AIR TEMPERATURE EVOLUTION AND CLIMATE PENALTY FACTOR IN THE [627167]

AIR TEMPERATURE EVOLUTION AND CLIMATE PENALTY FACTOR IN THE
CIUC DEPRESSION

Sándor Petres1, Ágnes Keresztesi2, Szabolcs Lányi3, Réka Boga4

1 University Politehnica of Bucharest & Sapientia University, Miercurea -Ciuc, Romania,
[anonimizat]
2Babeș -Bolyai University, Institute for Doctoral Studies, Environmental Doctoral School, Cluj –
Napoca, Romania, [anonimizat]
3 Unive rsity Politehnica of Bucharest & Sapientia University, Miercurea -Ciuc , Roma nia,
[anonimizat]
4 Sapientia University, Miercurea -Ciuc, Romania, [anonimizat]

Key words: air temperature, extreme temperature indices , tropospheric ozone, climate penalty factor ,
SOMO35

Abstract. This paper present s the most significant changes of air temperature and extreme temperature indices for the 2007 –
2016 decade in the city of Miercurea -Ciuc (Romania) . We used hourly data provided by the National Administration
for Meteorology weather station, situated at Miercurea -Ciuc at an altitude of 661 m . The results were compared with
relevant studies referring to temperature measurements for the 1961 -1990 reference period . Evolution of
ozone concentration for the 2007 -2016 decade was also overviewed, by means of climate penalty factor, SOMO35 and AOT40
calculation based on hourly data measured by the regional automatic background monitoring station HR 01 ,
situated at an altitude of 710 m in Jigodin -Bai suburb of Miercurea -Ciuc, and operated by the National Environmental
Protection Agency.

Introduction
Climate started to intrigue scientists centuries ago, academic societies from Eastern Europe
financed publication o f scientific work on climate as early as the 19th century ( Heller 1888 ). Global –
scale observations from the instrumental era began in the mid -19th century for temperature and other
variables, with more comprehensive and diverse sets of observations availab le for the period 1950
onwards (Stocker et al. 2013 ). The growing concern about climate changes and their effects on human
health and welfare led to intensified research and communication. Several recent studies are assessing
the global ( WMO 2016, WMO 2017 ), regional ( NAM 2008, Pongrácz et al. 2009 , Machidon et al.
2012 ) and local evolution of the climate (Petres et al. 2017 b).
Science shows with certainty that human activity is the dominant cause of observed warming
since the mid -20th century. Many of the observed changes are unprecedented over decades to
millennia: warming of the atmosphere and the ocean, diminishing snow and ice, rising sea levels and
increasing concentrations of greenhouse gases. Each of the last three decades has been successively
warme r at the Earth’s surface than any preceding decade since 1850 (Stocker et al. 2013 ).
On a regional scale, o ne of the top priorities in the '70s and '80s consisted in drainage works,
in order to obtain increasingly larger surfaces for extensive agriculture. These interventions caused
significant changes of the climate of Ciuc Depression (Korodi et al. 2017 ). As contribution of
evapotranspiration from local sources to the water cycle is vital, its lowering due to groundwater
drainage led to increasing static stability of the atmosphere, longer thermic inversion episodes and
pollutant accumulation similar to those of urban agglomerations (Szép et al. 2016a ). Groundwater
drainage led to the degradati on of peaty soils, changes in ecosystems and precipitation chemistry. The
above mentioned aspects were identified in a series of publications (Szép et al. 2016b, Korodi et al.
2017, Szép et al. 2018 ). The present paper highlights the evolution of key temper ature values for the
2007 -2016 timeframe.
Air pollution results from the combination of high emissions and unfavorable weather, the two
air pollutants of mos t concern for public health are surface ozone and particulate matter (Szép et al.
2016c , Szép et al. 2016 d). Observational and modeling evidence indicates that locally higher surface
temperatures in polluted regions will trigger regional feedbacks in chemistry and local emissions that
will increas e peak levels of ozone and PM ( Stocker et al. 2013 ). Studies find that climate change alone

