In the U.S.
the EPA and state environmental protection agencies design and deploy air
monitoring networks based on where potential sources of air pollution can be
found and prevailing weather patterns near those sources. However, these stationary
installations, though the most accurate, are expensive to deploy and generally
have inadequate coverage.
Clean Air is a Public Good
People have basic
expectations that they will not have to be exposed to toxic air pollution. We
know without a doubt that certain pollutants in the air cause serious health
problems. Thus, monitoring air quality supports a clear public good: clean air.
Air quality is one of the biggest environmental justice concerns. People who
live near landfills, cement plants, industrial facilities, power plants, and
many other potential sources of air pollution are rightfully concerned about air
quality. Air quality is more of a concern in certain places like California due
to weather inversions that increase smog, particulate matter, and NOx exposure.
One key study
that confirmed the detrimental effects of air pollution on children was the Children’s
Study, which began in Los Angeles, California in 1990. Los Angeles routinely
has among the poorest air quality in the country, due in significant part to
smog inversions. Researchers suspected that ground level ozone would be the
culprit for decreased lung function in children. Children are great as subjects
in such a study since lifestyle issues of adults like smoking do not have to be
filtered out. Instead of ground-level ozone, they found that the culprit was
particulate matter, mainly 2.5 PM, which can be breathed into the lungs. As air
quality improved, lung function in children improved, strongly confirming the
connection between air quality and lung function.
Air pollution
can affect humans and other mammals in multiple ways. Depending on the pollutant there
are respiratory, cardiovascular, carcinogenic, reproductive and hormonal, and
neurological effects. Air pollution also impacts ecosystems. It even affects materials
including metals, stone, fabrics, paints, paper, glass, and rubber. These
effects are mostly chemical effects. Quantifying and risk-assessing air
pollution is a complex science. Indoor pollution is another area of concern. In
particular, the dangerous substances of asbestos and radon are of great
concern. Formaldehyde outgassing from particle board, VOCs, and combustion gases
like CO and NOx can also be of concern.
Unfortunately,
some ‘anti-green’ advocates like lawyer and author Steve Milloy and contrarian
scientist James Enstrom, have strived to dispute the very obvious findings that
air pollution is dangerous. One need only look at the London Smog of 1952 when
smog from burning coal was kept at ground level for four days by a weather
inversion. That event is estimated to have killed 4000 people and made 100,000
people ill. Air pollution is harmful. That is indisputable. The level of harm
is, of course, dependent on exposure, length and frequency of exposure, and
concentration of pollutants.
Air Quality Improvements
Fortunately,
due to regulation, compliance with regulation, and the development of air
monitoring networks, air quality has improved in the U.S. It has improved
tremendously since the implementation of the Clean Air Act, which was enacted
in 1970 and amended in 1990. Improvements have continued to the present time. The
EPA reported in 2020:
“Nationally, the concentration of ground-level ozone
has decreased 21% from 2000 to 2019. All other air pollutants regulated under
NAAQS – sulfur dioxide, lead, carbon monoxide, nitrogen dioxide and particulate
matter – have also significantly decreased thanks to technological advances and
various air quality management and control strategies developed and implemented
at the local, state, regional, and national level.”
Information Sources
For my post
here I am relying heavily on the excellent and informative blog of Air Quality
Education Specialist Sienna Bishop at California-based air quality company Clarity.
There is a clear need for a greater density of air quality monitoring networks around
industrial sites, dense cities with significant traffic, and in other places
where air quality may be a concern. There is also a need for more sensors, and more
points of measurement. Newer, less expensive sensors can be deployed in more
places to keep monitoring networks from missing pollution sources. Data gaps
can be filled in from other sources, including satellite data. Air monitoring
companies and professionals can help fill in these gaps. I am also relying on lots
of information from the EPA, some from state agencies, environmental
groups, air monitoring companies and professionals, and books published about
air pollution, including Daniel Valero’s massive tome Fundamentals of Air
Pollution.
National Ambient Air Quality Standards (NAAQS) and
the Six Criteria Pollutants
The National Ambient
Air Quality Standards involve the six criteria pollutants: nitrogen oxides
(NOx), sulfur oxides (SOx), ozone (O3), carbon monoxide (CO), lead (Pb), and
atmospheric particulate matter (PM 2.5 in particular, but also PM10). These
criteria pollutants have specific concentrations, beyond which they are considered
to be in non-attainment. The map below from 2017 shows which counties around
the country are in non-attainment and for how many of the six criteria
pollutants.
