Abstract: Xishui National Forest Park in Heilongjiang Province hosts China’s most pristine temperate forests and serves as a key site for ecotourism and forest therapy. However, the emission patterns of phytoncides (key bioactive compounds) remain poorly understood, limiting their therapeutic application. This study provides the first comprehensive characterization of spatiotemporal dynamics in airborne phytoncides and their synergistic interactions with environmental factors throughout the autumn-early spring seasonal transition in a temperate forest ecosystem. We analyzed the compositional dynamics of phytoncides and terpenoid content variations using thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) from September 2024 to March 2025. This period encompassed seasonal transitions from autumn to early spring, including diurnal variations in September and snowfall events in November. The method demonstrated detection limits (LODs) ranging from 1.35 to 5.33 ng m⁻³ and quantification limits (LOQs) from 4.09 to 16.15 ng m⁻³. Our results revealed pronounced seasonal fluctuations in phytoncide composition. In September, terpenoids, esters, alcohols, and alkanes displayed a diurnal “decrease-increase” trend, whereas aldehydes and ketones peaked at midday. Notably, esters and alcohols were undetectable in November and January. By January, terpenoids reached their lowest proportion (0.17 ± 0.02%) at noon. Five terpenoids (α-pinene, myrcene, D-limonene, camphene, p-cymene) were detected in September, four (α-pinene, D-limonene, camphene, p-cymene) in November, two (D-limonene, p-cymene) in January, and only p-cymene in March. The total concentration and emission rate of the five terpenoids peaked in September afternoons at 1961.58 ± 106.67 ng m⁻³ and 653.86 ± 35.56 ng m⁻³ h⁻¹, respectively. Nocturnal emissions (32131.95 ± 2522.21 ng m⁻³) significantly surpassed daytime levels (14473.04 ± 958.49 ng m⁻³), with emission rates escalating from 1447.30 ± 95.85 ng m⁻³ h⁻¹ (day) to 5355.33 ± 420.37 ng m⁻³ h⁻¹ (night), marking a 3.7-fold increase. Snowfall dramatically elevated terpenoid concentrations (pre-snowfall: 158.58 ± 14.12 ng m⁻³; post-snowfall: 1080.57 ± 57.76 ng m⁻³) and emission rates (pre-snowfall: 52.86 ± 4.71 ng m⁻³ h⁻¹; post-snowfall: 360.19 ± 19.25 ng m⁻³ h⁻¹), reflecting a 6.8-fold surge. This study underscores the profound influence of light intensity, seasonal shifts, and climatic conditions on airborne phytoncide levels, offering a scientific foundation for optimizing forest therapy and ecotourism strategies.

Key words: Phytoncides, Seasonal variation, Diurnal nocturnal patterns, Snowfall impact, Emission patterns