will increase summertime surface ozone in polluted regions by 1 –10 ppb over the coming decades,
with the largest effects in urban areas and during pollution episodes (Jacob & Darrel 2009 ). The
increase in surface ozone as a result of future climate change represents a “climate change pena lty” or
climate penalty factor ( Wu et al. 2008 ). We calculated this factor to verify how climate change will
likely impact the effectiveness of current emission reduction strategies.
The tropospheric ozone is a determinative key element in the atmosphere oxidative
environment and it is the main component of photochemical smog, which affects the air quality i n
urban and regional levels ( Szép et al. 2016b ). The elevated concentrations of gr ound -level ozone have
harmful effects on human health and on agric ultural and natural vegetation ( Lagzi et al. 2004 ). Air
pollution is a serious health concern in many parts of the world. Several studies have shown that life
expectancy is reduced even in m oderately po lluted areas, by fine particles (PM10, PM2.5) and ozone
(O3), the two air pollutants of most concern for public health (Lacressoniere et al. 2016 ). The US
EPA, based on its review of the air quality criteria for ozone (O3) and related photochem ical oxidants
and national ambient air quality standards (NAAQS) for O3, revised the primary and secondary
NAAQS for O3 to 0.070 parts per million (ppm), and retained their indicators (O3), forms (annual
fourth -highest daily maximum, averaged across three consecutive years) and averaging times (eigh t
hours) ( EPA 2015 ). In the EU, Directive 2008/50/EC sets the current target value for ozone
concentration to 120 µg/m³ (EUR -lex 2008 ). This value should not be exceeded by the daily maximum
of eight -hour running averages on more than 25 calendar days per year. As a long -term objective,
Directive 2008/50/EC requires a strict compliance with the 120 µg/m³ limit, but without setting a
deadline for compliance . The United Nations Economic Commission for Europe (UNECE) suggested
a new indicator for the calculation of the adverse effects on health due to ozone. The indicator AOT60
(Accumulated excess concentration over the guideline value of 60 ppb – around 120 µg/m3) has been
replaced by the SOMO35 indicator as an annua l estim ate of human exposure to ozone (Szé p et al.
2016b) . The present paper contains an overview of ozone concentration evolutions in the 2007 -2016
decade, as well as AOT60, SOMO35 and AOT40 results .
Ozone is produced by the photolysis of NO2 (R1), where the resulting atomic oxygen
recombines rapidly with molecular oxygen to produce ozone (R2). Normally, this reaction is
counterbalanced by the reaction of NO with ozone , ending in NO2 (R3) ( Skalska et al.2010 ):
NO2+hϑ→NO+O (R1)
O+O2→O3 (R2)
NO+O3→NO2+O2 (R3)
Taken together, rea ctions (R1) and (R3 ) produce no net change in ozone. Each of these
reactions occurs rapidly, in 200 s or less. Usually, the two major components of NO x adjust to
establish a balance between reac tions (R1) and (R3), except at nighttime , when t here is always a net
loss of ozone since photolysis rates are zero , reaction (R3) dominates over reaction (R1) (Sillman
1999 ).
The other situation in which these reactions become unbalanced is ozone production
associated with daytime chemical processes involving NOx, VOC and CO . The ozone formation
occurs through series of reactions involving VOC, CO and NOx, which result in the conversion of NO
to NO2 through p rocesses other than reaction (R3 ). The conversion is followed by reaction ( R1) and
results in additional O3. A typical sequence of reactions would be:
RH+OH[O2]→ RO2+H2O (R4)
CO+OH[O2]→ CO2+HO2 (R5)
followed by reactions of RO2 and HO2 radicals with NO :
RO2+NO[O2]→ R′CHO+HO2+NO2 (R6)
H2O+NO[O2]→ NO2+OH (R7)