There are many
different sources of the six criteria pollutants and different reasons why some
areas are more prone to be in non-attainment. Combustion of fossil fuels in
power plants, industrial facilities, mining, transportation, and agriculture
are major sources. In parts of California, Nevada, Arizona, Utah, Wyoming, and
Colorado there are weather inversions that can keep these pollutants from
dispersing and keep them near ground level for longer periods of time and at
higher concentrations. Particulate matter can come from multiple sources,
including smoke and dust of many types. Particulate matter smaller than 2.5
micrometers (PM 2.5) is the most dangerous type of PM since it can be readily
breathed into the lungs. Along with the six criteria pollutants there are other
dangerous pollutants such as volatile organic compounds (VOCs), airborne
industrial chemicals, silica dust, and many others.
Natural Sources of Air Pollution
As many in the
Midwest and Northeast were reminded this summer of 2023, there are natural
sources of air pollution that can be dangerous. These include volcanic
eruptions, sandstorms, dust storms, pollen, and wildfire smoke. Areas prone to
these events where people are exposed also have seen negative health effects. I
did stay indoors as much as possible during the poor air quality days but when
I did go outside for any length of time I noticed solids in my nose, somewhat like
what we used to call rather crassly “sawdust boogers!”
Dangers of Wildfire Smoke and the Importance of Filtration
and Monitoring
Recently, my
local Nissan dealer offered a free cabin air filter change due to the wildfire
smoke. I took them up on the offer. I also recently learned (and relearned) that
the air recirculation button in the car is essential when running the A/C on
hot days because it makes the A/C cool better and run more efficiently by
cooling air inside rather than bringing in hot air from outside and cooling it.
This improves gas mileage and may extend the life of the A/C. It is also better
at keeping out toxic air, say the nasty exhaust from someone ahead of you, or of
industrial stench. The times not to use it are in the winter or at certain
moisture levels when it can cause window fogging. On long drives with multiple
passengers, you should periodically bring in fresh air from outside to keep CO2
levels from getting too high.
According to
the European Commission, global wildfire smoke is estimated to cause 339,000
premature deaths per year. Wildfire smoke can cause air quality concerns and alerts
far away from its source as we discovered this year here in the U.S. Midwest
and Northeast, far away from Canadian wildfires. What wood is being burned can
also add to the harm. Burning poison ivy can cause severe irritation. I discovered
this when we visited some acquaintances years ago who burned a large campfire
that had significant amounts of poison ivy. My young son was strongly affected,
with the poison ivy going systemic. He swelled up and was sick for a week or
two and had to be treated with cortisone shots. It was a scary experience.
Real-time air
quality monitoring can help us to know local air quality. This summer, I have
been relying on air quality data on my iPhone weather app, which always has a
frequently updated air quality index for each location. In areas where wildfire
smoke is more common and more frequent, it is important to establish air quality
monitoring networks with many data points that are updated frequently. Knowledge
of local air dispersion patterns and timing, often affected by terrain, is
essential to expanding coverage. Local, high-resolution data, with greater
coverage often provided by low-cost sensors, can be helpful in this regard. For
most of us away from wildfires the Air Quality Index (AQI) is usually sufficient
to keep us informed but to people in more frequent poor air quality zones,
there are other air quality monitoring networks and platforms such as Air Now that can give site-specific information
about AQI and pollution events like wildfire smoke concentrations.
Source: The Enhanced Air Sensor Guidebook. U.S. EPA. September 2022. ENHANCED AIR SENSOR GUIDEBOOK.PDF
The Construction Sector is a Major Source of Air
Pollution
23% of air pollution, including 30% of PM10, 8%
of PM2.5, and 4% of nitrous oxide emissions can be attributed to the construction
sector, according to the 2019 London Atmospheric Emissions Inventory. It is the
highest sector source of PM10. The dust produced from construction and
demolition is a major source of particulate matter. VOCs, NOx, SOx, CO, and
PM2.5 from diesel-powered heavy equipment are other sources of pollutants.
Construction
project managers should consider air quality in their projects and plan to minimize
unnecessary dust and equipment emissions. Spraying water for dust control is
one option. I have seen this used quite a bit in the oil and gas industry on
dusty lease roads. Mulch is another option that can be even more effective. Windbreaks
can help. Some sites can benefit from setting up air monitoring stations. Dust
control is especially important in arid regions. Other measures that can be
helpful are proper waste management and disposal and utilization of
low-emissions equipment and machinery. Electric equipment and machinery, though
not widespread, can reduce emissions as well as noise pollution. Another
advantage of electric construction equipment is that it can be built smaller,
which makes it easier to maneuver in smaller spaces. This is important since
most construction happens in urban environments. The electrification of
construction equipment is moving faster and is thus far more applicable in the near
term than the electrification of agricultural equipment for these reasons. Sienna
Bishop notes that air quality monitoring equipment needs to be frequently maintained
and calibrated to be effective. Her company, Clarity, offers a sensing-as-a-service
model that can be a good choice for construction projects.
