See an air quality report for any address within East Los Angeles, Boyle Heights, & West Commerce.

Inhaling microscopic fine particulate matter has been known to increase the likelihood of negative health effects ranging from respiratory and cardiovascular problems to an increased risk of developing cancer, reproductive and developmental issues, and reduced life expectancy.

Aclima‘s PMI enables air regulators, community members, researchers, and health professionals to see hyperlocal variations in typical concentrations of PM

Aclima has updated the LA 2021 public report to reflect our use of improved calculations for analyzing and mapping the data.

The data mapped from the Los Angeles measurement period, which covered July 1 through September 30, 2021, is now modestly different from those in the first version of the public report, released in February 2022.

The underlying 1-Hz, or 1-second, data as collected by the vehicles is unchanged. However, data products, including products that build on ambient concentration aggregates at the segment and hexagon scale, have changed modestly.

In these final reports, we used a streamlined order of calculations, which were completed using software for increased accuracy.

We improved the base algorithms that are used to calculate the data.

We fixed a timezone error in the final Black Carbon ambient concentrations. Because we use data obtained from a secondary source to normalize our data (see: Methodology), this error affected the normalization process and therefore what data showed in the first version of the report.

Overview of changes and impacts on the report:

The largest changes (~+/- 10%) are seen in BC (Black Carbon) data. There are smaller changes (~+/- 8%) in other pollutants.

Typically, the maps will now indicate that more hexagons are above the local regulatory median and that more segments are impacted by diesel pollution.

The new spatial aggregates reflect higher confidence, improving the spatial representativeness of the data and the ability to see differences between neighboring hexagons.

Now that the calculations are produced by software rather than manual calculations, there is increased accuracy and traceability.

stationary-sources-pm25

The PMI enables air regulators, community members, researchers, and health professionals to see hyperlocal variations in typical concentrations of PM

. Inhaling microscopic fine particulate matter has been known to increase the likelihood of negative health effects ranging from respiratory and cardiovascular problems to an increased risk of developing cancer, reproductive and developmental issues, and reduced life expectancy.

Decisions are only as good as the information behind them. Our high-resolution data provides the measurements required to make more informed decisions about emissions reductions. Aclima deployed its fleet of vehicles driven by local community members to measure air pollution on each block from July through September, 2021. Aclima combined measurements to calculate average pollution levels at any address. In East Los Angeles, Boyle Heights, and West Commerce, we looked at carbon monoxide (CO), carbon dioxide (CO

), and black carbon (BC) levels. We analyzed over 38 million 1-second data points based on these seven pollutants and discovered patterns and areas with elevated concentrations of unhealthy air pollutants.

Aclima uncovered where air pollution is the worst across more than 10,000 blocks

The world’s most detailed air quality maps, now available in your neighborhood.

High resolution measurements identify areas where elevated levels of harmful pollutants are typically present. Multiple measurements at each location over time leads to an understanding of 

 air quality. Each block has been measured over 20 times, which has been 

 of the persistent air quality at a given location during the measurement time frame. Mobile mapping is either continuous or performed on a quarterly or annual project basis to establish a baseline. This data can be used to make decisions that help people reduce exposure and risk where they live, work, and play. Through our hyperlocal measurements, regulators, community members and other decision makers are now equipped with the hard data needed to enhance the identification and characterization of sources and improve emissions reduction planning.

: average air pollution concentrations block by block.

SCAQMD has operated one stationary regulatory monitor in the AB 617 ELABHWC area since 1979. Data are available at the 

 at that site during our measurement period was 16 µg/m

. Nearly 39% of the road segments we measured were over this regulatory median value. Regulatory monitors collect data continuously at a single location meant to be 

 of the area. The EPA considers the stationary monitor in East Los Angeles to be representative of a neighborhood, which by definition covers a distance of 0.3 to 2.5 miles from the East Los Angeles monitor.

See current air quality, wind direction, and pollution trends over time.

Wind patterns impact the extent to which stationary measurements reflect emissions not immediately upwind. The strongest winds in the East Los Angeles, Boyle Heights, West Commerce Community during our measurement period were between 7-10 mph. They were most prevalent in the morning and came most often from the south and southwest. 

 can lead to increased pollutant levels as sources continue to release emissions. Mobile monitoring can capture the influence of sources in all directions that can result in elevated concentrations within the region.