Reactions (R6) and (R7) convert NO to NO2 , and their result is the formation of ozone when
followed by reaction (R3). The directly emitted hydrocarbons and intermediate organics are
collectively referred to as volatile organic compounds or VOC (Sillman 1999 ).
Numerical simulations of ozone show a dependence on the values for NOx concentrations
(Canty et al. 2015 ), previous findings suggesting that NOx emissions are the primary explanatory
variable in the observed decreasing trend in the climate penalty factor ( Bloomer et al. 2009 ). However,
recent works asser t that ozone concentrations are influenced by the absolute concentrations of NOx
and VOCs, and the ratio of NOx and VOCs too (Derwent et al. 2014 ). When NO x emissions are much
greater than VOC emissions, ozone concentration decreases with increasing temperature so the climate
penalty factor may become strongly negative (Rasmussen et al. 2013 ). Reducing NOx emissions,
primarily emitted as NO, in a NOx saturate d environment can exacerbate ozone pollution by both
decreasing O3 loss by NO titration and inc reasing the ratio of VOCs to NO x, favoring HO2 and RO2
formation, both of whi ch propagate the (R6) -(R7) reaction mechanism that produces ozone in the
troposphere ( Seinfeld & Pandis 2006 ). While NOx emission controls may be effective at decreasing
the climate penalty factor in NOx -limited environments ( Duncan et al. 2010 ), further decreases in
VOC emissions may be beneficial to reducing ozone pollution and may additionally be effective at
minimizing t he climate penalty factor. Anyway, t he main fa ctor driving future air quality projections is
air pollutant emissions, rather than climate change or intercontinental transport of pollution (Colette et
al. 2013 ). So even if climate penalty is a reality for o zone pollution, its magnitude compared to recent
trends and expected emission projections should not discourage from implementing ambitious
mitigation measures (Colette et al. 2015 ).
We analyzed daily, monthly and yearly values of temperatures, ozone and NOx concentrations
in order to find correlations and to investigate the impact of temperature variations and NOx
concentration on climate penalty factor.

Study area and method
The Ciuc Depression is an intermontane basin situated in the Eastern Carpathians, at an
altitude of 600 -700 m (Figure 1). Its main settlement is the city of Miercurea -Ciuc (Kristó 1994 ). The
main characteristics of the depression climate are low temperatures and high atmospheric stability
(Bogdan & Niculescu 2004 ), frequent and intense thermic inversions ( Petres et al. 2017a ) which can
fill the whole basin in the
case of polar air inva sion
(Bogdan & Niculescu 2004 ).
The local dominant wind
direction is 180 -270°, the
characteristic wi nd speed
being only 0 to 2 m/s ( Boga
et al. 2017 ).
The National
Administration for
Meteorology of Romania
operates a network of ground –
based automatic weather
stations, one of them being
situated at an altitude of 661
m, near the city of Miercurea –
Ciuc. The ground -based
regional automatic
background monitoring
station HR -01, situated at an altitude of 710 m in Jigo din-Bai suburb of Miercurea -Ciuc, is operated by the National
Environmental Protection Agency. Both stations are sampling air temperature with an hourly time
resolution, by similar -400C – +500C range TS Thermometer sensors installed at two meter above the
ground . The NO, N O2 and NOx data were measured by a ME9841B Monitor Europe nitrogen dioxide Figure 1. Miercurea -Ciuc, Ciuc Depression, Eastern Carpathians

analyzer using chemi -luminescence method, while O₃ results were obtained with an ME9810B
Monitor Europe ozone analyzer using UV absorption method. The equipment is installed two met er
high from the ground. The data processing was realized with hourly values validated by the National
Administration for Meteorology and by the Environmental Protection Agency of Harghita County .

Result s and discussion

The evolution of the temperature during the 2007 -2016 decade
All recent studies, concerning both global ( Stocker et al. 2013, WMO 2016, WMO 2017 ) and
regional ( Pongrácz et al. 2009, Machidon et al. 2012 ) evolutions, conclude that air temperature values
are higher than th e average for the 1961 -1990 reference period. In Ciuc Depression, average
temperature increased from 5.5°C for the 1961 -1990 period ( Bogdan & Niculescu 2004 ), or 5.2°C for
the 1983 -1992 decade ( Tamá s 1997 ), to 6.5 °C for the 2006 -2015 period ( Petres et al. 2017b ). If we
analyze the decade 2007 -2016, the average will be even higher, 6.55 °C. As Figure 2 shows, yearly
average values present an ascending trend, all of them being well above the average of the reference
period.

Figure 2 Yearly average values for air temperature between 2007 and 2016 (°C)