Air Pollution from Traffic in Big Cities
Big cities are
also dense cities, with large amounts of people, vehicles, and equipment in
small spaces, relative to other areas. While the density of big cities can
mitigate emissions in many ways, the effects of density on air quality are not
one of those ways. Dense traffic, often slow-moving and idling, means poor local
air quality. Particulate matter, nitrogen dioxide, volatile organic compounds,
and ground-level ozone are the most common traffic pollutants. Emissions
policies for cities such as London’s Ultra-Low Emission Zone (ULEZ) can help to
improve city traffic pollution. Dense air quality monitoring coverage in vulnerable
areas can measure it. The European Environment Agency reported that from
2014-2020 two-thirds of reported air quality exceedances were in areas of dense
city traffic and were mainly due to nitrogen oxide (NOx) emissions. This is
likely due to the high NOx emissions of diesel, which is very common in Europe,
compared to the U.S. where gasoline is the dominant fuel. Diesel engines combust
diesel at much higher temperatures than gasoline engines combust gasoline,
resulting in up to 10 times the NOx emissions, although newer diesel engines
produce much less than that. As mentioned, traffic congestion and idling are
major factors in localized air quality concerns. Congestion can also lead to a
buildup of precursors to ground-level ozone.
Long-term
solutions to traffic can include better urban design and more availability of
public transportation. Alternative transport such as walking and biking can
also help if infrastructure is available and convenient.
Air quality
monitoring is essential to understanding local traffic pollution patterns. People
living in areas with frequent weather inversions are at the highest risk from
traffic pollution. A newer strategy for addressing traffic pollution is Intelligent
Transportation Systems (ITS). “ITS collect, analyze, and communicate data
related to transportation in order to improve its efficiency, mobility, and
safety and can also work to reduce impacts on the environment. ITS also equips
transportation users with more information that helps them to reduce their
travel time, travel more safely and comfortably, and minimize traffic problems
they may encounter.” The EPA models traffic emissions with their complex MOBILE6
model, which provides exhaust and evaporative emissions calculations for a wide
variety of traffic pollutants.
Fortunately, traffic emissions are
magnitudes better per vehicle than they were in the past (up to 99% better than in the 1960s and up to 90% better than in 1998) and city air is much cleaner than
in the past. VOC emissions have also dropped by 99% in the past 50 years. Regulations
such as the Clean Air Act have led to these improvements and vindicate the
usefulness of environmental protection as a societal good.
I attended a local blues festival a few years ago that was right on the Ohio River. There were quite a few boats quite close in the water idling their diesel engines. The air was heavy with the smell of diesel. As it was a long festival I'm guessing the particulate exposure was at unhealthy levels. I read recently that the EPA has slowed its cracking down on altering pollution control equipment on diesel engines and the trend known as "rolling coal." I still see it occasionally, but apparently, the practice is out of favor. This is good. Most of us don't want to see arrogant rednecks asserting their freedom to pollute. It's rude and inconsiderate.
Air Quality Monitoring for Mining and Industry
Mining and
industry, including the oil and gas industry, are major sources of air
pollution. The best way to understand and monitor these sites is with continuous
air quality monitoring. Factories, oil refineries, metals mines, coal mines, coke
plants, and petrochemical facilities are especially major sources of criteria pollutants,
VOCs, and other pollutants. It is common for continuous air quality monitors to
be installed at the perimeters of these facilities.
Air quality
monitors for pollutants and dust levels are essential and required within mines.
Coal dust, and more commonly these days, silica dust, are major causes of black
lung disease and silicosis which often leads to debilitating illness and death.
Airflow monitors, toxic gas detectors, temperature, pressure and humidity level
sensors, and complete mine air quality stations (MAQS) are commonly utilized
within mines. Along with particulates and dust other toxic airborne pollutants
that may be present in metal and/or coal mines include arsenic, trioxide dust,
asbestos, antimony, iron, lead, and nickel. Adequate ventilation, adequate
filtration, adequate personal protective equipment, and continuous air quality monitoring
are essential in mines.
Anemometers that
measure wind speed and direction are also essential for outdoor sites to
understand the potential for air pollution build-up. Long-term and continuous
monitoring are obviously the best choices for understanding weather patterns, and the potential for air pollution events.
Mining, smelting,
and ore processing methods can all contribute to air pollution. Smelting, which
utilizes very high-temperature heat, can produce airborne toxins such as lead, sulfur,
mercury, sulfur dioxide, zinc, cadmium, and uranium. Coal-fired power plants
can also produce these toxins and more along with criteria pollutants and a build-up
of heavy metals in coal ash sludge. Mitigation methods for outdoor facilities include
dust suppression including sprinklers, windscreens, more frequent vehicle and
equipment maintenance, and wet drilling. When I worked frequently at oil and
gas wells in the early 1990s, during air drilling they sometimes drilled dry,
known as dusting, which produced copious amounts of dust, which quite obviously
was potentially dangerous. I did maintenance very close to where dust was
coming out, often unclogging pipes clogged with dust. There was no air
monitoring at the time and little effort or incentive to mitigate the dust. That
probably did not meet OSHA standards then and certainly does not now. Quarries
are another source of dust. I have written on this blog about historical Berea
Grit quarrying in northern Ohio and the many workers who died of silicosis.
