scholarly journals Semi-quantitative understanding of source contribution to nitrous acid (HONO) based on 1 year of continuous observation at the SORPES station in eastern China

2019 ◽  
Vol 19 (20) ◽  
pp. 13289-13308 ◽  
Author(s):  
Yuliang Liu ◽  
Wei Nie ◽  
Zheng Xu ◽  
Tianyi Wang ◽  
Ruoxian Wang ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Nitrous Acid ◽  
Heterogeneous Reaction ◽  
Total Concentration ◽  
Eastern China ◽  
Mean Value ◽  
Budget Analysis ◽  
Conversion Frequency ◽  
Yearly Average ◽  
Quantitative Understanding

Abstract. Nitrous acid (HONO), an important precursor of the hydroxyl radical (OH), has long been recognized as of significance to atmospheric chemistry, but its sources are still debated. In this study, we conducted continuous measurement of HONO from November 2017 to November 2018 at the SORPES station in Nanjing of eastern China. The yearly average mixing ratio of observed HONO was 0.69±0.58 ppb, showing a larger contribution to OH relative to ozone with a mean OH production rate of 1.16 ppb h−1. To estimate the effect of combustion emissions of HONO, the emitted ratios of HONO to NOx were derived from 55 fresh plumes (NO∕NOx > 0.85), with a mean value of 0.79 %. During the nighttime, the chemistry of HONO was found to depend on RH, and heterogeneous reaction of NO2 on an aerosol surface was presumably responsible for HONO production. The average nighttime NO2-to-HONO conversion frequency (CHONO) was determined to be 0.0055±0.0032 h−1 from 137 HONO formation cases. The missing source of HONO around noontime seemed to be photo-induced, with an average Punknown of 1.04 ppb h−1, based on a semi-quantitative HONO budget analysis. An over-determined system of equations was applied to obtain the monthly variations in nocturnal HONO sources. Besides the burning-emitted HONO (accounting for about 23 % of the total concentration), the contribution of HONO formed heterogeneously on ground surfaces to measured HONO was an approximately constant proportion of 36 % throughout the year. The soil emission revealed clear seasonal variation and contributed up to 40 % of observed HONO in July and August. A higher propensity for generating HONO on aerosol surfaces occurred in severe hazes (accounting for 40 % of the total concentration in January). Our results highlight ever-changing contributions of HONO sources and encourage more long-term observations to evaluate the contributions from varied sources.

Semi-quantitative understanding of source contribution to nitrous acid (HONO) based on 1 year of continuous observation at the SORPES station in eastern China

2020 ◽  
Author(s):  
Yuliang Liu
Keyword(s):  
Atmospheric Chemistry ◽  
Nitrous Acid ◽  
Heterogeneous Reaction ◽  
Total Concentration ◽  
Eastern China ◽  
Mean Value ◽  
Budget Analysis ◽  
Conversion Frequency ◽  
Yearly Average ◽  
Quantitative Understanding

<p>Nitrous acid (HONO), an important precursor of the hydroxyl radical (OH), has long been recognized as of significance to atmospheric chemistry, but its sources are still debated. In this study, we conducted continuous measurement of HONO from November 2017 to November 2018 at the SORPES station in Nanjing of eastern China. The yearly average mixing ratio of observed HONO was <span>0.69±0.58</span> ppb, showing a larger contribution to OH relative to ozone with a mean OH production rate of 1.16 ppb h<span><sup>−1</sup></span>. To estimate the effect of combustion emissions of HONO, the emitted ratios of HONO to <span>NO<sub><em>x</em></sub></span> were derived from 55 fresh plumes (<span>NO∕NO<sub><em>x</em></sub></span> > 0.85), with a mean value of 0.79 %. During the nighttime, the chemistry of HONO was found to depend on RH, and the heterogeneous reaction of <span>NO<sub>2</sub></span> on an aerosol surface was presumably responsible for HONO production. The average nighttime <span>NO<sub>2</sub></span>-to-HONO conversion frequency (<span><em>C</em><sub>HONO</sub></span>) was determined to be <span>0.0055±0.0032</span> h<span><sup>−1</sup></span> from 137 HONO formation cases. The missing source of HONO around noontime seemed to be photo-induced, with an average <span><em>P</em><sub>unknown</sub></span> of 1.04 ppb h<span><sup>−1</sup></span>, based on a semi-quantitative HONO budget analysis. An over-determined system of equations was applied to obtain the monthly variations in nocturnal HONO sources. Besides the burning-emitted HONO (accounting for about 23 % of the total concentration), the contribution of HONO formed heterogeneously on ground surfaces to measured HONO was an approximately constant proportion of 36 % throughout the year. The soil emission revealed clear seasonal variation and contributed up to 40 % of observed HONO in July and August. A higher propensity for generating HONO on aerosol surfaces occurred in severe hazes (accounting for 40 % of the total concentration in January). Our results highlight ever-changing contributions of HONO sources and encourage more long-term observations to evaluate the contributions from varied sources.</p>

