal-processing and finishing companies, in close proximity to each other as well as to residential neighborhoods and sensitive receptors (e.g., schools and hospitals). Between 2016 and 2019, the South Coast Air Quality Management District conducted an extensive air monitoring campaign in this community to identify and address sources of airborne particulate hexavalent chromium (Cr (VI)) and other toxic metals. Using portable air samplers, 24-hr time-integrated total suspended particulate (TSP) samples were collected every third or sixth day at a total of 49 different locations (including 12 local schools) throughout the city for Cr (VI) analysis. In certain areas, elevated levels of Cr (VI) were initially found; consequently, additional efforts were made to better characterize sources of Cr (VI) and other metals. As part of these efforts, hourly concentrations of 20 metals were also measured continuously over 1.5 years with Xact 625 (Cooper Environmental Services, OR, USA) at two locations within the community. Air monitoring results indicated a substantial reduction in ambient levels of Cr (VI) over time as a result of enforcement actions, rule developments, and voluntary emissions mitigations. Long-term continuous multi-metals measurements provided previously unknown information on the temporal trends of metals and elements, including their diurnal, day-of-the-week, and seasonal variations. The high time-resolution measurements also enabled investigating the impact of exceptional events (e.g., 4th of July fireworks) on the levels of ambient TSP-bound metals. A Positive Matrix Factorization (PMF) source apportionment analysis on the continuous multi-metals data identified five major sources, two of which were associated with the nearby industrial emissions (together accounting for 9.8%–13.8% of total metals concentrations), while the other three were linked with resuspended soil (48.8%–69.8%), brake wear (7.3%–19.1%), and road dust (13.1%–18.3%), all with distinct profiles and temporal variations. Results from this study show how a strategic air monitoring can lead to the discovery of emission sources, and how concurrent inspection and enforcement actions along with voluntary control measures by facilities can result in substantial emission reductions. Highly time-resolved source apportionment results coupled with wind data also provide valuable information on the dynamic variation in source activity and allowed for the identification of the most probable source locations that led to elevated concentrations at the receptor sites.

Field and laboratory performance evaluations of 28 gas-phase air quality sensors by the AQ-SPEC program

As interest in using low-cost sensors continues to grow among members of the public, robust evaluations of commercially available sensors are necessary. Information gained from independent evaluations can help ensure that the sensors selected by individuals or communities meet both user needs and their abilities. Appropriate sensor selection has the potential to ensure the collection of useful and informative data. The AQ-SPEC (Air Quality Sensor Performance Evaluation Center) program at the South Coast Air Quality Management District in California, USA aims at providing thorough characterizations of sensor performance through both field and laboratory evaluations. To date, 28 commercially available gas-phase sensors have been tested and the resulting evaluations have been made available to the public on the program's dedicated website. Here, we present our test methodologies for both lab and field evaluations as well as the evaluation results for the 28 sensors tested (14 devices in total, some containing multiple sensors per device). We also explore the effects of exposure to extreme environmental conditions on sensor performance and their responsiveness to potential interferents in the AQ-SPEC environmental chamber. Overall, the results suggest that there are commercially available sensors, for carbon monoxide (CO) and ozone (O3) are capable of providing useful quantitative and qualitative information when the devices are used “off-the-shelf”, as a member of the public would. Correlations (R2) with reference instruments as high as 0.86 and 0.96 and mean absolute errors as low as 144 ppb and 5.76 ppb were observed for CO and O3 sensor respectively. The results for nitrogen dioxide (NO2) sensors were more varied, one sensor performed well with a correlation and mean absolute error of 0.77 and 5.41 ppb, respectively. Overall, the results indicate a wide range of performances, as well as how these performances vary under different environmental conditions or when exposed to interferent gases, reaffirming the necessity for thorough evaluations and application-dependent sensor selection.