There are important changes in the monthly averages of temperature and extreme temperature
indices. Figure 3 presents the differences between monthly averages for the 2007 -2016 decade and the
1961 -1990 refere nce period. Excepting January, the highest differences, of 1.3 -1.6°C, were found for
June, July and August, the warmest months of the year . As many authors consider temperature as the
main factor influencing ozone concentrations ( Bloomer et al. 2009, Jacob et al. 2009, Rasmussen et al.
2013, Szép et al. 2016d, Szé p et al. 2017a ), this result is extremely important, stressing the need to
evaluate the climate penalty factor.
Temperature variations became more pronounced. T he annual average of monthly mean
amplitude increased from 24,5°C for the 1961 -1990 reference period ( Bogdan&Niculescu2004 ) with
more than 20%.The alteration is so sharp that, in fact, the annual average of minimum monthly
amplitudes for the 2007 -2016 timeframe is just 0.2 °C lower than the annual average of monthly mean
amplitude for the 1961 -1990 reference period.
The specific climate of the depression is highlighted by the occurrence frequency of days with
significant characteristics of air temperature, or extreme temperature indices, aff ecting air quality in
many ways. Analyzing the intensity and frequency of these extreme events is important s ince human
and natural systems may be especially affected by changes of extreme climate events (Klein Tank et
al. 2003, Bartholy &.Pongrácz 2007, Shepherd 2015, Morabito et al. 2017 ). The most prominent
changes in extreme temperature indices for the 2007 -2016 period are the increases in the number of
summer days (SU) and the number of hot days (Tx30GE).
y = 0,0268x + 6,4682
R² = 0,0291
5,05,56,06,57,07,58,0
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016Temperature, °C
Year Yearly av. Av. 1961-1990 Trend

Figure 3 The differences in the mont hly average air temperature values between 2007 -2016 and 1961 -1990 (°C)

Figure 4 Monthly average of the number of summer days (SU) for 1961 -1990 and 2007 -2016 periods

Figure 4 presents the monthly average numbers of summer days. As one can see, the biggest
part of the rise of this index from around 46.6 ( Bogdan & Niculescu 2004 ) to 57.1 is given by the
warmer temperatures during the summer. The number of hot days increased even more during the
2007 -2016 decade, from 3 -4 (Bogdan & Niculescu 2004 ) in t he 1961 -1990 reference period to 10.5.
July remains the warmest month of the year, but partly due to the lower intensity of night cooling
processes, as warming -related extreme temperature indices for August are higher.

Climate penalty factor
Surface ozone (O3) is a secondary pollutant produced by the photochemical oxidation of CO
and/or volatile organic compounds (VOCs) by the hydroxyl radical ( •HO) in the presence of oxides of
nitrogen (NO x ≡ NO2 + NO) ( Szép et al. 2016b ). Many studies have identi fied temperature as the
most important weather variable a ffecting surface O3 concentrations in polluted regions (Sillman &
Samson 1995, Rasmussen et al. 2013 ).
Surface O3 will be affected by warmer average surface temperatures, shifts in global
circulation patt erns, changes in the frequency of heat waves and frontal passages, altered surface
mixed -layer depths and variations in cloud cover, precipitation, and convection. Climate change will
likely also modify patterns in fires, vegetation, and land use, which ar e all large sources of O 3
precursors to the atmosphere ( Pusede et al. 2015 ). -101234
1 2 3 4 5 6 7 8 9 10 11 12Temperature, °C
Month
Difference of monthly average temperatures between 2007-2016 and 1961-
1990 periods
05101520
1 2 3 4 5 6 7 8 9 10 11 12Summer days, day
Month 1961-1990 2007-2016

Ozone pollution is in general mostly a summer problem because of the phot ochemical nature
of the source ( Jacob & Darrel 2009 ). There are several studies establishing air quality models that
quantified the change in O₃ due to a prescribed temperature perturbation but did not refer to this
sensitivity by a specific name ( Mahmud et al. 2008 , Abel et al. 2017 ). However, the name O3 -climate
penalty became frequently used for it, with varying definitions presented in the literature. Some
consider the climate penalty to represent either the additional decreases in NOₓ emissions to counter
any climate driven increase in O3 (assuming NOx is the limiting precursor) or the reduced benefits of
emissions controls due to the increase in O3 due to a warmer climate ( Wu et al. 2008 ). Some calculate
the “ozone -climate penalty factor” as the slope of the best fit line between long -term observational
measurements of O3 and temperature ( Bloomer et al. 2009 ). Other studies identified the relatio nship
between NOx emissions and temperature as a contributor to trends in ozone ( Pusede et al. 2015 ), or
quantified the dependence of NOx emissions on temperature in the context of the climate penalty
factor for O₃ production (He et al 2013 ). There are works that employ the temperature perturbation
approach. They re fer to the direct increase in O3 concentrations due to in creasing temperatur es as t he
“O3-climate penalty” or “climate penalty”, reporting it to be highly dependent of differing chemical
and meteorological envi ronments that influence O3 formation ( Mahmud et al. 2008, Fujita et al.
2013 ). The aggregate effects that m ake up the tota l derivative d[O3 ]/dT include at least three
components. The association between stagnant air masses and warm temperatures will facilitate the
accumulation of the precursors of O3 (Rasmussen et al. 2013 ). The increase in chemical reaction
rates, including the thermal decomposition of alkyl nitrates (AN) and subspecies peroxyacetylnitrate
(PAN), will supply NOx and HOx at low temperatures ( Sillman & Samson 1995 ). Temperature
dependent variations in biogenic emissions of VOCs act as a source of precursors fo r O3 formation
under high -NOx conditions and ten d to increase with temperature ( Rasmussen et al. 2013 ).
For the evaluation of the penalty factor we used the temperature interval 19 -37°C, we selected
3°C interval length groups and we evaluated percentile values, which gives the proportion in that
interval. The scaling goes from the lowest value (α = 0) up to the highest value (α = 1), α = 25%
meaning the quartile and α = 50% the median value. The average of the slopes (5, 25, 50, 75, 95%)
yields the climate penalty factor ( Bloomer 2008, Szé p et al. 2016d ).

