ATTACHMENT D Meteorological AnalysesMeteorological Analyses

Meteorology is a major factor in the formation and transport of ozone and its precursors. High ozone concentrations in southern New Hampshire occur most oftenwhen low pressure systems approach from the Great Lakes or southern Canada while high pressure is situatedjust offthe eastern seaboard. When such ascenario is in place, it provides warm temperatures, clear skies, and southwesterly winds to allow the transport ofprecursors into the Northeast. Following the NOx SIPcall, which went into effect in 2003, and other emission control programs, NOx andVOCemissions have been reduced throughout the region. Ozoneexceedances in recent years have been fewer in large part because ofthese emissions reductions. To confirmthat lower ozone levels in New Hampshire are not simply a result of anomalous weather conditions, such as lower summer temperatures or changing wind patterns, the following analyses were performed: Temperature versus ozone graphs Graphs ofwind frequency data Temperaturevs. Ozone Graphs Since ozone exceedances are typically associated with hot sunny summer days, NHDES staff compared maximumdaily temperatures to numbers of ozone exceedance days in NewHampshire. Concord Airport temperature data were downloaded fromthe National Weather Service's website for the months of April through September and the years 1985 to 2011 . Concord Airport was chosen as a representative site because it has historical data for the full period and is located in a central part of southern New

Hampshire. Formulas were then written to count the number of days during each year's ozone season that the maximumdaily temperature rose above 85 F. These counts, as well as the number ofdays in which one or more NewHampshire sites exceeded the 1997 NAAQS, were tabulated for each year 1985-2011 . Next, the data were sorted in ascending order by the number ofdays with a maximumtemperature over 85 F, and the sorted data were used to create the bar-line chart displayed in the figure below . This depiction creates an upward-sloping trend line for temperature and exceedance days. To emphasize the period 2003-2011, the data points for these years were circled and labeled. Number of Days with MaximumTemperatures above 85 F and Number of Days with

Ozone Exceedances in New Hampshire, 1985-2011 70 60

N T eo t7 O L ar a Z 50 40 30 ~ MaxTemperature >85 F -*--Ozone Exceedances -Linear (Ozone Exceedances) Notes: Temperatures are National Weather Servicedata from ConcordAirport. 20 10 0 Data are sorted by number of days with maximum temperature >85 F (therefore, years are not in chronological order) .Wind Direction Frequency Charts

NHDES staff explored historical wind direction frequencies in NewHampshire. Again, National Weather Service data were used to provide a consistent, long-termdataset. Wind directions and wind speeds were downloaded fromthe National Weather Service's website for the months ofApril through September to provide ozone season wind data for the years 1995-2010 . Data were gathered for two sites, centrally located Concord Airport and the coastal site at Pease International Airport in Portsmouth. The downloaded data were consolidated to produce once-hourly lists ofwind direction and wind speed observations. Because the number of observations each hour varied in the rawdataset, extraneous observations outside the regular measurement interval were removed to provide greater consistencyfor the final calculations. Also, to avoid bias fromthe inclusion ofwind directions during calmconditions, wind observations were excluded ifthecorresponding wind speedwas less than 3 mph. All rawwind direction data were measured in intervals of 10 degrees. Formulas were written to calculate the percentage of total hours for which the wind direction was recorded at each 10-degree interval . This was done separately for two time periods, 1995-2002 and 2003-2010 . The resulting percentages were then incorporated into wind roses to illustrate typical wind direction frequencies at each site, as shownhere.

New Hampshire Wind Direction Frequencies in the Months of April through September, 1995-2010 Wind Direction Frequencies at Concord Airport Wind Direction Frequencies at Pease Airport, Portsmouth

National Weather Service Data National Weather Service Data

1995-2010 1995-2010 --*-1995-2002 --*-- 1995-2002 -m-2003-2010 f-2003-2010