scholarly journals Contributions of different sources to nitrous acid (HONO) at the SORPES station in eastern China: results from one-year continuous observation

2019 ◽  
Author(s):  
Yuliang Liu ◽  
Wei Nie ◽  
Zheng Xu ◽  
Tianyi Wang ◽  
Ruoxian Wang ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Nitrous Acid ◽  
Heterogeneous Reaction ◽  
Eastern China ◽  
Early Morning ◽  
Mean Value ◽  
Budget Analysis ◽  
Yearly Average ◽  
Heterogeneous Formation ◽  
One Year

Abstract. Nitrous acid (HONO), a reservoir of the hydroxyl radical (OH), has been long-standing recognized to be of significant importance to atmospheric chemistry, but its sources are still debate. In this study, we conducted continuous measurement of HONO from November 2017 to November 2018 at SORPES station in Nanjing of eastern China. The yearly average mixing ratio of observed HONO was 0.69 ± 0.58 ppb, showing a larger contribution to OH relative to ozone with a mean OH production rate of 0.90 ± 0.27 ppb/h. To estimate the effect of combustion emissions of HONO, the emitted ratios of HONO and NOx were derived from 55 fresh plumes (NO / NOx > 0.85), with a mean value of 0.79 %. The well-defined seasonal and diurnal patterns with clear wintertime and early morning concentration peaks of both HONO and NOx indicate that NOx is the critical precursor of HONO. During the nighttime, the chemistry of HONO was found to depend on RH, and heterogeneous reaction of NO2 on aerosol surface was presumably responsible for HONO production. The average nighttime NO2-to-HONO conversion frequency (CHONO) was determined to be 0.0055 ± 0.0032 h−1 from 137 HONO formation cases. The missing source of HONO around noontime seemed to be photo-induced with an average Punknown of 1.13 ± 0.95 ppb h−1, based on a semiquantitative HONO budget analysis. An over-determined system of equations was applied to obtain the monthly variations in nocturnal HONO sources. Except for burning-emitted HONO (approximately 23 % of total measured HONO), the contribution of heterogeneous formation on ground surfaces was an approximately constant proportion of 36 % throughout the year. The soil emission revealed clear seasonal variation, and contributed up to 40 % of observed HONO in July and August. A higher propensity for generating HONO on aerosol surface occurred in heavily polluted period (about 40 % of HONO in January). Our results highlight ever-changing contributions of HONO sources, and encourage more long-term observations to evaluate the contribution from varied sources.

scholarly journals Exploration of the atmospheric chemistry of nitrous acid in a coastal city of southeastern China: results from measurements across four seasons

2022 ◽  
Vol 22 (1) ◽  
pp. 371-393
Author(s):  
Baoye Hu ◽  
Jun Duan ◽  
Youwei Hong ◽  
Lingling Xu ◽  
Mengren Li ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Nitrous Acid ◽  
Simulation Models ◽  
Oh Radicals ◽  
Vehicle Exhaust ◽  
Southeastern China ◽  
Coastal City ◽  
Budget Analysis ◽  
Four Seasons ◽  
Conversion Frequency

