31:[] 2f:{"title":"US EPA Particulate Matter NowCast AQI Algorithm","cells":[{"id":0,"value":"# US EPA Particulate Matter NowCast AQI Algorithm","pinned":false,"hidden":false,"mode":"md"},{"id":209,"value":"The US EPA generally uses 24 hours periods of data to calculate AQI. To calculate AQI at an hourly scale the NowCast algorithm is a more appropriate choice. This notebook walks through how to calculate particulate matter (PM2.5 and PM10) AQI using the NowCast method. By default, this demo uses the _Del Norte_ US EPA station in Albuquerque, New Mexico, USA, OpenAQ location 2178, fetched via the OpenAQ API. See the `fetchMeasurements()` function below for more details on how the data is queried.","pinned":false,"hidden":false,"mode":"md"},{"id":259,"value":"locationId = 2178","pinned":false,"hidden":false,"mode":"ojs"},{"id":263,"value":"Choose a date and time. `fetchMeasurements()` will automatically query measurements leading 12 hours before the chosen time.","pinned":false,"hidden":false,"mode":"md"},{"id":219,"value":"viewof datetime = Inputs.datetime({label: \"Datetime\", value: \"2022-10-27T00:00:00Z\"})","pinned":false,"hidden":false,"mode":"ojs"},{"id":80,"value":"","pinned":false,"hidden":false,"mode":"html"},{"id":65,"value":"

