Air Pollution Dispersion Models Applications with the AERMOD

Air Pollution Dispersion Models: Applications with the AERMOD Modeling System AERMET – PART 1 COURSE #423 DAY 1 AFTERNOON

DAY 1 AFTERNOON: AERMET – PART 1

OVERVIEW This lesson introduces: § Minimum Meteorological Data Requirements – Hourly Weather Observations – Upper Air Soundings § 1 -Minute Wind Data § Site-specific Data § Data Representativeness § Temporal Data Requirements § Surface Characteristics § Multistage Processing – Three stage process – Overview of the control file structure

LEARNING OBJECTIVES At the end of this session, you will understand: § AERMET data requirements § Data representativeness and substitution § General control file structure § Multistage processing

AERMET METEOROLOGICAL DATA REQUIREMENTS

AERMET DATA REQUIREMENTS § Minimum Requirements – Hourly Weather Observations – National Weather Service (NWS) › Observer-based vs. Automated Observations › Automated Surface Observation System (ASOS) – Commissioning Date – why is it important? › Basic elements collected – Sky conditions such as cloud height and cloud amount up to 12, 000 feet, – Surface visibility up to at least 10 statute miles, – Basic present weather information such as the type and intensity for rain, snow, and freezing rain, – Obstructions to vision like fog, haze, and/or dust, – Sea-level pressure and altimeter settings, – Air and dew point temperatures, – Wind direction, speed and character (gusts, squalls), – Precipitation accumulation, and – Selected significant remarks including- variable cloud height, variable visibility, precipitation beginning/ending times, rapid pressure changes, pressure change tendency, wind shift, peak wind

AERMET DATA REQUIREMENTS ASOS site instrumentation, Elko, NV http: //commons. wikimedia. org/wiki/File: Elko_ASOS_viewed_from_the_south. jpg © 2008 Famartin under a Creative Commons Attribution-Share Alike 3. 0 Unported license

AERMET DATA REQUIREMENTS § Minimum Requirements – Hourly Weather Observations – National Weather Service (NWS) › Minimum Data Elements to Run AERMET with NWS Data – Wind speed and direction, nominally about 10 meters – Temperature, about 2 meters – Cloud cover › Data Formats Recognized by AERMET – CD-144 (80 -character records primarily to comply with paper cards) – SCRAM – EPA’s reduced format of CD-144 with only required elements (28 char) – SAMSON, HUSWO – available from NCDC on CD; additional fields – TD 3280 – fixed and variable block – a format for magnetic tape – ISHD, ISH, ISD – latest incarnation; international; includes special observations

AERMET DATA REQUIREMENTS § Minimum Requirements – Hourly Weather Observations – NWS, cont’d › Notes on Formats – CD-144, SCRAM, SAMSON, HUSWO, TD 3280 report in local time; – ISHD reports in Greenwich Mean Time (GMT) – INSWO – NOT SUPPORTED - International Surface Weather Observations 19821997 › Availability of Data – Format dependent » CD-144, SCRAM – not available unless archived by 3 rd party » SAMSON, HUSWO – not available unless CD is available or archived » TD-3280 – not available unless archived » ISHD – available for download from NCDC – 1901 through present • ftp: //ftp. ncdc. noaa. gov/pub/data/noaa • Pick year • Pick station › Abbreviated ISHD – NOT SUPPORTED

AERMET DATA REQUIREMENTS § 1 -Minute ASOS Wind Data – Studies indicated that more calm winds are associated with hourly reported ASOS data – Annually, increased from a few percent with pre-ASOS, nonautomated observations to 10%, 20%, and possibly more – Biases concentration estimates in AERMOD since an hour with a calm wind is not processed – 1 -minute wind data archived at NCDC – AERMINUTE developed to process 1 -minute data compute a 1 -hour average to supplement hourly winds – Included in AERMET (stage 2) – TD-6505 (wind); also available is TD-6506 (temperature) but not used – 2000 – present

AERMET DATA REQUIREMENTS – Upper Air Data (Radiosondes, Rawinsondes) › Instrumented package typically released twice-daily to obtain profiles of height, pressure, temperature, relative humidity, and winds › Usually 0000 GMT and 1200 GMT; often seen about ± 1 hour; special soundings may be launched at other times such as 0600 and 1800

AERMET DATA REQUIREMENTS – Upper Air Data (Radiosondes, Rawinsondes) › 92 stations in North America; distance between stations in U. S. - ~200 km › 10 stations in Caribbean

AERMET DATA REQUIREMENTS – Upper Air Data (Radiosondes, Rawinsondes) › Data Elements Required by AERMET – Height, pressure, temperature; sounding winds are not used › Data Formats Recognized by AERMET – TD-6201: VB or FB – Forecast Systems Laboratory » Two versions – only difference is how missing data is indicated › Availability – CD: Radiosonde Data of North America 1946 -1996 from NCDC – Online: http: //www. esrl. noaa. gov/raobs/ 1990 -present

AERMET DATA REQUIREMENTS – Upper Air Data, cont’d › AERMET and Upper Air Sounding Times – AERMET searches for an ‘early morning sounding’ for the day being processed – For US stations this means a 1200 GMT sounding – AERMET looks in the period from 1100 GMT to 1300 GMT for the sounding – User can override this window and expand or move, e. g. » 1000 – 1400 » 1300 – 1600 – AERMET globalized to find appropriate upper air sounding to use

AERMET DATA REQUIREMENTS – Upper Air Data, cont’d › Mandatory and Significant Pressure Levels – Mandatory: at specific pressure levels » 1000 mb, 925 mb, 850 mb, 700 mb, 500 mb, 300 mb, 250 mb, 200 mb, 150 mb, 100 mb, and several above this level – Significant: a pressure level with an important characteristic, such as » surface » termination level (as a result of balloon burst, floating balloon, pressure or temperature sensor failure, weak signal) » tropopause, » base and top of an inversion with a temperature change greater than 2. 5°C or 20% RH below 300 mb – When downloading upper air data and the choice is give to download mandatory, significant, or both, ALWAYS CHOOSE BOTH – Why?