I have also written about Black
Lung disease and how its resurgence is really related to something called
slope mining where mining machines cut through high-silica areas between coal
seams which exposes miners to high levels of silica dust, the major cause of
silicosis.
Promoting sustainable mining practices can
decrease pollution and greenhouse gas emissions. This includes the electrification
of some equipment and processes. Diesel-electric hybrids and other lower emissions
technologies can also be utilized. According to the Canadian Mining Journal, 50%
of the energy consumed by mining operations is used to run the necessary
ventilation systems. They recommend the use of more energy-efficient automated
ventilation systems. These systems can optimize conditions better than manual
systems, thus improving safety as well as cost.
In the oil &
gas industry the use of diesel-electric hybrid drilling rigs, E-fracs, utilizing
braking on drilling rigs, automated drilling rigs, drilling with natural gas
power, and using gas-blending can all reduce emissions at well sites. In E-fracs
it is common for companies to utilize field natural gas to run “gen sets” which
can be sets of reciprocating natural gas engines or better yet natural gas turbines
(similar to jet engine turbines). These act as a power plant to power up the electric
pumps used for pressure pumping required for hydraulic fracturing. The emissions
and pollution reductions compared to using diesel generators are enormous. Many
truck trips to deliver diesel fuel are eliminated as well. Some LNG liquefaction
facilities have been electrified and some are partially powered by renewables
such as wind and solar. I actually wrote and self-published a book in 2022,
called Natural Gas and Decarbonization, which covers many of these topics
in detail. Drastically lower air pollution per drilling pad, per pipeline, per
facility, is one of the results of these new technologies and processes. After
initial investments, E-fracs and many of these innovations are cheaper to
operate than diesel-powered ops.
Clean Air Act Compliance
The EPA
monitors compliance with the Clean Air Act directly or through state environmental
agencies.
They do this in several program areas including 1) The Acid
Rain Inspection and Trading Program – which focuses on reducing the pollutants
that cause acid rain: sulfur dioxide and nitrogen oxides (NOx), from the power
sector, mainly from coal-fired plants. Pollution allowances are traded
according to a long-established cap-and-trade system that relies on
market-based incentives; 2) Applicability Determination Index (ADI) – this is
basically a database that helps operators or source owners determine whether a
rule applies to them or to request monitoring that may be different from
standards; 3) Asbestos Demolition and Renovation – this falls under the
Asbestos National Emission Standards for Hazardous Air Pollutants (NESHAP)
program and involves asbestos emissions from mining, manufacturing, demolition,
renovation, and waste disposal. Applicable sites are inspected by EPA or state
personnel; 4) EPA's Clean Air Act Mobile Sources Program – applies to developing
and enforcing air pollution standards for engines and vehicles, big and small,
and all fuels used in them; 5) National Emission Standards for Hazardous Air
Pollutants (NESHAP) Air Toxics – this program area establishes standards and maximum
achievable control technology (MACT) for hazardous air pollutants (HAPs); 6) New
Source Review/Prevention of Significant Deterioration (NSR/PSD)- this program
area deals with new sources and developing and improving standards by
establishing Best Available Control
Technology (BACT) or Lowest Achievable Emission Rate (LAER) technology, both of
which may be changed as newer and better technologies become available; 7) Prevention
of Accidental Releases – this section is involved with identifying hazards and
preventing accidental releases; 8) Standards
of Performance for New Stationary Sources – this program area develops
standards known as New Source Performance Standards (NSPS): “The NSPS apply
to new, modified, or reconstructed affected facilities in specific source
categories such as manufacturers of glass, cement, rubber tires and wool
fiberglass. As of 2012, EPA had developed 94 NSPS. EPA can delegate the
responsibility to implement and enforce the NSPS (or a subset) to its partners
(states, local, territorial, or tribal), however, even when delegated to the
states, EPA retains authority to implement and enforce the NSPS;” 9) Stratospheric
Ozone Protection including chlorofluorocarbon (CFCs) and other Ozone-Depleting
Substances (ODS) – this section is involved with protecting the stratospheric ozone
layer which protects Earth’s inhabitants from harmful UV rays. It has been
degraded by CFCs and HFCS, refrigerants used in refrigeration and air
conditioning that have been largely phased out; 10) wood heaters – these are
major sources of dangerous particulate matter – much worse for humans than say,
natural gas stoves. The EPA tests and certified wood stove models for
compliance; 11) Stack Testing – the program area tests smokestacks to determine
compliance and follows the Clean Air Act National Stack Testing Guidance; 12) The
Risk Management Plan Rule (RMP Rule) – this program provides guidance for chemical
accident prevention at facilities using extremely hazardous substances. The
rule requires companies that use certain flammable materials and toxic chemicals
to develop risk management programs that must be approved by EPA and resubmitted
every five years; 14) Area Source Rule Implementation Guidance - provides
guidance regarding the implementation of the CAA Area Source Rules. This
involves 30 HAPs identified by EPA in developing its Urban Air Toxics Strategy
for managing HAPs in urban areas.