Wind moves pollutants in the air and impacts how well stationary measurements reflect emissions.

Aclima uses climate and economic justice indicators to identify sensitive, underserved, overburdened, and at-risk populations. This map illustrates areas where sensitive populations live based on a calculated index that includes asthma prevalence, cardiovascular disease prevalence, population under age 5, population over 64, and low birthweight infants. Areas to the south and southwest are primarily commercial and industrial with a major railyard. Heavy industry and winds from the south and southwest may subject sensitive residents downwind of these areas to increased levels of pollution.

: we don't all breathe the same air; it affects each of us differently.

Schools, healthcare facilities (hospitals and other), childcare centers, community centers, libraries, public housing projects, and parks are locations where sensitive populations visit and spend their time. Many of these sites are located near major roads and freeways, which often have high fine particulate matter, nitrogen dioxide, black carbon, and carbon monoxide due to emissions from motor vehicles.

Air quality trends where sensitive populations spend time

The Community Steering Committee (CSC) and community members identified a number of locations where community members live, work, go to school, and spend the majority of their time. The East Los Angeles, Boyle Heights, and West Commerce Community is impacted by various mobile and stationary sources. A range of stationary sources impact air quality in the region and can affect sensitive population health. The community’s sensitive sites include 151 schools, 48 licensed daycare facilities, and 14 hospitals, among other sensitive sites. Most are in the general residential area in the central and eastern half of the monitoring area with fewer embedded in the general commercial, industrial area to the west and south. However, many are located close to the I-5, I-710, and I-10 freeways. Cars and trucks on freeways emit carbon monoxide (CO), nitrogen dioxide (NO

) and black carbon (BC) that result in elevated pollution nearby.

The community has high rates of poverty and unemployment and there are schools in close proximity to pollution sources. General source categories of concern include truck traffic, railyards, warehouses, metal processing, waste and rendering facilities, and auto body shops. Within this area, consistently high days or a high average level of pollutants over long periods of time can potentially result in health effects like respiratory, cardiovascular, and reduced life expectancy. Some pollutants (like ozone and PM

) have short-term effects like inducing asthma as well as long-term effects.

Sensitive Sites: air quality trends where sensitive populations spend time

Emissions come from a wide range of stationary sources. Regulated facilities are required to keep emissions below a threshold that is believed to keep ambient concentrations at or below safe levels as defined by the 

National Ambient Air Quality Standards (EPA)

. Despite the large number of regulated sources, fugitive emissions can make up a significant portion of primary emissions, especially for PM

Where is it all coming from? A look at emissions from known stationary sources.

Stationary and mobile air pollution sources can potentially result in air pollution levels that adversely impact human health. The AB 617 ELABHWC includes a wide range of stationary sources from single point sources that are regulated (industrial stack) to small sources (residential backyard grill) that are not regulated. Sources of most concern are neighborhood and freeway traffic (trucks and automobiles), railyards, metal processing facilities, rendering facilities, auto body shops, industrial facilities, and waste transfer stations.

Many small stationary sources are not regulated and are considered fugitive (sources that cannot be easily measured since they are individually relatively small and likely spread over a large area). Examples include road and industrial wind blown dust, some non-road equipment (diesel and gasoline), emissions from various mom and pop shops. Air quality modeling attempts to include fugitive emissions based on surrogates, such as population density, diesel fuel sold, sales.

On the other hand, regulated facilities are required to reduce emissions below a threshold that is believed to keep ambient concentrations at or below safe levels as defined by the National Ambient Air Quality Standards (EPA). ELABHWC is also bisected by major freeways including highways 101 and 60, and Interstates 5, 10, and 710, resulting in four major freeway junctions.

Stationary Sources: where is it all coming from? A look at emissions from known stationary sources

When Aclima measurements are aggregated to larger areas, patterns of high pollution emerge, which helps community members take steps to reduce exposure. Values of a hexagon can be compared to the nearest EPA regulatory site measurements, to the level of 

(World Health Organization) air quality guidelines

. Areas emitting higher than area average greenhouse pollutants (CO2, CH4, and BC, a component of PM2.5) can also be identified for further investigation or reductions.

