ATTACHMENT D 

Meteorological Analyses 
Meteorological 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 often when low pressure systems approach from 

the Great Lakes or southern Canada while high pressure is situated just off the eastern seaboard . When 

such a scenario is in place, it provides warm temperatures, clear skies, and southwesterly winds to allow 

the transport of precursors into the Northeast. 

Following the NOx SIP call, which went into effect in 2003, and other emission control programs, NOx 

and VOC emissions have been reduced throughout the region . Ozone exceedances in recent years have 

been fewer in large part because of these emissions reductions. To confirm that 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 of wind frequency data 

Temperature vs. Ozone Graphs 

Since ozone exceedances are typically associated with hot sunny summer days, NHDES staff compared 

maximum daily temperatures to numbers of ozone exceedance days in New Hampshire . Concord 

Airport temperature data were downloaded from the 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 

maximum daily temperature rose above 85 F . These counts, as well as the number of days in which one 

or more New Hampshire sites exceeded the 1997 NAAQS, were tabulated for each year 1985-2011 . 

Next, the data were sorted in ascending order by the number of days with a maximum temperature 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 Maximum Temperatures 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 

~ Max Temperature >85 F 

-*--Ozone Exceedances 

-Linear (Ozone 

Exceedances) 

Notes: 

Temperatures are National 

Weather Service data from 

Concord Airport. 

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 New Hampshire. Again, National 

Weather Service data were used to provide a consistent, long-term dataset. Wind directions and wind 

speeds were downloaded from the National Weather Service's website for the months of April 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 of wind direction and wind speed 

observations . Because the number of observations each hour varied in the raw dataset, extraneous 

observations outside the regular measurement interval were removed to provide greater consistency for 

the final calculations . Also, to avoid bias from the inclusion of wind directions during calm conditions, 

wind observations were excluded if the corresponding wind speed was less than 3 mph. 

All raw wind 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 shown here. 

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 

f-2003-2010 -m-2003-2010