Better Air Quality Saves and Extends Lives,
Improves the Environment, and Improves the Economy
It is
indisputable that air pollution is harmful and that mitigating it is
beneficial. Studies have also shown that the benefits of mitigation exceed the
costs by a ratio of 30:1. Thus, there are obvious economic benefits to improving
air quality. It avoids significant health care costs, lost work, and lost
productivity. This is simply because air pollution contributes to many health
problems including heart disease, stroke, asthma, cancer, low birth weight, and
likely many more conditions. Thus, healthier air supports a healthier economy. Air
pollution also negatively affects plants and ecosystems. It can reduce
agricultural yields, especially ground-level ozone. These effects also increase
air pollution’s cost to society. Nitrogen oxides and ammonia can negatively
affect ecosystems and contribute to eutrophication. Sulfur dioxide, nitrogen
oxides, and ammonia can contribute to the acidification of soils and bodies of
water which can lead to loss of biodiversity.
Regulatory-Grade Air Quality Monitoring Equipment
Governments
and environmental agencies utilize high-quality air monitoring equipment with
strict standards for measurement in order to support air quality policies. There
are two classes of these compliance monitors: Federal Reference Methods (FRMs)
and Federal Equivalent Methods (FEMs). According to the EPA: FRMs are “designed
to provide the most fundamentally sound and scientifically defensible
concentration measurement.” FRMs are the gold standard. FRMs are “intended
to provide a comparable level of compliance decision-making quality as provided
by FRM.” These equivalent methods may be cheaper and not quite as good as
the standard FEMs/FRMs but can add many high-quality/high-accuracy data points
to the network. FEMs and FRMs are actively reviewed in terms of new designs and
upgrades. The criteria for evaluating new designs and upgrades are as follows: accuracy,
precision, range, detection limit, pollutant specificity, freedom from co-pollutant
interferences, noise, drift (short-term and long-term), lag/rise/fall (gas
analyzers), and multi-site measurement performance. Each of these specs has
strict testing and acceptance requirements. They also need to be properly sited
and have competent instrument setup, calibration, operation, maintenance, and troubleshooting.
They are also periodically audited according to EPA’s Performance Evaluation
Program (PEP). EPA’s high-quality specs for FEMs/FRMs have led to these EPA-approved
devices being sold to governmental regulatory agencies around the world.
FEMs/FRMs are
expensive, typically $15,000 to $50,000 per monitor, and can often require a
temperature-controlled environment and routine calibration and maintenance by
skilled technicians, which increases operating costs. These devices can be
quite limited in terms of siting requirements. The high cost and siting issues
mean lower coverage for a process that works better with more data points. Thus,
air quality with FEMs/FRMs is more regional rather than local. There are,
however, good ways to fill in the missing data gaps. One is mobile air quality
monitoring, which can be FEM/FRM equipment or lower-cost sensors set up in
vehicles. Mobile air quality monitoring can increase spatial resolution. It can,
however, miss specific pollution events. Another method to increase data
coverage is stationary low-cost sensors, discussed below.
Calibration is
very important to both FEMs/FRMs and sensors. EPA defines it as follows: “procedures
for checking and adjusting a reference instrument’s settings so that the
measurements produced are comparable to a certified standard value.” Frequent
calibration is often recommended and required. Weather parameters such as relative
humidity, wind speed, wind direction, sunlight, and cloud cover also affect data
quality and must always be considered in the interpretation of data.
Non-Regulatory-Grade Enhanced Air Quality Sensors
to Fill in Data and Pinpoint New Sources
These sensors
have the advantage of being low-cost so that many can be employed to significantly
increase data coverage and spatiotemporal resolution. They can be deployed
quickly to respond to potential new emission events. There are many types, some
requiring dedicated electricity service, and others with Wi-Fi, solar-charged
batteries, GPS, display screens, weather sensors, and cloud connections. Sites
close to pollution sources and near vulnerable populations can be given good
coverage with low-cost sensors.
Sensors need
less training to operate but may need more training to interpret. They are
quite portable. They vary in quality and not enough is yet known about their
lifetimes as some can be short-lived and some may lose sensitivity over time. Original
Equipment Manufacture (OEM) sensors may be “raw” optical, metal oxide, or
electrochemical types, so only a few types for a given pollutant. One or more
OEM sensors may be integrated into a device. Particulate matter (PM) sensors use
optical sensors. Particles scatter light from a laser or LED as they move
through the measurement cell. The detector measures the scattered light to
estimate the volume of particles or the number of particles. The count is then
converted to a mass concentration based on mass calibration factors or density.