 (averaged over 3 years) and areas with darker red exceed this value. Extended exposure can potentially result in adverse health effects.

 pollution than the EPA threshold of 53 ppb.

100% of the measurement area has higher NO

 pollution than the WHO guidelines of 5.3 ppb and 5 µg/m

Regulatory air monitors are stationary and report air quality from one location for an entire area. Aclima mobile mapping data is gathered at different times of day and week throughout a community to give a zoomed in, hyperlocal view of how air quality differs from one block to the next. This is why lived experiences don't always match the regulatory site's data. Viewing sensitive sites and stationary facilities on these maps helps us understand the potential sources and the impact of emissions on the people who live here. Mobile mapping data complements regional data provided by regulatory monitors with hyperlocal data that reveals average air quality conditions where people live, work, and breathe.

Comparing Aclima maps to regulatory data from stationary monitors

Exposure to diesel pollution increases the risks of experiencing serious health problems, which is why Aclima developed a Diesel Pollution Indicator (DPI) visualization tool. This tool allows us to see, at a hyperlocal level, where diesel emissions may potentially affect human and environmental health, as well as where steps should be taken to reduce such pollution.

Aclima designed the DPI to identify diesel emissions based on nitrogen dioxide (NO

) and black carbon (BC), a component of  PM

 cause adverse health effects and are designated as 

, which the EPA monitors closely under the Clean Air Act. The DPI is based on these two components because emissions from sources that use diesel fuel, like heavy-duty trucks and the train locomotives and drayage trucks found in railyards, contain a higher concentration of BC and NO

 than other combustion sources. These measurements give us a detailed and scientifically rigorous approach to seeing the patterns that this indicator exhibits.

Truck routes, as identified by the Department of Transportation, in the East Los Angeles, Boyle Heights, West Commerce communities (ELABHWC), are primarily freeways. Aclima’s DPI clearly shows the presence of diesel emissions on the five major freeways in the community (I-5, I-10, I-710, SR-60, and SR-101). Road segments are categorized into two levels based on Aclima's DPI: High and Medium.

Here we show the DPI for the residential areas suspected to be most impacted by diesel pollution.

Diesel emissions measured on these residential roads may be caused by trucks driving or idling within local areas, particularly on roads near freeways and railyards, or on streets that lead to and from warehouses.

Diesel emissions can also be transported to residential areas by prevailing winds. Average winds over the monitoring period were 

 from the south and west, varying by time of day. Based on this and what scientists know about the distribution of diesel pollution in the area, we can infer that residential areas downwind (between north and east) of the BNSF railyard, major freeways, and some warehouses may experience higher diesel pollution than areas farther away from these sources.

Diesel Indicator: Residential Areas of Concern

Diesel Pollution Indicator: Residential Areas of Concern

Here we investigate the DPI within a 1,000 foot radius of schools, childcare centers, community centers, libraries, parks, and public housing. Percent segments refers to the sum of High and Medium DPI road segments divided by the total number of road segments in the 1,000 foot radius.  This map only shows High and Medium DPI road segments that are within the circles rather than all segments with High and Medium DPI throughout the map.

As seen in the map, several public housing locations are adjacent or in close proximity to busy freeways. Multi-family units like Ramona Gardens, Pico Gardens, LA Family Housing, and Found Inc. all fall into this category. The High and Medium DPI values found near these buildings are primarily located adjacent to freeways, though as noted, diesel emissions can easily be carried downwind from freeways to residential communities.

As seen in the map, the top five schools, childcare centers, community centers, libraries, parks, and public housing in the DPI percent segment listing are all located within 1,000 feet of freeways and major roads. Many are within 500 feet and some are immediately adjacent to freeways and major roads. While many of the residential streets within the circles are typically below Aclima’s DPI criteria, diesel emissions are still present but at lower levels than our DPI limit. The impact of freeways on these sensitive locations is evident, with all five being downwind of the average wind direction from freeways.