Figure 5 The climate penalty factor for HR-01 regional station for the year 2015

The average slope for the 2008 -2010 years is 1.967µg/m3/°C, slightly lower than the value
report ed for 2012 -2013, 2.05µg/m3/°C ( Szép et al. 2016d ). For the year 2015 (Figure 5), the average
slope was 2.014 µg/m3/°C. For the year 2016 (Figure 6), the average slope was 1.517 µg/m3/°C. All
values are similar to the values which one finds in literature ( Bloomer et al. 2009, Bloomer 2008 ). The
mean value for the entire 2007 -2016 period will be aroun d 1.9 µg/m3/°C. 1525354555657585
15 20 25 30 35Ozone, μg/m³
Temperature, °C5%
25%
50%
75%
95%
Trend 5%
Trend 25%
Trend 50%
Trend 75%
Trend 95%Av. slope: 2.0142

Figure 6 The climate penalty factor for HR-01 regional station for the year 2016

One can see that the slopes for the 95 percentile values are lower than those for smaller
percentiles, and, more important, that above 30°C, the increase of the ozone concentration with the
temperature is less steep . The results for the climate penalty factor indicate that a 1°C increase in
temperature can lead to an increase of around 1.9 µg/m3 o f the ozone concentration. Therefore , at
relatively high ozone concentrat ions in the Ciuc Depression, the increasing temperature can cause
further concentration increments, accumulations with harmful effects on human and vegetation health.

Tropospheric ozone concentrations in Ciuc Depression for the 2007 -2016 period
The HR -01 regional station started to operate in May 2007, thus we can analyze ozone
concentration values for almost a decade.
The Romanian legislation is in accordance with the EU directive. The ozone concentration,
expressed as a daily maximum value of eight -hour running averages, should not exceed the 120 µg/m³
limit on more than 25 days (averaged a cross three consecutive years) ( L. 104/2011 ). It also provides
that the minimum amount of data necessary for valid data, when three -year consecutive results are not
available, is a valid one -year data set. A yearly data set is valid if there are 75% or more available
daily maximum values of eight -hour running averages, both for April -September and January -March +
October -December periods for annual average, or if there are five valid months out of six in the April –
September period for number of limit breeches and annual maximum value calculations. The limit for
the vegetation is set to 18000 h*µg/m3 ((AOT40, May – July), the long -term target being 6000
h*µg/m3 (AOT40, May – July) ( Korodi et al. 2017 ).
In the following diagrams (Figure 7 -13), the evolution of daily maximum value of eight -hour
running averages is presented.
Regarding the 120 μg/m³ limit, there were 9 breeches in 2008, equally spread in the Februa ry-
August period. 2009 was a special year, with 26 daily maximum values over the limit, 19 of them
being recorded in April. The month of April 2009 was one with average April temperatures and high
static stability, but the driest in the 2007 -2016 period, w ith a total rainfall of 23.3 mm, less than half of
an average April month (46.8 mm). The monthly average of NOx concentration was also the highest
for a month of April in that decade, almost 50% higher than April averages. For the rest of the year, 7
excee dances were noted, from March to September. Year 2010 (3 breeches in January) and the non –
valid year of 2011 (3 breeches in March and April) were the last years with recorded daily maximum
values of eight -hour running averages over 120 μg/m³. We can conclu de that ozone concentration in
the Ciuc Depression is within the acceptable limits as far as EU and national regulations are
concerned.
152535455565758595105
15 20 25 30 35Ozone, μg/m³
Temperature, °C5%
25%
50%
75%
95%
Trend 5%
Trend 25%
Trend 50%
Trend 75%
Trend 95%Av. slope: 1.5171