High humidity can cause the mass of particles to be over-estimated. Electrochemical
sensors and metal oxide sensors are used for gases such as nitrogen dioxide and
ozone. Electrochemical sensors are sensitive to humidity and temperature and have
low power needs. Metal oxide sensors have higher power requirements due to the
need to heat up the sensor in order to increase sensitivity. There are many manufacturers
of air quality sensors. Some are interpreted immediately, some on the cloud,
and others after the data has been adjusted according to algorithms. According
to EPA:
“Data adjustments and algorithms take many forms:
• Factory “calibration” > Manufacturer
“calibration” > Field collocation > Network
correction check
• Manufacturer applied data correction > user
applied data correction
• Simple linear regression > more complicated data
model > machine learning/artificial
intelligence (AI)”
There are many
factors that make different sensors vary and sometimes provide questionable data.
One method of performance evaluation of sensors is to co-locate them with FEM/FRM
equipment and compare the results. Co-location can also be used to adjust or
correct sensors with data adjustment equations that result in better matches
with FEMs/FRMs. Sensor drift can also be better understood with co-location. Temperature,
humidity, drift over time, co-pollutants and noisy data can all interfere with
sensor accuracy. Since many pollution emission events may be temporary, these
issues could render the data useless or erroneous. FEMs/FRMs have much better
diagnostic parameters that can be validated. Ways to validate data with sensors
include co-locating with FEMs/FRMs, comparing and correcting to other sensors
in a close network, and drive-by validation with mobile monitors. While sensors
have lower-quality data, they can be useful when integrated with FEMs/FRMs. Since
sensors are deployed in less controlled environments than FEMs/FRMs, they also
need to be cleaned and maintained more as they can be more affected by things
like dust and moisture.
Key Differences Between Reference Monitors and Low-Cost Sensors. Source: U.S. EPA
An important factor
for evaluating an air sensor is its response time to an emission event. A sensor
with a quick response time, or high time resolution, can respond better to rapid
changes in pollutant concentrations at a stationary point, as the graphic below
shows:
Source: The Enhanced Air Sensor Guidebook. U.S. EPA. September 2022. ENHANCED AIR SENSOR GUIDEBOOK.PDF
In 2014, EPA first
published the Air Sensor Guidebook which can support users in planning and
collecting air quality measurements using air sensors. The latest version is
the Enhanced
Air Sensor Guidebook, last published in September 2022. It is a great
resource, not only for air quality sensor information, but for air pollution
studies in general. It gives useful strategies for developing sensor networks,
including strategies for quality assurance (QA) and quality control (QC). EPA
also provides information, including videos, on their Air Sensor Toolbox website.
Source: The
Enhanced Air Sensor Guidebook. U.S. EPA. September 2022. ENHANCED
AIR SENSOR GUIDEBOOK.PDF
Satellite Air Quality Monitoring
Another way to
increase air quality data coverage is with satellite data. One such satellite
is NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS). Air quality
monitoring from satellites is based on how sunlight is scattered by ambient
particles. The way NASA describes it is as follows: “Satellites measure
backscattered radiation, from which vertical column densities can be calculated.”
This is a form of remote sensing. Micro-satellites can photograph the entire
surface of the Earth each day with a resolution of about 3 meters per pixel. Researchers
at Duke University have used that data combined with metrics such as wind,
relative humidity, temperature, and other parameters combined with
meteorological data and trained the model through machine learning to predict
local PM 2.5 levels. Though accuracy is much lower than other measurements the
spatial resolution can be phenomenal.
Researchers
Alan Krupnick and Daniel Sullivan have found that for PM2.5 “EPA and its
land-based monitoring network have failed to identify 54 counties and another
25 million people in the United States who live in areas that violate these air
quality standards.” They think that the reason is simply that monitors are
too sparse, and they think that satellite data is the best way to fill in the
gaps. The article is from 2020 but they think that satellite data can do better
than low-cost sensors for filling in the data. The authors suggest that
pollution point sources and hotspots can be missed, even when abiding by EPA’s
recommendations for monitor placement, due to prevailing wind patterns,
distance from point sources, and other factors. Another huge problem they note
is that monitors don’t run all the time, especially older ones. They found that
while new PM2.5 monitors typically run more than 300 days per year, “56
percent of PM2.5 monitors gathered data on fewer than 121 days in 2015, and 23
percent gathered data on fewer than 80 days.” They also note that since EPA
announces when monitors are working or not working, this gives incentives for
some companies to pollute more when monitors are off-line. They think satellite
data can help.