Diesel Pollution Indicator: Exposure Reduction

Here we investigate warehouses in the East Los Angeles, Boyle Heights, West Commerce communities with DPI within a 2,000 foot radius. Percent segments refers to the number of High plus Medium DPI road segments divided by the total number of road segments in the 2,000 foot radius. This map only shows High and Medium DPI road segments that are within the circles rather than all segments with High and Medium DPI throughout the map. Most warehouses identified by the community are in the southern portion of this community, a majority of which are clustered around the BNSF and Union Pacific railyards and west of the busy I-5 freeway. A handful are located east of the I-5 in the same general southern area. Farther north, one warehouse is located near SR-60 and I-710 and another warehouse is located north of the I-10 by Ramona Gardens.

Road segments with High and Medium DPI around warehouses are located near the railyards in the southwest of the community. The majority of High and Medium DPI values are located on the freeways with most others found on roads surrounding the warehouses or roads to and from the freeways and the railyards. These DPI signatures are likely due to the consistent diesel truck traffic in the area and railyard operations. Diesel emissions associated with warehouses, such as those near the railyards, may also be the result of idling trucks waiting to load or unload cargo or of the railyard or trucks traveling to and from the freeway to the warehouses.

The DPI shows High and Medium DPI observed on roads adjacent to the group of railyards, which are located in the northwest section of West Commerce, the largest ones being the neighboring BNSF and Union Pacific railyards. Road segments with higher DPI near railyards may be caused by trains, trucks, and other diesel equipment. Aclima’s DPI shows that diesel emissions can also be transported by prevailing winds from railyards to residential areas.

Here we examined DPI around waste transfer stations. These facilities are located in commercial and industrial areas just inside the outer edge of the monitoring area to the south, west, and north. Road segments within 1,000 feet of the waste transfer stations do not appear to be impacted by the waste transfer stations but by emissions from other sources, like the railyard or freeways.

Diesel Pollution Indicator: Waste Transfer

The state of California is a champion of the federal Clean Air Act, having enacted some of the strictest diesel emissions standards in the world. South Coast AQMD closely followed this model by adopting the first-of-its-kind Indirect Source Rule to address pollution caused primarily by diesel trucks servicing distribution warehouses and other locations. However, more can and should be done to immediately reduce diesel people’s exposure at the local level. The DPI can help identify streets with the most heavy-duty diesel truck traffic, so that local community and non-profit leaders can continue to work with city and county officials to design or redesign truck-appropriate routes and clean air solutions. Studies have found that enacting truck bans on specific heavily-traveled roads in a community are successful in reducing exposure to higher levels of diesel pollution, especially for children or other vulnerable populations that may live or spend time along key distribution corridors.

In addition to mobile sources of pollution, the DPI can also help identify which specific stationary and off-road sources, such as warehouses, factories, and railyards, may have the highest air quality impact on nearby residents. The CSC can also use this Diesel Pollution Indicator to work with local school districts and officials to prioritize schools, childcare centers, libraries, and community centers near truck routes, railyards, and other industrial sources that may benefit from installation of air filtration systems.

While individuals should take steps to reduce their exposure to diesel particulate matter whenever possible, it is the federal, state, and local regulators’ duty to enact policies that protect the public’s health from significant off-road, on-road, and stationary diesel pollution sources. Installing air filtration devices in all buildings is recommended, particularly those along heavy truck routes and near railyards. This is a near-term option to reduce harmful impacts today; however, a systematic solution to eliminating diesel truck pollution would be to support the adoption of high-voltage electric vehicle charging and cargo transport infrastructure, whose locations can be prioritized using the DPI in collaboration with the air district and local utilities. Permits for new distribution centers or expanded operations/output should also take into account potential increases in diesel emissions. Siting of these facilities should be done in a way that will not lead to increased truck traffic near the sensitive sites shown in this Community Air Quality Report.

The Methane Indicator highlights areas in the community with elevated ambient methane concentrations above the typical background level. While the MI reports the levels of methane from all sources, elevated methane levels most likely reflect emissions from gas infrastructure, landfills, oil and gas wells, and sewage, given the context.

Aclima’s algorithms identify dangerous leaks that pose a combustion risk, in which case the local gas utility is immediately notified out of an abundance of caution for public safety. The purpose of the MI is to detect methane leaks at any level to reduce the effect methane has on public safety and exacerbating global climate change, the latter since it is a potent greenhouse gas, second only to carbon dioxide. Methane also has a shorter atmospheric lifetime than CO2, so achieving methane reductions may have a more rapid effect on reducing global warming.