Spatial trends and sources of PM2.5 organic carbon volatility fractions (OCx) across the Los Angeles Basin

In this study, we used the positive matrix factorization (PMF) model to apportion the sources of organic carbon volatility fractions (OCx) as well as total OC concentrations in five different locations across the Los Angeles Basin, including West Long Beach, Anaheim, central Los Angeles (CELA), Rubidoux, and Fontana over the period from July 2012 to June 2013. Total OC as well as OC volatility fractions (OC1-OC4), measured with the thermal-optical analysis as part of the fourth Multiple Air Toxics Exposure Study (MATES IV) by the South Coast Air Quality Management District (SCAQMD), in combination with gaseous and particulate source tracers (such as NOx, O3, particulate sulfate, K+/K ratio, and biomass-burning originated black carbon (BCbb)) were used as inputs to the PMF model. A 3-factor solution, including traffic, secondary organic aerosols (SOA), and biomass burning, was found to be the most physically interpretable solution. Average total OC concentrations showed an upward trend from the sites closer to the coast (i.e., 3.7 ± 1.9 μg m−3 at West Long Beach) to inland downwind sites (i.e., 4.8 ± 1.8 μg m−3 at Fontana), especially in the warm season, suggesting the major impact of SOA formation on total OC concentrations. Source apportionment results indicated that traffic is the dominant contributor to OC2 and OC3 fractions, especially at the sites that are near major primary sources such as CELA and West Long Beach, with corresponding contributions of 60 ± 1.0% and 79 ± 1.7% to OC2 and 53 ± 0.9% and 64 ± 1.3% to OC3, respectively. On the other hand, SOA was found to be the dominant contributor to OC4 fraction, especially at the receptor sites located further inland, with corresponding contributions of 66 ± 1.0% in Rubidoux and 56 ± 0.7% in Fontana. Our results also indicated that traffic is the dominant source of total OC concentrations, with an average contribution of 53 ± 2.4% at all the sites, followed by SOA formation and biomass burning, contributing to 40 ± 1.8% and 7 ± 0.8% of total OC concentrations, respectively. The contribution of traffic and biomass burning to total OC concentrations increased during the cold season, while that of SOA became more significant during the warm season when photochemical activities peak. Results from the present study provided important insight on the sources and spatio-temporal variations of OC volatility fractions as well as total OC concentrations in PM2.5 across the Los Angeles Basin.

Projected changes in particulate matter concentrations in the South Coast Air Basin due to basin-wide reductions in nitrogen oxides, volatile organic compounds, and ammonia emissions

ABSTRACTAn ozone abatement strategy for the South Coast Air Basin (SoCAB) has been proposed by the South Coast Air Quality Management District (SCAQMD) and the California Air Resources Board (ARB). The proposed emissions reduction strategy is focused on the reduction of nitrogen oxide (NOx) emissions by the year 2030. Two high PM2.5 concentration episodes with high ammonium nitrate compositions occurring during September and November 2008 were simulated with the Community Multi-scale Air Quality model (CMAQ). All simulations were made with same meteorological files provided by the SCAQMD to allow them to be more directly compared with their previous modeling studies. Although there was an overall under-prediction bias, the CMAQ simulations were within an overall normalized mean error of 50%; a range that is considered acceptable performance for PM modeling. A range of simulations of these episodes were made to evaluate sensitivity to NOx and ammonia emissions inputs for the future year 2030. It was found that the current ozone control strategy will reduce daily average PM2.5 concentrations. However, the targeted NOx reductions for ozone were not found to be optimal for reducing PM2.5 concentrations. Ammonia emission reductions reduced PM2.5 and this might be considered as part of a PM2.5 control strategy.Implications: The SCAQMD and the ARB have proposed an ozone abatement strategy for the SoCAB that focuses on NOx emission reductions. Their strategy will affect both ozone and PM2.5. Two episodes that occurred during September and November 2008 with high PM2.5 concentrations and high ammonium nitrate composition were selected for simulation with different levels of nitrogen oxide and ammonia emissions for the future year 2030. It was found that the ozone control strategy will reduce maximum daily average PM2.5 concentrations but its effect on PM2.5 concentrations is not optimal.