AERMET DATA REQUIREMENTS § Pairing Hourly Weather Observations with Upper Air Data – Collocated would be first choice, but there are many more surface stations than upper air stations – If not collocated, consider proximity, terrain or exposure § Pre-processed Data – Many states pre-process NWS hourly observations and upper data and make the files available on their web site

AERMET DATA REQUIREMENTS § Site-specific Meteorological Data – Data collected by a facility – Variables collected will often depend on purpose of data collection – Often only 1 level of wind speed and direction, 1 level of temperature; sometimes solar or net radiation, σv – No specific format for data storage – User must inform AERMET what variables are present and how to read them – Running AERMET with only site-specific data

AERMET DATA REQUIREMENTS § Data Representativeness – Important concept to understand apply – EPA Meteorological Monitoring Guidance states › “…meteorological data should be representative of conditions affecting transport and dispersion in the area of interest as determined by the locations of sources and receptors. ” – When using NWS data in AERMOD, data representativeness can be thought of in terms of constructing realistic ABL similarity profiles and adequately characterizing the dispersive capacity of the atmosphere – Case-by-Case and Variable-by-Variable Assessment – Factors to consider include (but not limited to) 1. 2. 3. 4. Proximity Complexity of terrain Exposure Period of time

AERMET DATA REQUIREMENTS § Meteorological Data Substitution – Reference level – what is it? – Manual › Hourly Surface › Upper Air (“morning”) › Site-specific – Automated › Why didn’t AERMET run with NWS data only? › AERMET’s Stage 3 METHOD keyword (concept to be discussed shortly) › AERMINUTE output

AERMET DATA REQUIREMENTS § Length of Meteorological Data Record – Regulatory requirements – Appendix W, Section 8. 3. 1. 2 › a. – five years of representative meteorological data – preferable for the period to be consecutive years from the most recent, readily available period – adequately representative and my be site-specific or nearby NWS › b. – 5 years NWS or 1 year site specific – if more than 1 year site-specific, quality assured data are available, then it should be used (only up to 5 years) › c. – if emission limits are based on a specific year of met data, that year must be added to the period (5 years NWS or 1 -5 years site-specific) › d, e. – long range transport (LRT) considerations (not AERMOD) › f. – where site-specific data are relied upon in complex wind situations, use of at least 1 year, or more if available, should be used; as before, quality-assured data must be used

AERMET DATA REQUIREMENTS § Length of Meteorological Data Record – Requirements for the new probabilistic standards › 1 -hour NO 2, 1 -hour SO 2, and 24 -hour PM 2. 5 – Appendix W: 5 -years NWS or 1 -year (up to 5 years if available) site-specific › Ambient monitoring design values – Standard based on three years data › Does NOT preempt or alter the Appendix W requirement

AERMET DATA REQUIREMENTS § Surface Characteristics – Quick definition – Albedo (noontime) (α) – surface reflectivity: 0 (100% reflected) to 1 (nighttime) – (Daytime) Bowen ratio (B, Bo) – surface moisture: typically 0. 1 for water to 10. 0 for desert – Surface roughness length (z 0) – surface obstacles: 0. 001 meters over water to order of 1 meter in urban and forested areas – Dual Characteristics – Why are these characteristics important? – AERSURFACE – shortly

MULTISTAGE PROCESSING § Three Separate Stages – Historical Perspective › Based on old MPRM › Limited computer memory – 640 Kb max with about 512 Kb memory to run programs › Force user to (hopefully) review data and reports after each processing stage and identify problems, if any › Two executables – Now only 1 executable but still 3 stages – Stage 1 – extract surface and upper air data from “archive” format and perform basic QA › QA only on on-site data – Stage 2 – combine QA’d data into 1 -day ‘chunks’ › Not really meant for review but can help troubleshooting problems – Stage 3 – develop the files needed by AERMOD › “Surface” file – boundary layer parameters › Profile – parameters at one or more heights

MULTISTAGE PROCESSING § Control File Structure/Formats - Overview – Pathway/keyword/parameter – Pathways › › › JOB – report files; also for just checking syntax (all stages) SURFACE – typically NWS hourly observations (stage 1) UPPERAIR – typically twice-daily NWS soundings (stage 1) ONSITE – site-specific data (stage 1) MERGE – stage 2 METPREP – stage 3 – Keyword › Many unique to each pathway › Some common to SURFACE, UPPERAIR, ONSITE – LOCATION, DATA, AUDIT, XDATES, RANGE, QAOUT › Mandatory/Optional › Repeatable/Non-repeatable › Reprocessed

MULTISTAGE PROCESSING § Control File Structure/Formats - Overview – Parameter › For most keywords, one or more parameters › Typically unique for each keyword › Inform AERMET on how to process data for the particular keyword

SUMMARY In this session, we covered the following topics: § AERMET meteorological data, including – NWS data – 1 -minute ASOS data – Site-specific data – Site characteristics § Data representativeness – Data substitution § Temporal requirements for compliance demonstrations § Multi-stage processing in AERMET § Control file basics