Abstract. Because nitrous acid (HONO) photolysis is a key source of hydroxyl (OH) radicals, identifying the atmospheric sources of HONO is essential to enhance the understanding of atmospheric chemistry processes and improve the accuracy of simulation models. We performed seasonal field observations of HONO in a coastal city of southeastern China, along with measurements of trace gases, aerosol compositions, photolysis rate constants (J), and meteorological parameters. The results showed that the average observed concentration of HONO was 0.54 ± 0.47 ppb. Vehicle exhaust emissions contributed an average of 1.45 % to HONO, higher than the values found in most other studies, suggesting an influence from diesel vehicle emissions. The mean conversion frequency of NO2 to HONO in the nighttime was the highest in summer due to water droplets evaporating under high-temperature conditions. Based on a budget analysis, the rate of emission from unknown sources (Runknown) was highest around midday, with values of 4.51 ppb h−1 in summer, 3.51 ppb h−1 in spring, 3.28 ppb h−1 in autumn, and 2.08 ppb h−1 in winter. Unknown sources made up the largest proportion of all sources in summer (81.25 %), autumn (73.99 %), spring (70.87 %), and winter (59.28 %). The photolysis of particulate nitrate was probably a source in spring and summer while the conversion from NO2 to HONO on BC enhanced by light was perhaps a source in autumn and winter. The variation of HONO at night can be exactly simulated based on the HONO / NOx ratio, while the J(NO3-_R) × pNO3- should be considered for daytime simulations in summer and autumn, or 1/4× (J(NO3-_R) × pNO3-) in spring and winter. Compared with O3 photolysis, HONO photolysis has long been an important source of OH except for summer afternoons. Observation of HONO across four seasons with various auxiliary parameters improves the comprehension of HONO chemistry in southeastern coastal China.

scholarly journals Exploration of the atmospheric chemistry of nitrous acid in a coastal city of southeastern China: Results from measurements across four seasons

2021 ◽  
Author(s):  
Baoye Hu ◽  
Jun Duan ◽  
Youwei Hong ◽  
Lingling Xu ◽  
Mengren Li ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Nitrous Acid ◽  
Simulation Models ◽  
Oh Radicals ◽  
Vehicle Exhaust ◽  
Southeastern China ◽  
Coastal City ◽  
Budget Analysis ◽  
Four Seasons ◽  
Conversion Frequency

Abstract. Because nitrous acid (HONO) photolysis is a key source of hydroxyl (OH) radicals, identifying the atmospheric sources of HONO is essential to enhance the understanding of atmospheric chemistry processes and improve the accuracy of simulation models. We performed seasonal field observations of HONO in a coastal city of southeastern China, along with measurements of trace gases, aerosol compositions, photolysis rate constants (J), and meteorological parameters. The results showed that the average observed concentration of HONO was 0.54 ± 0.47 ppb. Vehicle exhaust emissions contributed an average of 1.64 % to HONO, higher than the values found in most other studies, suggesting an influence from diesel vehicle emissions. The mean conversion frequency of NO2 to HONO in the nighttime was the highest in summer due to water droplets was evaporated under the condition of high temperatures. Based on a budget analysis, the rate of emission from unknown sources (Runknown) was highest around midday, with values of 4.35 ppb · h−1 in summer, 3.53 ppb · h−1 in spring, 3.13 ppb · h−1 in autumn, and 2.05 in winter. Unknown sources made up the largest proportion of all sources in summer (78.55 %), autumn (71.51 %), spring (69.67 %), and winter (55.63 %). The photolysis of particulate nitrate was probably a source in spring and summer while the conversion from NO2 to HONO on BC enhanced by light was perhaps a source in autumn and winter. The variation of HONO at night can be exactly simulated based on the HONO/NOx ratio, while the J(NO3−_R) × pNO3− should be considered for daytime simulations in summer and autumn, or 1/4 × (J(NO3−_R) × pNO3−) in spring and winter. Compared with O3 photolysis, HONO photolysis has long been an important source of OH except for summer afternoon. Observation on HONO across four seasons with various auxiliary parameters improves the comprehension of HONO chemistry in southeastern coastal China.

scholarly journals Influence of biomass burning plumes on HONO chemistry in eastern China

2015 ◽  
Vol 15 (3) ◽  
pp. 1147-1159 ◽  
Author(s):  
W. Nie ◽  
A. J. Ding ◽  
Y. N. Xie ◽  
Z. Xu ◽  
H. Mao ◽  
...  
Keyword(s):  
Surface Area ◽  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
Eastern China ◽  
Yangtze River Delta ◽  
Mean Value ◽  
Air Masses ◽  
Surface Areas ◽  
Agricultural Burning ◽  
Conversion Efficiencies