Figure 7 Daily maximum values of eight -hour running averages of O3 for 2008 at HR -01 regional station

Figure 8 Daily maximum values of eight -hour running averages of O3 for 2009 at HR -01 regional station

Figure 9 Daily maximum values of eight -hour running averages of O3 for 2010 at HR -01 regional station
0120Daily max 8h running av val
Date
Ozone ( μg/m3) SOMO35 ref. value AOT60 ref. value70
0120Daily max 8h running av val
Date
Ozone ( μg/m3) SOMO35 ref. value AOT60 ref. value70707070
0120Daily max 8h running av val
Date
Ozone ( μg/m3) SOMO35 ref. value AOT60 ref. value70

Figure 10 Daily maximum values of eight -hour running averages of O3 for 2012 at HR -01 regional station

Figure 11 Daily maximum values of eight -hour running averages of O3 for 2013 at HR -01 regional station

Figure 12 Daily maximum values of eight -hour running averages of O3 for 2015 at HR -01 regional st ation
0120Daily max 8h running av val
Date
Ozone ( μg/m3) SOMO35 ref. value AOT60 ref. value70
0120
2013. 2.
15.2013. 3.
15.2013. 4.
15.2013. 5.
15.2013. 6.
15.2013. 7.
15.2013. 8.
15.2013. 9.
15.Daily max 8h running av val
Date
Ozone ( μg/m3) SOMO35 ref. value AOT60 ref. value70
0120Daily max 8h running av val
Date
Ozone ( μg/m3) SOMO35 ref. value AOT60 ref. value70

Figure 13 Daily maximum values of eight -hour running averages of O3 for 2016 at HR -01 regional station

The results are different when we compare the ozone concentration values with the 70 μg/m³
SOMO35 reference value. More than 71% of the daily m aximum values of eight -hour running
averages for 2008 and 2009 are above the 70 μg/m³ mark, virtually all the March -September (2008)
and March -October (2009) figures exceeding it. For 2010, the rate of breeches decreased till 45%, and
the period of the yea r with all values beyond the reference value diminished to March -April. 2012,
2013 and 2015 presented much lower ozone concentrations, just 1 -5% of the daily maximum values
were above 70 μg/m³, the months with breeches being February -April and July -Septemb er. 2016 had
the ratio increasing to 22.5%, with exceedances in every month excepting January and February.
April -May and August -September were by far the periods with most breeches.
Table 1 contains the estimated values for SOMO35 and AOT40.
By definition, SOMO35 means the sum of means over
35 ppb (daily maximum 8 -hour) for ozone [EEA] , and is
calculated with the formula:
(E1) SOMO35 =∑Ovii
where
(E2) Ovi=Mi−70 with Mi≥70
represent s the excesses of ozone concentrations over 70
µg/m ³ and M i is the daily maximum value of eight -hour
running averages of ozo ne concentrations for day i ( Szép
et al. 2016b ).
AOT40 is defined as the accumulated excess of hourl y
ozone concentrations above 80 μg/m³ between 8:00 and
20:00 CET in th e months of May, June and July (EUR -lex
2008 ). According to the Romanian regulations, if not all
of the hourly values were measured, AOT40 can be
estimated with the formula:
(E3) AOT40 e=AOT40 m∗possible nr.of values
nr.of values measured
where AOT40 e is the estimated accumulated excess, and AOT40 m is the accumulated excess
determin ed from existing hourly values ( L. 104/2011 ).
The estimated AOT40 values for 2008 and 2009 were above the 18000 h*µg/m³ mark, and
below the long -term 6000 h*µg/m³ limit for the rest of the period.
We can conclude that the decreasing trend of ozone concentration values in Ciuc Depression
led to conformation with actual European and Romanian requirements regarding human and
vegetation health, but ozone concentration can easily increase above stricter SOMO35 limits. 0120Daily max 8h running av val
Date
Ozone ( μg/m3) SOMO35 ref. value AOT60 ref. value70
Year SOMO35
(h*µg/m³) AOT40 e
(h*µg/m³)
2008 5223.5 23985
2009 7260.5 24528
2010 2118.4 2997
2012 139.6 0
2013 6.8 0
2015 29.3 0
2016 645.8 418
Table 1 Estimated values of SOMO35 and
AOT40 for valid years in the 2007 -2016
period in Ciuc Depression