NowCast AQI

${nowCastAqi}

${lookupAqiValue(nowCastAqi).name}

","pinned":false,"hidden":false,"mode":"html"},{"id":90,"value":"## How to calculate","pinned":false,"hidden":false,"mode":"md"},{"id":92,"value":"Use the last 12 hours of hourly measurement data. For a valid NowCast AQI, 2 of the last 3 hourly measurements must _not_ be null.","pinned":false,"hidden":false,"mode":"md"},{"id":127,"value":"series = (await fetchMeasurements(2178)).map(o => o.value);","pinned":true,"hidden":false,"mode":"ojs"},{"id":94,"value":"Find the minimum and maximum measurements in the series:","pinned":false,"hidden":false,"mode":"md"},{"id":110,"value":" max = d3.max(series);","pinned":true,"hidden":false,"mode":"ojs"},{"id":113,"value":"min = d3.min(series);","pinned":true,"hidden":false,"mode":"ojs"},{"id":117,"value":"Calculate the range of the series by subtracting the minimum value from the maximum value.","pinned":false,"hidden":false,"mode":"md"},{"id":119,"value":"range = max - min","pinned":true,"hidden":false,"mode":"ojs"},{"id":134,"value":"Calculate the scaled rate of change by dividing the range by the maximum value in the series.","pinned":false,"hidden":false,"mode":"md"},{"id":132,"value":"scaledRateOfChange = range/max","pinned":true,"hidden":false,"mode":"ojs"},{"id":140,"value":"calculate the weight factor by subtracting the scaled rate of change from 1. This weight factor must be between 0.5 and 1.0, if the result of the difference of the scaled rate of change and 1 is less than 0.5, set the weight factor to 0.5.","pinned":false,"hidden":false,"mode":"md"},{"id":138,"value":"weightFactor = 1 - scaledRateOfChange < 0.5 ? 0.5 : 1 - scaledRateOfChange","pinned":true,"hidden":false,"mode":"ojs"},{"id":146,"value":"Apply the weight factor to the measurement series by multiplying the measurement value by the weight factor raised to the power of the number of hours ago, current measurements being hour zero (0)","pinned":false,"hidden":false,"mode":"md"},{"id":144,"value":"weighted = series.map((o,i) => o * Math.pow(weightFactor,i))","pinned":true,"hidden":false,"mode":"ojs"},{"id":151,"value":"Sum the weighted series values.","pinned":false,"hidden":false,"mode":"md"},{"id":153,"value":"weightedSum = weighted.reduce((a,b) => a + b)","pinned":true,"hidden":false,"mode":"ojs"},{"id":155,"value":"Sum the values of the weight factor raised to the power of the number of hours ago, current hour being hour zero (0).","pinned":false,"hidden":false,"mode":"md"},{"id":157,"value":"weightFactorSum = series.map((o,i) => Math.pow(weightFactor,i)).reduce((a,b) => a + b)","pinned":true,"hidden":false,"mode":"ojs"},{"id":160,"value":"Calculate the NowCast concentration number by dividing the weighted sum of values and sum of weight factor. Round the result to one decimal place.","pinned":false,"hidden":false,"mode":"md"},{"id":162,"value":"nowCastConcentration = parseFloat((weightedSum / weightFactorSum).toFixed(1))","pinned":true,"hidden":false,"mode":"ojs"},{"id":292,"value":"nowCastAqi = Math.round(concentrationToAqi(nowCastConcentration))","pinned":true,"hidden":false,"mode":"ojs"},{"id":294,"value":"function concentrationToAqi(concentration) {\n const concentrationBreakpoints = [0,12.0,35.4,150,200,300,500];\n const AqiBreakpoints = [0,50,100,150,200,300,500];\n const concHi = concentrationBreakpoints.find(o => concentration <= o)\n const concHiIdx = concentrationBreakpoints.indexOf(concHi)\n const concLo = concentrationBreakpoints[concentrationBreakpoints.indexOf(concHi) -1]\n const aqi = ((AqiBreakpoints[concHiIdx] - AqiBreakpoints[concHiIdx - 1])/(concHi - concLo)) * (concentration - concLo) + AqiBreakpoints[concHiIdx - 1]\n return aqi\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":281,"value":"To learn more about how to query data from OpenAQ read more at [https://docs.openaq.org](https://docs.openaq.org). If you have any questions or want to connect with others join our [Slack community](https://join.slack.com/t/openaq/shared_invite/zt-yzqlgsva-v6McumTjy2BZnegIK9XCVw)","pinned":false,"hidden":false,"mode":"md"},{"id":211,"value":"#### References\n* [How is the NowCast algorithm used to report current air quality?](https://usepa.servicenowservices.com/airnow?id=kb_article_view&sys_id=bb8b65ef1b06bc10028420eae54bcb98&spa=1)\n* [aqi-technical-assistance-document](https://www.airnow.gov/sites/default/files/2020-05/aqi-technical-assistance-document-sept2018.pdf)\n* [US EPA Forums - The NowCast for PM2.5 and PM10](https://forum.airnowtech.org/t/the-nowcast-for-pm2-5-and-pm10/172)","pinned":false,"hidden":false,"mode":"md"},{"id":72,"value":"function lookupAqiValue(aqi) {\n let aqiLevel;\n for (const value of AqiValues) {\n if (aqi <= value.max) {\n aqiLevel = value\n return aqiLevel\n }\n }\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":62,"value":"AqiValues = [\n {max: 50, color: \"green\", name: \"Good\"},\n {max: 100, color: \"yellow\", name: \"Moderate\"},\n {max: 150, color: \"orange\", name: \"Unhealthy for sensitive groups\"},\n {max: 200, color: \"red\", name: \"Unhealthy\"},\n {max: 300, color: \"purple\", name: \"Very unhealthy\"},\n {max: 500, color: \"maroon\", name: \"Hazardous\"}\n]","pinned":false,"hidden":false,"mode":"ojs"},{"id":242,"value":"dateCopy = new Date(datetime.getTime())","pinned":false,"hidden":false,"mode":"ojs"},{"id":245,"value":"dateFrom = new Date(dateCopy.setHours(dateCopy.getHours() - 12)).toISOString()","pinned":false,"hidden":false,"mode":"ojs"},{"id":257,"value":"url = `https://api.openaq.org/v2/measurements?location_id=${locationId}&date_from=${dateFrom}&date_to=${datetime.toISOString()}¶meter_id=2`","pinned":false,"hidden":false,"mode":"ojs"},{"id":122,"value":"async function fetchMeasurements(locationId) {\n const res = await fetch(url);\n const data = await res.json();\n const results = data.results;\n return results\n}","pinned":false,"hidden":false,"mode":"ojs"}],"files":"$W31","stdlib":"1","titling":"auto"}