: In the event that Aclima’s monitoring indicates a methane leak at such a scale that may pose a threat to human health or become a combustion risk, the local gas utility is immediately notified out of an abundance of caution for public safety.

In addition to daily actions the local utility and air regulators take to ensure public safety, community members can also take action if they are concerned about fugitive methane or gas leaks:

Notify the local utility or regional air quality district to investigate the area to determine whether the methane concentrations identified through the MI are being caused by sources that could be capped like abandoned oil and gas wells.

If landfills, wastewater treatment plants, agricultural waste sites, or sewer infrastructure are determined to be the likely source(s) of fugitive methane, biogas capture could be a viable option.

Work with leadership of the Los Angeles County Metropolitan Transportation Authority, logistics companies, distribution warehouses, railyards, drayage services, and other large vehicle fleet managers to convert to zero-emission electric vehicles. Many of these vehicles could be powered by electricity, and specifically by locally-generated solar energy from rooftops and covered parking areas. Covered parking areas have the added benefit of reducing the 

, which occurs when cities replace natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat.

Call before you dig. The local gas utility will be able to advise on the location of gas lines to avoid.

The TPI provides insights into light- and heavy-duty vehicle emissions, while the Diesel Pollution Indicator (DPI) is focused on diesel emissions primarily from heavy-duty trucks and trains. The TPI  is based on concentrations of carbon monoxide (CO) and carbon dioxide (CO

). The small distinction between gasoline and diesel emissions is possible with the TPI because gasoline engines emit a higher fraction of CO per unit of energy than diesel vehicles.

Road segments are identified as having elevated diesel emissions at their locations based on two levels of Aclima's TPI: High and Medium. These measurements give us a detailed and scientifically rigorous approach to seeing the patterns that this air pollutant exhibits.

Residential congestion is not only annoying, but also produces elevated levels of unhealthy pollution where people live and breathe. By focusing on residential roads and arterials, the TPI  can be used to prioritize areas in the community that would most benefit from interventions and policy enforcements.

This map shows the TPI for the residential areas suspected to be most impacted by traffic pollution.

Traffic emissions measured on these residential roads may be caused by cars and trucks within local areas. Traffic emissions can also be transported between residential areas by prevailing winds. During the monitoring period, average winds were gentle and from the south and west, varying by time of day.

Traffic Indicator: Residential Areas of Concern

Traffic Pollution Indicator: Residential Areas of Concern

Here we investigate TPI within a 1,000 foot radius of sensitive receptors where people live, work, and play, such as schools, childcare centers, community centers, libraries, parks, and public housing. Percent segments refers to the number of High plus Medium TPI segments divided by the total number of segments in the 1,000 foot radius. This map only shows High and Medium TPI road segments that are within the circles rather than all segments with High and Medium TPI throughout the map.

This map shows these sensitive receptors in relation to the TPI.  It may be unsurprising that many of these sensitive receptors also show up in high traffic areas.

As seen in the map, several public housing locations are adjacent or in close proximity to busy freeways, while also being located in residential areas. Multi-family units like Ramona Gardens, Pico Gardens, LA Family Housing, and Found Inc. all fall into this category. The High and Medium TPI values found near these buildings are primarily located adjacent to freeways, though as noted, traffic emissions can easily be carried downwind from these emissions sources to residential communities.

Understanding the relationship between both the Diesel Pollution Indicator and Traffic Pollution Indicator provides a thorough set of criteria that can help prioritize areas in the community for emission reductions and continued monitoring.

Traffic Pollution Indicator: Exposure Reduction

Here we investigate TPI within a 2,000 foot radius of warehouses in the ELABHWC community. Percent segments refers to the number of High plus Medium TPI road segments divided by the total number of road segments in the 2,000 foot radius. This map only shows High and Medium TPI road segments that are within the circles rather than all segments with High and Medium TPI throughout the map.

Most warehouses identified by the community are in the southern portion of this community, the majority of which are clustered around the BNSF and Union Pacific railyards and are west of the busy I-5. A handful are located east of the I-5 in the same general southern area, while farther north, one is located near SR-60 and I-710 and another is north of the I-10 by Ramona Gardens.