Future-Year Ozone Isopleths for South Coast, San Joaquin Valley, and Maryland

Many areas of the United States are working toward achieving the 2015 ozone National Ambient Air Quality Standard (NAAQS) attainment level. The objective of this study was to develop future-year (2030) volatile organic compounds and nitrogen oxides (VOC-NOx) isopleth diagrams of the 4th highest maximum daily 8-h average ozone design value concentrations at monitors of interest in the South Coast Air Basin (SoCAB) and San Joaquin Valley (SJV) in California, and in Maryland. The simulation results showed there would be attainment of the 2015 ozone NAAQS in 2030 without further controls at the selected monitors: 27% in SoCAB, 57% in SJV, and 100% in Maryland. The SoCAB ozone isopleths developed in this study were compared with those reported in the South Coast Air Quality Management District 2016 Air Quality Management Plan. There are several differences between the two modeling studies, the results are qualitatively similar for most of the monitors in the relative amounts of additional emission reductions needed to achieve the ozone NAAQS. The results of this study provide insight into designing potential control strategies for ozone attainment in future years for areas currently in non-attainment. Additional photochemical modeling using these strategies can then provide confirmation of the effectiveness of the controls.

Particulate matter emissions and gaseous air toxic pollutants from commercial meat cooking operations

This study assessed the effectiveness of three novel control technologies for particulate matter (PM) and volatile organic compound (VOC) removal from commercial meat cooking operations. All experiments were conducted using standardized procedures at University of California, Riverside's commercial test cooking facility. PM mass emissions collected using South Coast Air Quality Management District (SCAQMD) Method 5.1, as well as a dilution tunnel-based PM method showed statistically significantly reductions for each control technology when compared to baseline testing (i.e., without a catalyst). Overall, particle number emissions decreased with the use of control technologies, with the exception of control technology 2 (CT2), which is a grease removal technology based on boundary layer momentum transfer (BLMT) theory. Particle size distributions were unimodal with CT2 resulting in higher particle number populations at lower particle diameters. Organic carbon was the dominant PM component (>99%) for all experiments. Formaldehyde and acetaldehyde were the most abundant carbonyl compounds and showed reductions with the application of the control technologies. Some reductions in mono-aromatic VOCs were also observed with CT2 and the electrostatic precipitator (ESP) CT3 compared to the baseline testing.

Results of Plug-In Hybrid Medium-Duty Truck Demonstration and Evaluation Program

The Plug-In Hybrid Medium-Duty Truck Demonstration and Evaluation Program was sponsored by the United States Department of Energy (DOE) using American Recovery and Reinvestment Act of 2009 (ARRA) funding as well as the South Coast Air Quality Management District (AQMD). The purpose of the program was to develop a path to mitigate plug-in hybrid vehicle technology to medium-duty vehicles by demonstrating and evaluating in diverse applications. The program allows the fleets to develop interest in the technology. The 62 participants have deployed these vehicles into the field with their operators to achieve real—life experience with the vehicles in 23 different states. A total of 296 vehicles were delivered to the field prior to July 2015. This paper provides the results from the analysis of the data generated by these vehicles.

Do stringent environmental regulations cause firm relocations and job loss? A case study of the wood furniture industry in Southern California

Do stringent environmental regulations cause polluting companies to relocate from a particular region to avoid environmental compliance, resulting in job loss for communities left behind? We investigate this question through a case study of the wood furniture industry in Southern California. Since 1988, the wood furniture industry in the region has been heavily regulated by the South Coast Air Quality Management District (AQMD) due to the emission of volatile organic compounds (VOCs) from coatings applied to furniture. VOCs are a precursor of ozone formation, a major air quality problem facing most urban areas. Using a mix of quantitative and qualitative methods, we found that the regulations caused some firms, particularly larger ones, to relocate after the initial implementation of Rule 1136. However, the industry adjusted to the regulations in the context of other circumstances, including cyclical economic trends, high business costs, the globalisation of the US wood furniture industry, and the emergence of viable low-VOC and water-based coatings. Using a regression model that controls for the business cycle and secular trends, we estimate that job levels in the industry in Southern California are about one-third lower due to AQMD's regulations.

PM2.5 and ultrafine particulate matter emissions from natural gas-fired turbine for power generation