Abstract. Nitrous acid (HONO) plays a key role in atmospheric chemistry by influencing the budget of hydroxyl radical (OH). In this study, a two-month measurement of HONO and related quantities were analyzed during a biomass burning season in 2012 at a suburban site in the western Yangtze River delta, eastern China. An overall high HONO concentration with the mean value of 0.76 ppbv (0.01 ppbv to 5.95 ppbv) was observed. During biomass burning (BB) periods, both HONO concentration and HONO/NO2 ratio were enhanced significantly (more than a factor of 2, p < 0.01) compared with non-biomass burning (non-BB) periods. A correlation analysis showed that the HONO in BB plumes was more correlated with nitrogen dioxide (NO2) than that with potassium (a tracer of BB). Estimation by the method of potassium tracing suggests a maximum contribution of 17 ± 12% from BB emission to the observed HONO concentrations, and the other over 80% of the observed nighttime HONO concentrations during BB periods were secondarily produced by the heterogeneous conversion of NO2. The NO2-to-HONO conversion rate (CHONO) in BB plumes was almost twice as that in non-BB plumes (0.0062 hr−1 vs. 0.0032 hr−1). Given that the residence time of the BB air masses was lower than that of non-BB air masses, these results suggest BB aerosols have higher NO2 conversion potentials to form HONO than non-BB aerosols. A further analysis based on comparing the surface area at similar particle mass levels and HONO/NO2 ratios at similar surface area levels suggested larger specific surface areas and higher NO2 conversion efficiencies of BB aerosols. A mixed plume of BB and anthropogenic fossil fuel (FF) emissions was observed on 10 June with even higher HONO concentrations and HONO/NO2 ratios. The strong HONO production potential (high HONO/NO2 to PM2.5 ratio) was accompanied with a high sulfate concentration in this plume, suggesting a promotion of mixed aerosols to the HONO formation. In summary, our study suggests an important role of BB in atmospheric chemistry by affecting the HONO budget. This can be especially important in eastern China, where agricultural burning plumes are inevitably mixed with urban and industrial pollution.

scholarly journals Characteristics, sources, and reactions of nitrous acid during winter at an urban site in the Central Plains Economic Region in China

2020 ◽  
Vol 20 (11) ◽  
pp. 7087-7102
Author(s):  
Qi Hao ◽  
Nan Jiang ◽  
Ruiqin Zhang ◽  
Liuming Yang ◽  
Shengli Li
Keyword(s):  
Nitrous Acid ◽  
Heterogeneous Reaction ◽  
Urban Site ◽  
Steady Increase ◽  
Homogeneous Reaction ◽  
Economic Region ◽  
Central Plains ◽  
Mean Values ◽  
Budget Analysis ◽  
The Mean

Abstract. Nitrous acid (HONO) in the core city of the Central Plains Economic Region in China was measured using an ambient ion monitor from 9 to 31 January 2019. Measurement time intervals were classified into the following periods in accordance with the daily mean values of PM2.5: clean days (CDs), polluted days (PDs), and severely polluted days (SPDs). The HONO concentrations during CD, PD, and SPD periods were 1.2, 2.3, and 3.7 ppbv, respectively. The contributions of the homogeneous reaction, heterogeneous conversion, and direct emissions to HONO sources varied under different pollution levels. The mean values of the net HONO production of the homogeneous reaction (POH+NOnet) in CD, PD, and SPD periods were 0.13, 0.26, and 0.56 ppbv h−1, respectively. The average conversions of NO2 (CHONO) in CD, PD, and SPD periods were 0.72×10-2, 0.64×10-2, and 1.54×10-2 h−1, respectively, indicating that the heterogeneous conversion of NO2 was less important than the homogeneous reaction. Furthermore, the net production of the homogeneous reaction may have been the main factor in the increase of HONO under high-NOx conditions (i.e., when the concentration of NO was higher than that of NO2) at nighttime. Daytime HONO budget analysis showed that the mean values of the unknown source (Punknown) during CD, PD, and SPD periods were 0.26, 0.40, and 1.83 ppbv h−1, respectively. The values of POH+NOnet, CHONO, and Punknown in the SPDs period were comparatively larger than those in other periods, indicating that HONO participated in many reactions. The proportions of nighttime HONO sources also changed during the entire sampling period. Direct emissions and a heterogeneous reaction controlled HONO production in the first half of the night and provided a contribution that is larger than that of the homogeneous reaction. The proportion of homogenization gradually increased in the second half of the night due to the steady increase in NO concentrations. The hourly level of HONO abatement pathways, except for OH + HONO, was at least 0.22 ppbv h−1 in the SPDs period. The cumulative frequency distribution of the HONOemission∕HONO ratio (less than 20 %) was approximately 77 %, which suggested that direct emission was not important. The heterogeneous HONO production increased when the relative humidity (RH) increased, but it decreased when RH increased further. The average HONO∕NOx ratio (4.9 %) was more than twice the assumed globally averaged value (2.0 %).