Ozone concentrations, temperature and NOx concentration s in the 2007 -2016 period
Previous studies show that in Ciuc Depression, hourly an d daily variations of ozone are
strongly influenced by meteorological conditions (te mperature, solar radiation) and NOx levels (Szép
et al. 2016b, Boga et al. 2017 ).
VOCs can occur naturally due to emissions from trees and plants. Anthropogenic sources of
VOCs in Ciuc Depression include emissions from traffic and from organic solvents in small stationary
sources. The main natural sources to atmospheric NOx are a naerobic biolo gical processes and
lightning. T he main anthropogenic amounts of NOx originate from traffic and the combustion of fossil
fuels in power plants and home heaters (Korodi et al. 2017, Szé p et al. 2017b ).
Daily profile. Figure 14 shows the daily profiles for temperature, O3 concentration and NOx
concentration during the 2007 -2016 decade in Ciuc Depression.

Figure 14 Daily temperature, O3 concentration and NOx concentration profiles at HR -01 regional
station
As one can see, ozone concentration
slowly decreases during the night, with a
minimum value (28.34 μg/m³, 8 o’clock) in the
early morning due to titration with NO , abruptly
increases due to the usually growing solar
radiation and temperature values, peaks in the
middle of the afternoon (67.25 μg/m³, 4 o’clock),
than starts to drop in the evening till a value
close to the daily average (47.69 μg/m³, around 11 o’cloc k in the evening) because of increased
vertical mixing, horizontal advection and titration by fresh NO2 emissions. Temperature variation
presents the same pattern, with a minimum value just before sunrise (3.68°C, 7 o’clock), and a
maximum between 3 and 4 o’clock in the afternoon (11.9°C). However, NOx concentration shows a
completely different course. An intermediate maximum (16.25 μg/m³) occurs around midnight and a
narrowly lower intermediate minimum (14.84 μg/m³), almost equal to the daily average value of 14.71
μg/m³, at 6 o’clock in the morning. Afterwards, home and industrial heating processes, as well as
heavy traffic are leading to a sharp increase, with a maximum (19.73 μg/m³) at 9 o’clock in the
morning, followed by a decrease that leads to a pron ounced minimum value (11.35 μg/m³) at 4 o’clock
in the afternoon. The late afternoon and the evening lead the curve back till midnight.
The diagram suggests a positive correlation between temperature and ozone concentration
values, and a negative correlati on between ozone and NOx concentration values, a presumption we
verified through running a Spearman rank correlation test. According to the results presented in Table
2, there is a very strong positive correlation (+0.988) between temperature and ozone con centration
values, and a strong negative correlation ( -0.777) between ozone and NOx concentration values. 0510152025
01020304050607080
01234567891011121314151617181920212223
Temperature ( °C), NO x
(μg/m3)O3(μg/m3)
Hour of the day
Ozone ( μg/m3) Temperature (°C) Nox ( μg/m3)
Temp O3 NOx
Temp 1 0.988 -0.725
O3 0.988 1 -0.777
NOx -0.725 -0.777 1
Table 2 Spearman correlation between temperature,
O3 and NOx values of the daily profile

Monthly average values. The monthly average values of air temperature, NOx and O3 for the 2007 –
2016 period are presented in Figure 15 .