Road segments with High and Medium TPI around warehouses are located near the railyards in the southwest of the community. The majority of High and Medium TPI values are located on freeways and roads near the warehouses and outside the 2,000 foot circle with some TPI values indicated on major roads to and from the railyard and warehouses inside and outside the circles. Few are located in the circles on other types of roads. These TPI signatures are likely due to the consistent diesel truck and gasoline vehicle traffic in the area.

This map shows High and Medium TPI on roads within and adjacent to the group of railyards located in the northwest section of West Commerce, the largest ones being the neighboring BNSF and Union Pacific railyards. Near all railyards, road segments with higher TPI are likely due to the trains, trucks, and other equipment within the railyards that also emit CO and CO

We examined TPI around waste transfer stations. These facilities are located in commercial and industrial areas just inside the outer edge of the monitoring area to the south, west, and north. Road segments within 1,000 feet of the waste transfer stations do not appear to be impacted by the waste transfer stations but by emissions from other nearby sources, like the freeways or activities associated with commercial and industrial areas.

Traffic Indicator: Waste Transfer Stations

Traffic Pollution Indicator: Waste Transfer Stations

City and County agencies can utilize the TPI to reduce vehicle traffic near locations where populations that are highly sensitive to air pollution live and work, such as schools and parks.

The community could provide more support to the Los Angeles County Metropolitan Transportation Authority (MTA) to increase the number of electric buses and reduce the use of CNG. Improving public transportation service on corridors with High TPI could reduce single-occupancy vehicle trips. Public electric vehicle charging infrastructure should be equitably distributed for those who are unable to use public transit.

Another way to reduce car dependency is to support active transportation choices by working with the city and alternative transportation coalitions to provide training and to construct safe cycling lanes along streets with lower pollution levels and adjacent to those where gasoline-powered vehicles seem to travel most frequently.

In addition, traffic signals can be optimized to reduce idling at stop lights. Idling of all vehicles (trucks, buses, cars, etc.) outside of schools, childcare centers, parks, healthcare facilities, and other sensitive receptor locations should be minimized or eliminated through local law.

Green corridors and physical barriers can be effective in containing or mitigating pollutants along major roadways. The Traffic Pollution Indicator can help identify sections of roads and highways that could benefit most from these infrastructure improvements, which can be very costly. Areas like the East LA interchange and sections of the I-10 freeway and commuter rail tracks near Ramona Gardens could be good candidates for priority interventions. The City and County would need to work with CalTrans and the MTA to determine under whose jurisdiction each section falls, and what type of barriers or green infrastructure would be most appropriate if other critical infrastructure are present in the vicinity (for example, gas lines under the surface of streets).

By focusing on residential roads and arterials, the PMI can be used to prioritize areas in the community that would most benefit from interventions and policy enforcements.

This map illustrates areas of elevated levels of particulate matter pollution where people live and breathe. This map shows the PMI for the residential areas suspected to be impacted by particulate matter pollution.

High PMI identified on these residential roads may be caused by cars and trucks within local areas as well as industry, commercial activities, and wind blown dust. Particulate matter emitted by many sources can also be transported by prevailing winds between residential areas.

Over the monitoring period, the average winds over the monitoring period were 

from the south and west, varying by time of day.

PM Indicator: Residential Areas of concern

Particulate Matter Indicator: Residential Areas of concern

Here we investigate PMI within a 1,000 foot radius of sensitive receptors where people live, work, and play – schools, childcare centers, community centers, libraries, parks, and public housing. Percent segments refers to the number of High plus Medium TPI segments divided by the total number of segments in the 1,000 foot radius. This map only shows High and Medium TPI road segments that are within the circles rather than all segments with High and Medium TPI throughout the map.

This map shows these sensitive receptors in relation to the PMI.  It may be unsurprising that many of these same locations also show up in High traffic areas.

As seen in the map, several public housing locations are adjacent or in close proximity to busy freeways and located in residential areas. Multi-family units like Ramona Gardens, Pico Gardens, LA Family Housing, and Found Inc. all fall into this category. The High and Medium TPI values found near these buildings are primarily located adjacent to freeways, although PM can easily be carried downwind from these emissions sources to residential communities..

Understanding both the Diesel Pollution Indicator and Traffic Pollution Indicator provides a thorough set of criteria that can help prioritize areas in the community for emission reductions and continued monitoring.