Instead of
directly measuring PM2.5, satellites measure aerosol optical depth (AOD) from
which the density of aerosol particles can be estimated. The measurement involves
the difference between the solar radiation at the top of the atmosphere and the
radiation that reaches the Earth’s surface. When more airborne particles are
present less radiation reaches the Earth's surface. Unfortunately, these
measurements don’t work on cloudy days. AOD is converted to PM2.5
concentrations with statistical methods based on calibration and correction
with FEM/FRM monitors. The authors reiterate that they think satellite data can
do better than sensors to fill data gaps. They also note that satellite data
can be used to determine the boundaries of non-attainment areas. States
currently use five types of data to determine these boundaries: jurisdictional
boundaries, air quality data, emissions data, geography and topography
information, and weather data. They also use pollution modeling. EPA must
approve non-attainment boundaries. The authors note: “Because pollution
disperses, nonattainment boundaries work best when they err on the side of
being more geographically expansive, rather than precisely drawn.
High-resolution satellite data could provide for more tightly drawn boundary
estimates, which may cut abatement costs in the long run, but erring on the
side of public health with larger area boundaries seems wise, in general.”
NASA also uses
its ozone monitoring instrument (OMI) (launched in 2004) or TROPOspheric
Monitoring Instrument (TROPOMI) (launched in 2017) satellites to measure tropospheric
ozone but can also detect other pollutants and trace gases such as nitrogen
dioxide, sulfur dioxide, and formaldehyde. These can track changes in NO2
pollution over time. They have been used to track increases in NO2 over active
oil and gas basins such as the Williston Basin in Noth Dakota and the Permian
Basin in West Texas and Southeast New Mexico. OMI trends of NO2 correlate well
with surface measurements so its potential use for supplementing NO2 data is likely
to be very good.
Satellites can
offer great geographical coverage, although accuracy and calibration can be
considerably less reliable and both spatial and temporal resolution can be
lower. In spite of these shortcomings, satellite data is well situated to track the movement of pollution plumes through the atmosphere.
Source: NASA
Source: NASA
Potential Use of Moss and Lichen to Detect and Quantify
Heavy Metal Pollutants
Sienna Bishop
also notes some interesting studies done in the Pacific Northwest with moss and
lichen to measure levels of toxic heavy metals such as cadmium and arsenic.
Sampling is inexpensive and can cover a tight grid of local areas around known
point sources to supplement other data and catch missed emission events.
Measurement Strategies for Methane Emissions from
Oil & Gas Sites, Landfills, Sewage Treatment Facilities, Etc.
Due to the desire
to abate greenhouse gas emissions a whole industry has developed around methane
emissions abatement, particularly around oil and gas sites. Though not a
pollutant in the traditional sense, methane has a high global warming potential
in the short-term (10-20 years) and contributes significantly to global heating.
The industry also seeks to keep its ‘social license to operate’ by addressing
these concerns. In order to do so, each site requires monitoring of methane
emissions. In many cases involving emissions from certain equipment, methane
emissions measurements are coupled with measurements of air pollutants like VOCs,
so traditional air quality monitoring can be a co-benefit to methane emissions monitoring.
The chief
concern with methane emissions is methane escaping into the atmosphere, while
the main concern with traditional pollutants is their concentration near the
ground where humans live. Thus, the strategies for monitoring and abatement are
a bit different. Methane is not considered to be toxic, but it is flammable and
so is an explosion and fire hazard at higher levels.
Equipment and
protocols specific for measuring methane emissions include infrared optical imaging,
stationary sensors, LiDAR that may be carried by drones, and satellite-based
monitoring. Protocols have been developed to measure, verify, report, and
certify emissions per facility and per company so that natural gas and oil sold
by that company can be certified as methane abated.
References:
Air
Quality Monitoring 2.0: How different types of air monitoring technologies are
contributing to a more holistic understanding of air pollution. Sienna Bishop.
Clarity. August 4, 2021. What
is Air Quality Monitoring 2.0 & Air Sensing Technology (clarity.io)
Monitoring
Air Quality in Mining: Importance and Best Practices. Sienna Bishop. Clarity.
July 20. 2023. Best
practices for air quality monitoring at mining sites (clarity.io)
The
consequences of wildfires for air quality — and why it's important to have a
real-time air monitoring network for wildfire season. Sienna Bishop. Clarity. July
12, 2023. The
importance of having a real-time air quality monitoring network for wildfire
season (clarity.io)
Air
quality monitoring in construction zones: Minimizing health risks and enhancing
sustainability. Sienna Bishop. Clarity. June 28, 2023. Minimizing
construction's negative impacts on air quality (clarity.io)
Why it
is crucial for different levels of government to cooperate when it comes to
improving air quality and climate change. Sienna Bishop. Clarity. May 14, 2023.
