Before we jump into this, here are a few basics about ozone.
Now that we have that covered, we can talk about the implications of high ozone. When a standard the EPA has established cannot be met, the Clean Air Act imposes increasingly restrictive requirements on that area. These requirements are meant to "clean up" the area so one day it will meet the standard. An area that does not meet a particular standard is called a nonattainment area. Here's a PDF map of the Denver ozone nonattainment area. Here's an interactive map of all the nonattainment areas in the United States (turn on the layers of interest in the menu in the upper right). If an area is designated nonattainment and still cannot meet the standard, the designation and associated implications get worse over time.
Currently, the Denver area is classified as moderate nonattainment and is expected to be redesignated as serious within several months. Perhaps the most talked about subject regarding the Denver nonattainment area is the major source threshold. Major sources of air pollution (way over simplified: sources that emit more than a certain amount of pollution) have to comply with many more rules than smaller sources. Some examples are best available control technology (BACT) analysis, modeling for visibility and gaseous deposition, and air quality monitoring. These analyses are reserved for major sources not only because they're resource intensive, but also because the scale of the emissions at these types of facilities warrant additional analyses to ensure things like human health and important protected environments (e.g., national parks) are protected. If an area is meeting the air quality standard (in attainment), the major source threshold is 250 tons per year (tpy). With each nonattainment redesignation, that threshold drops (see below) requiring more and more facilities to perform these analyses. There are certainly benefits to (a) having a higher major source threshold, and (b) remaining below that threshold. That gets too political for this blog.
Nonattainment Designations (Major Source Thresholds for VOC or NOX)
Although stationary industrial facilities have the potential to emit pollutants that contribute to the ozone problem, so do I personally. I commute to work at least four days per week driving more than 200 miles per week (not including driving other than commuting). And guess what? My car emits VOCs and NOX, two of the three things necessary to form ozone. The third, remember, is sunlight...
This ozone season, we are encouraging our employees, our Colorado-based clients, and other contacts to work from home or use public transit during days with high forecasted ozone concentrations. If you'd like ozone forecast emails, please sign up here.
There is something we need to talk about honestly, though. We get it, you do laundry when you work from home. You probably even run to the grocery store, post office, and out to lunch, too. We won't tell your boss. Heck, you might even drive more than if you just went into the office. If you're considering implementing this practice in your personal life or in your workplace, we kindly ask you to consider the actual miles driven on high ozone days in an effort to lower the regional ozone problem.
On April 12, 2018, a PM₁₀ monitor in Pinal County, Arizona (specifically the Stanfield Monitor) reported an average daily concentration of 1,100 μg/m³. This number still technically has not been finalized, but it has been provided by Pinal County as a draft PM exceedance. For perspective, that concentration is more than 7 times more than the National Ambient Air Quality Standard (NAAQS) for 24-hour PM₁₀ (150 μg/m³)! This is the highest monitored 24-hour PM₁₀ concentration I've ever seen and as such, I figured I'd do a bit of investigating to see what led to this atypically high concentration.
From looking at the 2018 Draft PM Exceedance summary, it's not atypical for this monitor to have the highest monitored concentration among all PM₁₀ monitors in Pinal County, but to have a concentration this high is quite atypical. The 24-hour average PM₁₀ concentration at Stanfield has been above 500 μg/m³ six times so far in 2018 (as of the end of September). Interestingly, the Stanfield PM₁₀ monitor did not monitor any 24-hour average PM₁₀ concentrations above 500 μg/m³ in 2017, 2016, 2015, or 2014 (which is as far back as is archived on the Pinal County Monitoring Network website).
Here's the AQI map (airnow.gov) for 5:00 PM on April 12. The Stanfield monitor is located off the southern edge of the left map, but is south of Phoenix and west of I-10, presumably in the dark purple "Hazardous" area. Keep in mind this is the combined AQI, but on this particular day, the AQI is dominated by particulate.
This widespread and severe event is corroborated by the other nearby monitors which range from 244 to 780 μg/m³ 24-hour PM₁₀. I made a KMZ of the Pinal County monitors above the NAAQS from that day which can be downloaded here.