scholarly journals Influence of biomass burning plumes on HONO chemistry in eastern China

2014 ◽  
Vol 14 (6) ◽  
pp. 7859-7887 ◽  
Author(s):  
W. Nie ◽  
A. J. Ding ◽  
Y. N. Xie ◽  
Z. Xu ◽  
H. Mao ◽  
...  
Keyword(s):  
Surface Area ◽  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
Eastern China ◽  
Yangtze River Delta ◽  
Mean Value ◽  
Surface Areas ◽  
Agricultural Burning ◽  
Conversion Efficiencies

Abstract. Nitrous acid (HONO) plays a key role in atmospheric chemistry via influencing the budget of hydroxyl radical (OH). In this study, a two-month measurement period of HONO and related quantities were analyzed during a biomass burning season in 2012 at a suburban site in the western Yangtze River delta, eastern China. An overall high HONO concentration with the mean value of 1.1 ppbv was observed. During biomass burning (BB) periods, both HONO concentration and HONO / NO2 ratio were enhanced significantly compared with non-biomass burning periods. A correlation analysis showed that the HONO concentration was not associated potassium (a tracer of BB) in BB plumes, but showed a high correlation with the NO2 concentration, suggesting a principle role of secondary production rather than direct emissions in elevated HONO concentrations. A further analysis based on comparing the surface area at similar PM levels and HONO / NO2 ratios at similar surface area levels suggested larger specific surface areas and higher NO2 conversion efficiencies of BB aerosols. A mixed plume of BB and anthropogenic fossil fuel (FF) emissions was observed on 10 June with even higher HONO concentrations and HONO / NO2 ratios. The strong HONO production potential (high HONO / NO2 to PM2.5 ratio) was accompanied with a high sulfate concentration in this plume, suggesting a promotion of mixed aerosols to HONO formation. In summary, our study suggests an important role of BB in atmospheric oxidation capacity by affecting the HONO budget. This can be especially important in eastern China, where agricultural burning plumes are inevitably mixed with urban pollutions.

scholarly journals Exploration of the atmospheric chemistry of nitrous acid in a coastal city of southeastern China: Results from measurements across four seasons

2020 ◽  
Author(s):  
Baoye Hu ◽  
Jun Duan ◽  
Youwei Hong ◽  
Lingling Xu ◽  
Mengren Li ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Nitrous Acid ◽  
Simulation Models ◽  
Oh Radicals ◽  
Vehicle Exhaust ◽  
Southeastern China ◽  
Coastal City ◽  
Budget Analysis ◽  
Four Seasons ◽  
Logarithmic Relationship

Abstract. Because nitrous acid (HONO) photolysis is a key source of hydroxyl (OH) radicals, identifying the atmospheric sources of HONO is essential to enhance the understanding of atmospheric chemistry processes and improve the accuracy of simulation models. We performed seasonal field observations of HONO in a coastal city of southeastern China, along with measurements of trace gases, aerosol compositions, photolysis rate constants (J), and meteorological parameters. The results showed that the average observed concentration of HONO was 0.54 ± 0.47 ppb. Vehicle exhaust emissions contributed an average of 1.64 % to HONO, higher than the values found in most other studies, suggesting an influence from diesel vehicle emissions. The mean conversion frequency of NO2 to HONO in the nighttime was the highest in summer due to water droplets was evaporated under the condition of high temperatures. Based on a budget analysis, the rate of emission from unknown sources (Runknown) was highest at midday, with values of 14.78 ppb h−1 in summer, 6.49 ppb h−1 in autumn, and 2.18 ppb h−1 in spring. Unknown sources made up the largest proportion of all sources in summer (84.92 %), autumn (80.29 %), and spring (49.98 %), whereas the main source in winter was the homogeneous reaction of NO with OH (56.15 %), due to winter having the highest NO concentration of the four seasons. The value of Runknown had a positive logarithmic relationship with the photolysis of particulate nitrate in spring, summer, and autumn. However, Runknown was limited by particulate acidity under the condition of photolysis of particulate nitrate (J (NO3−_R) × pNO3−) > 1 µg m−3 s−1 in autumn and J(NO3−_R) × pNO3− > 2 µg m−3 s−1 in spring and summer. The variation of HONO at night can be exactly simulated based on the HONO / NOx ratio, while the main sources should be considered for daytime simulations. Compared with O3 photolysis, HONO photolysis has long been an important source of OH, particularly in the morning in spring and winter and around noon in summer and autumn. This study draws a full picture of the sources of HONO across all four seasons and improves the comprehension of HONO chemistry in southeastern coastal China.