The generation of electricity from natural gas-fired turbines has increased more than 200% since 2003. In 2007 the South Coast Air Quality Management District (SCAQMD) funded a project to identify control strategies and technologies for PM2.5 and ultrafine emissions from natural gas-fired turbine power plants and test at pilot scale advanced PM2.5 technologies to reduce emissions from these gas turbine-based power plants. This prompted a study of the exhaust from new facilities to better understand air pollution in California. To characterize the emissions from new natural gas turbines, a series of tests were performed on a GE LMS100 gas turbine located at the Walnut Creek Energy Park in August 2013. These tests included particulate matter less than 2.5 μm in diameter (PM2.5) and wet chemical tests for SO2/SO3 and NH3, as well as ultrafine (less than 100 nm in diameter) particulate matter measurements. After turbine exhaust was diluted sevenfold with filtered air, particle concentrations in the 10–300 nm size range were approximately two orders of magnitude higher than those in the ambient air and those in the 2–3 nm size range were up to four orders of magnitude higher. This study also found that ammonia emissions were higher than expected, but in compliance with permit conditions. This was possibly due to an ammonia imbalance entering the catalyst, some flue gas bypassing the catalyst, or not enough catalyst volume. SO3 accounted for an average of 23% of the total sulfur oxides emissions measured. While some of the SO3 is formed in the combustion process, it is likely that the majority formed as the SO2 in the combustion products passed across the oxidizing CO catalyst and SCR catalyst.The 100 MW turbine sampled in this study emitted particle loadings of 3.63E-04 lb/MMBtu based on Methods 5.1/201A and 1.07E-04 lb/MMBtu based on SMPS method, which are similar to those previously measured from turbines in the SCAQMD area (FERCo et al., 2014), however, the turbine exhaust contained orders of magnitude higher particles than ambient air.

Ethnic mobilization among Korean dry-cleaners

Korean immigrants in the USA rely heavily on ethnic resources to start up small businesses. Ethnic resources include business networks and knowledge, start-up capital and access to labour power, which are embedded in networks of family, friends and co-ethnics. This paper shows how Korean dry-cleaners in Southern California used ethnic resources to mobilize in response to an environmental policy initiated by the South Coast Air Quality Management District (AQMD). While Korean immigrants used ethnic resources to start up dry-cleaning businesses, they found themselves working with a toxic chemical. In 2002, the AQMD required dry-cleaners in Southern California to convert to costly alternative machines by 2020. Korean dry-cleaners used ethnic-based collective action, particularly the Korean Dry Cleaning Association, as a means of fighting for regulatory concessions. They also used ethnic resources to overcome cultural and linguistic barriers to facilitate the adoption of alternative cleaning machines in compliance with the regulation.

Heterogeneity among motorists in traffic-congested areas in southern California

Estimation of congestion costs, presumed to be one of the largest external costs of automobile travel, is typically based on a single value of time delay for motorists in metropolitan areas. However, the estimation may be wrong if the profiles of motorists are different at different times of day. This study uses a survival model to examine the demographic and socioeconomic profiles of motorists at different times of day at congested locations in southern California, by using on-road remote-sensing measurements and license plates images obtained in 2007 and 2008 by the California South Coast Air Quality Management District (SCAQMD). More than 80,000 vehicles were observed from fifteen selected study sites over fifteen days. Their plates, through anonymized registration records, revealed addresses at the census block group level, which have homogenous profiles by construction. Motorists’ profiles at different times of day display large variation, however, according to extended Cox model with a non-parametric baseline hazard, which is used to accommodate both the time-invariant and time-varying effects of the covariates. This study thus proposes a new approach to examine heterogeneity among motorists.

New Way to Utilize Remote Sensing Data

Travel behavior analysis and demand models have been relying on data collected from households through questionnaires. This study demonstrated a combined analysis of the license plates obtained through remote sensing of vehicle emissions, Department of Motor Vehicles (DMV) address records, and census proxies of those addresses, referred to collectively as an automated road travel survey (ARTS). This study demonstrated an application of the ARTS method to the analysis of the income distribution of motorists in Los Angeles, California, at a spatially and temporally disaggregated level. The demonstration used the data of 1 day from a single study site obtained in 2007 by the California South Coast Air Quality Management District. By a match of 4,704 license plate images to California DMV registration records, anonymized individual owner ship records were obtained. The missing demographic and socioeconomic profiles of vehicle owners were supplemented with census data at the level of census block groups. In contrast to household-based methods such as traditional travel surveys, ARTS provided several advantages: ( a) the precise time log of the trips, ( b) fewer missing data because correct license numbers are registered for most of the vehicles passing a monitoring site, and ( c) data for any desired length of monitoring time at minimal cost. When linked to ownership databases, remote sensing data opened new avenues for research into travel behavior, complementary to travel surveys.