The draft exceedance summary provides some information regarding what caused these elevated concentrations. It indicates there was a fast-moving springtime cold front that led to very high winds (47 mph max) and elevated PM concentrations. The daily weather maps for that day and the following day corroborate the passage of a cold front in the region. A map of the wind fields in the area (shown below and accessible through mesowest.utah.edu) indicates similar maximum wind speeds with winds blowing from the southwest and west throughout the day.
At this point, I've established that on April 12, 2018, Arizona was windy. The wind was caused by a speedy cold front and it kicked up quite a lot of dust. What I was still curious about is why this day was so dusty for so long, to the point where two Pinal County PM₁₀ monitors recorded concentrations over 500 μg/m³. I'd also like to know why the Hidden Valley PM₁₀ monitor, which is the same equipment as the Stanfield monitor and located less than 5 miles west, only monitored a concentration of 244 μg/m³. Cue the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) in reverse.
HYSPLIT is a model developed by NOAA that utilizes gridded meteorological data to estimate trajectories of atmospheric pollutants. This web-accessible model can be configured to run in reverse to help determine whether the concentration at a particular location (i.e., a particulate monitor) was influenced by the transport of a pollutant from another location (i.e., a known source of dust).
I configured HYSPLIT to run in several ways for both monitors and due to the consistency and magnitude of the wind present during the time in question, there was no configuration that showed anything other than very defined trajectories coming from the west-southwest for the hours leading up to and during the high monitored concentrations. Here is the HYSPLIT configuration for the trajectories below. All parameters are the same for both monitors except coordinates. The trajectories continue across southern Arizona and California.
Earlier this week I spent an hour or so in the middle of a cornfield in northern Colorado during a relatively windy day. It just so happens the week I decide to write a blog post about dust in an agricultural area in Arizona correlates with a week that I visit an oil and gas facility in the middle of a cornfield on a windy day north of Denver. While I was there, a tractor was spreading manure in the field with quite a plume of dust coming from the back of the tractor. It gave me the idea to look more into the agriculture near the Stanfield PM₁₀ monitor. Time to call in the experts.
I discussed my theory with an agricultural expert from the Pinal County Office of the University of Arizona's Cooperative Extension and unfortunately, there was likely little to no agricultural activity in this region in mid-April. The crops that exist there (in the rectangular fields) are likely either corn, alfalfa, or cotton. All three of which would have already been planted and left to grow by April. My conversation did, however, point me to another possible source of the dust, an empty lot. The monitor in Stanfield is located behind the Sheriff's office surrounded by empty lots, which by the looks of Google Street View, is frequently disturbed, and therefore susceptible to blowing dust during high-wind events.
I can't say for sure that a freshly-disturbed dirt lot during a day of exceptionally high winds caused 24-hour concentrations of PM₁₀ over 1,000 μg/m³, but in order for there to be such a difference between two monitors in relatively close proximity there either had to be a very localized activity which caused airborne particulate or an equipment issue (e.g., malfunction, audit). Assuming both monitors were functioning correctly, that leaves the option for a very localized source of dust that only affects one monitor. I can't say with 100% certainty, but if there's anything to Occam's Razor, I'd wager the origin of much of the PM was simply an empty lot downwind of the Stanfield monitor on a windy day during the third driest month of the year.
Have other ideas? Let me know!
If you don't know me when I get excited I can't help but share whatever I'm excited about with my friends, colleagues, and family. One of the recent things I'm excited about (other than freshly roasted New Mexican green chilis) is the idea that many companies in resource extraction industries have started taking offsets for their CO2e emissions seriously. One company, in particular, has asked Air Basics to help them develop a plan to offset all of their greenhouse gasses - on the order of 1,000,000 metric tonnes of CO2e annually. I recently made the whole office (thanks, team!) listen to a presentation about this client and asked for help with brainstorming ideas to reduce emissions, generate onsite electricity, and offset the remaining greenhouse gasses.