scholarly journals Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China

2012 ◽  
Vol 12 (3) ◽  
pp. 1497-1513 ◽  
Author(s):  
X. Li ◽  
T. Brauers ◽  
R. Häseler ◽  
B. Bohn ◽  
H. Fuchs ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Nitrous Acid ◽  
Southern China ◽  
Rural Site ◽  
Pearl River Delta Region ◽  
Additional Source ◽  
Mixing Ratios ◽  
Photolysis Frequency ◽  
The Pearl River

Abstract. We performed measurements of nitrous acid (HONO) during the PRIDE-PRD2006 campaign in the Pearl River Delta region 60 km north of Guangzhou, China, for 4 weeks in June 2006. HONO was measured by a LOPAP in-situ instrument which was setup in one of the campaign supersites along with a variety of instruments measuring hydroxyl radicals, trace gases, aerosols, and meteorological parameters. Maximum diurnal HONO mixing ratios of 1–5 ppb were observed during the nights. We found that the nighttime build-up of HONO can be attributed to the heterogeneous NO2 to HONO conversion on ground surfaces and the OH + NO reaction. In addition to elevated nighttime mixing ratios, measured noontime values of ≈200 ppt indicate the existence of a daytime source higher than the OH + NO→HONO reaction. Using the simultaneously recorded OH, NO, and HONO photolysis frequency, a daytime additional source strength of HONO (PM) was calculated to be 0.77 ppb h−1 on average. This value compares well to previous measurements in other environments. Our analysis of PM provides evidence that the photolysis of HNO3 adsorbed on ground surfaces contributes to the HONO formation.

scholarly journals Forest Soil Respirations are More Sensitive to Nighttime Temperature Change in Eastern China

2018 ◽  
Vol 47 (1) ◽  
pp. 249-254
Author(s):  
Zhaoyong SHI ◽  
Ke LI ◽  
Yongming WANG ◽  
Bede S. MICKAN ◽  
Weikang YUAN ◽  
...  
Keyword(s):  
Soil Respiration ◽  
Soil Temperature ◽  
Temperature Change ◽  
Global Climate ◽  
Eastern China ◽  
Growing Season ◽  
Mean Value ◽  
Apparent Temperature ◽  
Effect Of Temperature ◽  
The Difference

Soil respiration is one of the main fluxes in the global carbon cycle. The effect of temperature on soil respiration is well understood. The response of soil respiration to temperature warming is called apparent temperature sensitivity (Q10) of soil respiration, which is an important parameter in modeling soil CO2 effluxes under global climate warming. The difference of Q10 between daytime and nighttime was hardly reported although attentions are attracted by the differences of temperature change and its effects on vegetation productivity. In this study, we investigated the Q10 of soil respiration in daytime and nighttime by modeling empirical functions based on the in situ measurement of soil respiration and temperature in temperate and subtropical forests of eastern China. Our results showed that the Q10 of soil respiration is higher in nighttime with the mean value of 2.74 and 2.35 than daytime with the average of 2.49 and 2.18 in all measured months and growing season, respectively. Moreover, the explanatory rate of soil temperature to soil respiration in nighttime is also higher than in daytime in each site in both all measured and growing seasons. The Q10 and explanatory rate of soil temperature to soil respiration in nighttime is 1.08 and 1.15 times in daytime in growing season. These findings indicate that soil respiration has a bigger sensitivity to temperature in nighttime than daytime. The change of soil temperature explains more variation of soil respiration in nighttime than daytime.

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