Why
different levels of government must cooperate to mitigate air pollution and
climate change (clarity.io)
US EPA
Air Sensor Guidebook Series: How to select the right air quality monitoring
equipment for your project. Sienna Bishop. Clarity. April 19, 2023. How
to choose the most effective low-cost sensor equipment for your air quality
monitoring project (clarity.io)
Air
Pollution and Traffic: Monitoring Strategies for Reducing Emissions in Big
Cities. Sienna Bishop. Clarity. June 27, 2023. How
we can reduce vehicle emissions and air pollution in major cities (clarity.io)
A deep
dive on the economic impacts of air pollution. Sienna Bishop. Clarity. July 5,
2023. What
are the economic impacts of air pollution? (clarity.io)
The
benefits of air quality monitoring services for industrial and mining
operations. Sienna Bishop. Clarity. May 11, 2023. Why
air quality monitoring is important for mining and industry (clarity.io)
Clean
Air Act Compliance Monitoring. U.S. EPA. Clean
Air Act (CAA) Compliance Monitoring | US EPA
Criteria
Air Pollutants. U.S. EPA. Criteria
Air Pollutants | US EPA
Fundamentals
of Air Pollution (Fifth Edition). Daniel Valero. 2014. Academic Press/Elsevier.
Choked:
Life and Breath in the Age of Air Pollution. Beth Gardiner. University of
Chicago Press. 2019.
Scare
Pollution: Why and How to Fix the EPA. Steve Milloy. Bench Press. 2016
How a Contrarian
Scientist Helped Trump’s EPA Defy Mainstream Science. Marianne Lavelle. Inside
Climate News. May 28, 2020. How
a Contrarian Scientist Helped Trump’s EPA Defy Mainstream Science - Inside
Climate News
US EPA, July 13, 2020. EPA and Wisconsin Announce
All of Sheboygan County Now Meets Federal Air Quality Standard for Ozone. https://www.epa.gov/newsreleases/epa-and-wisconsin-announce-all-sheboygan-county-now-meets-federal-air-quality-standard
What
Does the Air Recirculation Button in Your Car Actually Do? Sean Cate. August
14, 2023. The Premier Dailey. What
Does the Air Recirculation Button in Your Car Actually Do? (msn.com)
A
guide to air pollution monitoring in mining. Catherine Hercus, Canadian Mining
Journal. November 14, 2022. A
guide to air pollution
monitoring in mining - Canadian Mining Journal
Natural
Gas and Decarbonization: Key Component and Enabler of the Lower Carbon,
Reasonable Cost Energy Systems of the Future: Strategies for the 2020’s and
Beyond. Kent C. Stewart. Amazon Publishing, 2022.
The
Continued Prevalance of Black Lung Disease Among Coal Miners: A Preventable
Tragedy and Yet Another Reason to Move Away from Coal. Kent C. Stewart. Blue
Dragon Energy Blog. July 31, 2018. Blue
Dragon Energy Blog: The Continued Prevalance of Black Lung Disease Among Coal
Miners: A Preventable Tragedy and Yet Another Reason to Move Away from Coal
The
Berea Sandstone, or Berea Grit: A Building Stone and Grindstone from Northern
Ohio. Kent C. Stewart. Blue Dragon Energy Blog 2.0. July 21, 2023. Blue
Dragon Energy Blog 2.0: The Berea Sandstone, or Berea Grit: A Building Stone
and Grindstone from Northern Ohio (bdeb2.blogspot.com)
A
Pollution-Free Future Doesn’t Only Save Lives: It will save money too. And a lot of
it. Mass Clean Air. Economics
of Pollution Reduction (bc.edu)
The
Enhanced Air Sensor Guidebook. U.S. EPA. September 2022. ENHANCED
AIR SENSOR GUIDEBOOK.PDF
EPA
Tools and Resources Webinar: FRMs/FEMs and Sensors: Complementary Approaches
for Determining Ambient Air Quality. Andrea Clements and Robert Vanderpool. Center
for Environmental Measurement and Modeling. US EPA Office of Research and
Development. December 18, 2019. PowerPoint
Presentation (epa.gov)
Scientists
develop pollution monitoring method for satellites. Thomas Barrett. April 27, 2020.
Air Quality News. Scientists
develop pollution monitoring method for satellites - AirQualityNews
Satellites
Can Supplement the Clean Air Act’s Land-Based Air Monitoring Network. Alan Krupnick.
Resources. June 15, 2020. Satellites
Can Supplement the Clean Air Act’s Land-Based Air Monitoring Network
(resources.org)
Trace
Gas Air Quality Products from OMI and TROPOMI. Melanie Follette-Cook and Pawan
Gupta. Application of Satellite Observations for Air Quality and Health
Exposure, Oct 9 and 11, 2019. D1P9_TraceGas_v1-final
(nasa.gov)
NASA
now has an instrument orbiting Earth that can see major air pollutants across
North America, tracing them down to an exact neighborhood. Katie Hawkinson. Business
Insider. August 26, 2023. NASA now has an instrument orbiting Earth that can see major
air pollutants across North America, tracing them down to an exact neighborhood
(msn.com)
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