Figure 15 Monthly average values of air temperatu re, NOx and O3 for the 2007 -2016 period at HR-01 regional
station

Autumn is the season with minimum
ozone concentration values. With warmer
September temperatures in the last decade, ozone
concentration is around the yearly average, but
decreases due to the frequent autumnal
instability periods, and reache s the minimum
value in November. Frequent and very intense
thermic inversion period s during the winter
[Petres2017b ] and increased emissions of NOx by heating trigger raising ozone concentration in
wintertime, February average values already exceeding the yearly average. High static stability,
increasing solar radiation and temperature values, together with still above or around average NOx
values, are c haracteristic for the spring. Photochemical production resulting from increased solar
radiation acting upon NO x and hydrocarbons accumulated during the winter period is the major cause
of the growing concentrations of ozone (Vingarzan 2004 ). March and Apri l are presenting the
maximum monthly ozone concentration averages. At summer, when the intense solar radiation and
longer day lengths stimulate the photochemistry, ozone concentration is still high.
NOx concentration has its maximum average value in January , the coldest month, but all
winter values are below 20 μg/m³. March presents an average well above the yearly average value,
then the concentration will drop till the minimum monthly average (8.52 μg/ m³ in June). Later on
concentration starts to raise, passing the yearly average value in the autumn, in October or November.
Table 3 shows the Spearman rank correlation values for the monthly averages of temperature,
ozone and NOx concentrations. There is a weak, but still significant positive correlation between
temperature and ozone concentration, and a moderate negative correlation between ozone and NOx
concentrations.
We can conclude that t here is an obvious influence of higher air temperatures on the m easured
ozone levels, and the limiting/facilitating effect of NOₓ values can also be clearly observed.
Yearly average values. Figure 16 presents the yearly average values and trends for valid yearly
averages of Ozone and NOx concentrations during the 2007 -2016 timeframe.
-10010203040506070
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecTemperature, O3, NOx
Month
Temp (°C) O3 (μg/m3) Nox ( μg/m3)
Temp O3 NOx
Temp 1 0.371 -0.909
O3 0.371 1 -0.427
NOx -0.909 -0.427 1
Table 3 Spearman correlation between temperature,
O3 and NOx monthly average values

Figure 16 Yearly averages and trend for NOx and O3 values at HR -01 regional station

As one can see, at Miercurea -Ciuc there is a decreasing trend of ozone concentrations, which
can be explained by the decre ase of the industrial activity (Szép et al. 2014 ) and changes in the heating
system, thus NOx emission is also lower. In the same time emission due to the motor cars and the burn
of biomass can con tribute to a partial rise of NOx concentration ( Szép et al. 2016 d).
The global climate change expectedly leads to the rise of the over ground temperature and
aggravat e the air pollution ( Jacob & Darrel 2009 ). The results for the climate penalty factor led us to
the conclusion that a 1°C increase in temperature can lead to an increase of arou nd 1.9 µg/m3 of the
ozone concentration. However, decreasing NOx concentrations caused decreased ozone levels,
emphasizing the importance of controlling the NOₓ emission, which may lead to the decrease of
photochemical smog and limit the effects of climate change. Our findings show that the impact of
recorded and projected climate changes is of smaller magnitude than the changes determined by
anthropogenic emission .

Conclusion
The annual average values of temperature at Miercurea -Ciuc are on a growing trend, the
difference between the average of the 2007 -2016 decade and the mean value for the 1961 -1990
reference period is 1.05°C. The differences for the average monthly temperatu res of Summer moths
are above 1.3°C. As for the extreme temperature indices, the occurrence frequency of summer days
has risen 22.5%, and the number of tropical days from 3 -4 to 10.5.
The calculation of the climate penalty factor showed that a 1°C growth i n temperature can lead
to a 1.9 µg/m3 increase of the concentration of tropospheric ozone in the atmosphere of Miercurea –
Ciuc.
Regarding the limits for human and vegetation health protection, there were few exceedances
of the 120 μg/m³ mark, and none after 2011, ozone concentration in the Ciuc Depression is within the
acceptable limits as far as EU and national regulations are concerned. The same results for the AOT40
indicator. Things are different when we refer to the stricter SOMO35 indicator, where the best three
years still present 1 -5% breeches of the 70 μg/m³ mark, the last recorded year (2016) being just below
the average of the decade with 22.5% of daily values above limit.
The decreasing trend of NOx concentration implied a decrease of ozone concen tration, showing
that the impact of anthropogenic factors is larger than the one due to temperature raises. Thus, we
realize the necessity of the control of NOx emission, in order to mitigate climate change effects.

y = -5,0046x + 64,48
y = -1,5895x + 20,164
010203040506070
0 1 2 3 4 5 6 7Yearly average concentration
(μg/m3)
Year
O3 NOx Trend O3 Trend NOx

Acknowledgments
We are grateful for the support of the National Administration for Meteorology and of the
Harghita Environmental Protection Agency for the meteorological and air quality data.

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