Particulate Matter Indicator: Exposure Reduction

Here we investigate warehouses in the ELABHWC community with PMI within a 2,000 foot radius. Percent segments refers to the number of High plus Medium PMI road segments divided by the total number of road segments in the 2,000 foot radius. This map only shows High and Medium PMI road segments that are within the circles rather than all segments with High and Medium PMI throughout the map.

Most warehouses identified by the community are in the southern portion of this community, a majority of which are clustered around the BNSF and Union Pacific railyards and west of the busy I-5. A handful are located east of the I-5 in the same general southern area, while further north one is located near SR-60 and I-710 and another north of the I-10 by Ramona Gardens.

Road segments with High and Medium PMI around warehouses are located near the railyards in the southwest of the community. The majority of High and Medium PMI values are located on the freeways with a few on roads surrounding the warehouses and roads running to and from the freeways and railyards. These PMI signatures are likely due to the consistent diesel truck and gasoline engine vehicle traffic in the area and railyard operations. Diesel emissions associated with warehouses, such as those near the railyards, may also be the result of idling trucks waiting to load or unload cargo or associated with the railyard or trucks traveling between the freeway and the warehouses.

The largest railyards in the community are located in the northwest section of West Commerce, the largest ones being the neighboring BNSF and Union Pacific railyards. These railyards appear to be a source of PM and BC, which is a component of PM, due to emissions from related combustion sources. High and Medium PMI is observed on accessible roads within these railyards and adjacent to the railyard. Road segments with High and Medium PMI north of these railyards are likely due to movement of trains and equipment that disturb PM that has settled on the ground back into the air. This allows particulate matter, generated within the railyard, to be transported by wind to downwind nearby residential communities like the “ABC'' neighborhood west of Bandini.

We examined PMI around waste transfer stations. These facilities are located in commercial and industrial areas just inside the outer edge of the monitoring area to the south, west, and north. Road segments within 1,000 feet of the waste transfer stations do not appear to be  impacted by the waste transfer stations but by emissions from other nearby sources, like the freeways or activities associated with commercial and industrial areas.

Particulate Matter Indicator: Waste Transfer Stations

 concentrations are highest. Analysts can utilize the PMI in conjunction with satellite imagery and meteorological data such as wind behavior to identify likely sources. Since PM

 in the atmosphere results from a range of natural and human-caused sources, actions to reduce exposure can include a mix of mitigation and adaptation approaches.

One substantial action could be working with local lawmakers to reduce traffic near sensitive locations like schools and parks, which can significantly reduce exposure to fossil fuel emissions, but also avoid brake dust, tire wear, and road erosion, which over time also causes increased PM

 levels and harmful exposure. Road-based PM

 can also be mitigated by physical barriers and increased street sweeping, ideally using vacuum-style equipment to avoid additional dust distribution.

 shows up largely in the form of dust and is difficult to mitigate in hot, dry climates, which necessitates adaptation strategies to capture and manage exposure for at-risk populations. Dust caused by construction should be mitigated using best available practices and technologies. Actions to reduce exposure could include the distribution of portable indoor filtration devices and/or building retrofits where higher PM

 concentrations are measured, using Aclima’s hyperlocal air pollution data as evidence for increased access to state and regional incentive programs. Since air filtration systems often require more energy use than natural ventilation (e.g. opening windows), efforts should also be made to pair filtration incentives with financial support for solar energy at the home or building scale to reduce energy costs.

Actions to reduce PM pollution can take many forms, and Aclima’s hyperlocal air pollution platform helps identify and prioritize interventions for the vulnerable populations that need them most urgently. This could include using this PM Indicator to prioritize the placement of school-based air monitoring for additional limited-term assessments.

It should always be noted during discussions and permitting processes with local businesses, that the people who are typically most exposed to harmful and toxic air are those who work in and around sources of these pollutants. Truckers, warehouse workers, railway employees, bus drivers, and those who work in industrial facilities can face long-term health effects of being exposed to unhealthy air. With Aclima's data in hand, environmental justice leaders can support employees as they advocate for themselves and ensure their employers adopt best practices to protect their workers and the community.

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Particulate Matter Indicator: overview

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