Having dedicated some serious brainpower to carbon emissions in industry, I started thinking about my own carbon impact. I've taken the online quizzes before to determine my carbon footprint. I'm an air quality engineer, what do you expect? This time though was different. I stumbled upon what I ultimately ended up using to (spoiler alert) offset my 2018 carbon footprint, although in hindsight this is not a terrible place to start: the United Nations Framework Convention on Climate Change. I was researching the Paris Agreement when I found Climate Neutral Now, which describes themselves like this:
Climate Neutral Now is an initiative launched by the UN Climate Change in 2015, aiming at encouraging and supporting all levels of society to take climate action to achieve a climate neutral world by mid-century, as enshrined in the Paris Agreement adopted the same year.
They promote quantification, reduction, and offsetting greenhouse gasses (in that order) for companies, events, and citizens. Considering the fact that I use at least one gallon of gasoline per day, I figured I'd check out what this quiz has to say about my personal carbon impact. To my surprise, it was detailed enough to be thorough, yet generic enough to be realistic. It quantified my carbon footprint considering things like house details, energy consumption, miles driven, gas mileage, flights, diet, and waste habits. It took less than ten minutes, including the time it took to log into my utility provider and estimate my annual average electricity consumption. It asked for the perfect amount of detail and uses averages in lieu of the minutiae.
I specified my 1,160 square-foot house, my 60 mpg hybrid, and the fact that I eat meat frequently. With those and the rest of my inputs, it estimated that my annual carbon footprint was 21 metric tonnes per year. If you're anything like me, you've done this exercise before and then promptly closed the window before the guilt of emitting over four times the global average sank in. This time, though, I was curious about what I would have to sacrifice in order to offset my carbon impact. If parts of industry were starting to get responsible for their impacts, what was stopping me?
I explored the projects that sell carbon offsets and was quite surprised to find that the cost per metric tonne ranged from $0.33 to $8.50. For my carbon footprint, that meant that I could offset it for a price as low as $6.93! So I did, mainly because I've spent more on La Croix in the last week than that. For a sum of money that was at least ten times less than I was expecting and in about 15 minutes, I offset my estimated 2018 carbon footprint. Granted, this is nowhere near the 1,000,000 metric tonnes our client is looking to offset, it's a start. You even get a certificate!
On a personal level, I'd like to encourage (guilt) you to take the quiz and see what your carbon footprint is and how inexpensive it can be to offset your annual carbon footprint. I'll buy you a La Croix. On a company level, feel free to reach out if you'd like help quantifying, reducing, and offsetting your carbon impact. I might still buy you a La Croix.
Carbon dioxide (CO2) is a colorless gas that occurs naturally in earth’s atmosphere. CO2 is known as a greenhouse gas (GHG): a gas that contributes to the greenhouse effect by absorbing thermal infrared radiation and heating the planet’s lower atmosphere. CO2 is one of several gasses that contributes to the greenhouse effect. Other GHGs include water vapor, methane (CH4), nitrous oxide (N2O), ozone (O3), perfluorinated compounds (PFCs), hydrofluorocarbons (HFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3) the most abundant of which are water vapor, CO2, CH4, and N2O (in earth’s atmosphere). Each pollutant has been assigned a global warming potential (GWP), “a concept to compare the ability of each greenhouse gas to trap heat in the atmosphere relative to another gas” (EPA). In this case, CO2 has been assigned a GWP of one and the GWP of all other GHGs is compared to CO2.
The three largest contributors of CO2e in the United States as a whole are CO2, CH4, and N2O. Their GWPs are 1, 25, and 298, respectively.
For each GHG, a CO2 equivalence (CO2e) can be calculated by multiplying the quantity of each GHG by its corresponding global warming potential (GWP). For example, if a facility emitted 10 metric tons (MT) of CH4, the facility-wide CO2e would be 250 MT.
In 2018, the EPA published a report containing GHG emission and sink data from 1990-2016. The gross US CO2e emissions are shown below, separated by gas type.
The following chart, from the same report, indicates which economic sectors emitted GHGs in the US.
If you'd like help reporting, reducing, or offsetting your carbon emissions, feel free to contact us.